Roberta Ghetti

Characterization of Nuclear Sources from Neutron-neutron, Proton-proton and Neutron-proton Correlation Functions

Two-neutron, two-proton and neutron–proton correlation functions have been measured simultaneously for the E/A=45 MeV 58 Ni + 27 Al reaction. Calculations from a statistical model have been compared to singles energy spectra as well as to total and gated correlation functions. This imposes very strong constraints on the model parameters. The use of directionally gated correlation functions helps to disentangle space and time information. Values of Gaussian radii, emission lifetimes, initial temperatures, source velocities and flow velocities are extracted. Correlation functions gated on total momentum of the nucleon pairs suggest that more energetic particles are emitted on a fast time scale ( < 100 fm / c ) and that the fraction of pre-equilibrium to equilibrium emission is larger for protons than for neutrons.

The complement: a solution to liquid drop finite size effects in phase transitions

The effects of the finite size of a liquid drop undergoing a phase transition are described in terms of the complement, the largest (but mesoscopic) drop representing the liquid in equilibrium with the vapor. Vapor cluster concentrations, pressure, and density from fixed mean density lattice gas (Ising) calculations are explained in terms of the complement generalization of Fishers model. Accounting for this finite size effect is important for extracting the infinite nuclear matter phase diagram from experimental data.

Energy calibration of CsI(T1) scintillator in pulse-shape identification technique

A batch of 16 CsI(TI) scintillator crystals, supplied by the Bicron Company, has been studied with respect to precise energy calibration in pulse-shape identification technique. The light corresponding to pulse integration within the time interval 1.6-4.5 mus (long gate) and 0.0-4.5 mus (extra-long gate) exhibits a power law relation, L(E, Z, A) a1 (Z, A)Ea2(Z-4), for (1.2.3) H isotopes in the measured energy range 5-150 MeV. For the time interval 0.0-0.60 mus (short gate), a significant deviation from the power law relation is observed, for energy greater than similar to30 MeV. The character of the a2(p)-a2(d) and a2(p)-a2(t) correlations for protons, deuterons and tritons, reveals 3 types of crystals in the batch. These subbatches differ in the value of the extracted parameter a2 for protons, and in the value of the spread of a2 for deuterons and tritons. This may be explained by the difference in the energy dependence of the fast decay time component and/or by the difference in the light output ratio of the fast/slow components. An accuracy well inside 1.0% is achieved in the energy calibration of the CsI(TI) crystals by using the DeltaE(Si) E(CsI(Tl))/PMT method. The batch of 16 CsI(TI) crystals is utilized to measure the correlations of light charged particles produced in E/A = 61 MeV, (36)Arinduced reactions. The preliminary correlation functions for two protons with small relative momenta are presented

Measurements of the response function of silicon diode detectors for heavy ions using a time of flight technique

Abstract A time of flight (TOF) method has been employed to study the response of silicon diode detectors to low energy (0.05–0.2 A MeV) recoiling nuclei from heavy ion collisions. The response function of five different silicon diode detectors to low energy 12 C, 31 P and 81 Br recoils has been investigated and closely follows a straight line law for each recoil isotope. A simple relation between energy, pulse height and mass number, can be applied to establish an energy scale for the low energy recoils, provided that detector specific constants are used. The energy resolution of silicon diode detectors was comparable to that of surface barrier detectors but varied considerably from one detector to another.

Possibility to deduce the emission time sequence of neutrons and protons from the neutron-proton correlation function?

Experimental information has been derived from the neutron-proton correlation function in order to deduce the time sequence of neutrons and protons emitted at 45 degrees in the E/A = 45 MeV 58Ni + 27Al reaction.

Influence of cross-talk rejection procedures on two-neutron intensity interferometry.

Abstract This work investigates the effects of a cross-talk rejection procedure on the two-neutron correlation function. The rejection method relies only upon simple kinematic relations between the energy of the detected neutrons and can be applied to commonly used detector configurations. It is demonstrated that the comparison of a cross-talk corrected correlation function with the theory is meaningful as long as the cross-talk rejection procedure and the response of the detector filter are consistently incorporated into the theoretical calculations.

Effects of energy deposition by nuclear scattering in silicon p-i-n diode detectors

Abstract The changes in thick (∼300 μm) and thin (15 μm) Si p-i-n diode detectors that take place as a result of alpha particle and 63Cu5+ ion irradiation have been studied by Deep Level Transient Spectroscopy (DLTS) and by monitoring the reverse-bias leakage currents. A linear increase in reverse-bias current with α-particle dose was observed that could be attributed to the formation of vacancy-associated defects (divacancy, A- and E-centres). Damage within the active layer of the device, characterised by the increase in leakage current per unit active volume, together with literature pion, proton and heavy ion data, exhibited a linear dependence on the energy deposited in nuclear processes over many orders of magnitude. Annealing at temperatures of 150°C for 4 h (vacuum bakeout) resulted in a reduction in leakage current and the size of the DLTS peaks became smaller. This temperature is much lower than expected for removal of divacancies, suggesting that recovery of the reverse bias current is mediated by other defect centres.

Isospin effects on two-particle correlation functions in E/A=61 MeV Ar-36+Sn-112,Sn-124 reactions

Small-angle, two-particle correlation functions have been measured for Ar-36+Sn-112,Sn-124 collisions at E/A=61 MeV. Total momentum gated neutron-proton (np) and proton-proton (pp) correlations are stronger for the Sn-124 target. Some of the correlation functions for particle pairs involving deuterons or tritons (nd, pt, and nt) also show a dependence on the isospin of the emitting source.

Simultaneous neutron-neutron proton-neutron and proton-proton interferometry measurements

Abstract This paper describes a technique to perform simultaneous neutron-neutron, proton-neutron and proton-proton nuclear interferometry measurements. Experimental arrangements for intermediate energy heavy ion interferometry experiments are presented and their limitations are investigated. The construction of correlation functions, particularly with respect to normalization and background corrections is discussed. Some new results on correlation functions from the reaction 30 A MeV 40 Ar+ 12 C are shown and possibilities to improve the interferometry technique are discussed.

Characterization of nuclear sources via two-neutron intensity interferometry

The neutron energy spectrum and the two-neutron correlation function have been measured for the E/A = 45 MeV Ni + Al reaction in order to assess the space-time characteristics of the neutron emitting source. When comparing the data to a statistical model,