Structural Evolution of Neutron-Rich Nuclei Using Thin-Target

Deep-Inelastic ReactionsPaddy Regan

Dept. of PhysicsUniversity of Surrey, UK

e-mail: P.REGAN@SURREY.AC.UK

Outline• Physics of high spins in 100Mo, -rich SD shell gaps• Importance of using all the experimental parameters to get at the

important physics– emission angle – recoil velocity– reaction fold– angular distribution of fragments– isomer tagging ?

• Our recent thin-target experiences using CHICO+GAMMASPHERE– 100Mo+136Xe + future work aims for– 208Pb/238U + 100Mo

Nuclei in the Sr-Sn region show dramatic change in structure around N~60.

Sudden explosion of 2 deformation in Sr-Ru isotopes at N=60 has been explained by strong spatial overlap of Spin-Orbit Partners (SOPs) g9/2 protons and g7/2 neutrons.

(see Federman and Pittel, Phys. Rev. C20 (1979) p820)

h11/2 neutron orbital responsible for 1st crossing in even-even systems.Energy appears to correlate with transition to deformed ground states at N~60

Nuclear Rotations and Vibrations

• What are the signatures (in even-even nuclei) ?– (extreme) theoretical limits

2 (4 ) 4(5) 20

( 1), 3.332 (2 ) 2(

(4 ) 2 = 2.00

3)

( 1

6

2 )N

J

EE N

EE J J

E

E

2

V

2

En

n=0

n=1

n=2

n=3

http://npl.kyy.nitech.ac.jp/~arita/vib

24

24

2 :Rotor

0 : Vibrator

)2(

242

),1(2

:Rotor

,2

:Vibrator

22

22

J

J

J

n

JR

JR

J

JJER

JEJJE

EJ

nE

Structural change from vibrator to rotator appears to be a regular feature of this region.

Rotation stabilized by core stiffening due to population of ‘rotation-aligned’ h11/2 neutrons.N=58 and Mo-Cd seem most dramatic cases.

Special type of crossing, Vibrator to Rotor ‘backbend’PHR, Beausang,Zamfir,et al., PRL 90 (2003) 152502 also using Cranked IBM, see Cejnar and Jolie, PRC69 (2004) 011301

From Dudek et al.,Phys. Rev. Lett.59 (1987) p1405

Single particle spectra (for minimised LDMenergy at spin 60 hbar) shows distinct gaps for 2~0.5 at Z=42, N=58 (100Mo).

Note these arethe homologs of A~80 SD (N=42)and A~130 SD (Z=58)

• SD (2=0.4) minimum predicted in 100Mo to become yrast around spins 25-30 h.

• ‘Doubly-Magic’ SD shell gaps at (Z=42, N=58) = 100Mo.

J. Skalski et al.,Nucl. Phys. A617 (1997) p282

2)12( LModified from Introductory Nuclear Physics, Hodgson, Gadioli and Gadioli Erba, Oxford Press (2000) p509

Aim? To perform high-spin physics in stable and neutron rich nuclei. Problem: Fusion makes proton-rich nuclei.Solutions? (a)fragmentation (b) binary collisions/multi-nucleon transfer

Backed target studies of DICs see eg. Broda et al. Phys. Rev Lett. 74 (1995) p868Juutinen et al. Phys. Lett. 386B (1996) p80Wheldon et al. Phys. Lett. 425B (1998) p239 Cocks et al. J. Phys. G26 (2000) p23Regan et al., Phys. Rev. C55 (1997) 2305Krolas et al., Nucl. Phys. A724 (2003) 289

CCMMAX

MAX

TB

TLF

VER

L

LAA

L

2

2

31

2

1

1

7

2

:limit Rolling

PHR et al., Phys. Rev. C55 (1997) 2305, backed target with DORIS 0.5% array with ~1010pps beam for 4 days (c 1997),- trigger

single gates,backed target

data

BGO Fold from 8 back target 136Xe+100Mo data

max

3

1blfmax

3

1tlf

max

3/13/1

0

221

max

1

1

7

2

1

1

7

2

fragments. twoebetween th mom. ang. relative the

and , intosplit is limit, mode rolling In the

25.12

cosec1.4

where, approach,closest of distance by thegiven is

max. issection -cross DIC the whereangle The

. and 219.0

is mom. ang. peripheral max. y theclassicall-Semi

l

AA

ll

AA

l

lll

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eZZd

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grazing

AA

AAVERl

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T

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TBgraz

k

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TBCMCM

Bock et al., Nukleonika22 (1977) 529

0

10

20

30

40

50

%>Ecoul

Ltlf (roll)

v/c graz tlf

Linear(%>Ecoul)

0

10

20

30

40

50

60

620 648 677 705 733 761 790E_beam (MeV)

blf_graz

tlf_graz

lmax/10

Kinematics and angular mom. input calcs (assumes ‘rolling mode’) for 136Xe beam on 100Mo target.

Estimate ~ 25hbar in TLFfor ~25% above Coul. barrier. For Eb(136Xe)~700 MeV, in labblf~30o and tlf~50o.

100Mo +136Xe (beam) DIC calcs.

-1

cos-1

by calculated then is correctionDoppler The

coscoscoscossinsinsinsin)cos(

where

)cos(r.r

by given is angleray -fragment/ the

k )cos( , j )sin()sin( ,i )cos()sin(

k, and j i, rsunit vectoCartesian For

2

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2121212112

122121

1,2

1,2

EE

rr

rzryrx

z

x

y

2

int

2

2

2

22

2

2

,,

cos11

cos

cos1

sin

cos1

1

E

E

E

E

EE restlab

From T. Glasmacher, Ann, Rev. Nucl. Part. Sci. 48 (1998) p1

scales linearlywith .

scales linearlywith .

Simon et al., Nucl. Inst. Meth. A452, 205 (2000)

BLF

TLF

beam tlftlf

blfblf

Ge

TOF ~5-10 ns.ns-s isomers can de-excite in bestopped by CHICO position detector. Delayeds can still be viewedby GAMMASPHERE.

Rochester Group

100Mo + 136Xe @ 700 MeV GAMMASPHERE + CHICOPHR, A.D. Yamamoto et al., AIP Conf. Proc. 701 (2004) p329

Wilczynski (‘Q-value loss) Plot A.D.Yamamoto, Surrey PhD thesis (2004)

PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313

TLFs

BLFs

elastics

100Mo + 136Xe at 700 MeV

PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313

Crossing and alignments well reproduced by CSM, although AHVs

relativeintensities.

Gating on anglegives a dramatic channel selection in terms of population.

Relative Intensitiesof 6+->4+ yrast transitions in TLFs (relative to 100Mo) for 136Xe beam on 100Mo target at GAMMASPHERE+ CHICO.

Q-values show how one expects the compound fragments to split.

TLFs

BLFs

elastics

Emission angle of TLFs can give information/selection on reaction mechanism (and maybe spins input ?)

+2n

-2n

+2p

PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313

Timing relative to prompt-gamma-triples master gate (Xe+Pt expt.).

Isomer gating very useful in DIC experiments. Test with known case…..

PHR, A.D.Yamamoto et al., Phys. Rev. C68. (2003) 044313

Use known delayed lines in 101Mo (182 and 57 keV) to identify previously unknown h11/2 band (+ 34 keV E1 decay).

0

10

20

30

40

50

60

620 648 677 705 733 761 790Beam Energy (MeV)

blf_ang

tlf_ang

lmax/10

020406080

Beam Energy (MeV)

mo ang

Pb ang

lmax/10

100Mo target + 136Xe beam

100Mo beam + 208Pb target

208Pb beam + 100Mo target

Need to think carefully about Beam/target combinations to maximise spine input for nucleus ofInterest…flow could go away from nucleus of choice depending on Q-value.

In general, larger mass beamprovides higher spin input, but beware of.……Q-value effects.

Summary and Conclusions• Gammasphere + CHICO results for 100Mo+136Xe @700 MeV show

importance of using ALL parameters (H,K,Q,) to get channel selection.

• AGATA for use with DIC must have ancillary detector to tag recoil direction and velocity (PRISMA, VAMOS, CHICO?). What about isomer tagging ?

• Fold (isolated hit probability) and neutrons may be problematic for the highest spins (100 hbar internally between the two fragments is likely!)

NUSTAR’05International Conference on

NUclear STructure, Astrophysics and Reactions

The University of Surrey, Guildford, UK

5-8 January 2005

http://www.ph.surrey.ac.uk/cnrp/nustar05