Chronology of particle emission from the E/A=61 MeV 36Ar+27Al reaction

The emission time chronology of neutrons, protons, and deuterons from the E/A=61 MeV 36Ar+27Al reaction is deduced from two-particle correlation functions.     

The correlation functions and emission time scales for light particles and light fragments in 40Ar+197Au reactions at 25 MeV/nucleon

Two-particle correlation functions were measured for the emission of protons, deuterons, tritons, α, and lithium fragment at small relative momenta in ⁴⁰Ar-induced reactions on ¹⁹⁷Au at 25 MeV/nucleon. Based on three-body trajectory calculations the emission time scales for the particles were extracted from p-d, d-d, t-t, and lithium-lithium correlation functions. The mean emission time was found to decrease with increasing sum of the kinetic energies of the particle in a correlated pairs, indicating the emission of more energetic particles at earlier stages of the reaction than at later stages. The time scale for the emission of lithium fragments emission suggests that sequential binary disassembly occurs in ⁴⁰Ar+¹⁹⁷Au reaction at MeV/nucleon. Mean emission temperature of 3.5_−0.8^+1.3 and 3.6±0.4 MeV were also extracted from the relative populations of the excited and ground states of the respective emitted nuclides ⁸Be and ⁴He.     

External Coulomb distortion of proton-deuteron final-state interactions for induced reactions on Au at E/A = 35 MeV

Correlations between coincident protons and deuterons were measured for induced reactions on Au at E/A = 35 MeV. Because of their different mass-to-charge ratios, protons and deuterons experience different accelerations in the Coulomb field of the heavy target residue. Correlations measured at small relative momenta are, therefore, influenced not only by the interaction between the coincident particles but also by this external field. The modification of the p−d correlation function by this field suggests that emission occurs close to the surface of the target residue.     

Electromagnetic form factors of the nucleon

Dynamical and thermal characterizations of excited nuclear systems produced during the collisions between two heavy ions at intermediate incident energies are presented by means of a review of experimental and theoretical work performed in the last two decades. Intensity interferometry, applied to both charged particles (light particles and intermediate mass fragments) and to uncharged radiation (gamma rays and neutrons) has provided relevant information about the space-time properties of nuclear reactions. The volume, lifetime, density and relative chronology of particle emission from decaying nuclear sources have been extensively explored and have provided valuable information about the dynamics of heavy-ion collisions. Similar correlation techniques applied to coincidences between light particles and complex fragments are also presented as a tool to determine the internal excitation energy of excited primary fragments as it appears in secondary-decay phenomena.     

Investigation of neutron emission in the interaction of relativistic protons and deuterons with lead targets

Measurements of neutron double-differential cross sections and yields in time-of-flight experiments with various lead targets and beams of protons and deuterons with an energy of about 2 GeV are discussed. Space and energy distribution of neutrons in an extended lead target is studied by threshold detectors in the proton energy range of 1–3.7 GeV. The average multiplicity of neutrons, neutron energy, and neutron multiplication in lead as functions of target dimension, type, and energy of the beam particle are analyzed.     

Anomalies of neutron and γ-ray emission in light charged particle accompanied fission of 252Cf

Correlations between the neutron and γ-ray emission and the kinetic energy of light charged particles (LCPs), such as protons, deuterons, tritons and alphas, from the fission of ²⁵²Cf were studied in a four parameter experiment. A ⊘ 16 cm × 5 cm liquid scintillator with n-γ discrimination and a ⊘ 10 cm × 10 cm NaI(Tl) crystal were employed to detect the neutrons and the γ rays, respectively, while a thin CsI(Tl) crystal, which had the ability to separate the LCPs, was used to determine the LCP energy. The experimental results show that for the α particle accompanied fission, the average total number of neutrons emitted per fission increases in the case of varying the alpha particle energy E_α from 7 to 11 MeV and then falls off linearly in a first approximation with increasing E_α, and the average total energy and the average total number of γ-rays per fission as well as the average γ-ray energy as functions of E_α show similar correlation features. For the hydrogen-ion accompanied fission, the correlations of the neutron and γ-ray emission with hydrogen ion (t, d and p) energy are very similar to those for the alpha-particle accompanied fission. The correlations of the neutron and γ-ray emission in the low LCP energy region, in contrast to that observed in the high LCP energy range, are called anomalies. On the basis of the results obtained by the three-point charge model and the liquid drop model calculation with shell and pairing correction, the anomalous behavior of the neutron and γ-ray emission is explained tentatively.     

Effects of subfemtosecond quantum correlations in neutron scattering on water

Several recent experiments have shown that protons, and to some extent also deuterons, show anomalous cross sections when the neutrons have energies in the range 10-100 eV (this results in a Compton scattering process where an essential part of the energy is transferred to one of the scattering particles). Here, an experiment on partially deuterated water, carried out by Chatzidimitriou-Dreismann et al., is analyzed in terms of a theory, which assumes that during the short duration (<10(-15) s) of this scattering process, protons are exchange correlated and cannot be considered as independent scattering objects. The quantum decoherence time for protons in liquid water is estimated from a simple model for the interaction of the water protons with hydrogen bonds.     

Hadronic expansion dynamics in central Pb+Pb collisions at 158 GeV per nucleon

Two-particle correlation functions of negative hadrons over wide phase space, and transverse mass spectra of negative hadrons and deuterons near mid-rapidity have been measured in central Pb+Pb collisions at 158 GeV per nucleon by the NA49 experiment at the CERN SPS. A novel Coulomb correction procedure for the negative two-particle correlations is employed making use of the measured oppositely charged particle correlation. Within an expanding source scenario these results are used to ext ract the dynamic characteristics of the hadronic source, resolving the ambiguities between the temperature and transverse expansion velocity of the source, that are unavoidable when single and two particle spectra are analysed separately. The source shape, the total duration of the source expansion, the duration of particle emission, the freeze-out temperature and the longitudinal and transverse expansion velocities are deduced. Received: 25 November 1997 / Published online: 24 March 1998     

Optical potential for composite particles

Optical potentials for the elastic scattering of deuterons, ³He and tritons are calculated in terms of the optical potentials of neutrons and protons forming the projectile. The angular distributions for the elastic scattering of these particles from various targets are calculated and compared with experimental results.     

Interaction of 32-GeV positrons with photoemulsion nuclei

An analysis of evaporated particles originating from the interaction of 32-GeV positrons with photoemulsion nuclei was performed. The yields of protons, deuterons, tritons, and alpha particles were measured, and the results were compared with evaporation-theory predictions. The energy spectra of protons, deuterons, and tritons agree with a Maxwellian distribution. The excitation energy of photoemulsion nuclei complies with the theoretical estimate for the emission of these particles from the equilibrium state.     

Emission order of light particles and light fragments from hot nuclei followed by binary fission

Emission orders of light charged particles and Li fragments from highly excited fissioning nuclei in the reaction of ⁴⁰Ar+¹⁹⁷Au at E _beam /A=25 MeV have been studied by measuring difference velocity distributions of two correlated particles at small relative angles in coincidence with two fission fragments. By comparing the data with three-body trajectory calculations, we found that high velocity deuterons are emitted prior to high velocity Li fragments but low velocity deuterons are emitted after low velocity Li fragments. On the other hand, no preferential emission was observed among light particles, such as protons and deuterons. Furthermore, the emission orders are found to depend only weakly on the mass asymmetry of fission fragments. Received: 3 June 1997 / Revised version: 23 July 1997     

Pion absorption reactions on N, Ar and Xe

The absorption of π⁺ on Ar was studied at pion energies of 70, 118, 162, 239 and 330MeV, and on N and Xe at 239MeV. Twenty-six absorption reaction channels with at least two energetic charged particles in the final state have been evaluated. Partial cross-sections have been determined according to the number of protons, neutrons and deuterons in the final state. Received: 16 October 2000 / Accepted: 1 December 2000     

Tutorial on neutron physics in dosimetry

Almost since the time of the discovery of the neutron more than 70 years ago, efforts have been made to understand the effects of neutron radiation on tissue and, eventually, to use neutrons for cancer treatment. In contrast to charged particle or photon radiation which directly leads to release of electrons, neutrons interact with the nucleus and induce emission of several different types of charged particles such as protons, alpha particles or heavier ions. Therefore, a fundamental understanding of the neutron–nucleus interaction is necessary for dose calculations and treatment planning with the needed accuracy. We will discuss the concepts of dose and kerma, neutron–nucleus interactions and have a brief look at nuclear data needs and experimental facilities and set-ups where such data are measured.     

Asymmetry in the scattering of protons on polarized deuterons at 1.21 GeV/c

By using a polarized deuteron target we have measured the asymmetry in the differential cross section for elastic scattering of protons on deuterons and for quasi-elastic scattering of protons on protons bound in deuterons between the two states of opposite polarization, normal to the scattering plane of the initial deuteron. The beam momentum was 1.21 GeV/c. It is checked that the neutrons bound in the deuterons are polarized to approximately 20%.     

Neutron-induced production of protons, deuterons and tritons on copper and bismuth

Inclusive cross sections for production of protons, deuterons and tritons by neutrons in the energy range of 300–580 MeV on copper and bismuth have been measured at five angles between 54° and 164°. The systematic dependence of the invariant cross sections on incident energy and emission angle are evaluated. For the study of the mass-number dependence earlier data on carbon are included. The results are discussed on the basis of different models, like quasi-two-body sealing or moving-source model.     

Pion-proton correlations and asymmetry measurement in Au + Au collisions at √<Emphasis Type="Italic">s</Emphasis><Subscript><Emphasis Type="Italic">NN</Emphasis></Subscript> = 200 GeV data

Correlations between non-identical particles at small relative velocity probe asymmetries in the average space-time emission points at freeze-out. The origin of such asymmetries may be from long-lived resonances, bulk collective effects, or differences in the freeze-out scenario for the different particle species. STAR has extracted pion-proton correlation functions from a dataset of Au+Au collisions at √s _NN = 200 GeV. We present correlation functions in the spherical harmonic decomposition representation, for different centralities and for different combinations of pions and (anti-)protons.     

Emission of deuterons in the interactions of 9 GeV protons with lead nuclei

The emission of deuterons with energies ranging from 17 to 104 MeV in interactions of 9 GeV protons with lead nuclei has been studied using nuclear emulsion. These deuterons constitute about $\text{1}\text{6}$ of the secondary heavily ionising particles (β < 0.7). Observed features of the emission of the deuterons with energies above 28 MeV can be interpreted in terms of the mechanism proposed by Butler and Pearson.     

中心集体流对带电粒子关联函数的影响

讨论了中心集体流对带电粒子关联函数的影响,采用蒙特卡罗方法研究了热源发射出的单粒子能谱与双粒子关联谱受中心集体流的影响. 利用QMD模型计算了100MeV/u的Ni+Ni系统在b=0fm条件下的双质子关联函数. 在计算中发展了一种交换粒子计算方法并证实了在100MeV/u Ni+Ni的中心碰撞中存在中心集体流. 计算结果表明,在中重系统中关联函数对中心集体流是灵敏的,为在100MeV/u以上能区研究中重系统中心碰撞形成的中心集体流提供了一种可行的方法.     

Nonadiabatic corrections to the adiabatic Efimov potential

Abstact: The composition of forward-going projectile spectator matter in fixed-target Pb+Pb collisions at 158 A · GeV at the CERN SPS has been studied as a function of centrality. The data were measured with the NA49 veto calorimeter. We observe that forward-going spectator matter in central collisions consists of 9 neutrons, 7 protons, and half a deuteron on average. At large impact parameters most spectator nucleons are bound in fragments. The relative resolution of the average impact parameter derived from the measurement of spectator neutrons is roughly 19% in the range from zero to half maximum impact parameters. Received: 16 February 1998 / Revised version: 30 March 1998     

Properties of pairing in nuclei demonstrated in a solvable model

In the sense of a simulation a model is considered, which is to reflect the effect of the residual interaction at the nuclear surface. It consists of two energetically separated shells of equal one-particle spin and opposite parity. Initially the lower level is filled and the upper empty. We are interested in the short-range nuclear force taken asδ-force. The model is considered for equivalent particles and extended to protons and neutrons. The energy spectra of both types forj=3/2 are similar, and resemble real spectra of even nuclei. For the equivalent particles, the BCS theory leads to a good approximation of the ground-state wave function, if after the variation the projection to definite particle number is performed. For the case of protons and neutrons, mixing of them and performing projection prior to the variation proves to be necessary. It is suggested that here the mixing of the parity is also important. In the configurations of the model a new sort of pairing matrix elements appears, which are larger than any other matrix elements, and act between two-particle states withJ=T=0 andΠ=?1.