ReA3 12 Workshop, MSU, East Lancing, MI August 20, 2015 - - PowerPoint PPT Presentation

LLNL-PRES-676029

This work was performed under the auspices of the U.S. Department

• f Energy by Lawrence Livermore National Laboratory under contract

DE-AC52-07NA27344. Lawrence Livermore National Security, LLC

ReA3 – 12 Workshop, MSU, East Lancing, MI

August 20, 2015

Lawrence Livermore National Laboratory

LLNL-PRES-676039

2

• Funding provided by DOE Office of Nuclear Physics

Lawrence Livermore National Laboratory

LLNL-PRES-676039

3

• Introduction
• A case study
• Instrumentation
• Summary

Lawrence Livermore National Laboratory

LLNL-PRES-676039

4

• How is the shape evolution for neutron-rich nuclei toward

the r-process path if the N= 82 shell weaken? How are we going to measure it?

• The excitation of the first 2+ state of even-even nuclei allows a

qualitative measure of the quadrupole collectivity.

• The absolute E2 transition rate and static moment are the

measure of the magnitude and asymmetry of the quadrupole collectivity.

— Can be measured by the sub-barrier Coulomb

excitation method.

Lawrence Livermore National Laboratory

LLNL-PRES-676039

5

Lawrence Livermore National Laboratory

LLNL-PRES-676039

6

Nomura, Shimizu, and Otsuka, PRC 81, 044307 (2010) 104 stable 112 1.75 s 120 45 ms Beam intensity (pps) 1.18 102 1.58 106 3.36 105 7.52 103 1.63 106 A A

Lawrence Livermore National Laboratory

LLNL-PRES-676039

7

Wu et al., PRC 73, 034312 (2006)

• 112Ru (T1/2 = 1.75 s) has been studied

extensively by exploring the prompt - ray emission of fission fragments

• Example given was derived from the

238U(,2n f) reaction using

Gammasphere/CHICO at LBNL

• States with spin up to 22+ of K = 0

band and 19+ of K = 2 band were populated

• Level staggering pattern of the even-
• dd spin in the K = 2 band shows the

signature of -rigid rotor

Lawrence Livermore National Laboratory

LLNL-PRES-676039

8

• knowledge on the electromagnetic properties limited
• Electromagnetic properties are the direct probe of the wavefunction
• f both the ground and excited states, particularly, the collective

states

• Can be explored using the sub-barrier Coulomb excitation

method

• which is one of major experimental techniques to measure the

electromagnetic transition matrix elements between states and the static quadrupole moment of excited states

Lawrence Livermore National Laboratory

LLNL-PRES-676039

9

• Imaginary experiment: 460 MeV 112Ru on a 208Pb target of

1 mg/cm2 using the p-p- coincident technique

• A total of ~ 90 counts accumulated over a 3-day period assuming

the beam intensity of 105 pps, cross section of 1 mb, and 10% of  efficiency

Population of ground-state band

Lawrence Livermore National Laboratory

LLNL-PRES-676039

10

• Ratio of cross section between   5o and 30o for the

ground-state band

• A 5% uncertainty in the -ray yield leads to ~ 10% uncertainty or

0.1 – 0.2 eb for the quadrupole moment

Lawrence Livermore National Laboratory

LLNL-PRES-676039

11

• Ratio of cross section between   5o and 30o for the K = 2

band

• Precision determination is possible for the electromagnetic

properties of the K = 2 band

Lawrence Livermore National Laboratory

LLNL-PRES-676039

12

• 432 MeV 110Ru (T1/2 = 12 s)
• n a 208Pb target of 1 mg/cm2
• ~ 2,000 pps over ~ 10 days

using GRETINA/CHICO2

Courtesy of M. Allmond

Lawrence Livermore National Laboratory

LLNL-PRES-676039

13

• CHICO consists of two mirror-image hemispheres with

solid-angle coverage of 69% of 4 and each holds 10

‪ individual parallel-plate position-

sensitive avalanche counters. It covers the angular range of 12o    85o and 95o    168o.

• CHICOx has the matching

position resolution to that of GRETA.

Lawrence Livermore National Laboratory

LLNL-PRES-676039

14

• The fine position resolution is realized by fully pixelating

the cathode board and reached 1.6o in  and 2.5o in  in

‪ recent experiments

fielded at ANL.

• Beam contaminants
• ther than isobars can

be discriminated by the measured two-body kinematics.

Lawrence Livermore National Laboratory

LLNL-PRES-676039

15

• Explore the shape evolution for neutron-rich nuclei toward

the r-process path, under the influence of the possibly weaken N = 82 shell.

• Determine their electromagnetic properties such as the

absolute transition rate and static moment

• Utilize the sub-barrier Coulomb excitation method with

GRET(IN)A/CHICOx