J Helgesson

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.

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.

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.

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,

Transport Simulations with Pi and Delta In-Medium Properties

Abstract Transport simulations including in-medium properties derived in a microscopic π + NN −1 + ΔN −1 model in infinite nuclear matter are presented. In-medium pion dispersion relations, partial Δ decay widths, pion absorption cross sections and Δ cross sections are incorporated into the transport description by means of a local-density approximation. Strong modifications of π and Δ production and absorption rates are found, but only small effects on pion observables.

Mobility determination of lead isotopes in glass for retrospective radon measurements

In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)Pb is often considered to be relatively immobile in glass after alpha recoil implanted by (222)Rn progenies. The diffusion of (210)Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if (210)Pb is mobile and can escape from glass, or lost as a result of cleaning-induced surface modification. This diffusion was studied by a radiotracer technique, where (209)Pb was used as a tracer in a glass matrix for which the elemental composition is known. Using the ion guide isotope separator on-line technique, the (209)Pb atoms were implanted into the glass with an energy of 39 keV. The diffusion profiles and the diffusion coefficients were determined after annealing at 470-620 degrees C and serial sectioning by ion sputtering. In addition, the effect of surface cleaning on diffusion was tested. From the Arrhenius fit, the activation enthalpy (H) was determined, which is equal to 3.2 +/- 0.2 eV, and also the pre-exponential factor D(0), in the order of 20 m(2)s(-1). This result confirms the assumption that over a time period of 50 y (209)Pb (and (210)Pb) is effectively immobile in the glass. The boundary condition obtained from the measurements had the characteristic of a sink, implying loss of (209)Pb in the topmost surface at high temperatures.

Correlation functions of light charged particles from projectile-like fragment source in E/A=44 and 77 MeV 40Ar + 27Al collisions

Abstract Two-particle correlation functions, involving protons, deuterons, tritons, and α -particles, have been measured at very forward angles ( 0.7 ° ⩽ θ lab ⩽ 7 ° ), in order to study projectile-like fragment (PLF) emission in E / A = 44 and 77 MeV 40 Ar + 27 Al collisions. The observed correlations are similar for the two reactions at E / A = 44 and 77 MeV, except for peaks originating from resonance decays, which are larger at the lower bombarding energy. Particle-velocity gated correlation functions are presented, and possible implications on the time sequence of the light charged particles, emitted from the PLF, are discussed.

Implications of two-body fragment decay for the interpretation of emission chronology from velocity-gated correlation functions

From velocity-gated small-angle correlation functions, the emission chronology can be deduced for nonidentical particles, if the emission is independent. This is not the case for nonidentical particles that originate from two-body decay of fragments. Experimental results may contain contributions from both independent emission and two-body decay, so care is needed in interpreting the velocity-gated correlation functions. It is shown that in some special cases, it is still possible to deduce the emission chronology, even if there is a contribution from two-body decay.

Particle emission time sequence in intermediate energy heavy ion reactions

The CHIC Collaboration has performed a series of simultaneous pp, np and nn fermion interferometry experiments in order to study the space-time evolution of the emission sources in intermediate energy heavy ion reactions. Furthermore, when correlations of non-identical particles are available, additional model independent information on the emission chronology of the particles is obtained. In this contribution, after reviewing the method to determine the order of emission of non-identical particles, we discuss the emission chronology of neutrons and protons from the E/A = 45 MeV Ni-58 + Al-27 reaction and from the E/A = 60 MeV Ar-36 + Al-27 reaction, shown here for the first time.