A comparative study of the neutron-γ Pulse Shape Discrimination (PSD) with seven organic scintillators is performed using an identical setup and digital electronics. The scintillators include ...plastics (EJ-299-33 and a plastic prototype), single crystals (stilbene and the recent doped p-terphenyl) and liquids (BC501A, NE213 and the deuterated liquid BC537). First, the overall PSD performance of the different scintillators is compared and threshold neutron energies for a given discrimination quality are determined. Then, using statistical arguments, two intrinsic contributions to the PSD capability of the scintillating materials are disentangled: the light yield and the specific pulse shapes induced by neutrons and γ-rays. This separation provides additional insight into the behaviour of organic scintillators and allows a detailed comparison of the discrimination performance of the various materials. On the basis of this analysis, limitations of current organic scintillators and of recently proposed alternative scintillators are discussed.
An abnormal production of events with almost equal-sized fragments was theoretically proposed as a signature of spinodal instabilities responsible for nuclear multifragmentation in the Fermi energy ...domain. On the other hand finite size effects are predicted to strongly reduce this abnormal production. High statistics quasifusion hot nuclei produced in central collisions between Xe and Sn isotopes at 32 and 45 A MeV incident energies have been used to definitively establish, through the experimental measurement of charge correlations, the presence of spinodal instabilities. N/Z influence was also studied.
The FAZIA apparatus exploits Pulse Shape Analysis (PSA) to identify nuclear fragments stopped in the first layer of a Silicon-Silicon-CsI(Tl) detector telescope. In this work, for the first time, we ...show that the isotopes of fragments having atomic number as high as Z∼20 can be identified. Such a remarkable result has been obtained thanks to a careful construction of the Si detectors and to the use of low noise and high performance digitizing electronics. Moreover, optimized PSA algorithms are needed. This work deals with the choice of the best algorithm for PSA of current signals. A smoothing spline algorithm is demonstrated to give optimal results without requiring too much computational resources.
A systematic analysis of the data obtained by the FAZIA collaboration during a recent experiment with a neutron rich projectile is presented. The main goal was to compare the experimental results ...with the HIPSE event generator simulations to investigate the influence of the neutron rich entrance channel on the quasi-projectile fragment properties. The full isotopic range of charged particles detected in this experiment was within the limit of the resolution of the FAZIA detector. A majority of quasi-projectile fragments were detected thanks to the forward angular acceptance of the experimental setup which was confirmed through the HIPSE calculations. Essentially, the lowering of
N
/
Z
of quasi-projectile fragments with the beam energy was found to be present since the initial phase of the reaction. Thus, pre-equilibrium neutron emissions might be a possible candidate to explain such an effect.
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In the Fermi energy domain, the temperature of hot nuclei can be determined using the energy spectra of evaporated light charged particles. But this method of measurement is not without ...difficulties both theoretical and experimental. The present study aims to disentangle the respective influences of different factors on the quality of this measurement: the physics, the detection (a
4
π
detector array such as INDRA) and the experimental procedure. This analysis demonstrates the possibility of determining from an energy spectrum, with an accuracy of about 10%, the true apparent temperature felt by a given type of particle emitted from a hot nucleus. This temperature allows to deduce the initial temperature using an appropriate method. However, three conditions are necessary: a perfect particle detector, important statistics and very weak secondary emissions. According to the GEMINI event generator, for hot intermediate mass nuclei, only deuterons and tritons could meet these conditions. In this case the determination may be better than 15%. With a realistic experimental device, insufficient angular resolution and topological distortions, caused by detection, can distort spectra to the point where it is very difficult to determine the apparent temperature correctly. Experimental reconstruction of the moving frame of the hot nucleus can also be responsible for this deterioration.
The polarization of the electron-hole pairs induced by 80
MeV
C
12
ions in a silicon detector was considered and connected to the relative dielectric permittivity. The dissociation of pairs was ...supposed to take place with a constant probability in a time unit. The exact coordinate dependence of the modified electric field, inside and outside the ion range, was found as the solution of the one-dimensional Maxwell's equation for the electric field in this inhomogeneous medium. The improvement of the current signal simulation with that time-dependent treatment is encouraging, as compared to a prompt carrier collection in an undisturbed electric field.
We report on first experimental observations of nuclear fermionic and bosonic components displaying different behaviours in the decay of hot Ca projectile-like sources produced in mid-peripheral ...collisions at sub-Fermi energies. The experimental setup, constituted by the coupling of the INDRA 4π detector array to the forward angle VAMOS magnetic spectrometer, allowed to reconstruct the mass, charge and excitation energy of the decaying hot projectile-like sources. By means of quantum-fluctuation analysis techniques, temperatures and local partial densities of bosons and fermions could be correlated to the excitation energy of the reconstructed system. The results are consistent with the production of dilute mixed systems of bosons and fermions, where bosons experience higher phase-space and energy density as compared to the surrounding fermionic gas. Our findings recall phenomena observed in the study of Bose condensates and Fermi gases in atomic traps despite the different scales.
We present a model-independent method to reconstruct the impact parameter distributions of experimental data for intermediate energy heavy ion collisions, adapted from a recently proposed approach ...for ultra-relativistic heavy ion collisions. The method takes into account the fluctuations which are inherent to the relationship between any experimental observable and the impact parameter in this energy range. We apply the method to the very large dataset on heavy ion collisions in the energy range 20-100 MeV/nucleon obtained with the INDRA multidetector since 1993, for two observables which are the most commonly used for the estimation of impact parameters in this energy range. The mean impact parameters deduced with this new method for "central" collisions selected using typical observable cuts are shown to be significantly larger than those found when fluctuations are neglected, and as expected the difference increases as bombarding energy decreases. In addition, we will show that this new approach may provide previously inaccessible experimental constraints for transport models, such as an estimation of the extrapolated mean value of experimental observables for b = 0 collisions. The ability to give more realistic, model-independent, estimations of the impact parameters associated to different experimental datasets should improve the pertinence of comparisons with transport model calculations which are essential to better constrain the equation of state of nuclear matter.
Nuclear stopping has been investigated in central nuclear collisions at intermediate energies by analyzing kinematically complete events recorded with the help of the 4π multidetector INDRA for a ...large variety of symmetric systems. It is found that the mean isotropy ratio defined as the ratio of transverse to parallel momenta (energies) reaches a minimum near the Fermi energy, saturates or slowly increases depending on the mass of the system as the beam energy increases, and then stays lower than unity, showing that significant stopping is not achieved even for the heavier systems. Close to and above the Fermi energy, experimental data show no effect of the isospin content of the interacting system. A comparison with transport model calculations reveals that the latter overestimates the stopping power at low energies.
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