δVpn is a particular double difference of nuclear binding energies serving as a filter isolating the valence proton-neutron interaction. δVpn is known to exhibit spikes in light nuclei at N=Z, explained by the SU(4) Wigner supermultiplet. Recently, it has been found that δVpn values in the rare earth region show similar peaks, occurring at Nval~Zval. These peaks, evident for both even and odd Z values, are interpreted in terms of large spatial overlaps of respective proton and neutron wave functions whose Nilsson quantum numbers are related by ∆K[∆N, ∆n_z, ∆Λ] = 0[110], i.e., the wave functions differ only by a single oscillator quantum in the z-direction. The implications of this for the development of collectivity and deformation in heavy nuclei, and the locus of this development, are dicussed. The double difference of binding energies δVpn(Z,N)=[B(Z,N)+B(Z-2,N-2)-B(Z,N-2)-B(Z-2,N)}/4 (1) is known [1] to be a measure of the average interaction between the last two protons with the last two neutrons in a given nucleus having Z protons and N neutrons. δVpn is known [1] to exhibit spikes in light nuclei with N=Z, shown in Fig. 1. These spikes are justified [2] by the existence of the SU(4) Wigner supermultiplet in this region. Recently, it has been shown [1] that δVpn also exhibits similar spikes in rare earth nuclei with equal numbers of valence neutrons and valence protons, Nval=Zval, shown in Fig. 2. Since the SU(4) Wigner supermultiplet is not present in this region, destroyed by the strong spin-orbit interaction, an alternative justification has to be found. A detailed study of the orbitals occupied by the last two neutrons and the last two protons in the rare earths exhibiting the spikes, reveals [1] that they are Nilsson orbitals differing by ∆K[∆N, ∆n_z, ∆Λ] = 0[110], as shown in the upper part of Fig. 3. These orbitals show similar evolution as functions of the nuclear deformation, as shown in the lower part of Fig. 3. They are expected to have maximal spatial overlaps, thus leading to enhanced proton-neutron interactions, in a situation reminiscent of the Federman-Pittel mechanism [3]. A more careful look at these orbitals reveals that they correspond to proton-neutron pairs with S=1, T=0. When plotted in the nuclear chart vs. Z and N, the spike-exhibiting nuclei appear on a straight line bordering the plateau of high deformation.

A large volume (1m3) spherical proportional counter has been developed at CEA/Saclay, for low flux neutron measurements. The high voltage is applied to a small sphere 15mm in diameter, located in the center of the counter and the wall of the counter is grounded. Neutrons can be measured successfully, with high sensitivity, using 3He gas in the detector. The proton and tritium energy deposition in the drift gaseous volume, from the reaction 3He(n,p)3H, can provide the neutron spectra from thermal neutrons up to several MeV.The detector has been installed in the underground laboratory in Modane (LSM) to measure the neutron background. The sphere has been has been filled with gas mixture of Ar + 2% CH4 +3gr He-3, at 275 mbar. The thermal neutron peak is well separated from the cosmic ray and gamma background, permitting of neutron flux calculation. Other potential applications requiring large volume of about 10 m in radius are described in detail in reference

A new type of radiation detector based on a spherical geometry is presented. The detector consists of a large spherical gas volume with a central electrode forming a radial electric field. Charges deposited in the conversion volume drift to the central sensor where they are amplified and collected. We introduce a small spherical sensor located at the center acting as a proportional amplification structure. It allows high gas gains to be reached and operates in a wide range of gas pressures. Signal development and the absolute amplitude of the response are consistent with predictions. Sub-keV energy threshold with good energy resolution is achieved. This new concept has been proven to operate in a simple and robust way and allows reading large volumes with a single read-out channel. The detector performance presently achieved is already close to fulfill the demands of many challenging projects from low energy neutrino physics to dark matter detection with applications in neutron, alpha and gamma spectroscopy.

The Edelweiss Dark Matter Experiment is installed in the Modane Underground Laboratory since 1994. In 1997 the first detector of a 70 g heat and ionization Ge low-temperature detector built by the collaboration showed its discrimination capabilities. During the last two years the installation was upgraded, and a new generation of 70 g Ge detectors is operational. The detector environment is drastically controlled to avoid radioactive contamination. A test run with two new 70 g detectors shows a reduction by a factor of ten in the background level before 7-ray rejection which is now around 2 events/kg/keV/day. Three 320 g Ge cryogenic detectors have been constructed and are now being tested and should soon be operational in the present cryostat. A new cryostat is being built and will allow a detection volume of 100 1. It is expected to be installed in Modane next year. In a first step of 21×320 g Ge detectors, the Edelweiss-II experiment should test an important fraction of the MSSM Susy parameter space.

The Bugey 3 experiment, designed to measure oscillations of reactor neutrinos, has used 3 identical detection modules, each of 600 liters, filled with a new 6Li-loaded liquid scintillator. These modules were located in two shielding bunkers, respectively 15 and 40 m away from the reactor core. We describe here the mechanical characteristics of these modules, their shielding, the associated electronics, the trigger, the acquisition systems, the calibration and monitoring of these detectors, and the Monte Carlo simulations of their response to particles. We conclude on the overall performance of this new detection technique which has allowed the recording of 120000 neutrino interactions with good neutron efficiency (49%), low background (2.5 evts/hr) and good energy resolution (4% at 4.4 MeV).