Measurements of βnenergy

Transcription

1 Measurements of βnenergy spectra with VANDLE M. Madurga University of Tennessee

2 New/calculated half-lives for spherical nuclei affect r-process abundances New Ni, Cu, Zn, Ga, Ge values Changes in A~85 half-lives affect the whole pattern Models with robust microscopic foundations are required M. Madurga et al., PRL 109, (2012) FRDM + ff. gr. th. I. Borzov halflives `

3 β-decay in hot r-process Change in abundance pattern Effect individual decay rates Half-lives known today + FRIB

4 Beta decay of neutron rich nuclei Ei Q 1 = T1 / 2 E 0 i β S E f Z,Q E i β i S E i = f O mother ˆ Neutron spectroscopy S n Valence Total absorption spectroscopy High Resolution spectroscopy 8/20/2013 M. Madurga UTK 4

5 Beta decay of neutron rich nuclei: First Forbidden vs. Gamow-Teller Pigmy-resonance decay x x N=50 N=50-1 1s1/ FF 1d5/2 N=50 0g9/2 x o g9/2 1p1/2 1p3/2 0f5/2 p n p n -11 1p1/2 1p3/2 GT -13 0f5/ Z= f7/2 78 Ni

6 Neutron spectroscopy of fission fragments (1970s-1990s) Great Energy resolution Pandemonium B(GT) is the goal!

7 Holifield Radioactive Beam Facility Intense beam (~10 μa) of (50MeV) protons on UCx targets Isobar separation essential for success of the experiments! IRIS-1/IRIS-2 platforms, negative and positive ions. IRIS-1 ORIC IRIS-2 LERIBSS LIS

8 VANDLE at LeRIBSS: The Versatile Array for Neutron Detection at Low Energies Time of Flight detector 2 clovers, 3% 1MeV 48 x 60 cm VANDLE bars 45% 1MeV Ω = 26% of 4π 12% total 1MeV Fully instrumented using XIA s Pixie 16 digitizers VANDLE efficiency calibration performed at Ohio university

9 First scan of delayed neutron emitters studied at the HRIBF/LeRIBSS in February 2012 Proton number N=50 Z=50 Neutron number

10 VANDLE 2012 campaign highlights 78 Cu Z= Sb N-Z 84 Ga 100 Rb T 1/2 =51ms

11 100 Rb at LeRIBSS: neutron emission populates rotational bands Neutron gated γ spectrum Parity matters!

12 February 2012 VANDLE highlights: 77 Cu Gammow-Teller decays at 0.5 and 2 MeV above Sn 100 kev neutrons detected! ~70 kev neutrons? Level 50 kev above Sn previously LeRIBSS S.V Ilyushkin et al. PRC 80, (2009)

13 But The picture is more complicated 2 MeV Counts/ch x15 TOF (0.5ns/ch)

14 VANDLE highlights: Resonant decay of 84 Ga Preliminary Decay probability from area

15 Preliminary Strength distribution Cheating!: all neutron transitions feeding 83 Ge ground state

16 Neutron-Gamma coincidences J.A. Winger Phys. Rev. C 81

17 Statistical model of 84 Ga delayed neutron emission Hauser-Feshbach calculation T. Kawano

18 Summary: A renaissance of β- decay spectroscopy 84 Ga Models of beta decay require experimental input of decay strength 30 delayed neutron emitters studied at HRIBF Neutron-Gamma coincidences are fundamental Resonant-like strength in 84 Ga cannot be explained using statistical theory

19 ORNL support People C. Gross, C. Jost, A.J. Mendes II, D. Stracener Decay Spectroscopy group L. Cartegni, R. Grzywacz, A. Kuzniak, D. Miller, S. Padgett, S. Paulauskas J.C. Batchelder, S. Liu, M. Wolinska-Cichocka. K. Rykaczewski, K. Miernik, C. Mazzochi, M. Karny, A. Korgul, S. Ilyushkin, J. Winger, W. Krolas, J.H. Hamilton, N. Brewster, A.V Ramaya, J.K. Hwang, E. Zganjar, VANDLE colaboration C. Matei and I. Spassova ORAU; P.D. O'Malley, M. Howard, B. Manning, E. Merino, and J. Cizewski, Rutgers U.; D. Bardayan, ORNL; C. Brune and T. Massey, Ohio U.; F. Raiola, D. Walter, S. Ilyushkin, and F. Sarazin, Colorado School of Mines; J. Blackmon, Louisiana State U