Program - Brookhaven National Laboratory

was recently measured using a metallic magnetic calorimeter [1]. The energy resolution, 29 eV at 5.9 keV,
and the energy threshold, 300 eV, allow testing the theoretical beta spectra calculations with an accuracy
never before achieved. The spectrum from [1] has already been compared to classical beta calculations
[2], and in this framework a significant deviation of the experimental spectrum below 5 keV could not
be explained. The exchange effect has been given as a possible cause, and indeed calculations confirm
that this atomic effect explains a large part of this deviation. More recently, the beta spectrum of Ni-63
was measured with the same experimental technique. Comparison with a theoretical spectrum calculated
taking into account the exchange effect exhibits an excellent agreement. Calculation of exchange effect is
detailed following the formalism set out in [3]. The remained discrepancy at low energy in the Pu-241 beta
spectrum is discussed reviewing the influence of possible other effects. Exchange correction is found to be
very sensitive to screening effect due to the electron cloud of the daughter nucleus. For radionuclides with
high Z, this work has demonstrated the necessity to take into account the spatial variation of the nuclear
charge experienced by the ejected electron to accurately correct for screening.
[1] M. Loidl, M. Rodrigues, B. Censier, S. Kowalski, X. Mougeot, P. Cassette, T. Branger, and D. Lacour,
Appl. Radiat. Isot. 68, 1460 (2010). [2] X. Mougeot, M.-M. Bé, V. Chisté, C. Dulieu, V. Gorozhankin,
and M. Loidl, in LSC2010, International Conference on Advances in Liquid Scintillation Spectrometry,
edited by P. Cassette, Radiocarbon (University of Arizona, Tucson, 2010) pp. 249-257. [3] M. R. Harston
and N. C. Pyper, Phys. Rev. A 45, 6282 (1992).
Session OE Beta delayed neutrons
Thursday March 7, 2013
Room: Central Park West at 1:30 PM
OE 1 1:30 PM
Beta Delayed Neutron Spectroscopy on the r-process Path
R. Grzywacz, S.V. Paulauskas, M. Madurga, D. Miller, M. Al-Shudifat, L. Cartegni, A. Fija̷lkowska, C.U.
Jost, S. Padgett, Dept. of Phys. and Astr., University of Tennessee, Knoxville, TN 37996, USA. C.J.
Gross, D.W. Bardayan, A.J. Mendez II, K. Miernik, K. Rykaczewski, K.T. Schmitt, D.W. Stracener, M.
Wolińska-Cichocka, Phys. Div., Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA. W.A.
Peters, J.C. Batchelder, S. Liu, C. Matei, I. Spassova, Oak Ridge Associated Universities, Oak Ridge, TN
37831, USA. J. Blackmon, M. Matos, C. Rasco, E.F. Zganjar, Dept. of Phys. and Astr., Louisiana State
University, Baton Rouge, LA 70803, USA. N.T. Brewer, E.H. Wang, Dept. of Phys. and Astr.,
Vanderbilt University, Nashville, TN 37235, USA. J.A. Cizewski, M.E. Howard, P.D. O’Malley, A.
Ratkiewicz, D. Walter, Dept. of Phys. and Astr., Rutgers University, Piscataway, NJ 08854-8019 USA.
P.A. Copp, Phys. Dept., University of Wisconsin-La Crosse, La Crosse, WI 54601, USA. S. Ilyushkin, F.
Raiola, F. Sarazin, Dept. of Phys., Colorado School of Mines, Golden, CO 80401, USA.
Beta-delayed neutron emission (βn) is a dominant decay channel for the majority of very neutron-rich
nuclei on the r-process path. This is due to nuclear structure effects, which drive the population of
neutron-unbound states in beta-decay daughters. A majority of the r-process nuclei cannot be synthesized,
thus astrophysical nucleosynthesis calculations are forced to use input data provided by theory, which
may not always be reliable due to inherent complexity of the many body problem. Because they directly
probe relevant physics on the microscopic level, energy-resolved measurements of the beta-decay strenght
distribution constitute a better test of nuclear models than traditionally used gross properties like lifetimes
and branching ratios. Neutron spectroscopy is required for investigations of decays of the most neutronrich
isotopes because the dominant part of the beta decay strength is encoded in the decay energy carried
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