Program - Brookhaven National Laboratory

[1] Y. Kojima et al., Nucl. Instr. Meth. A 193-197 659 (2011) . [2] Y. Kojima et al., KURRI Prog. Rept.
(in press).
OD 3 2:20 PM
Scissors Mode Strength in Rare Earth Nuclei Studied from (n,γ) reaction
J. Kroll, F. Becvar, M. Krticka, S. Valenta, Charles University in Prague, CZ-180 00 Prague 8, Czech
Republic. B. Baramsai, G. E. Mitchell, C. L. Walker, North Carolina State University, Raleigh, NC 27695
and Triangle Universities Nuclear Laboratory, Durham, NC 27708. J. A. Becker, A. Chyzh, D. Dashdorj,
W. Parker, C. Y. Wu, Lawrence Livermore National Laboratory, Livermore, CA 94551. T. A. Bredeweg,
A. Couture, R. C. Haight, M. Jandel, J. M. O’Donnell, R. S. Rundberg, J. L. Ullmann, D. J. Vieira, J. B.
Wilhelmy, J. M. Wouters, Los Alamos National Laboratory, Los Alamos, New Mexico 87545. M. Heil, R.
Reifarth, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstr. 1, 4291 Darmstadt,
Germany. F. Kaeppeler, Karlsruhe Institute of Technology, Campus North, Institute of Nuclear Physics,
76021 Karlsruhe, Germany.
The existence of the scissors M1 vibrational mode built on ground states of even-even deformed nuclei, predicted
by the theory [1], has already been firmly established from extensive nuclear resonance fluorescence
(NRF) studies [2]. Later, the measurements of gamma-ray spectra of two-step cascades (TSCs) following
the thermal neutron capture in 162 Dy strongly indicated that, in line with Brink hypothesis, this mode is
built not only on the ground state, but also on each excited level of deformed nuclei [3]. Results of later
studies of the scissors mode of excited nuclear levels will be reported with emphasis on data from three
different kinds of neutron capture experiments: (i) TSC experiments performed at LVR-15 reactor in Rez
on targets 155,157 Gd, 159 Tb, 161 Dy and 176 Lu, (ii) the experiments at the LANSCE/DANCE neutron timeof-flight
facility in Los Alamos which made it possible to retrieve gamma-ray spectra of multi-step cascades
(MSCs) accompanying the neutron capture at isolated resonances of 152,154−158 Gd, and (iii) the experiments
undertaken at Karlsruhe Van de Graaff facility using pulsed neutrons produced via the 7 Li(p,n) 7 Be
reaction – in this case the spectra of MSCs following the neutron capture in 155−158 Gd in the energy region
of unresolved resonances were analyzed. These classes of experiments are, to a large extent, complementary.
Their noteworthy feature is that they also provide information on scissors mode of odd and odd-odd
nuclei, for which the present state-of-the-art of the NRF technique meets with difficulties. Systematic
trends in the energy, damping width and B(M1) reduced strength of the observed scissors mode built on
excited levels will be discussed and compared with what has been deduced from the NRF data for the
ground-state scissors mode and from the data on 3 He-induced γ emission. The impact of knowledge of the
scissors mode on understanding the systematic behaviour of total radiation width of neutron resonances
will be highlighted.
[1] N. Lo Iudice and F. Palumbo, Phys. Rev. Lett. 41, 1532 (1978). [2] U. Kneissl, H. H. Pitz and A.
Zilges, Prog. Part. Nucl. Phys. 37, 349 (1996). [3] M. Krticka at al., Phys. Rev. Lett. 92, 172501 (2004).
OD 4 2:40 PM
Evidence for the Exchange Effect in Low-Energy Beta Decays
X. Mougeot, M.-M. Bé, C. Bisch, and M. Loidl
CEA, LIST, LNHB, Gif-sur-Yvette, F-91191, France
Metallic magnetic calorimeters have been shown to be a powerful experimental technique to study the
energy spectra of beta particles having a maximum energy of about 1 MeV. The beta spectrum of Pu-241
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