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Inverse-kinematic studies with Gretina and Phoswich WallInverse-kinematic studies with Gretina and Phoswich Wall

Walter Reviol and Demetrios Sarantites (Washington University)

Gretina Workshop, ANL, March 2013

Plastic-CsI(Tl) phoswich

Angle range: 8º ≤ θ ≤ 74º

4 PMT’s, 64 pixels each

Pixel size: 6 x 6 mm

Sub-pixel positioningresolution

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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

CLARION + Hyball detector combination

γPLF− particleTLF coincidences

136Xe + 13C, Elab = 560 MeV (ATLAS)

Channel of interest: 137Xe83

Gammasphere + Microball

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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3

Next: 139Xe85 − level confirmation and spectroscopic factor

No theory yet, but this argument can be made:

The N = 83, 85 nuclei are cases for the emergenceof collectivity just above 132Sn.

A phenomenological model (coupling i13/2 states to

quadrupole and octupole vibrations) was used.

The lowest 13/2+ states ought to be rather pure(little admixture of 3−,f7/2). Hence S-factor data

help to improve shell model calculations for132Sn and neighboring nuclei.

Heyde et al., PLB 57, 429 (1975)

Data for Xe are, in general, sparse compared to heavier isotones.

?

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Re-accelerated CARIBU beams, some nuclei of interest, and related parameters:

single-particle transfer and both safe and unsafe Coulex

1) Beam intensity in 105 s-1 (Cf252-upgrade-proposal-final-Rev4.pdf)2) Q values and energies in MeV

Beam Intens.1) Target PLF Qgg 2) ECoul,lab

2) Ebeam 2) θgraz,lab TLF

138Xe 7.2 13C 139Xe -1.35 491 560 40.5º138Xe 7.2 9Be 139Xe 1.94 474 540 40.3º138Xe 7.2 9Be 139Xe 1.94 474 380 -140Xe 5.0 13C 141Xe -2.08 496 565 40.3º140Xe 5.0 11B 141Cs -2.46 489 557 40.4º

Large TLF angles = safe, small TLF angles = unsafe Coulex

Red: for 13/2+ in 139Xe, = 17 mb (Ptolemy DWBA code)

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Symbols

Open: Raman et al., ADNDT 78 (2001)

Full: recent RIB Coulex experiments

Sn and Te: Radford et al. (Holifield)

Xe: Kröll et al. (REX-ISOLDE) AIP Conf. Proc. 1012, 84 (2008)

“N > 82 Anomaly” (Radford et al.)

Large error for 138Xe suggests newmeasurement.

“Standard” SM calculations aren’t able to reproduce small 136Te B(E2).

B(E2;0+→21+) values in Sn region around N = 82

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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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Summary

The Phoswich Wall is, in a sense, the successor for Microball/Hyball. The experiments discussed are logic continuations of the inverse-kinematic radioactive-beam experiments pioneered by the group at ORNL-HRIBF.

The starter experiment would be neutron-transfer (and simultaneous Coulex) studies using a 138Xe beam from CARIBU and a 13C target. As for the transfer, the focus is on i13/2 physics.

For the very asymmetric “inverse” reactions the coverage, 8º ≤ θ ≤ 74º, of the Phoswich Wall can probably not be met by any other detector.

The Phoswich Wall will be keeping up with future high-intensity radioactive-beam experiments (and stable-beam experiments).

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Backup Slides

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1p1/2

1p3/2

1s1/22

6

8 13C

9Be

(cross sections to j> states are higher)

(cross sections to j< states are higher)

Fra

nle

y et

al.,

NP

A 3

24, 1

93 (

1979

)

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Observations• Assignment for 13/2+ (1512.2 keV) uses in part systematics.• Distinction between 13/2+ and 13/2-

(1085.8 keV) is not firm.

Issues• Populate preferably 13/2+.• Spin assignment by γ−particle angular correlations.• Fragmentation of i13/2 strength.

248Cm source experiment

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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:

10Be - 9Be distinction: by ΔE (except at large θ), γ rays.

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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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Some one-neutron transfer studies near 132Sn - continued

134Te + 13C, CLARION + Hyball

Use Hyball rings 3, 4: 28° ≤ θC ≤ 60°12 detectors/ring, same set of angles ɸC

For each event: reaction plane w/ angle ɸC

Use the CLARION ring with θγ = 90°5 detectors with different angles ɸγ

Construct angular correlations:Δɸ = ɸγ − ɸC , 5 · 12 = 60 data points

TLF-γ angular correlations

Allmond et al., PRC 86 (2012)

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High-l states are strongly populated in inverse-kinematics reactions w/ C or Be targets. Let’s focus on the i13/2 and f7/2 orbitalsA = 137 (N = 83): Isospin dependent modification of residual interactionA ≥ 139 (N ≥ 83): Shape evolution with N

A focus in studies of A ≥ 139 Xe’s is the angular distribution of candidate 13/2 →11/2 transitions and, perhaps, their linear polarization

13/2+: only one state not seen inSF. But the decay intensity isvery different (compared to SF).

143Xe: levels seen inSF experiment. But no assignments made.

Onset of collectivity.

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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 θTLF,Lab , we then calculate θPLF,CoM (since we are dealing with a

binary reaction).

• If only PLF is excited, θPLF,CoM (θTLF,Lab) and ETLF,Lab(θTLF,Lab) are single

curves (if TLF is excited too, two curves are obtained, and the one

corresponding to the lower EPLF,CoM is picked).

What angle ranges can be covered?

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Ordinate:Degree or MeV

ε ≈ 0.85 2π

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Design requirements for the Phoswich Wall

The main application is in reverse-kinematics binary reactions.

An example: 13C(140Xe,141Xe)12C (CARIBU).

Details:• The observables are TLF particles and coincident PLF γ rays (12C − 141Xe γγ).

• The important derived quantity is dσ/dΩPLF,CoM(θ) → spectroscopic factors/ANC’s.

• Δθ ~ 1º and Δφ(θ) = 4º to 1º.

• Microball/Hyball segmentation (Δθ = 18º on average) is inadequate.

• High rate capability due to high “pixilation”.

• Z-identification of TLF’s, hence use phoswich detectors.

• No 4π coverage (e.g. 12C θgraz,lab = 40.3° for 465 MeV 140Xe + 13C).

• Optimal Doppler correction of PLF γ rays comes for free.