Mass Analyzer of SuperHeavy Atoms

Some recent results

2012 Student Practice in JINR Fields of Research 9.oct.2012

I. Sivacek flerovlab.jinr.ru

MASHA scheme

1 – focal strips (3x64) - width 1,1 mm2, 3 – up & down side strips 2x(2x32)4 – left & right side strips 2x(16)

Well-shape silicon strip detector:

Mass separator MASHA

Mass separator MASHA

Mass separator MASHA

Hot catcher and ECR ion source

Ion source scheme. Schematic view of target and hot catcher chamber.

MASHA ion-optical system

•4 dipole magnets (D resp. M)•3 quadrupole lenses (Q)•2 sextupoles (S)•2 focal points – F1 (rough separation) a F2 (precise mass analysis)

Schemes of vertical (a) and horizontal (b) ion trajectories trough separator (c).

(a)

(b)

(c)

SETUP PARAMETERSMass separator MASHA

Mass resolution and efficiency• Mass resolution of Xe isotopes by calibrated leaks

into ECR ion source• Efficiency (ξIon ξSep) by leaks of inert gases (Xe: 84%)

cislo stripu

inte

nzi

ta [n

A]

hmotnostné [ ]číslo a.m.u.

efek

t[

]ív

nos

ť %

Strip number Mass [a.m.u.]

Inte

nsity

Effici

ency

[%]

Time charasteristics• Exponential character of gas extraction from

catcher chamber, measured time constants for noble gases

hmotnostné [a.m.u.]číslo

τ

[s]

vzduch

Time constants of exponential decrease of pressure in catcher chamber.

Efficiency dependence on proton number of gas.

airAir

A

effici

ency

Time response – diffusion from graphite

• Overlapping 40Ar beam by Faraday cup (~ 0,5 s)• By decrease of secondary beam intensity the

time constant was estimated

beam off beam off

beam on

s

čas [s]

inte

nzi

ta [n

A]

Inte

nsity

Time

Total efficiency of setup by 222Rn

• Accumulation of 226Ra recoils in graphite plate with shape and matrix of catcher (saturation)• Measuring alpha decay of 222Rn implanted to detector with 24 hrs time of implantation (diffusion from catcher)• For the same time of implantation Si detector of the same dimensions as plate measured decay of activity implanted into this graphite plate• Overall efficiency of mass separator was estimated for isotope 222Rn was estimated to 13 ± 1,3 %Time [hrs] beginning 24 hours after accumulation

Coun

ts

ON-BEAM MODEL REACTIONSMethodology

Experiments on 40Ar beam

Reactions:284 MeV 40Ar+natSm→ yHg+xn (Hg: chem. analogue 112th element)

255 MeV 40Ar+166Er→206−xnRn+xn (Rn: α – radioactive noble gas)

2-dimensional mass spectra of isotopes Hg (a) and Rn (b).

(a) (b)

RnHg

60 80 100 120 140 160 180 2004,5

5,0

5,5

6,0

6,5

7,0

185184183182

180 (2.56 s)

181(3.6 s)

2

6

10

14

18

22

26

30

34

38

42

46

50

40Ar+ Smt

nat

catch=1600 Со

Ene

rgy,

MeV

Strip number

40 60 80 100 120 140 160 180 2005,0

5,5

6,0

6,5

7,0

7,5

8,040 166Ar+ Ertcatch=1600 Со

206

204202

201(3.8 s, 7 s)200(1.06 s)

2

27

52

77

102

127

152

177

200

Strip number

Ene

rgy,

MeV

205

40Ar+natSm→ yHg+xn

Mass spectrum of Hg isotopes (a), energy spectrum from strips with mass A = 182 (b).

• Registered decays from 180Hg to 186Hg in focal plane Si detector• Decays of daughter nuclei were observed

60 80 100 120 140 160 180 2000

1000

2000

3000

4000

5000

40Ar(255 MeV)+

natSm,

tгр= 1600oC

185Hg (49.0 s)

184Hg (30.6 s)

183Hg (8.8 s)

182Hg (10.8 s)

181Hg (3.6 s)

180Hg (2.56 s)

Strip number

Alp

ha c

ount

40Ar+166Er→206−xnRn+xn

• Mass spectrum with decay of daughter nuclei

Obr. Mass spectrum of Rn isotopes with beam energy E = 217 MeV (a) and energy spectrum from strips with mass A = 202 (b).

40Ar+166Er→206−xnRn+xn

• Measured Rn spectra from A = 199 (EAr = 231 MeV) to A = 206 (EAr = 202 MeV).

• Energy were 3-times (3 measurements) changed by Ti degraders in front of target.

E(Ar), МeV 199Rn 200Rn 201Rn 202Rn 203Rn 204Rn 205Rn 206Rn

202 266 90729 58535 30309 5169 3575 105217 1597 10635 5603 4047 969 243231 21 94 378 279 140 24

Rn yields normed total beam integral on target (with given energy).

Tab. Rn isotopes yields.

Assembly testing• Confirmed ability of MASHA setup for mass

measurement of 112th and 114th elements• By observation of radon isotopes yields was

estimated “speed” of setup as < 5s (mean lifetime of 201Rn)

• Measured energies of alpha particles are in perfect accordance with table values.

• 40Ar beam and calibrated leaks measurement showed 1,3s and 2,5s time constants for catcher chamber evacuation and evacuation + diffusion from graphite respectively.

Conclusions

• Off-line measurements showed efficiency of ionization 84 ± 10 % for Xe isotopes with mass resolution R = M/ΔM = 1300.

• 40Ar beam measurements showed transport efficiency 25 ± 20 %.

• Measurements with 222Rn provided estimation of total MASHA efficiency to 13 ± 1,3 %.

• MASHA is ready for experiment48Ca + 238U → (283)Cn + 3n.

Spring in Dubna…

CHARACTERISTICS OF SILICON DETECTOR

Dead layer problem

Monte carlo simulations in Geant 4

• Geometrical efficiency of Si well-shaped detector

• Energy losses of alphas and recoils in detector materials

• Angular dependency of alpha particles energy losses in detector (dead layers)

• Energy calibration of detector by 226Ra (real energies measured by detector)

• Analysis of alpha registration processes - elimination of peak “tails”

Geometrical efficiency

0 20 40 60 80 100 120 140 160 180 20090

91

92

93

94

95

96total geometrical efficiency

0 10 20 30 40 50 60 700

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

UstripDstrip

0 2 4 6 8 10 12 14 16 180

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

DstripUstrip

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160

5

10

15

20

25

LstripRstrip

beam F96

beam F1

Geometrical efficiency

beam f-96 beam 1st 2nd 3rd beam 1st 2nd beam 1st beam

jadro A B C D B C D C D Dfocal 96,8% 56,4% 49,6% 46,5% 97,0% 59,0% 52,3% 97,2% 62,8% 97,4%U+D 9,7% 31,8% 34,6% 35,8% 8,9% 29,7% 32,4% 8,0% 27,0% 7,3%L+R 0,3% 2,0% 2,5% 2,7% 0,3% 1,9% 2,3% 0,4% 1,8% 0,4%lost 2,5% 7,4% 4,1% 2,5% 2,3% 7,8% 3,9% 2,2% 8,8% 2,2%

total 106,9% 90,2% 86,7% 85,0% 106,2% 90,6% 87,0% 105,6% 91,6% 105,1%

Systematic error ≈ +5 %.

beam-f96 A B Cfocal.[192] 44,9% 29,8% 26,7%

bok.[64] 40,5% 36,0% 31,1%kraj.[16] 2,7% 3,4% 3,4%

total 88,1% 69,3% 61,3%

Tab. Registrácia of alphas in detector planes.

Tab. Registration of recoils by detector planes.

Transport trough dead layer

• Depending on source position:– Energy calibration (energy loss from source to

sensitive volume of detector)– Depth of implantation (40 keV secondary beam)– Alpha peak “tails” (decay if implanted nuclei)

Alpha tails

Simulation of decay of implanted 202Rn compared to real values.

Conclusions

• Geometrical efficiency of registering of alpha particles is 92 – 95 % depending on beam position and decreases by ~ 10 % with each decay (100 % alpha decaying isotope)

• Depth of implantation into silicon is ≈ 10-9m• Energy calibration of all 352 strips (accordance

with table values up to ± 10 keV)• Peak tails are mainly due to inhomogenity of

electric field inside silicon crystal