203 research outputs found
MACHe3, a prototype for non-baryonic dark matter search: KeV event detection and multicell correlation
Superfluid He3 at ultra-low temperatures (100 microKelvins) is a sensitive
medium for the bolometric detection of particles. MACHe3 (MAtrix of Cells of
Helium 3) is a project for non-baryonic dark matter search using He3 as a
sensitive medium. Simulations made on a high granularity detector show a very
good rejection to background signals. A multicell prototype including 3
bolometers has been developed to allow correlations between the cells for
background event discrimination. One of the cells contains a low activity Co57
source providing conversion electrons of 7.3 and 13.6 keV to confirm the
detection of low energy events. First results on the multicell prototype are
presented. A detection threshold of 1 keV has been achieved. The detection of
low energy conversion electrons coming from the Co57 source is highlighted as
well as the cosmic muon spectrum measurement. The possibility to reject
background events by using the correlation among the cells is demonstrated from
the simultaneous detection of muons in different cells
Excitation energy and deformation of the 1/2+[431] intruder band in
The already detailed study of nucleus was complemented by a search for microsecond isomers at very low energy. For this purpose, this neutron-rich nucleus was produced by thermal-neutron-induced fission of . We have found a new 30.1 keV microsecond isomeric state which deexcites to the ground state by a strongly-hindered E1 transition. This isomer was identified as the 3/2+ level of the 1/2+[431] intruder band in and is also the lowest-lying member of the band. The very low energy of the band head suggests a large quadrupole deformation. From a comparison with ,where more information is known about the intruder band, it is deduced that the 1/2+[431] band has a quadrupole deformation, 0.35 and a possible triaxial shape, 20°
First observation of low-lying excited states in the very neutron-rich
Microsecond isomers of neutron-rich nuclei in the mass A=95 chain were investigated at the ILL reactor, Grenoble. These nuclei were produced by thermal-neutron induced fission of . The detection is based on time correlation between fission fragments selected by the Lohengrin mass spectrometer and the -rays from the isomers. In this paper the decay scheme of an isomer of half life 1.4(2) micro second in is reported. It is the first time that excited states of this nucleus have been measured. These data show that this neutron rich N = 59 isotone is spherical at low excitation energy
Shape coexistence in the very neutron-rich odd-odd
Microsecond isomers of neutron-rich nuclei in the masses A=96 and 98 were reinvestigated at the ILL reactor (Grenoble). These nuclei were produced by thermal-neutron induced fission of Pu. The detection is based on time correlation between fission fragments selected by the Lohengrin mass spectrometer, and the rays and conversion electrons from the isomers. A new level scheme of Rb is proposed. We have found that the ground state and low-lying levels of this nucleus are rather spherical, while a rotational band develops at 461 keV energy. This bans has properties consistent with a Nilsson assignment and a deformation . It is fed by a microsecond isomer consistent with a sperical configuration. It is interesting to note that the same unique-parity states and are present in the same nucleus in a deformed and in a spherical configuration. The neighbouring odd-odd nucleus Y presents a strong analogy with Rb and is also discussed
High spin microsecond isomers in In and Sb
In this work the microsecond isomers in 129In and 129Sb were investigated. These nuclei were produced by the thermal-neutron-induced fission of 241Pu. The detection is based on a time correlation between the fission fragments selected by the LOHENGRIN spectrometer at the ILL (Grenoble) and the Îł rays or conversion electrons from the isomers. The decay schemes of the new 17/2â isomer in 129In and 23/2+ isomer in 129Sb are reported. A shell-model study of these two nuclei was performed using a realistic effective interaction derived from the CDâBonn nucleon-nucleon potential. Comparison shows that the calculated energy levels and electromagnetic transition rates are in very good agreement with the experimental data. (APS
Recent measurements of the spherical and deformed isomers using the Lohengrin fission-fragment spectrometer
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New Spins for ground states and isomers in Pd and Pd
Levels in 115Pd and 117Pd nuclei, populated in the spontaneous fission of 248Cm were studied by means of prompt gamma spectroscopy using the EUROGAM2 array of Anti-Compton spectrometers. Negative-parity, I = 9/2 excitations were identified, which are associated with the long-lived isomers in these nuclei, reported previously as 11/2- excitations. The new data indicate spin and parity 3/2 + for ground states in 115Pd and 117Pd instead of 5/2 + proposed in previous works. This result implicates changes of spin assignments to other levels in both nuclei
HARD PHOTON PRODUCTION IN NUCLEUS-NUCLEUS COLLISIONS AT 30 MeV/u AND 44 MeV/u
Doubly differential cross-sections for Bremsstrahlung production have been measured in the reactions 40Ar + 197Au at 30 MeV/u and 86Kr +12C, AgNat and 197Au at 44 MeV/u. A qualitative analysis of the characteristics of the Îł-ray emission suggests strongly that the initial proton-neutron collisions are the main source of nuclear Bremsstrahlung
Suppression of soft nuclear bremsstrahlung in proton-nucleus collisions
Photon energy spectra up to the kinematic limit have been measured in 190 MeV
proton reactions with light and heavy nuclei to investigate the influence of
the multiple-scattering process on the photon production. Relative to the
predictions of models based on a quasi-free production mechanism a strong
suppression of bremsstrahlung is observed in the low-energy region of the
photon spectrum. We attribute this effect to the interference of photon
amplitudes due to multiple scattering of nucleons in the nuclear medium.Comment: 12 pages, 3 figures, submitted to Phys. Rev. Let
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