S. Brambilla

A multi-element detector array for heavy fragments emitted in intermediate energy nuclear reactions

Abstract To investigate complex fragment emission in intermediate energy nucleus-nucleus collisions, an array of three-element telescopes has been constructed. The array is designed to measure energy, charge and emission angles of fragments with Z values from 2 up to the projectile atomic number when studying reactions in reverse kinematics. In this case it has a good efficiency even for events with complex fragment high multiplicity. Each telescope is made of an ionization chamber (filled with CF 4 at a pressure up to 300 mbar), a Si detector (500 μm thick, position sensitive in two dimensions) and a CsI(Tl) scintillator with photodiode readout.

Evidence for the Jacobi shape transition in hot46Ti

The gamma-rays from the decay of the GDR in 46Ti compound nucleus formed in the 18O+28Si reaction at bombarding energy 105 MeV have been measured in an experiment using a setup consisting of the combined EUROBALL IV, HECTOR and EUCLIDES arrays. A comparison of the extracted GDR lineshape data with the predictions of the thermal shape fluctuation model shows evidence for the Jacobi shape transition in hot 46Ti. In addition to the previously found broad structure in the GDR lineshape region at 18-27 MeV caused by large deformations, the presence of a low energy component (around 10 MeV), due to the Coriolis splitting in prolate well deformed shape, has been identified for the first time.

Position sensitivity of large volume LaBr 3 :Ce detectors

The position sensitivity of two large volume (1” × 1” and 3” × 3”) LaBr<inf>3</inf>:Ce crystals has been measured using collimated beams of 662 keV γ-rays. The crystals have been coupled to a Position Sensitive Photo Multiplier Tube (PSPMT) and/or shielded phototube. The results indicate that, in the case of 662 keV γ -rays, both crystals should allow identification of the the position of the γ-ray first interaction with a 1-2 cm resolution. Similar tests have been done in the past using 140 keV γ-rays and no sensitivity was found. Using GEANT4 simulations we confirmed these results.

Hybrid low-noise charge preamplifiers for heavy-ion detectors

Abstract The characteristics of hybrid low-noise general-purpose preamplifiers are described. The basic performances are reported. They have been used in connection with ionization chambers, large-area Si detectors and photodiodes.

Probing the Order-to-Chaos Region in Superdeformed {sup 151}Tb and {sup 196}Pb Nuclei with Continuum {gamma} Transitions

The gamma decay associated with the warm rotation of the superdeformed nuclei 151Tb and 196Pb has been measured with the EUROBALL IV array. Several independent quantities provide a stringent test of the population and decay dynamics in the superdeformed well. A Monte Carlo simulation of the gamma decay based on microscopic calculations gives remarkable agreement with the data only assuming a large enhancement of the B(E1) strength for 1-2 MeV gamma rays, which may be related to the evidence for octupole vibrations in both mass regions.

Neutron-skin thickness from the study of the anti-analog giant dipole resonance

The γ-decay of the anti-analog of the giant dipole resonance (AGDR) to the isobaric analog state has been measured following the p( 124Sn,n) reaction at a beam energy of 600 MeV/nucleon. The energy of the transition was also calculated with state-of-the-art self-consistent relativistic random-phase approximation (RPA) and turned out to be very sensitive to the neutronskin thickness (ΔRpn). By comparing the theoretical results with the measured one, the ΔRpn value for 124Sn was deduced to be 0.21 ± 0.07 fm, which agrees well with the previous results. The present method offers new possibilities for measuring the neutron-skin thicknesses of very exotic isotopes.

Active voltage divider for improved estimation of interacting radiation energy with photomultiplier tubes coupled to high light yield scintillators

New materials with very high light yield and short scintillation decay time have been developed in the past few years: e.g. Cerium doped Lanthanum Bromide (LaBr3:Ce), Europium doped Strontium Iodide (SrI2: Eu).

An advanced pulse stretcher for the acquisition of the "Fast" component of BaF/sub 2/ detectors signals

A fast gateless pulse stretcher has been developed for an easy acquisition of pulse-shape information of BaF/sub 2/ scintillator signals. Commonly, this information is obtained by the use of two QDCs with different integration windows. This technique becomes complex and rather inconvenient when signals need to be delayed. The developed circuit uses a fast-stretcher technique to generate pulse-shape information, which requires no delay lines or gate signals. The outputs consist of two Gaussian signals whose amplitudes are proportional to the height of the BaF/sub 2/ fast component and to the total energy deposited into the scintillator. These outputs are easily acquired with a standard peak ADC with no gate-timing problems. An excellent Fast-Slow separation has been obtained even with small input signals of only few millivolts. This technology is general purpose and can be used with any other scintillator whose light emission is characterized by two components with different lifetimes.

An eight-channel time-to-digital converter on a VME board

Abstract An eight-channel time-to-digital converter in a one-slot VME module has been developed. It is based on eight TAC sections and a 1 μs conversion time ADC unit with 12 bit resolution. Start and Stop input signals can be either NIM or ECL pulses and the Common-Start mode is available. The full-scale time range can be on-board selected between four values from 100 to 800 ns. The integral nonlinearity is less than ±0.04% for all ranges. The Low and High thresholds of any channel and other functions can be remotely controlled.

A remotely controlled four-channel spectroscopy amplifier

Abstract A four channel spectroscopy amplifier is described where coarse and fine amplification gains can be remotely adjusted using high speed CAENET serial line controllers.