G.L. Raselli

Detection of the VUV liquid argon scintillation light by means of glass-window photomultiplier tubes

Abstract The experimental results coming from an intense R&D study about the possibility of detecting the light produced by the liquid argon scintillation certify the use of glass-window photomultiplier tubes. The devices, working in cryogenic liquid, are made sensitive to the VUV photons by means of a wavelength shifter coating. This is a useful detection method to provide an effective way for the absolute time measurement and trigger of ionizing events occurring in Time Projection Chambers.

A FULL-INTEGRATED PULSE-SHAPE DISCRIMINATOR FOR LIQUID SCINTILLATOR COUNTERS

A low-cost high-performance pulse-shape discriminator for neutron—gamma discrimination using liquid scintillation counters equipped with two photomultipliers is developed. Two independent methods of pulse-shape discrimination are exploited to achieve an optimum neutron—gamma identification. The circuit is especially designed to study the low-intensity neutron background field in the Gran Sasso underground laboratory. A detailed layout and the main performances of the electronic circuit are described. ( 1998 Elsevier Science B.V. All rights reserved.

FLUKA simulations for low-energy neutron interactions and experimental validation

Abstract The response functions of a commercial neutron detector filled with BICRON BC501A liquid scintillator are computed using the FLUKA Monte Carlo program. The simulation results are necessary to perform a direct spectroscopy by unfolding the measured proton recoil spectrum by means of the response functions of the detector using the SAND II code. The measurement of the flux intensity and of the energy distribution of a calibrated AmBe neutron source validates the method showing a good agreement with the known quantities.

Some considerations on 242mAm production in thermal reactors

Abstract Recently, it has been suggested to consider 242mAm as a potential nuclear fuel. This artificial nuclide can be produced through 241Am neutron capture carried on in a neutron field typical of a thermal reactor. In order to suppress the thermal neutron flux, which will cause 242mAm depletion mainly through fission, proper neutron filters should be adopted. In a very intense neutron field, the 242mAm enrichment depends mainly on the energy distribution of the neutrons, the sample thickness, and the cutoff energy of the neutron filter. An investigation on different geometries of the sample to be irradiated using Cd, B, Sm, and Gd as neutron filters has been carried out by means of Monte Carlo simulation. The most favorable results have been obtained irradiating thin 241Am samples (11 μg/cm2) covered with a Gd (0.2-mm-thick) or Sm (1-mm-thick) filter. In these cases the theoretical 242mAm enrichment can reach 20%. The preparation of significant quantities of this unconventional nuclear fuel implies isotopic separation techniques operating in high radioactive environments and hopefully characterized by very high recovery factors, which are in no way trivial problems.

Americium 242m and its potential use in space applications

The isotope Am242m is an interesting nuclide as it shows one of the known highest neutron fission cross section. This could be useful in some special applications, like the nuclear reactor for space propulsion proposed by C. Rubbia. A detailed measurement of the energy transfer from the fission fragments to the gas as a function of the path and the gas type is an important item for the evaluation of the engine performances. This was carried out by means of an ionisation chamber. However the Am242m availability, in particular at high isotopic abundance, is still at present a serious drawback. A production model, experimentally tested in thermal nuclear reactors, has been used to evaluate the achievable isotopic abundances. The results are quite below 70% and advise the use of separation techniques for further enrichment. The use of Am242m for other applications like nuclear pumped laser is suggested.

The suppression of beam-related background in the ILL neutron-antineutron oscillation experiment

Abstract The search for neutron-antineutron ( n n ) oscillations conducted by a Heidelberg-ILL-Padova-Pavia collaboration at the European slow neutron facility at Grenoble requires a very strong cold neutron beam, but an extremely low neutron-induced radiation background. This article describes the analysis and suppression of neutron-beam-related background in the n n experiment. In particular, the fabrication of a 20 m2 shield of isotopically pure sintered 6LiF ceramics which protects the annihilation detector from the inside against neutrons scattered from the annihilation target is described.

The resistive plate counter as a neutron detector

Abstract The resistive plate counter technique allows the easy and cheap construction of position-sensitive large area detectors. The use of such counters for thermal neutron detection is investigated.

Non-destructive diagnostics of thin fissile layers

We have developed a non-destructive nuclear technique useful for the diagnostic of thin layers of fissile element. The method is based on the correlation between the fission fragment energy losses and the distortion of the energy spectrum of the alpha-particles emerging from the layer itself. We have also measured the sputtering rate of atoms from a fission layer which can be the cause of an important degradation in a working apparatus.

Measurement of fission fragments energy loss

Abstract The mean energy of 252 Cf fission fragments emerging from an absorber and the determination of the capture rate in the absorber itself have been measured using two independent and complementary nuclear techniques. The results can be applied to the measurement of the energy self-absorption in a non-zero thickness source and can be used to validate simulation programs.

A 12-bit ADC with independent gates for fast neutron spectrometry

We have developed a new integrating 12-bit analog-to-digital converter with independent gates. The circuit is especially designed for fast neutron spectrometry at very low intensity fields using multi-cell liquid scintillator detectors. A detailed layout and the main performances of the electronic circuit are described.