B. Chambon

Pulse shape discrimination and dark matter search with NaI(Tl) scintillator

Abstract An extensive study of NaI(Tl) as a Dark Matter particle detector is presented. Emphasis is put on the response of the detector, both in energy and pulse shape, to all particles interacting in the detector, namely high energy (MeV) photons, low energy photons (X-rays), betas from external radioactivity, and neutrons, which induce nuclear recoils. The initial hope that the shorter decay times of nuclear recoils induced by WIMPs could be statistically separated from Compton interactions is weakened by the fact that low energy X-rays and betas exhibit pulse shapes similar to recoils. As a consequence, any indication of shorter decay time pulses leads to an ambiguous interpretation. Underground data for the WIMP search were obtained in a low activity environment at the Laboratoire Souterrain de Modane (LSM), with a 10 kg crystal having high photoelectron yield and 2 keV energy threshold. The data contain pulse shapes with decay times shorter than for Compton interactions and are not compatible with calibration reference shapes or a mixture of these. The effect is shown to come from a population with decay times even shorter than nuclear recoils but its origin was not identified. The Compton rejection efficiency is limited to factors ranging from 3 at 5 keV to 8 at 20 keV (electron equivalent energy). It is shown that the sensitivity of NaI(Tl) detectors to the cross section of Spin Independent coupling WIMPs is only slightly improved by the pulse shape analysis, while it is mostly determined by the differential energy rate at threshold. The sensitivity to the cross section of Spin Dependent coupling WIMPs is improved by about an order of magnitude by the pulse shape analysis.

Cross talk and diaphony in neutron detectors

Abstract A neutron which enters a detector can be scattered into a neighbouring detector. If the neutron is registered in each detector the effect will be calle

Calibration of the EDELWEISS cryogenic heat-and-ionization germanium detectors for dark matter search

Several aspects of the analysis of the data obtained with the cryogenic heat-and-ionization Ge detectors used by the EDELWEISS dark matter search experiment are presented. Their calibration, the determination of their energy threshold, fiducial volume and nuclear recoil acceptance are detailed.

Calibration of a Ge crystal with nuclear recoils for the development of a dark matter detector

Abstract The ionization deposited in a Ge crystal by the scattering of ≈ 1 MeV neutrons on Ge nuclei is measured and its lowenergy behavior is investigated down to recoil energies of 3 keV. This calibration study is fundamental for the discrimination of Weakly Interacting Massive Particles (WIMPs) from the radioactive background. Experimental results are compared with theoretical predictions.

Decay of highly excited nuclei following 48Ti(16O, 12C) at 120 MeV

Abstract Discrete gamma rays were detected in coincidence with light charged fragments produced in the 48 Ti + 16 O reaction at 120 MeV. Results for the ( 16 O, 12 C) reaction are presented and compared to the data from the α + 48 Ti fusion reaction within similar excitation energy range.

Indium disilicate, a new fast scintillator

Abstract We describe the luminescence and scintillation of indium disilicate (In 2 Si 2 O 7 ), an inorganic scintillator containing a large amount of 115 In. The maximum fluorescence occurs in the near UV range at 335 nm with a complicated decay including a fast component of less than 100 ns and a long one of more than a microsecond. Room temperature emission intensity was quite weak while the quantum efficiency became reasonably good at cryogenic temperature. Scintillation was measured using α-particles of 6.09 MeV and 8.785 MeV from 300 to 4 K. A maximum of intensity is observed at 50 K. A fast component (τ ⋍ 20 ns) with a constant intensity superimposes to a slow one of which the intensity has a maximum at 50 K and for which the decay constant rises as the temperature decreases.

Testing the level density of A ∼ 100 hot nuclei from evaporative charged-particle spectra

Abstract Alpha particles and protons emitted in the 32S + 74Ge reaction at E = 160, 210, 259, 335 and 435 MeV were measured in coincidence with evaporation residues. The average inverse level-density parameter 〈 K 〉 for hot evaporation residues with A ∼ 100 was obtained by comparing the slope of the charged-particle spectra with the predictions from a full statistical model calculation. Spectral shapes are well reproduced by calculations using the standard values 〈K〉 = 7.5 MeV , except for alpha particles at the highest bombarding energy, which corresponds to an excitation energy ϵ = 2.2 MeV/nucleon . The present results are compared with other experimental investigations in the A ∼ 100 and A ∼ 160 regions and with predictions from theoretical models. Difficulties in extracting the nuclear temperature from the slope of the particle spectra for A ∼ 100 are discussed.

Particle Dark Matter search with low activity scintillators

A review updating on particle Dark Matter direct detection by low activity solid scintillators (BPRS collaboration) and by liquid xenon target-detector (DAMA group) is presented.

Transfer and break-up reactions in the 30 A · MeV22Ne + 93Nb system

Abstract Peripheral interactions of the 22 Ne + 93 Nb system at 30 A· MeV incident energy have been investigated using the forward 48 CsI scintillators of the AMPHORA multidetector array for the detection of light charged particles at forward angles. In addition fragments have been identified near the grazing angle in 4 Si-CsI telescopes. It is found that the transfer probability remains large at this intermediate energy. The stripping of one or two nucleons from the projectile to the target and the pick-up of one nucleon have been clearly observed. Binary quasi-projectile break-up events involving emission of one α are dominant. Dissociation of the projectile into up to five products has also been observed. The production of fragments is deduced to result mainly from sequential decay of the primary fragments rather than from a direct break-up process. The yields of fragments, except for the lightest ones, have been reproduced in the framework of a random-walk model.

Gaseous ΔE-type phoswiches

Results are presented on the use of gaseous xenon as the ΔE stage of a phoswich scintillator detector. The timing characteristics of the xenon detector have been investigated and found to be suitable as either the fast or the slow component of a phoswich detector depending on the operating pressure of the xenon. A xenon-CsI(Tl) and a xenon-plastic phoswich have been built and tested. The xenon-plastic detector is expected to be more suitable for high energies. In addition to the ease of obtaining various thicknesses by adjusting the pressure, the excellent uniformity of a gaseous ΔE can provide an improved identification of heavy ions.