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

ReA3 – 12 Workshop, MSU, East Lancing, MI August 20, 2015 LLNL-PRES-676029 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC

 Funding provided by DOE Office of Nuclear Physics Lawrence Livermore National Laboratory 2 LLNL-PRES-676039

 Introduction  A case study  Instrumentation  Summary Lawrence Livermore National Laboratory 3 LLNL-PRES-676039

 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 4 LLNL-PRES-676039

Lawrence Livermore National Laboratory 5 LLNL-PRES-676039

A Beam intensity A (pps) 112 1.63 10 6 1.75 s 1.58 10 6 104 stable 3.36 10 5 7.52 10 3 120 1.18 10 2 45 ms Nomura, Shimizu, and Otsuka, PRC 81, Lawrence Livermore National Laboratory 044307 (2010) 6 LLNL-PRES-676039

 112 Ru (T 1/2 = 1.75 s) has been studied extensively by exploring the prompt  - ray emission of fission fragments  Example given was derived from the 238 U(  ,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- odd spin in the K = 2 band shows the signature of  -rigid rotor Wu et al ., PRC 73, 034312 (2006) Lawrence Livermore National Laboratory 7 LLNL-PRES-676039

 knowledge on the electromagnetic properties limited • Electromagnetic properties are the direct probe of the wavefunction of 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 8 LLNL-PRES-676039

 Imaginary experiment: 460 MeV 112 Ru on a 208 Pb target of 1 mg/cm 2 using the p-p-  coincident technique • A total of ~ 90 counts accumulated over a 3-day period assuming the beam intensity of 10 5 pps, cross section of 1 mb, and 10% of  efficiency Population of ground-state band Lawrence Livermore National Laboratory 9 LLNL-PRES-676039

 Ratio of cross section between   5 o and 30 o 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 10 LLNL-PRES-676039

 Ratio of cross section between   5 o and 30 o for the K = 2 band • Precision determination is possible for the electromagnetic properties of the K = 2 band Lawrence Livermore National Laboratory 11 LLNL-PRES-676039

Courtesy of M. Allmond  432 MeV 110 Ru (T 1/2 = 12 s) on a 208 Pb target of 1 mg/cm 2  ~ 2,000 pps over ~ 10 days using GRETINA/CHICO2 Lawrence Livermore National Laboratory 12 LLNL-PRES-676039

 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 12 o    85 o and 95 o    168 o .  CHICOx has the matching position resolution to that of GRETA. Lawrence Livermore National Laboratory 13 LLNL-PRES-676039

 The fine position resolution is realized by fully pixelating the cathode board and reached 1.6 o in  and 2.5 o in  in ‪ recent experiments fielded at ANL.  Beam contaminants other than isobars can be discriminated by the measured two-body kinematics. Lawrence Livermore National Laboratory 14 LLNL-PRES-676039

 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 Lawrence Livermore National Laboratory 15 LLNL-PRES-676039