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

Realistic shell-model calculations for proton particle-neutron hole nuclei around 132Sn

We have performed shell-model calculations for nuclei with proton particles and neutron holes around 132Sn using a realistic effective interaction derived from the CD-Bonn nucleon-nucleon potential. For the proton-neutron channel this is explicitly done in the particle-hole formalism. The calculated results are compared with the available experimental data, particular attention being focused on the proton particle-neutron hole multiplets. A very good agreement is obtained for all the four nuclei considered, 132Sb, 130Sb, 133Te and 131Sb. We predict many low-energy states which have no experimental counterpart. This may stimulate, and be helpful to, future experiments.Comment: 8 pages, 6 figures, to be published on Physical Review

Excitation energy and deformation of the 1/2+[431] intruder band in 107Tc^{107}Tc

The already detailed study of $^{107}Tc$ 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 $^{241}Pu$. 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 $^{107}Tc$ 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 $^{105}Tc$,where more information is known about the intruder band, it is deduced that the 1/2+[431] band has a quadrupole deformation, $\epsilon_{2} \geq$ 0.35 and a possible triaxial shape, $\gamma \approx$ 20°

High spin microsecond isomers in 129^{129}In and 129^{129}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 γ rays or conversion electrons from the isomers. The decay schemes of the new 17/2− 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 CD–Bonn nucleon-nucleon potential. Comparison shows that the calculated energy levels and electromagnetic transition rates are in very good agreement with the experimental data. (APS

First observation of low-lying excited states in the very neutron-rich 95Kr^{95}Kr

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 $^{241}Pu$. The detection is based on time correlation between fission fragments selected by the Lohengrin mass spectrometer and the $\gamma$-rays from the isomers. In this paper the decay scheme of an isomer of half life 1.4(2) micro second in $^{95}Kr$ 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

Recent measurements of the spherical and deformed isomers using the Lohengrin fission-fragment spectrometer

International audienc

Shape coexistence in the very neutron-rich odd-odd 96Rb^{96}Rb

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 $^{241}$Pu. The detection is based on time correlation between fission fragments selected by the Lohengrin mass spectrometer, and the $\gamma$ rays and conversion electrons from the isomers. A new level scheme of $^{96}$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 $\pi[431 3/2] x \nu[541 3/2]K = 3^-$ Nilsson assignment and a deformation $\beta_2 > 0.28$. It is fed by a $10^-$ microsecond isomer consistent with a $\pi(g_{9/2})\nu(h_{11/2})$ sperical configuration. It is interesting to note that the same unique-parity states $\pi(g_{9/2})$ and $\nu(h_{11/2})$ are present in the same nucleus in a deformed and in a spherical configuration. The neighbouring odd-odd nucleus $^{98}$Y presents a strong analogy with $^{96}$Rb and is also discussed

Proton-Neutron Interaction near Closed Shells

Odd-odd nuclei around double shell closures are a direct source of information on the proton-neutron interaction between valence nucleons. We have performed shell-model calculations for doubly odd nuclei close to $^{208}$Pb, $^{132}$Sn and $^{100}$Sn using realistic effective interactions derived from the CD-Bonn nucleon-nucleon potential. The calculated results are compared with the available experimental data, attention being focused on particle-hole and particle-particle multiplets. While a good agreement is obtained for all the nuclei considered, a detailed analysis of the matrix elements of the effective interaction shows that a stronger core-polarization contribution seems to be needed in the particle-particle case.Comment: 8 pages, 6 figures, Proccedings of the International Conference "Nuclear Structure and Related Topics", Dubna, Russia, September 2-6, 2003, to be published in Yadernaia Fizika (Physics of Atomic Nuclei

Low-lying levels in 119^{119}Xe

The decays of ${}^{119m}$Cs and ${}^{119g}$Cs to ${}^{119}$Xe have been studied on mass separated samples, using $\gamma\rm{-ray}$ and internal conversion electron measurements. Several new low-lying levels have been established in the ${}^{119}$Xe level scheme. Half-life evaluations for ${}^{119m}$Cs and ${}^{119g}$Cs have been revisited. The results are compared with other experimental data known in light odd-mass xenon isotopes and with calculations performed in the frame of the multi-shell interacting boson-fermion model