Analysis and first order correction of signal saturation effects in photomultiplier tubes for improved estimation of interacting radiation energy in Lanthanum bromide scintillators

The huge amount of optical photons emitted in burst by Cerium doped Lanthanum bromide scintillators poses a severe constraint on the specifications of photomultipliers, namely they must operate at very large instantaneous current values with minimum saturation of output pulse signals. Acquisition in shape and processing of photomultipliers output pulses by means of high-speed free-running analog to digital converters and processing devices allows specific correction for pulse saturation and distortion effects, due to high-gain tubes operated at relatively high power supply voltage. We analyze the effects of output signal saturation in photomultiplier tubes as a function of the high voltage level and the amount of energy released in the scintillator crystal, proposing a simple model to characterize this complex phenomenon. According to the proposed model, a preliminary first-order correction is calculated and applied to the energy estimations obtained by a traditional analog spectroscopy system, for energies up to 9 MeV, reducing the maximum estimation error by almost an order of magnitude

Recent developments in gamma-ray spectroscopy with new scintillators, LaBr3(Ce), to investigate nuclear structure at high excitation and far from stability

Lanthanum bromide scintillators are among the new most promising detectors for nuclear spectroscopy experiments. Their relevant performances in terms of energy resolution, time resolution and high density make them a suitable alternative even with respect to germanium-based solid-state detectors, which, on the other side, are more expensive and difficult to operate. However, the huge amount of optical photons emitted in burst by cerium-doped lanthanum bromide scintillators poses severe constraints on the specifications of photomultipliers, namely they must operate at very large instantaneous current values with minimum saturation of output pulse signals. We analyse the effects of output signal saturation in photomultiplier tubes as a function of the power supply high voltage level and the amount of energy released in the scintillator crystal and propose a simple model to characterize this very complex phenomenon. According to the proposed model, a preliminary first-order correction has been extracted. This technique reduces the non-linear response of a LaBr 3(Ce) scintillator by almost an order of magnitude for \u3b3-rays of 9MeV

Study of high-lying states in 208Pb with the AGATA demonstrator

An experiment aiming at the study of the gamma decay from the Giant Resonance region in the nuclei 208Pb, 90Zr has recently been performed with the AGATA Demonstrator coupled to an array of large-volume scintillators (LaBr3:Ce, BaF2) to increase the overall gamma detection efficiency. The 208Pb and 90Zr nuclei were excited with inelastic scattering of 17O at the incident energy of 20MeV/u. The ejectiles were detected in a pair of silicon E-\u394E telescopes placed at forward angles. Preliminary results concerning the first partial analysis of the measurement with the 208Pb target are here presented. \ua92011 by Societ\ue0 Italiana di Fisica

Measurement of isospin mixing in 80Zr* at finite temperature

Isospin mixing induced by Coulomb interaction has been measured in the compound nucleus Z=N=4080Zr at T 3c2MeV produced in a fusion-evaporation reaction. The observable sensitive to the isospin purity of the compound nucleus is the Giant Dipole Resonance \u3b3 decay. The degree of mixing of the compound nucleus has been obtained via Statistical Model analysis of the measured \u3b3 spectrum

Measurement of isospin mixing in hot 80Zr compound nucleus

Isospin mixing induced by Coulomb interaction has been measured in the compound nucleus 80Zr*with Z = N = 40 at T 3c 2 MeV produced in a fusionevaporation reaction. The observable sensitive to the isospin purity of the compound nucleus is the giant dipole resonance \u3b3 decay. The Coulomb spreading width of the I = I0 +1 state and the degree of isospin mixing of the compound nucleus has been obtained via statistical model analysis of the measured \u3b3 spectrum

Order-to-chaos transition in warm rotating 174W nuclei

The transition between order and chaos is studied in the warm rotating nucleus 174W by gamma-spectroscopy, focusing on the conservation of selection rules of the K quantum number with the excitation energy. The 174W nucleus was populated at high spins by the fusion-evaporation reaction of 50Ti (at 217MeV) on a 128Te backed target. The experiment was performed in Legnaro National Labo- ratory using the AGATA Demonstrator HPGe-array (AD) coupled with an array of 27 BaF2 scintillator detectors. High-energy \u3b3-rays measured in the AD and in the scintillators array will be also analyzed to study the Giant Dipole Resonance (GDR) in the compound nucleus 178W. The discrimination between n and \u3b3 in the AD detectors will be employed, following a procedure recently developed by Monte Carlo simulations and using digital Pulse Shape Analysis timing techniques. \ua92011 by Societ\ue0 Italiana di Fisica

Order-to-chaos transition in warm rotating 174W nuclei

The transition between order and chaos is studied in the warm rotating nucleus 174W by gamma-spectroscopy, focusing on the conservation of selection rules of the K quantum number with the excitation energy. The 174W nucleus was populated at high spins by the fusion-evaporation reaction of 50Ti (at 217MeV) on a 128Te backed target. The experiment was performed in Legnaro National Labo- ratory using the AGATA Demonstrator HPGe-array (AD) coupled with an array of 27 BaF2 scintillator detectors. High-energy \u3b3-rays measured in the AD and in the scintillators array will be also analyzed to study the Giant Dipole Resonance (GDR) in the compound nucleus 178W. The discrimination between n and \u3b3 in the AD detectors will be employed, following a procedure recently developed by Monte Carlo simulations and using digital Pulse Shape Analysis timing techniques. \ua92011 by Societ\ue0 Italiana di Fisica

Study of high-lying states in 208Pb with the agata demonstrator

An experiment aiming at the study of the gamma decay from the Giant Resonance region in the nuclei 208Pb, 90Zr has recently been performed with the AGATA Demonstrator coupled to an array of large volume scintillators (LaBr 3:Ce, BaF 2) to increase the overall gamma detection efficiency. The 208Pb and 90Zr nuclei were excited with the inelastic scattering of 17O at the incident energy of 20 MeV/u. The ejectiles were detected in a pair of silicon E-\u3b4E telescopes placed at forward angles. Preliminary results concerning the first partial analysis of the measurement with the 208Pb target are here presented

Study of the order-to-chaos transition in 174W with the AGATA-demonstrator

The transition between order and chaos is studied in the warm rotating nucleus 174W by \u3b3-spectroscopy, focusing on the conservation of selection rules of the K quantum number with the excitation energy, where K is the projection of the total angular momentum on the symmetry axis. The 174W nucleus was populated by the fusion-evaporation reaction of 80Ti (at 217 MeV) on a 128Te backed target. The measurement was performed in July 2010 at Legnaro National Laboratories of INFN using the AGATA Demonstrator HPGe-array coupled to an array of 27 BaF 2 scintillators, named Helena. The data analysis concentrates on \u3b3-\u3b3 coincidence matrices selecting the \u3b3-decay flow populating low-K and high-K structures. By a statistical fluctuation analysis the total number of low-K and high-K bands can be evaluated as a function of excitation energy. Comparisons with cranked shell model calculations at finite temperature are used to extract information on the onset of the chaotic regime as a function of excitation energy