Photofission of heavy nuclei at energies up to 4 GeV

Total photofission cross sections for 238U, 235U, 233U, 237Np, 232Th, and natPb have been measured simultaneously, using tagged photons in the energy range Egamma=0.17-3.84 GeV. This was the first experiment performed using the Photon Tagging Facility in Hall B at Jefferson Lab. Our results show that the photofission cross section for 238U relative to that for 237Np is about 80% over the entire energy range, implying the presence of important processes which compete with fission. If we assume that for 237Np the photofission probability is equal to unity, we observe a significant shadowing effect, starting below 1.5 GeV.     

Interactions of 10.6 GeV/n gold nuclei with light and heavy target nuclei in nuclear emulsion

Zeitschrift für Physik C Particles and Fields - We have investigated the particle production and fragmentation of nuclei participating in the interactions of 10.6 GeV/n gold nuclei in nuclear...     

Complete destruction of heavy nuclei by hadrons and nuclei

The total disintegration is considered of nuclei with atomic weights ～100 and 200 by high energy hadrons and He⁴, C¹² nuclei with a momentum of 4.5 GeV/c per nucleon. It is shown that mainly nucleons are emitted, and there is no residual nucleus the mass of which is comparable to that of the primary nucleus. The probability of total disintegration is considered as a function of projectile energy and mass. The multiplicity, energy and emission angle of particles are considered as well. It is shown that the density of nuclear matter in the overlap zone of colliding nuclei exceeds the usual one by a factor of ～4. A comparison is made with interaction models. A conclusion is drawn of the collective interaction mechanism (perhaps, of the shock wave type) of particle ejection from the target nucleus at the first stage of interaction and of explosive decay of the residual nucleus at the next one.     

Inelastic scattering of heavy ions from deformed light nuclei at near-barrier energies

Angular distributions have been measured at energies near the Coulomb barrier for the systems ¹⁸O + ²⁴Mg, ¹²C + ²⁸Si and ^{16, 18}O + ²⁸Si for elastic scattering and inelastic scattering to the first 2⁺ states in ¹⁸O, ²⁴Mg and ²⁸Si. Coupled-channel calculations were required in order to reproduce the details of the strong Coulomb-nuclear interference minima. However, a satisfactory account of the main features of the data was obtained in a first-order DWBA analysis and with the closed formalism of Frahn. With the exception of ¹⁸O, it was sufficient to assume equal charge and optical-potential deformation lengths.     

Fission and fragmentation of 208Pb nuclei in collisions with gold nuclei at an energy of 158 GeV per nucleon

The fission and fragmentation of ultrarelativistic ²⁰⁸Pb nuclei in collisionswith gold nuclei were studied by using a beam from the SPS accelerator at CERN at an energy of 158 GeV per nucleon. The detectors of the target area of the NA45/CERES spectrometer were used in respective measurements. The value obtained for the fission cross section is 301 ± 44 mb, where about 77% of events stem from the electromagnetic interaction of colliding nuclei, while the remaining part is the contribution of peripheral nuclear interactions. The spallation of lead nuclei that involves the formation of heavy fragments occurs only in collisions where the impact parameter satisfies the condition b > 10 fm. A complete disintegration of lead nuclei to intermediate-mass fragments and light particles is observed in some peripheral collisions.     

Fragmentation and particle production in interactions of 10.6 GeV/N gold nuclei with hydrogen, light and heavy targets

We have investigated the interactions of 10.6 GeV/n Au in nuclear emulsion. Two methods of separating interactions into those with hydrogen, light (C,N,O) and heavy (Ag,Br) target nuclei were used, giving almost identical results, which strengthened our confidence in the correctness of these methods. We also measured the angular distributions of singly and multiply charged relativistic particles emitted from the interaction vertices and the charges of the multiply charged projectile fragments. The fragmentation of the projectile Au nuclei and of the target nuclei were analyzed. The multiparticle production was studied as a function of the mass of the target nucleus. The multiplicity and the pseudorapidity distributions of relativistic singly charged particles were compared with the predictions of the RQMD Model. Received: 22 April 1998 / Published online: 8 September 1998     

Effective nucleon-nucleon forces and interaction of light exotic nuclei with stable nuclei at low energies

The effect of the density dependence of effective nucleon-nucleon forces on the folded potential of the interactions of the light exotic nuclei ⁶He, ¹¹Li, ¹¹Be, and ⁸B with the stable nucleus ¹²C is studied, and the corresponding experimental data on the total reaction cross sections and on elastic scattering are analyzed. A semimicroscopic double-folding model featuring various density-dependent forces based on the M3Y interaction is used together with the nucleon densities as calculated within the density-functional method by using a unified set of parameters for all the above nuclei. It is shown that the angular distributions recently measured for elastic ⁶He scattering on ¹²C at an energy of 41.6 MeV per projectile nucleon and for elastic ¹¹Be scattering on ¹²C at an energy of 49.3 MeV per projectile nucleon can be described satisfactorily if the real part of the optical folded potential is supplemented with a surface term mimicking the contribution of the dynamical polarization potential.     

Structure of light unstable nuclei in continuum energies

The Coulomb breakup reaction of ⁶He into a ⁴He+n+n 3-body system is analyzed by applying the complex scaling method (CSM). We can derive the contributions to El and E2 transitions, not only from resonances, but also 2- and 3-body continuum states, which show the characteristic structure of the many-body unbound states in ⁶He.     

Coulomb breakup of light nuclei in the field of a heavy ion at relativistic collision energies

A simple method for calculating the amplitude and the cross section for the Coulomb breakup of a light nucleus into two fragments in the field of a heavy ion at relativistic collision energies is proposed on the basis of time-dependent perturbation theory. It is shown that the resulting amplitude for the process in question has a correct nonrelativistic limit. The contribution of the longitudinal component of the Coulomb field of a heavy ion tends to zero in the ultrarelativistic limit. A specific implementation of the method is demonstrated by taking the example of the Coulomb breakup reaction ²⁰⁸Pb(⁸B, ⁷Bep)²⁰⁸Pb at various collision energies. The results are found to be in agreement with experimental data.     

Cross sections of Au at 10 A GeV and of Pb at 158 A GeV

We have measured total and elemental charge changing cross sections fro the fragmentation of 10 AGeV ¹⁹⁷Au- and 158 AgeV ²⁰⁷Pb-beams interacting with different targets (C, CH₂, Al, Cu, Ag, and Pb) using stacks of CR-39 and of BP-1 nuclear track detectors. Electromagnetic dissociation (ED) significantly contributes to these interactions besides nuclear fragmentation. Based on the factorization of elemental cross sections it is possible to separate electromagnetic dissociation cross sections from the measured data. The analysis of the Au 10 AGeV experiment is completed. For the Pb-beam the analysis is in progress. First results will be reported.     

Fast helium production in interactions of 3.7 A GeV <Superscript>24</Superscript>Mg with emulsion nuclei

We have studied the properties of the relativistic helium fragments emitted from the projectile in the interactions of ²⁴Mg ions accelerated at an energy of 3.7 A GeV with emulsion nuclei. The total, partial nuclear cross-sections and production rates of helium fragmentation channels in relativistic nucleus-nucleus collisions and their dependence on the mass and energy of the incident projectile nucleus are investigated. The yields of multiple helium projectile fragments disrupted from the interactions of ²⁴Mg projectile nuclei with hydrogen H, light CNO and heavy AgBr groups of target emulsion nuclei are discussed and they indicate that the breakup mechanism of the projectile seems to be independent of the target mass. Limiting fragmentation behavior of fast-moving helium fragments is observed in both the projectile and target nuclei. The multiplicity distributions of helium projectile fragments emitted in the interactions of ²⁴Mg projectile nuclei with the different target nuclei of the emulsion are well described by the KNO scaling presentation. The mean multiplicities of the different charged secondary particles, normally defined shower, grey and black ( n_s, n_g and n_b) emitted in the interactions of 3.7 A GeV ²⁴Mg with the different groups of emulsion nuclei at different ranges of projectile fragments are decreasing when the number of He fragments stripped from projectile increases. These values of n_i ( i = s, g, b and h particles) in the events where the emission of fast helium fragments were accompanied by heavy fragments having Z 3 seem to be constant as the He multiplicity increases, and exhibit a behavior independent of the He multiplicity.     

Isospin dependence of kinetic energies in light neutron-rich nuclei

Energy spectra andelectric dipole transitions ofN=7 isotones are studied by shell model calculations with isospin dependent kinetic energies for s-d shell orbits. The ground states of¹⁰Li and⁹He are predicted. Electric dipole transitions in¹³C and¹¹Be are studied by using the realistic single-particle wave functions in Woods-Saxon potential.JSPS Fellow for Japanese Junior Scientists.     

Yields of projectile fragments in sulphur-emulsion interactions at 3.7 A GeV

This work presents the basic characteristics of singly,doubly and heavily charged projectile fragments(PFs) emitted in inelastic interactions of ~(32)S ions with photo-emulsion nuclei at Dubna energy(3.7 A GeV).Our experimental data are compared with the corresponding data for other projectiles at the same incident energy.The study of mean multiplicities of different charged PFs against the projectile mass shows a power-law relationship.The multiplicity distributions of singly and doubly charged PFs have been fitted well with a Gaussian distribution function.The yields of PFs broken up from the interactions of ~(32)S projectile nuclei with different target nuclei are studied.The beam energy dependence in terms of the various order moments is studied as well.     

π−-meson and nucleon yields from light targets irradiated by deuterium and tritium nuclei beams at energies of 1 GeV/nucleon

In this paper, we present a model of calculation with respect to the interactions of high-energy nuclei with matter. Based on this model, we obtain results on energy and angular spectra of the n- and π⁻-particles produced in collisions of deuterium and tritium nuclei at energiesT _d=1 GeV/nucleon with light targets such as Li, Be. We have also estimated the production yields of neutrons and π⁻-mesons in targets of various radii, as well as mean energies of these these particles. Summarizing, we find that the lithium target of radiusR=10−12 cm for which the energy cost ε_π to produce one π⁻-meson is estimated as 6.7 GeV/π for a d-beam and 5.3 GeV/π for a t-beam is the most preferred pion-production target.     

Fission cross sections of medium-weight and heavy nuclei induced by 1 GeV protons

Coincidence studies performed in 4π geometry with silicon detectors and parallel plate avalanche counters have been used to measure total fission cross sections of²³⁸U,²³²Th,²⁰⁹Bi,²⁰⁸Pb,¹⁹⁷Au,^natYb,^natHo,^natTb,^natSm,^natTe,^natAg and^natNi nuclei induced by 1 GeV protons. The experimental results agree qualitatively with cascade-evaporation calculations.     

Light and heavy ion transfer reactions among light nuclei

A comparison is made between two transfer reactions involving the same target and final nuclei, ²⁶Mg and ²⁸Si. The (τ, n) and (¹⁶O, ¹⁴C) ground band reactions are considered, representing light and heavy ion projectiles. Despite the rather complicated nuclear structure transition involved in these reactions, the spectroscopic features of the two reactions are very similar. In both cases inelastic transitions entail major contributions from multistep processes.     

Transverse momenta of fragments of relativistic sulfur and lead nuclei after their interaction with track-emulsion nuclei at energies of 200 and 160 GeV per nucleon

Transverse-momentum distributions of doubly charged fragments of sulfur and lead nuclei having energies of 200 and 160 GeV per nucleon and interacting with nuclei in a track emulsion were investigated. No trace of compression or heating of nuclear matter in the interaction of these nuclei with track-emulsion nuclei was revealed experimentally. Transverse momenta of fragments of relativistic nuclei were found to obey a normal distribution that corresponds to a degenerate momentum distribution of nucleons in the ground state of a nucleus before its interaction with a track-emulsion nucleus. There is no piece of evidence that fragments of relativistic nuclei originate from some excited state of an intermediate nucleus. This picture of the fragmentation of relativistic nuclei complies with the naive parton model proposed by Feynman and Gribov. In summary, the fragmentation of relativistic nuclei at energies of 160 and 200 GeV per nucleon is cold and fast.