The Phoswich Wall – features, applications, performance
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Transcript of The Phoswich Wall – features, applications, performance
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The Phoswich Wall – features, applications, performanceThe Phoswich Wall – features, applications, performance
Walter Reviol and Demetrios Sarantites (Washington University)
ATLAS User Workshop, ANL, May 2014
Plastic – CsI(Tl) phoswich
Angle range: 9º ≤ θ ≤ 72º
4 PMT’s, 64 pixels each
Sub-pixel positioningresolution: Δx ≈ 1 mm
Tailored to run with a4π γ-ray array
Coincidence measurement:particleTLF – γPLF
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Some one-neutron transfer studies near 132Sn
134Te + 13C, Elab = 565 MeV, I= 3·105 s-1 (Holifield)
Channel of interest: 135Te83
Hyball + CLARION detector combination
particleTLF − γPLF coincidences
136Xe + 13C, Elab = 560 MeV (ATLAS)
Channel of interest: 137Xe83
Microball + Gammasphere
Allmond et al., PRC 86 (2012); Radford et al., EPJA 15 (2002)
[principle of experiment]
gate 929
gate 1180
gate 533 (narrow)
gate 1220
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Transfer reaction vs. spontaneous fission
Selectivity (can dial state of interest)
Vast amount of information
248Cm SFDaly et al.PRC 59, 3066 (1999)
136Xe + 13C 137Xe + 12CAllmond et al., PRC 86, 031307(R)(2012) 137Xe
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Lessons learned so far
• Using comparatively heavy targets (13C, 9Be) is a good way of studying
high-j, high-ℓ states; complementary to (d,p), (α,3He)
• Combining HPGe array and Phoswich Wall (Microball) is beneficial for
studying heavy nuclei; here the density of states is high
• Using the selectivity of transfer reactions allows to improve level schemes
previously studied via SF, fusion-evaporation, or deep-inelastic collisions;
for example, the transition intensity helps to determine the state’s parity
New tasks
• Extract nucleon-transfer spectroscopic factors from dσ/dΩCoM,PLF; based
on TLF angular-distribution data
• Explore the potential of cluster transfer, e.g., 142Ce(7Li,α)145Pr; suppress
incomplete-fusion channels, get a handle on 3H spectroscopic factors
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What can be determined and how?
• For every excited state of the PLF, the Q value is obtained from the level energy and the calculated Qgg value (Q = Qgg – Elev).
• From θLab,TLF , we then calculate ΘCoM,PLF (since we are dealing with a
binary reaction).
• If only PLF is excited, ΘCoM,PLF (θTLF) and ELab,TLF(θLab,TLF) are single curves .
(If TLF is excited too, two curves are obtained, and the one corresponding to the higher ELab,TLF is picked.)
• The derived quantity is dσ/dΩCoM,PLF (θLab,TLF).
(What angle ranges can be covered?)
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Example: study of one-proton transfer in heavy rare-earth nuclei
1) Ground-state to ground-state Q value in MeV2) Nitride target3) CARIBU beam
Beam Target PLF + TLF Qgg 1) Beam Targ. PLF + TLF Qgg
142Ce 14N 2) 143Pr + 13C -1.726 148Ce 3) 14N 149Pr + 13C 0.379142Ce 14N 141La + 15O -1.590 148Ce 14N 147La + 15O -3.712142Ce 14N 143Ce + 13N -5.409 148Ce 14N 149Ce + 13N -6.211142Ce 14N 141Ce + 15N 3.665 148Ce 14N 147Ce + 15N 4.378
Red Case of interest: location of πh11/2 , occupancy of πg7/2 vs. N
Experimental issue: separate C from N and O (20 MeV < ELab,TLF < 150 MeV)~~
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Phoswich Wall in-beam performance (Notre Dame FN Tandem)
Scattering experiments:• α’s, heavy ions off 197Au
(5 – 6 energies)
• 197Au(α,p)202Hg (27 MeV)
• consider energy deposited
in CsI(Tl)
• gating
Findings: Ions are well separated down to low energies (14N: Edep= 8.46 MeV) Some may be mass-identifiable at higher energies (7Li vs. 6Li)
A: Fast, B: Early, C: Late
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Used square masks of different sizesThe algorithm is pulse-height independent
Applying the algorithm gives uniform distributions
4.8 x 4.8 mm2 mask
Phoswich Wall 252Cf tests: the position algorithm
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Summary and Outlook
The Phoswich Wall was designed for strongly inverse kinematics binary reactions near the Coulomb barrier. It is not a “stand-alone” device. The new device is, in a sense, the successor for Microball/Hyball.
Starter experiments are: 7Li breakup/transfer and single-nucleon transfer studies, the latter with comparatively heavy targets. Projectile Coulomb excitation will be performed simultaneously, large angles θLab,TLF favor safe Coulex (not discussed).
The PID among the particles of interest is as good as expected. The fast-plastic and CsI(Tl) components are calibrated. The device is ready for production runs. The readout is VME based and can be easily coupled to the Myriad system of DGS and to Gretina (not discussed).
High-quality stable and CARIBU reaccelerated beams from ATLAS are crucial (timing, beam spot).
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Acknowledgement
Very valuable discussions with J.M. Allmond and
D.C. Radford are gratefully acknowledged.
Thanks for your attention!
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Backup Slides
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Faller et al.,PRC 38,905 (1988)
11B(140Xe,141Cs)10Be or 14N(140Xe,141Cs)13C , one-proton transfer
πh11/2Negative-parity statesin the isotopic chainon both sides of theN = 82 “mark”
Additional thoughts on studying odd-Z nuclei:
10Be - 9Be distinction: by ΔE (except at large θ), γ rays.
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1p1/2
1p3/2
1s1/22
6
8 14N
11B
cross sections to j> states are higher (like 16O)
cross sections to j< states are higher (like 12C)
Fra
nle
y &
Ph
illip
s, N
PA
324
, 193
(19
79)
1, 2: initial, finalbound state
no extra angular momentum(that would influence the phase of the distorted wave)
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Q-value considerations for studying odd-Z nuclei in the rare-earth region
1) Q value in MeV2) Also considered as incomplete-fusion channel3) Odd-N nucleus, for comparsion only
Beam Target PLF + TLF Qgg 1) Beam Target PLF + TLF Qgg
142Ce 7Li 145Pr + α 7.58 148Ce 7Li 151Pr + α 8.86142Ce 7Li 144Pr + αn 2) 0.63 148Ce 7Li 150Pr + αn 2.31142Ce 7Li 143Pr + α2n 2) -5.13 148Ce 7Li 149Pr + α2n -3.02142Ce 7Li 143Ce + 6Li 3) -2.11 148Ce 7Li 149Ce + 6Li -2.91142Ce 7Li 141La + 8Be 8.37 148Ce 7Li 147La 6.25142Ce 11B 143Pr + 10Be -5.40 148Ce 11B 149Pr -3.30142Ce 14N 143Pr + 13C -1.73 148Ce 14N 149Pr 0.38142Ce 3He 143Pr + d 0.33 - - - -
Red: suggested cases for a simultaneous study
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Comment on Coulomb excitation
134,136Te + natC, Elab = 396 MeV, I= 105 s-1 (A=136)
12C-γ coincidences with CLARION + Hyball
(Hyball rings 1 – 3; 4° ≤ θC ≤ 44°)
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Phoswich WallPhoswich Wall
Tilted “Gobbi” geometry
Average target -detector distance: 55 mm
Angle range: 9º ≤ θ ≤ 72º
Multi-anode PMT (H8500):• # pixels: 64• active fraction of surface: 0.89• pixel size: 6.02 × 6.02 mm2
Phoswich: 12 μm fast plastic, 2.2 mm CsI(Tl)
Optical cross talk: sub-pixel positioning
Expect: Δθ ≈ 1° , Δφ(θ) ≈ 4° - 1°
Microball: Δθ ≈ 18°
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Phoswich Wall 252Cf tests: particle identification (PID)
gating
Gates: Fast (A) , Early (B) , Late (C)
Pixel neighbor pulse heights are added in
ASIC chip readout (so-called PSD chip)
Early (B) (A)
Lat
e (
C)
Ear
ly (
B)
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142142Ce + Ce + 1414N → N → 137137Xe + Xe + 1313C, EC, Elablab= 560 MeV= 560 MeV
ΔE* = 3.089 MeV (13C: 1/2+)ΔELab,TLF ≈ 5.5 MeV
Good separation at the smaller anglesε ≈ 0.85 2π
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ΔθLab ≈ 1° ↔ ΔθCoM ≈ 2°
142142Ce + Ce + 1414N → N → 137137Xe + Xe + 1313C, EC, Elablab= 560 MeV= 560 MeV