11th international workshop on positron and positronium chemistry

11thInternationalWorkshopon

PositronandPositroniumChemistry(PPC11)

BookofAbstracts

CidadedeGoa,Goa,INDIANovember914,2014

International Scientific Committee A. Alam UK C. Q. He China T. Hirade Japan Y. C. Jean USA Y. Kobayashi Japan J. Kuriplach Czech Republic F. H. J. Maurer Chair Sweden Y. Nagashima Japan P. K. Pujari India K. Ratzke Germany D. M. Schrader Emeritus USA S. V. Stepanov Russia

Advisory Committee R. K. Sinha, Chairman, Atomic Energy Commission, India S. Basu, Director, BARC, Mumbai P. R. Vasudeva Rao, Director, IGCAR, Kalpakkam K. L. Ramakumar, Director, RC&I Group, BARC, Mumbai D. Srivastava, Director, VECC, Kolkata M. K. Sanyal, Director, SINP, Kolkata S. K. Aggarwal, Asso. Director, RC&I Group, BARC, Mumbai B. N. Jagatap, Director, Chemistry Group, BARC, Mumbai S. R. Shetye,Vice Chancellor, Goa University, Goa C. S. Sundar, Director, Materials Group, IGCAR, Kalpakkam S. L. Chaplot, Director, Physics Group, BARC, Mumbai S. G. Markandeya, Controller, BARC, Mumbai N. Ramamoorthy, Asso. Director, IC&TC, BARC, Mumbai

11thInternationalWorkshoponPositronandPositroniumChemistry(PPC11)

BhabhaAtomicResearchCentre

Organized by

11thInternationalWorkshoponPositronandPositroniumChemistry(PPC11)

Organizing Committee A. Goswami, RCD, BARC Chair P. K. Pujari, RCD, BARC Convener A. V. R. Reddy, ACD, BARC B. S. Tomar, RACD, BARC P. Singh, IADD, BARC G. K. Dey, MSD, BARC M. G. R. Rajan, RMC, BARC D. Srivastava, MSD, BARC S. K. Gupta, TPD, BARC S. K. Gupta, IADD, BARC I. Samajdar, IIT, Mumbai C. Ranganathaiah, University of Mysore V. Ravindrachary, Mangalore University Y. K. Vijay, University of Rajasthan G. Amarendra, IGCAR B. Ganguly, SINP P. M. G. Nambissan, SINP M. Patri, NMRL A.V. Salker, Goa University K. Madangopal, GAMD, BARC C. S. Bal, AIIMS K. Sivaji, University of Madras

Local Organizing Committee P.K. Pujari, BARC Chair R. Acharya, BARC Suparna Sodaye, BARC K. Sudarshan, BARC Secretary R. Tripathi, BARC D. Dutta, BARC S. K. Sharma, BARC Priya Maheshwari, BARC S. Mukherjee, BARC S.K. Rath, NMRL

Co-organized by

IndianAssociationofNuclearChemistsand

AlliedScientistsSahaInstitute

ofNuclearPhysicsIndiraGandhiCentrefor

AtomicResearch

11thInternationalWorkshoponPositronandPositroniumChemistry

CidadedeGoa,Goa,IndiaNovember914,2014

Sunday November 9, 2014

15:30 Registration and Fellowship

19:00 Dinner

Monday November 10, 2014

9:00-10:00 Inauguration

10:00-10:30 In Memoriam

10:30-11:00 Tea Break

11:00-13:00 Technical Session I : Polymer/Nanocomposite/Membrane

11:00-11:35 PL1 Nanoparticle filled polymers: Dispersion, Interactions and Free Volume Frans H. J. Maurer

11:35-12:00 IT1 Aging and Free Volume in Thin Polymer Membranes K. Rtzke

12:00-12:12 OP1 Accounting for lack of Nano-effect in a thermoset/clay nanocomposite: A positron annihilation study S. K. Rath

12:12-12:24 OP2 Carborane-siloxane polymers and cross-linked hybrid elastomers studied by Positron Annihilation Lifetime Spectroscopy and Differential scanning Calorimetry. D. Hughes

12:24-12:36 OP3 Gas transport and free volume study in polyethylene based membranes Pushkar N. Patil

12:36-12:48 OP4 The effect of UV irradiation on per-fluorinated sulfonic acid/PTFE copolymer studied by positron annihilation Hamdy F. M. Mohamed

13:00-14:00 Lunch

14:00-15:30 Technical Session II : Fundamental

14:00-14:35 PL2 Early intratrack processes initiated by fast positrons and Auger-electrons S. V. Stepanov

TechnicalProgram



14:35-15:00 IT2 Understanding the enigmas of Positron/Positronium chemistry B. N. Ganguly

15:00-15:12 OP5 High-precision calculation of loosely bound states of LiPs+ and NaPs+ T. Yamashita

15:12-15:24 OP6 Kinetic energy of Ps formed by Ore mechanism in Ar gas Y. Sano

15:30-16:00 Tea Break 16:00-17:30 Technical Session III : Nanomaterials and Alloys

16:00-16:25 IT3 Nuclear material studies by positron annihilation spectroscopy

Y. Nagai

16:25-16:45 IP1 Positron Annihilation Spectroscopy and TEM studies on Zr base alloys used for nuclear reactor application D. Srivastava

16:45-16:57 OP7 Effect of yttria nanoparticles on steels for nuclear applications I. Bartoov

16:57-17:09 OP8 Positron annihilation spectroscopy of dilute Uranium based alloys S. Mukherjee

17:09-17:21 OP9 The investigation of implanted alloys using positron annihilation spectroscopy with combination of nanoindentation technique V. Sabelov

17:21-17:31 New products and technologies in radiation measurements Paul Davidson

19:00 Cultural program and Dinner

Tuesday November 11, 2014

9:00-10:30 Technical Session IV : Metals and Semiconductors

9:00-9:35 PL3 Theoretical positron and positronium studies of condensed matter and their relation to experiment J. Kuriplach

9:35-10:00 IT4 Characterization of thin transparent metal-oxide semiconductors Rafael Ferragut



10:00-10:12 OP10 Effect of alkali metal ions in vacancy defect and defect cluster in MgO nanocrystallites by positron annihilation spectroscopy S. Selvakumar

10:12-10:24 OP11 Study of positron systematics in Li irradiated Alumina (-Al2O3) P. V. Gaikwad

10:24-10:36 OP12 Unmanageable defects in proton-irradiated silicon: a factual outlook for positron probing N. Yu. Arutyunov

10:36-11:00 Tea Break 11:00-13:00 Technical Session V: Fundamentals

11:00-11:25 IT5 Optical Preparation and Manipulation of Positronium Atoms

D. B. Cassidy

11:25-11:50 IT6 Ps Spin conversion reaction during Ps-Xe collisions K. Shibuya

11:50-12:02 OP13 Wave packet dynamics of vibrational Feshbach Resonances in positron scattering from fluoromethane J. R. Mohallem

12:02-12:14 OP14 H Production from collisions between positronium and keV antiprotons for GBAR P. A. Hervieux

12:14-12:26 OP15 Precise measurement of energy spectrum of orthopositronium decay S. Adachi

12:26-12:36 New products and technologies in radiation measurements C. Sudeesh

12:36-12:46 Instruments for measurement of ionizing radiation P. C. Swain

13:00-14:00 Lunch 14:00-16:00 Technical Session VI : Liquids/Confinement

14:00-14:25 IT7 Silica gel loaded with ionic liquids studied by positron annihilation

techniques C. Hugenschmidt



14:25-14:50 IT8 N-heptane adsorption and desorption in mesoporous materials monitored in situ by positron annihilation lifetime spectroscopy R. Zaleski

14:50-15:10 IP2 Phase behaviour of water confined in nanodomain Priya Maheshwari

15:10-15:30 IP3 Positronium bubble oscillation in room temperature ionic liquids T. Hirade

15:30-15:42 OP16 Positron annihilation in benzene, aniline and cyclohexane K. Fedus

15:42-15:54 OP17 Manifestation of the tunnelling effect in positronium and muonium liquid-phase reactions P. S. Stepanov

16:00-16:30 Tea Break 16:30-19:30 Technical Session VII : Poster Presentation

19:30 Dinner

Wednesday November 12, 2014

9:00-10:30 Technical Session VIII : Polymers/Nanocomposites

9:00-9:35 PL4 Free volume, molecular mobility and polymer structure an outline of some practical applications M. Ashraf Alam

9:35-9:55 IP4 Characterization of interfaces in binary and ternary polymer blends by Positron Lifetime Spectroscopy C. Ranganathaiah

9:55-10:07 OP18 PLT and DBAR investigations on MPDMAPP doped PVA-PVP blend R. F. Bhajantri

10:07-10:19 OP19 Physical selectivity of molecularly imprinted polymers evaluated through free volume size distributions derived from Positron Lifetime Spectroscopy T. Pasang

10:19-10:31 OP20 Investigation of PCM microcapsules at low temperature and high pressure by PALS method B. Zgardziska



10:31-11:00 Tea Break

11:00-13:00 Technical Session IX : Surfaces, Interfaces and Polymer Blends

11:00-11:25 IT9 Positron surface processes Yasuyuki Nagashima

11:25-11:50 IT10 Total-reflection high-energy positron diffraction (TRHEPD) T. Hyodo

11:50-12:10 IT11 Depth profiles and free volume in aircraft primer films J. D. Van Horn

12:10-12:22 OP21 Direct correlation between free volume and dielectric constant in a fluorine-containing polyimde blend R. Ramani

12:22-12:34 OP22 PALS and DBAR study on LiClO4 doped PVA - NaAlg blend based polymer electrolyte T. Sheela

12:34-12:44 Absolute method for estimation of beta activity K. R. Kasyapa

13:00 Lunch & Excursion

Thursday November 13, 2014

9:00-10:30 Technical Session X: Nanomaterials, Metallic and Non-metallic Solids

9:00-9:35 PL5 Understanding materials behaviour: Role of Positron annihilation Spectroscopy C. S. Sundar

9:35-9:55 IP5 Positron annihilation spectroscopic studies of multiferroic Bi1-xPrxFeO3 nanocrystalline compounds P. M. G. Nambissan

9:55-10:07 OP23 Temperature dependent positron annihilation characterization of Fe based and other superconductors D. Sanyal

10:07-10:19 OP24 Investigation on the oxygenation effect of porous silicon from the EMD by Positron Annihilation K. Sivaji



10:19-10:31 OP25 Positron annihilation spectroscopy of Eu and Dy doped -Sr2SiO4: Understanding difference in their local site occupancy S. K. Gupta

10:31-10:43 OP26 Vacancy structure in niobium monoxide ceramics by meansof PALS, DBS spectroscopy and QM calculations A. A. Valeeva

10:43-11:00 Tea Break 11:00-13:00 Technical Session XI : Soft matter, Liquids and Defects

11:00-11:25 IT12 Depth resolved positron beam studies of defect in graphite

G. Amarendra

11:25-11:50 IT13 Application of localized annihilation of positron and o-Ps Y. Honda

11:50-12:10 IP6 Positronium chemistry in liquids - first investigations at the GiPS setup M. Butterling

12:10-12:22 OP27 Effect of local electric field on the Positronium formation in irradiated polymer V. Ravindrachary

12:22-12:34 OP28 Electron beam induced microstructural changes and electrical conductivity in Bakelite polymer RPC detector material -A positron lifetime study K. V. Aneesh Kumar

12:34-12:46 OP29 Positron Annihilation Spectroscopy on LiBH4 and LiBH4:LiI superionic lithium conductors Morten Eldrup

12:46-12:58 OP30 Investigation on correlation between defects and conductivity of Sb-doped SnO2 thin films W. Mao

13:00-14:00 Lunch 14:00-15:30 Technical Session XII : Biological Applications

14:00-14:25 IT14 The potential of newer PET radiopharmaceuticals in enhancing the

scientific basis of clinical practice S. Basu



14:25-14:50 IT15 Nanostructural characterization of complex carbohydrate polymers: Recent progress M. Roussenova

14:50-15:02 OP31 Novel applications of PALS in biophysics and cancer research E. Axpe

15:02-15:14 OP32 Positron studies in biopolymer composites A. Coveney

15:14-15:26 OP33 A study of synthetic and natural dyes by the positron annihilation lifetime spectroscopy A. Pivtsaev

15:30-16:00 Tea Break 16:00-17:30 Technical Session XIII: Porous Material

16:00-16:25 IT16 Ps cooling in silica-based porous materials

R. S. Brusa

16:25-16:50 IT17 Positronium annihilation in mesoporous silica thin films Chunqing He

16:50-17:15 IT18 Positron annihilation study in metal organic framework D. Dutta

17:15-17:27 OP34 Examination of a coal by means of positron annihilation spectroscopy C. A. Palacio

17:27-17:39 OP35 Bose-Einstein condensation of positronium in silica pores O. Morandi

17:39-17:51 OP36 Cesium loading capacity of iron phosphate glasses studied by positron annihilation spectroscopy S. Abhaya

19:00 Banquet

Friday November 14, 2014

9:00-10:30 Technical Session XIV : Facilities and Experimental

9:00-9:35 PL6 The MePS System at Helmholtz-Zentrum Dresden-Rossendorf R. Krause-Rehberg



9:35-10:00 IT19 Evidence for a positron bound state on the surface of a topological insulator and details of a new positron beam system for materials studies under development at The University of Texas at Arlington A. H. Weiss

10:00-10:25 IT20 AIST positron probe microanalyzer and its application N. Oshima

10:30-11:00 Tea Break 11:00-12:00 Technical Session XV : Facilities and Experimental

11:00-11:25 IT21 Positron-Annihilation Lifetime spectroscopy using electron

bremsstrahlung A. Wagner

11:25-11:37 OP37 Spin polarized low-energy positron source V. N. Petrov

11:37-11:49 OP38 Nanoparticles based transparent ceramics for scintillation and detection applications F. A. Selim

12:00-13:00 Summary Talk and Conclusion

PL:PlenaryTalkIT:InvitedTalkIP:InvitedPresentationOP:OralPresentationP:PosterPresentation



Plenary Talks Page

No. PL1 Nanoparticle filled polymers: Dispersion, Interactions and Free Volume

2

PL2 Early intratrack processes initiated by fast positrons and Auger-electrons

3

PL3 Theoretical positron and positronium studies of condensed matter and their relation to experiment

4

PL4 Free volume, molecular mobility and polymer structure an outline of some practical applications

5

PL5 Understanding materials behaviour: Role of Positron annihilation Spectroscopy

6

PL6 The MePS System at Helmholtz-Zentrum Dresden-Rossendorf

7

Invited Talks

IT1 Aging and free volume in thin polymer membranes

9

IT2 Understanding the enigmas of positron/positronium chemistry

10

IT3 Nuclear material studies by positron annihilation spectroscopy

11

IT4 Characterization of thin transparent metal-oxide semiconductors

12

IT5 Optical preparation and manipulation of positronium atoms

13

IT6 Ps spin conversion reaction during Ps-Xe collisions

14

IT7 Silica gel loaded with ionic liquids studied by positron annihilation techniques

15

IT8 N-heptane adsorption and desorption in mesoporous materials monitored in situ by positron annihilation lifetime spectroscopy

16

IT9 Positron surface processes

17

IT10 Total-reflection high-energy positron diffraction (TRHEPD)

18

IT11 Depth profiles and free volume in aircraft primer films

19

IT12 Depth resolved positron beam studies of defect in graphite

20

IT13 Application of localized annihilation of positron and o-Ps

21

IT14 The potential of newer PET radiopharmaceuticals in enhancing the 22



scientific basis of clinical practice

IT15 Nanostructural characterization of complex carbohydrate polymers: Recent progress

23

IT16 Ps cooling in silica-based porous materials

24

IT17 Positronium annihilation in mesoporous silica thin films

25

IT18 Positron annihilation study in metal organic framework

26

IT19 Evidence for a positron bound state on the surface of a topological insulator and details of a new positron beam system for materials studies under development at The University of Texas at Arlington

27

IT20 AIST positron probe microanalyzer and its application

28

IT21 Positron-Annihilation lifetime spectroscopy using electron bremsstrahlung

29

Invited Presentations

IP1 Positron Annihilation Spectroscopy and TEM studies on Zr base alloys used for nuclear reactor application

31

IP2 Phase behaviour of water confined in nanodomain

32

IP3 Positronium bubble oscillation in room temperature ionic liquids

33

IP4 Characterization of interfaces in binary and ternary polymer blends by positron lifetime spectroscopy

34

IP5 Positron annihilation spectroscopic studies of multiferroic Bi1-xPrxFeO3 nanocrystalline compounds

35

IP6 Positronium chemistry in liquids - first investigations at the GiPS setup

36

IP7 A dynamical calculation method of an electron and a positron slowing down process in liquid water

37

Oral Presentations

OP1 Accounting for lack of Nano-effect in a thermoset/clay nanocomposite: A positron annihilation study

39

OP2 Carborane-siloxane polymers and cross-linked hybrid elastomers studied by positron annihilation lifetime Spectroscopy and differential scanning calorimetry.

40

OP3 Gas transport and free volume study in polyethylene based membranes

41



OP4 The effect of UV irradiation on per-fluorinated sulfonic acid/PTFE copolymer studied by positron annihilation

42

OP5 High-precision calculation of loosely bound states of LiPs+ and NaPs+

43

OP6 Kinetic energy of Ps formed by Ore mechanism in Ar gas

44

OP7 Effect of yttria nanoparticles on steels for nuclear applications

45

OP8 Positron annihilation spectroscopy of dilute Uranium based alloys

46

OP9 The investigation of implanted alloys using positron annihilation spectroscopy with combination of nanoindentation technique

47

OP10 Effect of alkali metal ions in vacancy defect and defect cluster in MgO nanocrystallites by positron annihilation spectroscopy

48

OP11 Study of positron systematics in Li irradiated Alumina (-Al2O3)

49

OP12 Unmanageable defects in proton-irradiated silicon: a factual outlook for positron probing

50

OP13 Wave packet dynamics of vibrational feshbach resonances in positron scattering from fluoromethane

51

OP14 H Production from collisions between positronium and keV antiprotons for GBAR

52

OP15 Precise measurement of energy spectrum of orthopositronium decay

53

OP16 Positron annihilation in benzene, aniline and cyclohexane

54

OP17 Manifestation of the tunnelling effect in positronium and muonium liquid-phase reactions

55

OP18 PLT and DBAR investigations on MPDMAPP doped PVA-PVP Blend

56

OP19 Physical selectivity of molecularly imprinted polymers evaluated through free volume size distributions derived from Positron Lifetime Spectroscopy

57

OP20 Investigation of PCM microcapsules at low temperature and high pressure by PALS method

58

OP21 Direct correlation between free volume and dielectric constant in a fluorine-containing polyimde blend

59

OP22 PALS and DBAR study on LiClO4 doped PVA - NaAlg blend based polymer electrolyte

60

OP23 Temperature dependent positron annihilation characterization of Fe based 61



and other superconductors

OP24 Investigation on the oxygenation effect of porous silicon from the EMD by Positron Annihilation

62

OP25 Positron annihilation spectroscopy of Eu and Dy doped -Sr2SiO4: Understanding difference in their local site occupancy

63

OP26 Vacancy structure in niobium monoxide ceramics by meansof PALS, DBS spectroscopy and QM calculations

64

OP27 Effect of local electric field on the positronium formation in irradiated polymer

65

OP28 Electron beam induced microstructural changes and electrical conductivity in Bakelite polymer RPC detector material -A positron lifetime study

66

OP29 Positron Annihilation Spectroscopy on LiBH4 and LiBH4:LiI superionic lithium conductors

67

OP30 Investigation on correlation between defects and conductivity of Sb-doped SnO2 thin films

68

OP31 Novel applications of PALS in biophysics and cancer research

69

OP32 Positron studies in biopolymer composites

70

OP33 A study of synthetic and natural dyes by the positron annihilation lifetime spectroscopy

71

OP34 Examination of a coal by means of positron annihilation spectroscopy

72

OP35 Bose-Einstein condensation of positronium in silica pores

73

OP36 Cesium loading capacity of iron phosphate glasses studied by positron annihilation spectroscopy

74

OP37 Spin polarized low-energy positron source

75

OP38 Nanoparticles based transparent ceramics for scintillation and detection applications

76

OP39 When Some Elementary Free Volumes in Polymers are not seen by Positron Annihilation Experiments

77

Poster Presentations

P1 An experiment to observe positronatom bound states

79

P2 Nonlinear dynamics of electronpositron clusters 80



P3 Study of the positronium thermalization in porous materials

81

P4 Positron nitrogen molecule scattering using ro-vibrational close coupling method

82

P5 The collision between two positronium (Ps) atoms

83

P6 The collision between positronium (Ps) and muonium (Mu)

84

P7 Positron transport in a dense structured media

85

P8 Positron annihilation characteristics in polar liquids and the first-principle modeling

86

P9 Study of lamellar lyotropic liquid crystalline structure by positron lifetime spectroscopy

87

P10 PET in clinical medicine

88

P11 Positron Trapping Studies on PVA/MPDMAPP Photochromic Nanocomposite

89

P12 Amorphous structure of the degraded poly(ethylene-terephthalate) in weathering test

90

P13 DBS investigation on films of Cobalt Chloride doped PVA-PVP blend

91

P14 Computation of DBAR parameters in polypyrrole incorporated PVA films

92

P15 Computation of size of spherical and non-spherical voids in semi-crystalline polymeric materials

93

P16 Change of chemical structure, free volume, and mechanical property of polyethylene irradiated by gamma-ray

94

P17 Influence of fillers on the structural and thermo-mechanical properties of recycled high density polyethylene using PAS and other techniques

95

P18 Study of the structural and thermo-mechanical properties of high density polyethylene composites using PAS and other techniques

96

P19 A free volume study on the miscibility of PEEK/PEI blend using Positron Annihilation and Dynamic Mechanical Thermal Analysis

97

P20 Positron Annihilation Spectroscopy and orientation study of PMMA/MWNT

98

P21 Confined water in controlled pore glass CPG-10-120 studied by positron annihilation lifetime spectroscopy and differential scanning calorimetry

99



P22 PALS study of free voids in ion exchanged low-silica zeolites

100

P23 Characterization of contaminated clay with radioisotope using positron annihilation spectroscopy

101

P24 Comparison study between energy-tunable positron annihilation and flow-type ellipsometric porosimetry

102

P25 Very low energy positron scattering from W(100)

103

P26 Probing defects at the buried interfaces/layers in organic semiconductor devices

104

P27 Metal-semiconductor interfaces investigated by positron annihilation spectroscopy

105

P28 Development of a method to measure the positron diffusion constants in metals by the observation of positronium negative ions

106

P29 Positron annihilation in layer high temperature superconductors

107

P30 Positron interactions with quartz materials

108

P31 Defects study on magnetic fluorescent Fe3O4/ZnSe nanocomposites by positron annihilation spectroscopy

109

P32 Electronic properties of transition metals and alloys by positron annihilation spectroscopy

110

P33 PAS study of Zr-2.5%Nb alloy irradiated by Ar9+ heavy ions

111

P34 Study of Doppler broadening in neutron irradiated ADS related materials using positron annihilation spectroscopy (PAS)

112

P35 Investigation of helium implanted RAFM steel by positron beam Doppler broadening spectroscopy

113

P36 Defect studies in large samples using Photon Induced Positron Annihilation (PIPA) Spectroscopy

114

P37 Development of a vertical, slow positron beamline facility at AIST and application to the study of liquids

115

P38 Design of a pulsed positron beam at Trombay

116

P39 Development of a solar spectrum monitor using coloured LEDs and Arduino for studying celestial positronium

117

P40 A triple coincidence PALS setup based on fast pulse digitizers 118



PLENARYTALKS



Nanoparticle Filled Polymers: Dispersion, Interactions and Free Volume*

Frans H. J. Maurer

Department of Chemistry, Polymer & Materials Chemistry,

Lund University, Lund, Sweden

A theoretical approach, based on micromechanical and Simhas molecular statistic mechanical theories of the description of the appearance of interphases and their thermal expansivities and bulk moduli in particulate filled polymers will be presented [1,2]. Some recent free volume data measured by PALS on nanoparticle filled polymers will be reviewed. The addition of nano-size silica particles, exfoliated clay, graphene and graphene oxide particles dispersed in polymer matrices have a large effect on the viscoelastic properties in the melt state as well as in the solid state.

Several questions still exist in relation to possible changes in free volume properties in these complex systems and their characterization. In particular, results from PALS measurements of graphene oxide filled amorphous and semi-crystalline polymers will be presented. [1] R. Simha, R.K. Jain, F.H.J. Maurer. Rheol. Acta 25 (1986) 161. [2] R. Simha, E. Papazoglou, F.H.J. Maurer. Polymer Composites 10 (1989) 409. * Acknowledgement: National Science Foundation, Sweden. e-mail: [email protected]

PL1



Early Intratrack Processes Initiated by Fast Positrons and Auger-electrons

S. V. Stepanov1,2,, V. M. Byakov1,3, D. S. Zvezhinskiy1,2, G. Dupltre4, Yu. D. Perfiliev5 and L. A. Kulikov5

1 Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya, 25,

117218, Moscow, Russia 2 National Research Nuclear University MEPhI, Kashirskoye shosse 31,

115409, Moscow, Russia 3 D. Mendeleyev University of Chemical Technology of Russia, Miusskaya sq., 9,

125047, Moscow, Russia 4 Institut Pluridisciplinaire Hubert Curien, CNRS/IN2P3, BP 28 67037 Strasbourg, France

5 Lomonosov Moscow State University, Chemical Department, GSP-1, Leninskie Gory, 119991, Moscow, Russia

It is well known that positrons (e+) as well as positronium atoms (Ps) are convenient

probes of the local nanoscale structure in a condensed phase and the radiolytic processes occurring therein [1, 2]. There are several steps of evolution of a fast e+:

1) ionization slowing down, thermalization, formation of the e+ track and terminal positron blob, effect of local heating of the e+ blob;

2) formation of the quasifree positronium and its further localization on structural defects or formation of the Ps bubble state (in liquids). Non-point positronium: the pick-off annihilation rate and shape of the Ps narrow component;

3) nonhomogeneous diffusion-controlled reactions in the e+ blob: Ps oxidation and ortho-para conversion by radiolytic products, reaction rate constants, interpretation of the PAL spectra in aqueous solutions at different temperatures.

Intratrack radiation chemical processes can be initiated not only by energetic positron irradiation, but also by fast Auger-electrons in EMS experiments (EMS= Emission Mssbauer Spectroscopy). The radioactive transformation of 57Co into 57Fe (E-capture by the 57Co nucleus) is accompanied by emission of several Auger-electrons having a total kinetic energy of about 6 keV. Their ionization slowing down leads to the formation of 200-300 ion-electron pairs (H2O+, e- in the case of aqueous solutions) around the Mssbauer 57Fe ion (within a sphere of 100 radius). Such a cloud (the Auger-blob [3]) is formed within 10-13 s. Further fast intrablob processes (ion-electron recombination, electron localization and scavenging) can be observed experimentally by measuring the yields of final chemically stable ions 57Fe3+ and 57Fe2+ by means of EMS. The observation of these processes is restricted within the lifetime of the excited Mssbauer nuclei 57Fe, which is about 10-7 s. We have studied experimentally the reaction ability of NO3- anions towards quasifree track electrons in frozen aqueous solutions of acids and salts [3]. It was shown that NO3- scavenges the track electron more efficiently than H3O+, but only by a factor of 3. This is in drastic contradiction with the known behavior of nitrate ions in liquid water, where they are very efficient electron scavenger.

[1] Y.C. Jean, P.E. Mallon, D.M. Schrader (Eds.), Positron and Positronium Chemistry,

World Scientific, Singapore, 2003. [2] S.V. Stepanov et al., Advances in Physical Chemistry, 2012 (2012) 431962. [3] S.V. Stepanov et al., Bulletin of the Russian Academy of Sciences. Physics series, 77(6)

(2013) 770. e-mail: [email protected]

PL2



Theoretical Positron and Positronium studies of Condensed Matter and their Relation to Experiment

J. Kuriplach

Department of Low Temperature Physics, Charles University, Prague, Czech Republic

Positrons and positronia can probe condensed matter and bring detailed information

about studied systems via annihilation gamma-quanta. Several sophisticated experimental techniques are available to examine such annihilation events. The role of theory is to allow understanding of measured data and, in favorite cases, to predict quantitatively also the results of measurements or even to forecast new phenomena. A close relationship between theory and experiment is highly desirable in order to advance understanding of various aspects of condensed matter which are accessible by means of positron annihilation.

In this lecture, principles of theoretical description of positron annihilation events are briefly summarized, and several examples dealing with mainly defect studies in oxides are discussed. It is pointed out that in some respects these theoretical/computational approaches reached maturity, especially when the relation of the electronic structure and positron characteristics is concerned. Persisting problems are reminded.

On the other hand, the description of positronium behavior in condensed materials is not that developed and is substantially more complex, involving also Ps chemical aspects, compared to positrons alone. In addition to shortly reviewing the current status of Ps theoretical description in condensed matter, the possibilities how to unify or merge positron and positronium theoretical concepts are discussed. Basically, there is no substantial difference to measure the positron and positronium lifetime. Then, why it differs so much at the theoretical level? e-mail: [email protected]

PL3



Free Volume, Molecular Mobility and Polymer Structure An Outline of Some Practical Applications

M. Ashraf Alam1,, Mina Roussenova1, David Hughes1, Abigail Coveney1, P. Beavis2,

A. Swain2, Job Ubbink1, 3, Easan Sivaniah4, Concetta Tedeschi5 and Bruno-H Leuenberger5

1H.H. Wills Physics Laboratory, University of Bristol, Tyndall Ave. Bristol BS8 1TL, UK

2AWE, Aldermaston, Reading, RG7 4PR, UK 3Food Concept & Physical Design, Mhleweg 10, CH-4112 Flh, Switzerland

4University of Cambridge, Cavendish Laboratory, Biological and & Soft Systems Section, Cambridge CB3 0HE, UK

5DSM Nutritional Products Ltd, Wurmisweg 576, CH-4303 Kaiseraugst, Switzerland

It is now well established that Positron Annihilation Lifetime Spectroscopy (PALS) is a unique and versatile technique for direct evaluation of the local free volume which exists in polymeric matter due to their irregular molecular packing, density fluctuations and topological constraints [1]. This local free volume, consisting of a large number of sub-nanometre sized free volume elements (commonly referred to as holes), plays an important role in molecular mobility related phenomena such as self-diffusion, the glass transition, mechanical strength and a host of other physical behaviour [2]. Over the past decade, PALS has been successfully used to study a range of practical implications of the free volume in the applications of polymers in a variety of industrial scenarios.

In this presentation, we attempt to give an overview of activities within the positron community in recent years which aim to provide insights into the aspects of the design of polymers for specific industrial applications with the view to attracting potential interest from relevant industries. This talk would concentrate on relevant work of the Bristol positron group in this area together with a summary of other similar activities within the positron community. The talk would incorporate the following themes: (i) free volume and barrier properties of edible biopolymers for their applications in encapsulation of bioactive ingredients in the pharmaceutical and food industries [3], (ii) barrier / permeation properties of appropriate polymers with the view to enable gas permeation / separation etc. [4], and (iii) role of free volume in polymer nano-composites [5]. [1] Y.C. Jean, P.E. Mallon and D.E. Schrader, Principles and Applications of Positron and

Positronium Chemistry (2003). [2] G. Dlubek, in Polymer Physics: From Suspensions to Nanocomposites and Beyond, eds.

L.A. Utracki and A.M. Jamieson, John Wiley & Sons (2011). [3] M. Roussenova et al., New J. Phys. 14 (2012) 035016. [4] Q. Song et al., Energy & Environmental Science, 5 (2012) 8359. [5] see for example D.J. Hughes et al., J. Phys: Conf Series, 443 (2013) 012045. e-mail: [email protected]

PL4



Understanding Materials Behavior: Role of Positron Annihilation Spectroscopy

C. S. Sundar

J.C. Bose Fellow, Materials Science Group, Indira Gandhi Centre for Atomic Research,

Kalpakkam, India

In this talk, I shall present an overview of positron annihilation studies of defects in materials, being pursued at IGCAR, that encompass systems of relevance to the fast breeder reactor programme, as also investigation of defects in novel materials. Results on the investigation of nanoprecipitates in steels aimed towards the development of radiation resistant steels, and on Fe-phosphate glassy matrices for radioactive storage will be presented. As an illustration of the studies on novel materials, we present results on the evolution of pore structure with annealing temperature in nanoporous gold and its influence on hardness, as also investigations on Se vacancies in Bi2Se3 that influences the observation of magnetoresistance quantum oscillations in this topological insulator. The scope of the presentation will be to illustrate as to how positron studies, coupled with other experimental techniques can provide insight into the behavior of traditional and exotic materials. e-mail: [email protected]

PL5



The MePS System at Helmholtz-Zentrum Dresden-Rossendorf

R. Krause-Rehberg1,, W. Anwand2, M. Butterling2, T. E. Cowan2, M. Jungmann1, A. Mller1 and A. Wagner2

1 Univ. Halle, Dept. of Physics, 06099 Halle, Germany

2 HZDR, Institute of Radiation Physics, P.O. Box 510119, 01314 Dresden, Germany

MePS is the Mono-energetic Positron Source at ELBE (Electron LINAC for beams with high Brilliance and low Emittance) at the HZDR (Helmholtz-Zentrum Dresden-Rossendorf). The user operation started in 2013. The chopper was also added to the system in 2013 leading to very clean spectra almost without any spurious signals and a peak-to-background ratio of >104. The current time resolution of about 400 ps is expected to be further improved during the next beam times in summer 2014. The MePS system is especially suited for the lifetime spectroscopy of positronium. The reason is that the repetition frequency can be reduced to 26 MHz 2-n, n=0, 1, 2 16. This is possible without noticeable losses in intensity in this range. The reason is that the transported charge of individual electron bunches can be increased until either the average beam power of > 40 kW or the maximum bunch charge of > 77 pC is exceeded. In the moment an electron bunch repetition time of 615 ps is our standard time setting. This is ideal for rather long o-Ps lifetimes which are to be expected in porosimetry studies of mesoporous pore systems.

In the talk, the recent progress of the MePS system will be demonstrated. Examples for porosimetry studies will be shown. Furthermore, planned improvements such as an MCP-PMT diagnostic stage and the concept of a new sample chamber including a sample magazine and a temperature sample stage will be introduced. e-mail: [email protected]

PL6



InvitedTalks



Aging and Free Volume in Thin Polymer Membranes

K. Rtzke1,, S. Harms1, T. Koschine1, C. Ohrt, F. Faupel1, L. Ravelli2 and W. Egger2

1 Materials Science, University of Kiel, Kiel, Germany 2 University of Armed Forces, Munich, Gemany

Polymers are widely used nowadays, from simple plastic bags via insulating materials

to high tech applications like adhesives or gas separation membranes, and many applications like gas separation membranes or adhesive applications require thin polymeric films on substrates. Important for properties like diffusion, viscosity, and permeability of membranes is the free volume, which is, to a first approach, the unoccupied space between atoms. This free volume can be probed by positron annihilation lifetime spectroscopy, in particular, as a simple quantum mechanical model allows semi-quantitative calculation of average hole size from measured o-Ps lifetime.

In the present talk, selected applications of positron annihilation lifetime spectroscopy to various problems of thin polymeric films on substrates will be presented. For high free volume membrane materials, on the one hand, aging, i.e. decreasing of the available free volume and thus the performance with time has to be taken into account. As an example, we have measured the change in free volume during aging of thin films of a polymer of intrinsic microporosity (PIM-1) by depth resolved positron annihilation lifetime spectroscopy [1]. For films with thickness, d, smaller than 1 m, aging is nearly complete after 3 months, whereas for films with d > 1 m, aging continues even after several months. Aging is thickness and time dependent and the free volume diffuses through the film to the free surface. A recent investigation [2] shows that this effect can be partially reduced by incorporating carbon nanotubes without reducing membrane performance.

On the other hand, the substrate might affect the free volume due to restrictions in alignement of polymer chains or interaction. We performed positron annihilation lifetime spectroscopy experiments at Teflon AF/silicon interfaces as function of the positron implantation energy to determine the free volume hole size distribution in the interfacial region and to investigate the width of the interphase [3]. While no interphase was detected in very short chained, solvent-free, thermally evaporated Teflon AF, an interphase of some tens of nm in extension was observed for high molecular weight spin-coated Teflon AF films. Recent experiments with a focussed beam through a hole in the substrate show even larger reduction in free volume at the interface [4]. [1] S. Harms, K. Rtzke, F. Faupel, N. Chaukura, P. M. Budd W. Egger, L. Ravelli, The

Journal of Adhesion 88, (2012) 608. [2] T. Koschine, K. Rtzke, F. Faupel, M. M. Khan, T. Emmler, V. Filiz, V.Abetz, L.

Ravelli, W. Egger, In preparation [3] S. Harms, K. Rtzke, V. Zaporojtchenko, F. Faupel W. Egger, L. Ravelli, Polymer 52,

(2011) 505. [4] C. Ohrt, T. Koschine, K. Rtzke, F. Faupel, N. Oshima, Y. Kobayashi, R. Suzuki, A.

Uedono, (2014) to be published. e-mail: [email protected]

IT1



Understanding the Enigmas of Positron/Positronium Chemistry

Bichitra Nandi Ganguly

Applied Nuclear Physics Division, Saha Institute of Nuclear Physics,

Kolkata, INDIA. Pin: 700064.

Positron as simplest as well as the lightest antimatter enters as the mystic world to unravel Natures manifestos by simply striking the material domain and emitting 511keV gamma line, as the resultant consequence. The marvelous discovery since (1930s), has continued to explore the enormous phenomenological studies related to multifaceted aspects, all of which relates to one but a vital phenomenon of its association with the various electronic states in the matter. Accordingly, an exotic-bound state of positronelectron (positronium) was found to exist and endowed with its annihilation characteristics, indeed offers much to be explored in the material architecture, where its functional properties are intimately related. This subject enlightens many interesting aspects of investigations which will be summarized (from liquids to chemically important solid substances), the subtleties and usefulness of the unique probe in various physico-chemical and biological systems will be covered. Application of positron annihilation with short-lived radiotracers forming the basis of nuclear medicine and medical diagnostics will be described briefly. Some of the upcoming technological advances in producing many positrons and their exciting field may be attractive and challenging to the young minds, the other field related to astrophysical nature may still bring in more curiosity and enthusiasm, these will briefly touched. The importance in the presentations will bring in the aspects where chemical perspective is sought. e-mail: [email protected]

IT2



Nuclear Material Studies by Positron Annihilation Spectroscopy

Y. Nagai1,, K. Inoue1, T. Toyama1, K. Nagumo1, Y. Shimizu1, N. Ebisawa1, M. Hasegawa1 and Y. Kobayashi1,2

1 Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan

2 Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology, Umezono, Tsukuba, Ibaraki 305-8568, Japan

It is well known that positron and positronium are very useful tools to study the

degradation of the various materials related to nuclear reactors, which is very important for the safety issues, especially after the Fukushima Dai-ichi nuclear accident. In this talk, we will introduce the several examples to apply positron annihilation spectroscopy to the nuclear materials.

The first topic is the neutron irradiation induced embrittlement of the reactor pressure vessel (RPV) steels of light water reactors. The embrittlement is considered to be mainly caused by the irradiation-induced changes in the microstructures such as the formation of the Cu rich nano-clusters (CRNCs) and matrix damages (MDs) due to irradiation-induced point defect clusters. The advantage to use positron annihilation, compared with other microstructural tools such as transmission electron microscopy (TEM) and three-dimensional atom probe (3D-AP), is that positron can detect both the MDs and the CRNCs due to positron affinity trapping. In the presentation, we will show the applications of age-momentum correlation (AMOC) of positron annihilation to the RPVs and their model alloy systems [1]. This technique expects to give useful information on the interaction between MD and CRNC formations.

The second topic is the structural study on high level radioactive waste glasses (RWGs) [2,3]. The intrinsic structural open spaces in RWGs (supposed to use silica-based glasses) are of particular importance, because they act as stable containers to confine the radioactive nuclei of nuclear waste for long periods. The radioactive nuclei are expected to occupy the intrinsic structural open spaces surrounded by the glass random networks of RWGs. Therefore, information on the structural open spaces is strongly desirable with respect to the safe storage of radioactive nuclei. Usually, positron lifetime method (o-Ps lifetime) is employed to estimate the size of the open spaces in glass materials using Tao-Eldrup model. However, momentum distribution study using angular correlation of annihilation radiation (ACAR) technique is very useful and reliable in the presence of chemical and/or spin reaction with Ps. In the presentation, we will compare ACAR results with o-Ps lifetimes for several model glasses of RWG, and discuss the possible interaction between Ps and the impurity centers in the glasses. [1] K. Inoue, Y. Nagai, Z. Tang, T. Toyama, Y. Hosoda, A. Tsuto, and M. Hasegawa, Phys.

Rev. B 83 (2011) 115459. [2] K. Inoue, H. Kataoka, Y. Nagai, M. Hasegawa, Y. Kobayashi, J. Appl. Phys. 114 (2013)

154904. [3] K. Inoue, H. Kataoka, Y. Nagai, M. Hasegawa, and Y. Kobayashi, J. Appl. Phys. (2014)

in press. e-mail: [email protected]

IT3



Characterization of Thin Transparent Metal-Oxide Semiconductors

Rafael Ferragut

L-NESS and Physics Department, Politecnico di Milano, Como, Italy Istituto Nazionale di Fisica Nucleare, Milan, Italy

Most conductors are opaque and most transparent materials are insulators. However, a

small group of materials exhibit coexistence of both attributes. This effect is manifested only in few metal-oxide thin films (ZnO, InGaZnO, TiO2 and few other). Past explanations have largely assumed at the outset the origin of the carrier-producers (e.g. oxygen vacancies as the source of electrons) and proceeded to explain other properties such as mobility. Recently, a variant of growing techniques have been used to produce amorphous and crystalline transparent thin films with an accurate thickness control. Characterization and identification of defects in the produced films become an important task and paves the way to dominate the nanostructural characteristics and to obtain films with good quality. In this sense, Positron Annihilation Spectroscopy (PAS) using a variable-energy positron beam is a powerful tool. Conventional and coincidence Doppler broadening (CDB) and positronium (Ps) fraction measurements of thin TiO2 crystalline films, thin InGaZnO amorphous films and hybrid solar cells based in a porous TiO2 matrix infiltrated with P3HT (poly[3-hexylthiophene]) are presented in the present work. Vacancies in crystalline TiO2 were identified and the chemical environment depends of the inclusion or not of Ta impurities. Based on the thickness values of amorphous InGaZnO and porous TiO2 films which were measured accurately by means of XRD or SEM, the film density were estimated after minimizing fits of the experimental results with a realistic layered model (VEPFIT). Particularly, a step-change improvement in the performance of the hybrid solar cells was enabled by engineering the hybrid interface by the insertion of a proper molecular interlayer namely 4-mercaptopyridine (4-MP). PAS techniques were used to monitor the effect of the interlayer on the P3HT implantation in the porous TiO2 as a function of the molecular weight of the P3HT infiltrated. We note a remarkable difference in terms of the positronium fraction when the 4-MP interlayer is introduced. This difference is consistent with a better contact between the porous TiO2 and P3HT phases and a closer polymer packing at the interface. e-mail: [email protected] web site: http://www.como.polimi.it/positron

IT4



Optical Preparation and Manipulation of Positronium Atoms*

D. B. Cassidy

Department, of Physics and Astronomy, University College London, Gower Street, WC1E 6BT, London UK

The use of a Surko-type buffer gas trap [1] has made it possible to turn ordinary neon-

moderated d.c. positron beams [2] into devices that can deliver high quality cold positrons for high resolution scattering studies [3] or pulses containing up to 107 positrons in a ns burst [4]. The latter can be used to make a gas of positronium having a pressure of around 1 Torr, which in turn can be probed with pulsed lasers in much the same way as any other atomic species. The ability to create a Ps gas makes feasible a vast array of hitherto impractical or impossible experiments, such as the production of molecular positronium [5]. In this talk I will discuss some experiments in which excited atomic states of Ps can be created and studied, including Doppler-free 2-photon state-selective production of Rydberg Ps [6] and electrostatic manipulation thereof [7], measurement of the spin polarization of a positron beam via optical excitation of n=2 Ps states with circularly polarized light in a magnetic field, and the production of e+A complexes [8] via the reaction eAeA*Ps , where the Ps* is in an excited state chosen to have the right binding energy to maximize the reaction rate. [1] C. M. Surko, M. Leventhal, and A. Passner, Phys. Rev. Lett. 62 (1989) 901. [2] Positron Beams and Their Applications, edited by P. G. Coleman (World Scientific,

Singapore, 2000). [3] S. J. Gilbert, R. G. Greaves, and C. M. Surko, Phys. Rev. Lett. 82 (1999) 5032 [4] D. B. Cassidy, S. H. M. Deng, R. G. Greaves, and A. P. Mills Jr., Rev. Sci. Instrum. 77

(2006) 073106. [5] D. B. Cassidy, T. H. Hisakado, H. W. K. Tom, and A. P. Mills Jr., Phys. Rev. Lett. 108

(2012) 133402. [6] T. E. Wall, D. B. Cassidy and S. D. Hogan, to be published. [7] S. D. Hogan and F. Merkt, Phys. Rev. Lett. 100 (2008) 043001 [8] C. Harabati, V. A. Dzuba, and V. V. Flambaum, Phys. Rev. A 89 (2014) 022517. e-mail: [email protected]

IT5



Ps Spin Conversion Reaction during Ps-Xe Collisions

K. Shibuya, Y. Kawamura, and H. Saito

1 Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan

A Ps atom can undergo orthopara spin conversion reaction during PsXe collisions due to spinorbit interaction [1,2]. When o-Ps atoms are converted into p-Ps atoms, the annihilation rate is considerably increased. We investigated energydependence of this reaction rate and developed a new method for measuring Ps temperature.

First, we measured o-Ps annihilation rate in gaseous Xe at several temperatures (T , 300623 K) at 250 kPa using a digital-oscilloscope-based positron annihilation lifetime spectrometer. Owing to Zeeman mixing of Ps spin states in a magnetic field, the two-photon annihilation rate was analytically divided into two components: one was due to the Ps spin conversion, while the other was due to pick-off annihilation. We found that the spin-conversion annihilation rate was proportional to 2.1T , which can be explained by a model assuming that the spin conversion occurs only in p-wave scattering and that, Ps velocity profile follows a Maxwell-Boltzmann distribution after thermalization (Fig. 1). We also found that the pick-off annihilation rate was almost proportional to 1.0T ,which is a dependence exceptionally stronger than that observed in many other gases by unknown reasons.

Second, we developed a new method measuring Ps temperature by applying the fact that the spin conversion annihilation rate strongly depends on the o-Ps kinetic energy. In other words, a small change in the energy leads to a large change in the two-photon annihilation rate. Utilizing the reaction as a "lens" to magnify the o-Ps kinetic energy, we obtain its time

evolution by measuring the time-resolved two-photon annihilation rate using an age-momentum correlation spectrometer. The time evolution of o-Ps kinetic energy can be explained by a classical model [3] that assumes elastic collisions in a time range later than 20 ns and an energy range of lower than 60 meV (Fig. 2). The PsXe momentum-transfer cross section is found to be 1612(2) 10 cm2. [1] J. Mitroy and S. A. Novikov, Phys. Rev. Lett. 90 (2003) 183202. [2] H. Saito and T. Hyodo, Phys. Rev. Lett. 97 (2006) 253402. [3] Y. Nagashima et al., Phys. Rev. A 52 (1995) 258. e-mail: [email protected]

Fig. 1: Annihilation rates as a function of temperature. The spin-conversion annihilation rate is plotted with circles and the pick-off annihilation rate is plotted with triangles.

Fig. 2: Time evolution of o-Ps kinetic energy. The fit curve is based on a classical model assuming elastic collisions.

IT6



Silica Gel Loaded with Ionic Liquids Studied by Positron Annihilation Techniques

C. Hugenschmidt1,, H. Ceeh1, T. Gigl1, , M. Haumann2, C. Herold1,

M. Reiner1, and A. Schnweiz2

1 Heinz Maier-Leibnitz Zentrum (MLZ) and Physik Department E21, Technische Universitt Mnchen, Garching, Germany

2 Lehrstuhl fr Chemische Reaktionstechnik, Friedrich-Alexander Universitt, Erlangen-Nrnberg, Germany

Novel materials for catalytic applications in chemical industry consist of an ionic liquid,

dispersed as a thin film on the inner surface of a highly porous solid. Dissolving homogeneous transition metal complexes in the ionic liquid film allows tailoring of solid materials with defined properties and a controlled chemical reactivity. These materials can be handled like classical heterogeneous catalysts or adsorbents. Since it is of great importance to study the film forming process in the volume of a porous support in a non-destructive manner positron annihilation techniques have been applied.

In the present experiment we have studied silica gel samples loaded with 0-70% ionic liquids. First, the samples were analyzed by Doppler broadening spectroscopy (DBS) and coincident DBS. In a second step, all samples have been characterized by positron lifetime spectroscopy (PLS) in order to observe variations of the pore size distribution. The results of the DBS showed a very high decrease of the S-parameter of about 8% between the as-received and the 70% loaded material. This trend is clearly supported by the CDBS measurements. All samples show an almost linear dependence on the S- and W-parameter. In order to get a deeper insight to the positron state in the different samples the lifetime spectra were decomposed, and the mean void radii were determined using the Tao-Eldrup model. e-mail: [email protected]

IT7



N-heptane Adsorption and Desorption in Mesoporous Materials Monitored in situ by Positron Annihilation Lifetime Spectroscopy*

R. Zaleski1,, M. Gorgol1, A. Baewicz1, A. Kierys2, J. Goworek2

1 Institute of Physics, 2 Faculty of Chemistry, Maria Curie-Sklodowska University,

pl. M. Curie-Sklodowskej 3, 20-031 Lublin, Poland

The pore structure of solids is of significant importance for their numerous applications. The most commonly used methods of pore characterization are gas adsorption experiments. The proper interpretation of the adsorption data requires complete and precise description of the related mechanisms (e.g., the adsorbate multilayer formation on the solid surface or adsorbate condensation as well as pore blocking percolation and cavitation during desorption processes). Recently positron annihilation lifetime spectroscopy (PALS) was successfully used to investigate adsorption phenomena [1]. The in situ monitoring of n-heptane adsorption and desorption in porous materials by PALS may give an extended insight in the mechanism of these processes.

The intensity of the PALS component related to the mesopores is the parameter most comparable to the results of a typical adsorption experiment. (Fig.1). However, only the interpretation of other parameters of the PALS components, such as mean lifetime and its dispersion, is required for better insight into the sorption process. The components related to n-heptane inside the filled pores and silica n-heptane interface present in the PALS spectra reveal phenomena unknown so far. Among them is the possible reorganisation of n-heptane molecules being in contact with the adsorbent surface when pores are filled. Moreover, the formation of the n-heptane multilayer made of island-like during adsorption was observed, while a much smoother layer of adsorbed n-heptane is present during desorption.

Fig. 1: The intensity of the mesopore-related component as a function of the n-heptane relative pressure during adsorption (open symbols) and desorption (full symbols) for different silicas with bell-mouthed (left), ink-bottle (middle) and cylindrical (right) pores. [1] R. Zaleski et al., Micropor. Mesopor. Mater. 154 (2012) 142; A. Kierys et al., Micropor.

Mesopor. Mater. 179 (2013) 104; A. Kierys et al., Adsorption 19 (2013) 529. * The research was supported by Polish Ministry of Science and Higher Education through the grant no. 2013/09/D/ST2/03712. e-mail: [email protected]

IT8



Positron Surface Processes*

Yasuyuki Nagashima

Department of Physics, Tokyo University of Science 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan

When low-energy positrons impinge on solid surfaces, they will penetrate into the bulk,

lose their energy until thermalized, and then diffuse back to the surface [1, 2]. The positrons may be trapped in the surface potential well and annihilate there. If the positron work function is negative, the positrons may be emitted with a characteristic energy . The positrons may be also emitted as positronium (Ps). In the case of insulators such as SiO2, Ps atoms are formed in the bulk.

In this presentation, I will discuss positron surface processes including (1) emission of the positronium negative ion (Ps-) from tungsten and molybdenum surfaces [3], (2) efficient emission of Ps- from alkali-metal coated surfaces [4,5] and (3) Ps emission from alkali-metal coated surfaces [6]. I will also discuss about O+ emission from TiO2 induced by positron annihilation with core electrons, which has been explored recently [7]. [1] P. Mills Jr., Positron Solid State Physics, Proceedings of the International School of

Physics Enrico Fermi, Course LXXXIII, North-Holland 1983, p.432. [2] P. J. Schultz and K. G. Lynn, Rev. Mod. Phys. 60 (1988) 701. [3] Y. Nagashima and T. Sakai, New J. Phys. 8 (2006) 319. [4] Y. Nagashima, T. Hakodate, A. Miyamoto and K. Michishio, New J. Phys. 10 (2008)

123029. [5] H. Terabe, K. Michishio, T. Tachibana and Y. Nagashima, New J. Phys. 14 (2012)

015003. [6] H. Terabe, S. Iida, K. Wada, T. Hyodo, A. Yagishita and Y. Nagashima, J. Phys. Conf.

Series. [7] T. Tachibana, T. Hirayama and Y. Nagashima, to be published in Phys. Rev. B. * The author is grateful for collaboration with Koji Michishio, Hiroki Terabe, Shimpei Iida, Takashi Yamashi, Takayuki Tachibana, Izumi Mochizuki, Ken Wada and Toshio Hyodo. This work is supported in part by a Grant-in Aid for Scientific Research (No. 24221006) from the Ministry of Education, Science and Culture of Japan and Matsuo Foundation. e-mail: [email protected]

IT9



Total-Reflection High-Energy Positron Diffraction (TRHEPD)*

T. Hyodo1,, Y. Fukaya2, I. Mochizuki1, M. Maekawa2, K. Wada1, T. Shidara3, A. Ichimiya4 and A. Kawasuso2

1Institute of Materials Structure Science, KEK, Tsukuba 305-0801, Japan

2Advanced Science Research Center, JAEA, Takasaki 370-1292, Japan 3Accelerator Laboratory, KEK, Tsukuba 305-0801, Japan

4Dept. of Phys., Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan

A station for the reflection high-energy positron diffraction (RHEPD) [1,2] which is the positron counterpart of reflection high-energy electron diffraction (RHEED) has been installed in the Slow Positron Facility, KEK. With a high-intensity slow positron beam (initial intensity 5107 slow e+/s) [3] and a transmission-type brightness enhancement [4] quality of the data obtained has been drastically improved.

Fast positrons of energy 10keV, for example, are totally reflected from a solid surface when the incident glancing angle is less than certain critical angle, typically 2-3, covering one third or one half of the whole measurement range (about 6) of the glancing angle. This feature, resulting from the positive average electrostatic potential in every solid, makes RHEPD very unique compared with other diffraction methods. We have thus renamed RHEPD as TRHEPD (total-reflection high-energy positron diffraction) to put stress on this feature. Moreover, when the glancing angle is slightly larger than the critical angle, the diffraction pattern includes information on the layer just beneath the surface also. By increasing the glancing angle gradually, one can take the information of the layers of interest without bothering about the effect of the deeper layers.

The sensitivity of TRHEPD to the atomic configuration on the topmost surface and the immediate subsurface is demonstrated in ref. [5]. The method has been applied to determine the one-dimensional (nano-wire) structure formed on Ge (001) when Pt atoms are deposited [6], the buckling structure of silicene on Ag(111) [7], and the long-unresolved structure of TiO2(110)-(12) surface [8]. [1] A. Ichimiya, Solid State Phenom. 28/29 (1992) 143. [2] A. Kawasuso and S. Okada, Phys. Rev. Lett. 81 (1998) 2695. [3] K. Wada, et al., Eur. Phys. J. D 66 (2012) 37; J. Phys.: Conf. Series 443 (2013) 012082. [4] M. Maekawa et al., to be published in Eur. Phys. J. D (2014). [5] Y. Fukaya, M. Maekawa, et al., Appl. Phys. Express 7, (2014) 056601. [6] I. Mochizuki, et al., Phys. Rev. B 85 (2012) 245438. [7] Y. Fukaya, et al., Phys. Rev. B 88 (2013) 205413. [8] I. Mochizuki, et al., in preparation. * We thank the staff of the Photon Factory and the Accelerator Laboratory of KEK for their support in the operation of the Slow Positron Facility. This work has been partly supported by Grant-in-Aid for Scientific Research (S) 24221007 and for Young Scientists (B) 25800182 from the Japan Society for the Promotion of Science e-mail: [email protected]

IT10



Depth Profiles and Free Volume in Aircraft Primer Films*

J. D. Van Horn1,, H. Chen1, Y. C. Jean1, W. Zhang2 and M. R. Jaworowski2

1 Department of Chemistry, University of Missouri-Kansas City, Kansas City, USA 2 Physical Sciences Department, United Technologies Research Center, East Hartford, USA

An understanding of materials properties is crucial for the design and use of materials

and coatings in extreme conditions. Positron annihilation lifetime spectroscopy (PALS) and associated techniques provide non-destructive methods to study the free volume inside polymeric materials, and to study material characteristics over a depth profile [1-3]. Cast free films of solvent- and water-borne, non-chromated aerospace primers, when cured for about one week, had very different water vapor transport (through-plane) behavior [4]. In addition, both types of primer films showed strong anisotropic behavior in in-plane versus through-plane water vapor transport rates [4]. We evaluated the solvent- and water-borne aircraft primer films and report the differences between the samples and their surface depth profiles.

In bulk PALS measurements, an aged, solvent based film exhibited typical lifetimes and intensities for a particulate-containing polymer film on both faces. In contrast, aqueous-based films exhibited differences, dependent on the orientation of the face (see Fig. 1). In all water-borne samples, the I3 value of the back of the sample was smaller and the associated free fractional volume decreased in value. Primer film samples were also evaluated with monoenergetic positron beam techniques to generate depth profile information. The heterogeneity in the samples was verified by Doppler broadening of energy spectroscopy (DBES). A model for the differences in the faces of the films, and their layered structure is discussed. Table 1. Mean pick-off lifetimes, intensities, free volumes and fractional free volumes for aqueous- versus organic-base primer films in differing orientations. ((#) = calc. error in last sig. digit reported).

Primer Film Sample 3 (ns) I3 (%) fv(3) ffv(%) Aqueous-base face-to-face 2.00(1) 11.2(1) 98(1) 1.98(4) Aqueous-base back-to-back 1.98(2) 6.8(1) 96(2) 1.18(3) Organic-base face-to-face 2.20(2) 6.5(1) 117(2) 1.39(3) Organic-base back-to-back 2.17(2) 7.2(1) 114(2) 1.49(3) [1] Y.C. Jean, et al., Progress in Organic Coatings 52 (2005) 1. [2] D.W. Gidley, et al., Annual Review of Materials Research 36 (2006) 49. [3] H. Chen, et al., Macromolecules 40 (2007) 7542. [4] W. Zhang and M.R. Jaworowski, ECS Transactions 35 (2011) 53. * This work was performed under SERDP Project WP-1620. e-mail: [email protected]

100

1000

10000

100000

185 225 265 305 345 385

Counts

Channel Number

Front Face Back Face

Fig. 1: In bulk PALS analysis, a significant difference is observed in front and back faces of an aqueous base aircraft primer film.

IT11



Depth Resolved Positron Beam Studies of Defect in Graphite

Varghese Anto Chirayath* and G. Amarendra

Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam-603 102, T.N, India

Graphite has been extensively studied owing to its interesting basic properties as well as

its applications in nuclear industry. Structural transformations induced by temperature and pressure are of particular interest from applications point of view. Defects comprising of point defects viz., vacancy and interstitial as well as their higher order complexes play a crucial role in influencing these transformation. It was also recently found that the presence of defects can induce magnetic ordering as well as alter its transport properties. Therefore, the investigation of point defects, their clustering and thermal stability are of immense interest in understanding physical and chemical properties of Graphite. Among various experimental tools, positron annihilation spectroscopy has unique sensitivity and selectivity to vacancy-defects and hence, can be effectively used to study graphite. We have carried out detailed positron beam studies [1] on highly oriented pyrolytic graphite (HOPG) samples, which are self ion irradiated two different doses. Depth-resolved S-parameter is monitored on these samples subjected to various annealing temperatures, so as to get detailed information on thermal stability of the defects. The similarities and differences in annealing dynamics of the defect complexes between low and high dose samples will be presented along with characteristic S-W correlation plots. [1] Varghese Anto Chirayath, Study of near surface defects using positrons and

Development of a pulsed positron beam system, Ph.D thesis, Homi Bhabha National Institute (HBNI), October 2013

* Present address: Sacred Heart College, Thevara-682013, Kerala, India e-mail: [email protected]

IT12



Application of Localized Annihilation of Positron and o-Ps

Y. Honda1,, Y. Akiyama2 and S. Nishijima2

1ISIR, Osaka University, Ibaraki, Osaka, Japan 2Graduate School of Engineering, Osaka University, Suita, Osaka, Japan

Whenever some properties relating to functionality of material are evaluated by using

positron annihilation spectroscopy, special attention must be paid for the location where positron and o-Ps annihilate. In many of such materials polarization due to functional group or impurity would bring about inhomogeneous annihilation and formation of positronium and annihilation of positron and positronium would be influenced by such local field. We have investigated annihilation process of positron/o-Ps in PTFE related electrolyte membranes through degradation process of the membrane, and found that o-Ps stays near the hydrophilic site, i.e. just in the skin of inverse micelle which is formed by aggregation of hydrophilic site. The lifetime of o-Ps is not so influenced by the condition of hydrophilic site where HOMO level locates, but sensitive to the deformation of micellar skeleton. Localization of o-Ps would be caused by the presence of local electric field near the micelle. There is no such local field in PTFE and annihilation would occur homogeneously. However it is known that PTFE is composed of crystal part and amorphous part, which is found by measuring lifetime of o-Ps. Such information would be used for reprocessing of PTFE and related materials.

Crown ether is known to form a chelate complex with radioactive cation which is selected by the size of cavity. As o-Ps is trapped in the cavity of crown ether, the size of cavity would be found by its lifetime. Positron can be used to find suitable extraction condition of radioisotopes. HOMO level in crown ether also locates inside of the cavity. Taking into account of the neutrality of o-Ps, it would be formed near the cavity and trapped there. Much of the fallout from Fukushima nuclear power plant has been kept in clay around there. The ability of storage of radioisotopes depends both on the electronic and the physical structure. These properties can also be analyzed by positron as shown in another presentation.

Thus positron seems to approach a location of interest where chemical reaction is easy to take place and eventually annihilate near there. However, it is crucial to identify where positron and o-Ps annihilates and what kind of information can be brought.

e-mail: [email protected]

IT13



The Potential of Newer PET Radiopharmaceuticals in Enhancing the Scientific Basis of Clinical Practice

Sandip Basu

Radiation Medicine Centre, BARC, Tata Memorial Centre Annexe, Parel, Mumbai-400012,

India

Currently, 18F-fluorodeoxyglucose (18F-FDG) represents the most commonly utilized PET tracer in the parlance of clinical imaging. The major two shortcoming of 18F-FDG for using it for cancer is that [a] it is not an specific tracer for cancer and several benign conditions especially the infection-inflammatory disorders demonstrate very high grade FDG uptake; also [b] a number of malignancies like prostate cancer, hepatocellular carcinoma, renal cell carcinoma, neuroendocrine tumors are not FDG avid and hence cannot be adequately assessed by 18F-FDG-PET. Newer radiopharmaceuticals thus have been investigated to (a) give more specific information and (b) provide better sensitivity. In addition, they can aid in (c) complementing 18F-FDG-PET results by demonstrating valuable information with respect to tumor biology (Table 1).

Table 1. The Salient Clinical expectations from Newer PET Radiopharmaceuticals

(a) Be more tumor-specific

(b) Provide superior sensitivity in FDG non-avid malignancies

(c) Complementing 18F-FDG-PET results in terms of tumor biology

The mostly investigated and promising newer radiopharmaceuticals include: [i] Somatostatin receptor imaging tracers (e.g. 68Ga-DOTA-TOC/NOC/TATE), [ii] Amino acid analogues(e.g. 11C-Methionine, 18F-fluoroethyl-L-tyrosine and L-3, 4-dihydroxy-6-[18F]fluorophenylalanine), [iii] Hypoxia Imaging Tracers ([18F]Fluoromisonidazole, [18F]EF5, 18F-FAZA, 64Cu-ATSM diacetyl-bis-N4-methylthiosemicarbazone),[iv] Radiolabeled cell membrane components ([11C]Choline), [v] Tracers for lipid synthesis and metabolism (11C-acetate), [vi] Radiolabeled nucleosides ([18F]Fluorothymidine). In the present discourse will explore critically the potential clinical utilities of the newer PET tracers in enhancing clinical oncology practice in the future. Their implications will be seen particularly from the perspectives of: (a) accuracy of disease staging, (b) guiding therapy and (c) assessing cancer biology and heterogeneity. e-mail: [email protected]

IT14



Nanostructural Characterization of Complex Carbohydrate Polymers: Recent Progress

M. Roussenova and M. A. Alam

H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL,

United Kingdom

Carbohydrates have versatile physical and structural properties, linked to their conformational degrees of freedom and propensity to form extended hydrogen bond networks [1, 2]. These materials are of utmost importance for the pharmaceutical industry due to their ability to form films, particles, and matrices with adjustable morphologies [2]. In addition, under controlled conditions in the glassy state, they combine good physical stability with excellent barrier properties towards gases [3] and organic molecules [4]. Carbohydrates are thus commonly used in low water content dense matrices for the formulation of pharmaceutical excipients and encapsulation matrices for labile bioactive ingredients [2].

It is now well recognised that in the glassy state, the molecular organisation of carbohydrates has a profound effect on a number of their physical properties (e.g.: the sorption of water [5] and the diffusion of small penetrant molecules [6]) which are of key importance for the formulation of pharmaceutical encapsulants. In our recent studies, we used Positron Annihilation Lifetime Spectroscopy (PALS) to probe the free volume in a variety of carbohydrate polymers, and used the notion of molecular organisation to explain a number of hitherto not well understood phenomena [7] observed in the physics of these systems. Here, we present an overview of our recent and current PALS studies on model oligo- and poly-saccharide systems [1, 7-11]. We show that PALS can be used to probe changes in thermodynamic state, as well as the molecular organisation of these materials as a function of temperature, matrix composition and water content [1, 7-11]. By combining our PALS data with measurements from complementary techniques we aim to establish composition-structure relationships for these model systems. This provides a promising route towards the eventual rational design of pharmaceutical encapsulants, rather than the current largely trial-and-error approach. [1] M. Roussenova et al., Carbohydr. Polym. 102 (2014) 566. [2] S. Kasapis et al., Modern Biopolymer Science (2009) San Diego: Academic Press. [3] A. Schoonman et al., Biotechnol. Prog. 18 (2002) 139. [4] Y. Gunning et al., Carbohydr. Res. 329 (2000), 377. [5] J. Ubbink et al., Biomacromol. 8 (2007) 2862. [6] S. Anandaraman et al., Food Technol. 40 (1986) 88. [7] D. Kilburn et al., J. Phys. Chem. B 108 (2004) 12436. [8] D. Kilburn et al., Nat. Mater. 5 (2006) 632. [9] S. Townrow et al., J. Phys. Chem. B 111 (2007) 12643. [10] S. Townrow et al., J. Phys. Chem. B 114 (2010) 1568. [11] M. Roussenova et al., Biomacromol. 11 (2010) 3237.

e-mail: [email protected]

IT15



Ps Cooling in Silica-based Porous Materials

R. S. Brusa

Department of Physics,University of Trento and INFN-TIFPA,38123 Povo (Tn), Italy

Positronium (Ps), the bound state of an electron and a positron, can be produced in vacuum implanting positrons in a suitable material. The use of silica-based ordered or disordered porous materials allows to obtain Ps at cryogenic temperature by decreasing the Ps kinetic energy by collisional cooling [1-3]. Many open questions involving the process of Ps cooling wait for an answer. New knowledge on Ps cooling and Ps spectroscopy open the possibility to characterize closed porosities with size larger than five nanometers. Furthermore, a huge number of cooled Ps in vacuum is necessary for new exciting experiments like Ps spectroscopy and antimatter-matter comparison with antihydrogen beams [4].

After a brief description of positronium formation mechanism in solids, the physics of collisional Ps cooling will be discussed according to the latest results obtained by three gammas spectroscopy, lifetime spectroscopy and time of flight spectroscopy measurements carried out in ordered nanochannelled silicon [5-7].

Present running Ps spectroscopy [8] and antihydrogen experiments at CERN (AEgIS experiment) [4] and TOF at NEPOMUC facility in Mnich [5], will be presented. Future possible use of Ps TOF and Ps spectroscopy for characterizing porosities will be discussed. [1] S. Mariazzi, P. Bettotti, S. Larcheri, L. Toniutti and R. S. Brusa, Phys. Rev. B 81 (2010)

235418. [2] S. Mariazzi,P. Bettotti, and R. S. Brusa, Phys. Rev. Lett. 104 (2010) 243401. [3] Positronium formation and cooling R.S. Brusa and A. Dupasquier in International

School of Physics Enrico Fermi CLXXIV Course: Physics with many positrons, edited by A. Dupasquier, A. P. Mills, Jr. and R.S. Brusa, (IOS, Amsterdam; SIF, Bologna 2010).

[4] M. Doser and the AEgIS collaboration, Physics Procedia 17 (2011) 49. [5] L. Di Noto, S. Mariazzi, M. Bettonte, G. Nebbia, R. S. Brusa, Eur. Phys. J. D 66 (2012)

118. [6] S Mariazzi, L Di Noto, L Ravelli, W Egger and R S Brusa, Journal of Physics:

Conference Series 443 (2013) 012061. [7] R. S. Brusa, L. Di Noto, G. Nebbia, S. Mariazzi, Journal of Physics: Conference Series

505 (2014) 012038. [8] L Penasa, L Di Noto, M Bettonte, S Mariazzi, G Nebbia and R S Brusa, Journal of

Physics: Conference Series 505 (2014) 012031. e-mail: [email protected]

IT16



Positronium Annihilation in Mesoporous Silica Thin Films*

Chunqing He, Bangyun Xiong, Wenfeng Mao, Xiuqin Tang

Key Laboratory of Nuclear Solid State Physics Hubei Province School of Physics and Technology, Wuhan University, Wuhan 430072, China

Various silica thin films were deposited on Si wafers via a sol-gel method, using either

triblock copolymers or a cationic surfactant as structure-directing agents. Positronium (Ps) formation and annihilation in the prepared mesoporous films with various structures were studied using positron annihilation lifetime spectroscopy (PALS), Doppler Broadening of annihilation radiation (DBAR) and Ps time-of-flight (Ps-TOF) measurements based on slow positron beams. Issues about porosities, pore surfaces and pore morphologies on Ps annihilation characteristics in mesopores will be presented.

1. Strong correlations between positronium 3 annihilation fraction, S parameter and porosity of the mesoporous silica films with isolated pores are obtained, which may provide a complementary method to determine closed porosities of mesoporous silica films by DBAR.

2. Ps emission/3 annihilation depends not only on the pore interconnectivity but also on pore morphologies due to Ps localization in larger pores;

3. Pore entrance size of cage-like pores may be estimated by PALS from Ps lifetime trapped in connecting channels between cages of thin films with surface treatment, or from the emission energy of cooled Ps from mesoporous thin films using Ps-TOF measurements;

4. Because of the nature of Ps confinement in nano-channels, orientation of tubal pores could be distinguished by measuring S, W parameters of positron annihilation in ordered pores aligning along silica film surface using DBAR.

[1] B. Xiong, et al., J. Appl. Phys. 115/9 (2014) 094303. [2] B. Xiong, et al., Phys. Lett. A. 378 (2014) 249. [3] C. He, et al., Chem. Phys. Lett. 590 (2013) 97. [4] C. He, et al., Phys. Rev. B 86 (2012) 075415. [5] C. He, et al., Phys. Rev. B 75 (2007) 195404. [6] C. He, et al., Appl. Phys. Lett. 91 (2007) 024102. *This work was supported in part by National Natural Science Foundation of China (NSFC) under Grants 10975108 & 11375132, and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry. e-mail: [email protected]

IT17



Positron Annihilation Study in Metal-Organic Frameworks (MOFs)

Dhanadeep Dutta1,2,, Jeremy I. Feldblyum3,4 David W. Gidley2, James Imirzian2, Ming Liu5,6, Adam J. Matzger3,4, Richard S. Vallery7 and Antek G. Wong-Foy3

1Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai-400 085, India

2Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, Michigan 48109, USA

3Department of Chemistry, University of Michigan, 930 North University Street, Ann Arbor, Michigan 48109, USA

4Macromolecular Science and Engineering, University of Michigan, 2300 Hayward Avenue, Ann Arbor, Michigan 48109-2136, USA

5NIST Polymers Division, 100 Bureau Dr. M/S 8541, Gaithersburg, Maryland 20899-8541, USA

6Nuclear Reactor Program, Department of Nuclear Engineering, North Carolina State University, P.O. Box 7909, Raleigh, North Carolina 27695, USA

7Department of Physics, Grand Valley State University, 151 Padnos Hall, Allendale, Michigan 49401, USA

Metal-organic framework crystals have attracted immense interest over the last decade

because of their application in gas storage, separation and catalysis. Positronium has shown great promise as a unique, in situ probe to reveal the pore structure in these new crystals. Positronium is seen to exist in a delocalized state in these self-assembled metal-organic framework crystals with large (~1.5 nm) cell sizes. The transport properties of long-lived triplet positronium hypothesized to be in a Bloch-state was probed for the first time with simple positron annihilation lifetime technique [1]. Delocalized positronium has shown unprecedented high mobility driven primarily by weak phonon. The unique behaviour of long lived positronium in metal organic frameworks will be discussed. The evolution of nano scale pore structure during chemical exposure as well as the collapse of pores under humidity will also be discussed.

[1] D. Dutta et al., Phys. Rev. Lett. 110 (2013) 197403. e-mail: [email protected]

IT18



Evidence for a Positron Bound State on the Surface of a Topological Insulator and Details of a New Positron Beam System for Materials Studies

Under Development at The University of Texas at Arlington*

A. H. Weiss1,, K. Shastry1, B. Barbiellini2, B. A. Assaf2, D. Heiman2, P. V. Joglekar1, Z. H. Lim1, and A. R. Koymen1

1 Physics Department, The University of Texas at Arlington, Arlington, TX 76019-0059 USA

2 Physics Department, Northeastern University, Boston, MA 02115 USA

Experiments carried out in our laboratory have demonstrated that Positron Annihilation induced Auger spectroscopy (PAES) has greatly enhanced surface selectivity relative to electron based surface spectroscopies such as Electron induced Auger Spectroscopy or XPS. This sensitivity stems from the fact that positrons implanted into a metal or semiconductor at low energies have a high probability of becoming trapped in an surface localized state before they annihilate. Consequently the information carried by the annihilation-induced signals (including Auger electrons and gamma rays) originates from the top-most atomic layer.

First we will present the results of studies of a topological insulator (Bi2Te2Se) system in which a magnetically guided positron beam was used to deposit positrons at the surface of the material. The energy spectra and intensities of electrons and gamma rays emitted as a result of the positron irradiation were measured. The electron energy spectra showed features that can be identified with Positron Annihilation induced Auger transitions from Bi, Te, and Se providing evidence that the incident positrons were trapped into a surface localized bound state at the time of annihilation. Changes in the gamma ray spectra indicating an in

11th international workshop on positron and positronium chemistry

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