L. Pienkowski

The liquid to vapor phase transition in excited nuclei

The thermal component of the 8 GeV/c pi+ Au data of the ISiS Collaboration is shown to follow the scaling predicted by Fishers model when Coulomb energy is taken into account. Critical exponents tau and sigma, the critical point (p(c),rho(c),T(c)), surface energy coefficient c(0), enthalpy of evaporation DeltaH, and critical compressibility factor C(F)(c) are determined. For the first time, the experimental phase diagrams, (p,T) and (T,rho), describing the liquid vapor coexistence of finite neutral nuclear matter have been constructed.

NEUTRON PRODUCTION BY HADRON-INDUCED SPALLATION REACTIONS IN THIN AND THICK PB AND U TARGETS FROM 1 TO 5 GEV

Abstract The reliability and relevance of experimental data and calculations for the design and construction of the target assembly of spallation neutron sources are discussed. New experimental data obtained in a new approach for neutron production in thick targets of Pb and U are presented for 2–5xa0GeV/ c hadrons. It is found that the observed mean neutron multiplicities depend essentially on the incident available energy only while the variation with particle species for p, d, p , K, and π is within 10%.

Neutron density distributions from antiprotonic Pb 208 and Bi 209 atoms

The x-ray cascade from antiprotonic atoms was studied for 208 Pb and 209 Bi. Widths and shifts of the levels due to the strong interaction were determined. Using modem antiproton-nucleus optical potentials, the neutron densities in the nuclear periphery were deduced. Assuming two-parameter Fermi distributions (2pF) describing the proton and neutron densities, the neutron rms radii were deduced for both nuclei. The difference of neutron and proton rms radii Δr nP equal to 0.16 ± (0.02) stat ± (0.04) syst fm for 208 Pb and 0.14 ± (0.04) stat ± (0.04) syst fm for 209 Bi were determined, and the assigned systematic errors are discussed. The Δr nP values and the deduced shapes of the neutron distributions are compared with mean field model calculations.

A combination of two 4π detectors for neutrons and charged particles.: Part I. The Berlin neutron ball—a neutron multiplicity meter and a reaction detector

Abstract Two 4π detectors for neutrons and charged particles have been combined for the investigation of GeV-proton and antiproton induced spallation reactions. It is a large neutron scintillator tank with a high-granularity charged-particle detector in its central vacuum chamber. Together they register the whole, neutral and charged, de-excitation cascade of the excited reaction complex as well as heavier reaction products, i.e. intermediate-mass and fission fragments and heavy residues. Part I of our communication describes the neutron detector Berlin neutron ball (BNB): Its spherical tank is filled with 1.5 m 3 scintillator liquid, loaded with 0.4 wt % Gd. BNB recognizes each reaction in the target with a low inelasticity threshold of 2.5 MeV ee and records event-wise the multiplicity of evaporated neutrons with ≈75% efficiency. Part II [12] describes the charged particle detector Berlin silicon ball (BSiB) assembled from 151 independent Si-detectors and six ancillary four-fold telescopes, considers its detection efficiency for various particle species and provides experience gained from the joint operation of both detectors, BNB and BSiB, as a filter on the excitation energy dissipated event-by-event in the spallation reaction.

Breakup time scale studied in the 8 GeV/c pi- + 197Au reaction

Experimental data from the reaction of an 8.0 GeV/c pi- beam incident on a 197Au target have been analyzed in order to investigate the integrated breakup time scale for hot residues. Alpha-particle energy spectra and particle angular distributions supported by a momentum tensor analysis suggest that at large excitation energy, above 3-5 MeV/nucleon, light-charged particles are emitted prior to or at the same time as the emission of the heavy fragments. Comparison with the SMM and GEMINI models is presented. A binary fission-like mechanism fits the experimental data at low excitation energies, but seems unable to reproduce the data at excitation energies above 3-5 MeV/nucleon.

Vaporization and multifragmentation in the reaction 1.2 GeV + Cu and Ag

Abstract Reactions of 1.2 GeV antiprotons with Cu and Ag targets have been studied. It was found that in such reactions, excitation energies are generated in excess of the total binding energy of the nuclei involved. Accordingly, one observes in these reactions the onset of vaporization and multifragmentation processes. In the p + Cu reaction, the vaporization is observed to set in at about 7.5 MeV/nucleon. However, its probability remains relatively small and below 15% up to the highest excitation energies identified in the present studies (approximately 15 MeV/nucleon). The threshold excitation energy for multifragmentation processes, defined as the detection of at least 3 intermediate mass fragments, is observed at about 4 MeV/nucleon for both studied reactions. Multifragmentation is seen to account for no more than approximately 5% and 20% of the corresponding inclusive yield for Cu and Ag targets, respectively.

Caloric curve of 8 GeV/c negative pion and antiproton + Au reactions

The relationship between nuclear temperature and excitation energy of hot nuclei formed by 8 GeV/c negative pion and antiproton beams incident on 197Au has been investigated with the ISiS 4-pidetector array at the BNL AGS accelerator. The double-isotope-ratio technique was used to calculate the temperature of the hot system. The two thermometers used (p/d-3He/4He) and (d/t-3He/4He) are in agreement below E*/A ~ 7 MeV when corrected for secondary decay. Comparison of these caloric curves to those from other experiments shows some differences that may be attributable to instrumentation and analysis procedures. The caloric curves from this experiment are also compared with the predictions from the SMM multifragmentation model.

Caloric curve of8GeV/cπ−,p¯+197Aureactions

The relationship between nuclear temperature and excitation energy of hot nuclei formed by 8 GeV/c negative pion and antiproton beams incident on 197Au has been investigated with the ISiS 4-pidetector array at the BNL AGS accelerator. The double-isotope-ratio technique was used to calculate the temperature of the hot system. The two thermometers used (p/d-3He/4He) and (d/t-3He/4He) are in agreement below E*/A ~ 7 MeV when corrected for secondary decay. Comparison of these caloric curves to those from other experiments shows some differences that may be attributable to instrumentation and analysis procedures. The caloric curves from this experiment are also compared with the predictions from the SMM multifragmentation model.

Thermal expansion effects in the 8-GeV/c pi- + Au-197 reaction

Fragment kinetic energy spectra for reactions induced by 8.0 GeV/c

A combination of two 4π-detectors for neutrons and charged particles.: Part II. The Berlin silicon ball BSiB for light- and heavy-ion detection

rm{pi^-}