F. Yermia

New antineutrino energy spectra predictions from the summation of beta decay branches of the fission products

In this Letter, we study the impact of the inclusion of the recently measured beta decay properties of the (102;104;105;106;107)Tc, (105)Mo, and (101)Nb nuclei in an updated calculation of the antineutrino energy spectra of the four fissible isotopes (235,238)U and (239,241)Pu. These actinides are the main contributors to the fission processes in pressurized water reactors. The beta feeding probabilities of the above-mentioned Tc, Mo, and Nb isotopes have been found to play a major role in the γ component of the decay heat of (239)Pu, solving a large part of the γ discrepancy in the 4-3000 s range. They have been measured by using the total absorption technique, insensitive to the pandemonium effect. The calculations are performed by using the information available nowadays in the nuclear databases, summing all the contributions of the beta decay branches of the fission products. Our results provide a new prediction of the antineutrino energy spectra of (235)U, (239,241)Pu, and, in particular, (238)U for which no measurement has been published yet. We conclude that new total absorption technique measurements are mandatory to improve the reliability of the predicted spectra.

Front-end electronics for the RPCs of the ALICE dimuon trigger

A dedicated front-end electronics has been developed for the trigger chambers of the ALICE muon spectrometer under construction at the future LHC at CERN. This trigger detector is based on RPCs (Resistive Plate Chambers) working in streamer mode. The number of electronics channels (about 21000) and the fact that RPC signals have specific characteristics have led to the design of an 8 channel front-end ASIC using a new discrimination technique. The principle of the ASIC is described and the radiation hardness is discussed. Special emphasis is put on production characteristics of about 4000 ASICs.

A novel segmented-scintillator antineutrino detector

The next generation of very-short-baseline reactor experiments will require compact detectors operating at surface level and close to a nuclear reactor. This paper presents a new detector concept based on a composite solid scintillator technology. The detector target uses cubes of polyvinyltoluene interleaved with 6LiF:ZnS(Ag) phosphor screens to detect the products of the inverse beta decay reaction. A multi-tonne detector system built from these individual cells can provide precise localisation of scintillation signals, making efficient use of the detector volume. Monte Carlo simulations indicate that a neutron capture efficiency of over 70 % is achievable with a sufficient number of 6LiF:ZnS(Ag) screens per cube and that an appropriate segmentation enables a measurement of the positron energy which is not limited by γ-ray leakage. First measurements of a single cell indicate that a very good neutron-gamma discrimination and high neutron detection efficiency can be obtained with adequate triggering techniques. The light yield from positron signals has been measured, showing that an energy resolution of 14%/√E(MeV) is achievable with high uniformity. A preliminary neutrino signal analysis has been developed, using selection criteria for pulse shape, energy, time structure and energy spatial distribution and showing that an antineutrino efficiency of 40% can be achieved. It also shows that the fine segmentation of the detector can be used to significantly decrease both correlated and accidental backgrounds.

Dependence of bakelite resistivity on temperature and humidity

The use of bakelite as electrodes for resistive plate chambers is widespread. The performance of RPCs, in particular its rate capability, strongly depends on the bulk resistivity of the electrodes. Since the bakelite resistivity changes as a function of temperature and humidity, we have performed several resistivity measurements of a melaminic bakelite sample in order to investigate this dependence. Two sets of measurement at well controlled environmental conditions were performed: the former after relative humidity changes in the range from 80% to 20% at constant temperature, the latter varying the temperature from 15/spl deg/C to 35/spl deg/C at constant relative humidity.

The proton zero degree calorimeter for the ALICE experiment

The proton zero degree calorimeter (ZP) for the ALICE experiment will measure the energy of the spectator protons in heavy ion collisions. The ZP is a spaghetti calorimeter, which collects and measures the Cherenkov light produced by the shower particles in silica optical fibres embedded in a brass absorber. The details of its construction will be shown. The calorimeter has been tested at the CERN SPS in July 2004 with pion and electron beams of various momenta ranging from 50 to 200 GeV/c. The linearity of the response of the calorimeter and its energy resolution as a function of the beam energy have been measured. The preliminary results of the test are presented.