New constraints on WIMPs from the Canfranc IGEX dark matter search

The IGEX Collaboration enriched 76Ge double-beta decay detectors are currently operating in the Canfranc Underground Laboratory with an overburden of 2450 m.w.e. A recent upgrade has made it possible to use them in a search for WIMPs. A new exclusion plot has been derived for WIMP-nucleon spin-independent interaction. To obtain this result, 30 days of data from one IGEX detector, which has an energy threshold of ~4 keV, have been considered. These data improve the exclusion limits derived from other germanium diode experiments in the ~50 GeV DAMA region, and show that with a moderate improvement of the background below 10 keV, the DAMA region may be tested with an additional 1 kg-year of exposure.Comment: 7 pages, 2 figures, submitted to Physics Letter

Pulse Shape Discrimination in the IGEX Experiment

The IGEX experiment has been operating enriched germanium detectors in the Canfranc Underground Laboratory (Spain) in a search for the neutrinoless double decay of 76Ge. The implementation of Pulse Shape Discrimination techniques to reduce the radioactive background is described in detail. This analysis has been applied to a fraction of the IGEX data, leading to a rejection of ~60 % of their background, in the region of interest (from 2 to 2.5 MeV), down to ~0.09 c/(keV kg y).Comment: 18 pages, 10 figure

Fine structure in the α decay of 223U

Fine structure in the α decay of 223U was observed in the fusion-evaporation reaction 187Re(40Ar, p3n) by using fast digital pulse processing technique. Two α-decay branches of 223U feeding the ground state and 244 keV excited state of 219Th were identified by establishing the decay chain 223U →α1 219Th →α2 215Ra →α3 211Rn. The α-particle energy for the ground-state to ground-state transition of 223U was determined to be 8993(17) keV, 213 keV higher than the previous value, the half-life was updated to be 62−10+14 μs. Evolution of nuclear structure for N = 131 even-Z isotones from Po to U was discussed in the frameworks of nuclear mass and reduced α-decay width, a weakening octupole deformation in the ground state of 223U relative to its lighter isotones 219Ra and 221Th was suggested

Entry states in subbarrier fusion

The cross section for fusion of heavy ions below the Coulomb barrier can be orders of magnitude larger than the predictions of models that are quite successful above the barrier. Recent studies of ..gamma..-ray multiplicity have shown that the average l of the partial waves participating in subbarrier fusion is much higher than expected. The discrepancies become larger as the mass asymmetry of the projectile and target decreases. We have used the Spin Spectrometer in coincidence with identified products from two reactions leading to the same compound nucleus, /sup 164/Yb, to study entry-state angular-momentum effects. The reactions were /sup 64/Ni + /sup 100/Mo and /sup 16/O + /sup 148/Sm; the conditions of bombardment are listed. The O + Sm energies were chosen to match two of the Ni + Mo compound-nucleus excitation energies. Exit channels were identified by known ..gamma..-ray lines from the residual nuclei observed in six Compton-suppressed Ge detectors which replaced a like number of pentagonal NaI units of the Spin Spectrometer. Recording of events was triggered by detection of a ''clean'' Ge pulse (i.e., no ..gamma.. ray detected in its surrounding Compton shield). 10 refs., 5 figs., 2 tabs

THE SPIN SPECTROMETER AT THE HOLIFIELD HEAVY-ION RESEARCH FACILITY AND SOME PLANNED EXPERIMENTS

The 4π multidetector γ-ray spectrometer at the Holifield Heavy-ion Research Facility (HH IRF) is described in some detail. The following important features of this spectrometer are discussed : (a) the geometric arrangement, (b) the actual performance of the individual detector elements, (c) the associated electronics and data acquisition system, and (d) the response of the system to input γ-cascades including the effect of crystal-to-crystal scattering and the response to neutrons. The first few experiments to be performed are briefly described

gamma. -ray decay and nuclear shapes in /sup 158/Yb

The decay of the entry states in /sup 158/Yb populated in the reactions of 149 MeV /sup 20/Ne with /sup 144/Nd and /sup 146/Nd has been investigated with a 4 ..pi.. multidetector system gated by a Ge counter. The average exitation energy, the ..gamma..-ray spectra and the angular distributions as a function of multiplicity show several changes in the ..gamma..-ray decay. These changes suggest a transition from prolate to particle aligned oblate configuration at I approx. 28. At I 38 to 48 collective transitions with dipole and quadrupole component are observed. Possible explanations for these transitions are discussed in terms of nuclear shapes. Furthermore, above I approx. 48 the dipole component disappears suggesting a further change toward more triaxial shape. 19 references

Spin spectrometer at the holified heavy-ion research facility and some planned experiments

The 4..pi.. multidetector ..gamma..-ray spectrometer at the Holified Heavy-ion Research Facility (HHIRF) is described in some detail. The following important features of this spectrometer are discussed: (a) the geometric arrangement, (b) the actual performance of the individual detector elements, (c) the associated electronics and data acquisition system, and (d) the response of the system to input ..gamma..-cascades including the effect of crystal-to-crystal scattering and the response to neutrons. The first few experiments to be performed are briefly described