Total Charge-changing Cross Sections Research Articles

Nuclear fragmentation of high-energy heavy-ion beams in water

As a part of the physical-technical program of the heavy-ion therapy project at GSI we have investigated the nuclear fragmentation of high-energy ion beams delivered by the heavy-ion synchrotron SIS, using water as a tissue-equivalent target. For a direct comparison of fragmentation properties, beams of 10B, 12C, 14N, and 16O were produced simultaneously as secondary beams from a primary 18O beam and separated in flight by magnetic beam analysis. The Z-distributions of beam fragments produced in the water target were measured via energy loss in a large ionisation chamber and a scintillator telescope. From these data we obtained both total and partial charge-changing cross sections. In addition we have performed Bragg measurements using two parallel-plate ionization chambers and a water target of variable length. The detailed shape of the measured Bragg curves and the measured cross sections are in good agreement with model calculations based on semi-empirical formulae.

Fragmentation cross sections of relativistic 8436Kr and 10947Ag nuclei in targets from hydrogen to lead.

With the addition of krypton and silver projectiles we have extended our previous studies of the fragmentation of heavy relativistic nuclei in targets ranging in mass from hydrogen to lead. These projectiles were studied at a number of discrete energies between 450 and $1500A$ MeV. The total and partial charge-changing cross sections were determined for each energy, target, and projectile, and the values compared with previous predictions. A new parametrization of the dependence of the total charge-changing cross sections on the target and projectile is introduced, based on nuclear charge radii derived from electron scattering. We have also parametrized the energy dependence of the total cross sections over the range of energies studied. New parameters were found for a previous representation of the partial charge-changing cross sections in hydrogen and a new parametrization has been introduced for the nonhydrogen targets. The evidence that limiting fragmentation has been attained for these relatively light projectile nuclei at Bevalac energies is shown to be inconclusive, and further measurements at higher energies will be needed to address this question.

Charge-changing fragmentation of 10.6 GeV/nucleon 197Au nuclei.

We have measured the charge-changing cross sections of 10.6 GeV/nucleon $^{197}\mathrm{Au}$ nuclei interacting in targets of ${\mathrm{CH}}_{2}$ (polyethylene), C, Al, Cu, Sn, and Pb. Cross sections for H are calculated from those measured in C and ${\mathrm{CH}}_{2}$. The total charge-changing cross sections are higher than those measured at energies of \ensuremath{\le}1 GeV/nucleon. The measured cross sections for the heavier targets are somewhat larger than those predicted by a model based on data taken at lower energies with lighter targets. Partial charge-changing cross sections for the production of fragments from the incident Au projectiles were measured for charge changes (\ensuremath{\Delta}Z) from \ensuremath{\Delta}Z=+1${,}_{80}$Hg, down to approximately \ensuremath{\Delta}Z=-29${,}_{50}$Sn. In comparison to lower energy measurements, these partial cross sections are found to be smaller for small \ensuremath{\Delta}Z and larger or the same for large \ensuremath{\Delta}Z. The H partial cross sections are found to follow a power law in \ensuremath{\Delta}Z similar to that for heavier targets, instead of the exponential form observed at lower energies. Factorization is found to hold for all partial cross sections with \ensuremath{\Delta}Z greater than two. In the heavier targets, the cross sections for one and two proton removal have significant contributions from electromagnetic dissociation. The electromagnetic dissociation contribution to the total cross section is derived and found to be relatively small, but with a strong dependence on the charge of the target nuclei of the form ${\mathit{Z}}_{\mathit{T}}^{1.75\ifmmode\pm\else\textpm\fi{}0.01}$.

One- and two-neutron removal from the radioactive secondary projectiles 56Ni and 52Fe

Abstract A method for measuring the cross sections for the neutron removal from relativistic secondary projectiles by means of a two-stage magnetic spectrometer is presented. Its application to the 1n- and 2n-removal from 56 Ni and 52 Fe at 470 A ·MeV in an aluminum target is described. The results are compared to the intranuclear-cascade plus evaporation model and to the statistical abrasion-ablation model. The influence of the nuclear surface on the few-nucleon removal reactions is discussed. The neutron-removal cross sections are combined with total charge-changing cross sections to obtain the total interaction cross sections of 56 Ni and 52 Fe.

Charge-changing interactions of 197Au at 10 GeV/nucleon in collisions with targets from H to Pb.

Total and elemental charge-changing cross sections for reactions \ensuremath{\Delta}Z=+1, -1, -2, -3 were measured for 10 GeV/nucleon $^{197}\mathrm{Au}$ ions colliding with ${\mathrm{CH}}_{2}$, C, Al, Cu, Ag, and Pb targets. Contributions to the total cross sections by the process of electromagnetic dissociation are discussed.

Total charge-changing cross sections for neutron-deficient isotopes from58Ni fragmentation

At the projectile-fragment separator FRS of GSI, relativistic secondary beams of about 520 MeV/nucleon were produced by fragmentation of a primary beam of58Ni at 650 MeV/nucleon in a beryllium target. By means of aΔE—Bρ—TOF measurement, the fragments have been identified and their charge-changing probabilities in targets of CH2, C, Al, and Pb have been determined. We describe the results for the total charge-changing cross sections in this first paper, whereas a second article deals with the partial charge-changing cross sections. At the drip line, the measured charge-changing cross sections exhaust close to 100% of the total interaction cross sections as calculated with semiempirical models. The measurements at the proton drip line with low-Z targets indicate that only a very small increase of the cross sections may be observed, whereas the measurements with a lead target show that no significant increase of the total charge-changing cross sections is present which would be a hint for low-lying dipole strength. Our experimental data are compared to Glauber-type calculations.

Total charge-changing cross sections of stable and neutron-deficient secondary projectiles around A = 60

Abstract Total nuclear charge-changing cross sections σΔz in a CH2 target were measured for 54 isotopically identified secondary beams around A = 60 produced from a 1A·GeV86Kr beam via projectile fragmentation. With secondary beams between T z = 1 2 and −3, the isospin dependence of σΔz was investigated systematically. Contrary to the predictions of so-called overlap formulae, the σΔz values are not a function of the projectile mass alone, but are found to depend on the projectile isospin. A comparison of the data with the predictions of the statistical abrasion model reveals that this behaviour can be understood by the combined influence of the abrasion and the ablation phase in relativistic heavy-ion collisions. On the basis of this improved understanding, previous findings of anomalously large cross sections of secondary-reaction products are discussed.

Projectile fragmentation of 16O and 32S at 3.65 GeV/n on several targets

We investigate the charge changing collisions for 16O and 32S beams at 3.65 GeV/n on several targets, by using Solid State Nuclear Track Detectors (SSNTD). Track measurements were performed by an automatic measurement system. We determined the total charge changing cross sections and the elemental cross sections for the production of fragments of charge 9 ≤ Z ≤ 14. Comparison with theoretical models as well as with experimental data are given.

Interactions in hydrogen of relativistic neon to nickel projectiles: Total charge-changing cross sections.

A liquid hydrogen target was used to study the nuclear fragmentation of beams of relativistic heavy ions, Ne22 to Ni58, over an energy range 400 to 900 MeV/nucleon. The experiments were carried out at the Lawrence Berkeley Laboratory Bevalac HISS facility, using the charge-velocity-rigidity method to identify the charged fragments. Here we describe the general concept of the experiment and present total charge-changing cross sections obtained from 17 separate runs. These new measured cross sections display an energy dependence which follows semiempirical model predictions. The mass dependence of the cross sections behaves as predicted by optical models, but within the experimental energy range, the optical model parameters display a clear energy dependence. The isospin of the projectile nuclei also appears to be an important factor in the interaction process.Received 19 November 1993DOI:https://doi.org/10.1103/PhysRevC.49.3200©1994 American Physical Society

Fragmentation of 1.2 GeV per nucleon 139La.

The fragmentation of 1.2 GeV per nucleon $^{139}\mathrm{La}$ nuclei has been studied. Total charge changing cross sections for H (${\mathrm{CH}}_{2}$-C), C, and Pb target nuclei, and elemental production cross sections for C and ${\mathrm{CH}}_{2}$ targets for 1\ensuremath{\le}\ensuremath{\Delta}Z\ensuremath{\le}30 have been measured. For heavy projectile fragments, the projected transverse momenta extracted are generally larger than predicted by models based on the internal momenta of nucleons in nuclei. Fits to the heavy fragment momentum distributions yield additional transverse momenta or ``bounce-off'' which range from \ensuremath{\simeq}500 to 1000 MeV/c.

SOME PRELIMINARY RESULTS FROM THE NEW 10.6 GeV/NUCLEON GOLD BEAM AT BROOKHAVEN

Preliminary results are described from three separate experiments observing the interactions of gold nuclei accelerated to 10.6 GeV/nucleon at the Brookhaven AGS. Nuclear emulsion results present a global picture of the various interaction modes and reveal the production of mesons, copious multifragmentation and the angular distributions of the emitted particles. Electronic detectors make a more precise measurement of the heavy fragments emitted from interactions in a wide range of well defined targets. Etchable glass detectors provide unique charge resolution of these heavy fragments but give results that are discordant with those from the other detectors. Very significant differences are seen between these interactions and those observed at energies of ≤1.0 GeV/nucleon. Fission appears to be almost entirely suppressed while charge pickup is reduced by a factor of two to three. Total charge changing cross-sections are increased but partial cross sections for small charge changes are reduced. Frequent examples of multifragmentation are observed and central collisions result in copious particle production with total multiplicities as great as 370 singly charged particles being emitted from a single interaction. Other interactions show the emission of as many as 15 alpha particles or 7 heavier fragments. The implications of these results on the problem of the propagation of cosmic ray nuclei through the interstellar medium are considered.

Behaviour of 200 A GeV 32S and fragments in collisions with a Cu target

Using CR-39 nuclear track detectors and an automated scanning system, the behaviour of 200 A GeV 32S and projectile fragments with charges 9<or=Z<or=15 produced in collisions with a Cu target was studied. The total and partial fragmentation charge-changing cross sections of 32S, and the total cross sections of fragments, were measured. The authors studied the dependence of the mean free path of secondary fragments on the distance from the emission point. We also measured the angular distributions of projectile fragments and the charge pick-up cross section of 32S in Cu.

Response of BP-1 to 197Au heavy ions at 11.3 GeV/nucleon

BP-1 track detectors were exposed to a 11.3 GeV/nucleon 197Au beam. BP-1 is found to be very sensitive to relativistic heavy ion beams and offers the possibility for accurate systematic measurement of spallation cross sections. The total charge changing cross section and some elemental cross sections for a carbon target were determined.

Charge-changing cross sections of the neutron-rich isotopes8,9,11Li

Total charge-changing cross sections have been measured for8Li on C and Pb targets, for9Li on C, Al, Cu, Sn and Pb targets, as well as for11Li on C, Sn and Pb targets at about 80 MeV/nucleon. These data are compared to measured total reaction cross sections and Glauber-type calculations using Hartree-Fock density distributions. These comparisons allow to draw conclusions on the proton density distribution of the neutronrich lithium isotopes. The results show that even for the most exotic nucleus11Li the proton distribution is only very weakly influenced by the long tail in the neutron density distribution already established in several experiments.

Fragmentation cross sections of 16O between 0.9 and 200 GeV/nucleon.

Inclusive cross sections for high energy interactions at 0.9, 2.3, 3.6, and 13.5 GeV/nucleon of 16O with C, CR-39 (C12H18O7), CH2, Al, Cu, Ag, and Pb targets were measured. The total charge-changing cross sections and partial charge-changing cross sections for the production of fragments with charge Z = 6 and Z = 7 are compared to previous experiments at 60 and 200 GeV/nucleon. The contributions of Coulomb dissociation to the total cross sections are calculated. Using factorization rules the partial electromagnetic cross sections are separated from the nuclear components. Energy dependence of both components are investigated and discussed.

Behavior of nuclear projectile fragments produced in collisions of 14.5A GeV 28Si with Pb and Cu targets.

Using CR-39 nuclear track detectors and an automated scanning system, we have studied the behavior of projectile fragments with charges 8\ensuremath{\le}${\mathit{Z}}_{\mathit{F}}$\ensuremath{\le}13 produced in interactions of 14.5A GeV $^{28}\mathrm{Si}$ nuclei with Pb and Cu targets. Both nuclear and electromagnetic spallation contribute to fragmentation of beam nuclei in Pb and Cu. The total charge-changing cross sections of nuclear projectile fragments with 9\ensuremath{\le}${\mathit{Z}}_{\mathit{F}}$\ensuremath{\le}13 interacting in Pb are found to be enhanced by 10 to 30 % relative to charge-changing cross sections of stable nuclides. The enhancement occurs primarily in interactions with large loss of charge. In Cu the charge-changing cross sections of secondaries show no significant excess. The mean free path of secondary fragments shows no dependence on the distance from the point of origin. This result rules out at 95% confidence level the production of nuclear fragments with interaction cross sections enhanced by a large factor as conjectured by some workers, but the result is consistent with a two-component model in which \ensuremath{\sim}30% of secondary beams are off-stability isotopes with total cross sections enhanced by \ensuremath{\sim}25%. Our measurements of angular distributions of projectile fragments showed that the transverse momentum distributions are similar to those measured at (1--2)A GeV. The charge pickup cross section of 14.5A GeV Si is measured to be 0.07--1.3 mb in Pb and \ensuremath{\le}0.9 mb in Cu, which is of the same order of magnitude as that measured at \ensuremath{\sim}1A GeV.

Determination of the cross sections for the production of fragments from relativistic nucleus-nucleus interactions. I. Measurements.

Relativistic iron, lanthanum, holmium, and gold projectile nuclei with several different energies have been fragmented in targets of polyethylene, carbon, aluminum, copper, and lead. Our detectors cleanly resolve the individual charges of the heaviest of these fragments and provide some limited information on the masses. We have measured 1256 elemental partial cross sections for the production of fragments from interactions in these target materials. Values have been derived for another 417 cross sections in a hydrogen medium. These cross sections depend on the energy and mass of the projectile nuclei as well as on the nature of the target. Total charge-changing cross sections were also found, but only in a composite target, and have been shown to be weakly dependent on energy. The mean mass losses observed for fragments that have lost a few protons show that typically many neutrons are lost with each proton, producing fragment nuclei that must be highly proton rich, and consequently very unstable. The cross sections for charge pickup on heavy targets show a rapid increase with decreasing energy, particularly for the heaviest targets. The systematics of the dependencies of the partial cross sections will be discussed in a companion paper.

ELECTROMAGNETIC DISSOCIATION IN ULTRARELATIVISTIC HEAVY ION REACTIONS

Over the last years ultrarelativistic heavy ion beams with energies from 14.5 GeV/nucleon up to 200 GeV/nucleon were accelerated at the Brookhaven and CERN accelerators. We measured total charge changing cross sections and partial fragmentation cross sections for 16 O , 28 Si and 32 S projectiles breaking up into fragments with charges ZF≥6. The measured contributions of electromagnetic dissociation (ED) to the total charges changing cross sections are in agreement with theoretical calculations. By application of factorization rules it is possible to separate measured partial cross sections into a pure nuclear component and into a component caused by ED. The ED component shows a significant contribution from fragmentation events with ΔZ&gt;2 which can be explained by interactions of energetic photons with generation and decay of nucleon resonances in the projectile.

Fragmentation cross sections of16O at 60 and 200 GeV/nucleon

We used CR39 plastic nuclear track detectors (C12H18O7) in combination with automatic track measurement to determine total charge changing and partial cross sections for the production of fragments of chargeZ=6 andZ=7 in collisions of16O beam nuclei at energies of 60 GeV/nucleon and 200 GeV/nucleon in targets H, C, CR39, CH2, Al, Cu, Ag and Pb. Total charge changing cross sections due to the process of electromagnetic dissociation are calculated based on a theoretical model and found to be consistent with total and partial electromagnetic dissociation cross sections derived from this experiment. The energy dependence of pure nuclear fragmentation is investigated.

Systematics of the release of residual nuclei from relativistic nucleus-nucleus interactions

We have examined relativistic nuclei of krypton, xenon, holmium, and gold, accelerated in a partially stripped state to a maximum rigidity of about 5.6 GeV, interacting with targets of aluminum, carbon, and polyethylene. For each projectile and target combination we determined the total and partial charge changing cross sections for the production of lighter fragments. From these measurements we have developed a new representation of the dependence of the total charge changing cross sections on beam and target charge. We have also identified simple representations of the variation of the partial cross sections with the charge of the produced fragments and shown that they are dependent on the charge and energy of the beam. The fission of gold nuclei at high energies in these various targets has also been studied.