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

Abstract

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.

Charge-changing interactions of ultrarelativisticPbnuclei

“…In contrast to earlier studies performed at intermediate energies [48,49] and at 10.6A GeV [46,50], we observe a strong, almost quadratic increase of the nuclear-charge pickup ͑⌬Z = +1͒ cross sections with target charge. Our experimental findings can be described quantitatively with RELDIS calculations showing that in collisions with high-Z nuclei the dominant contribution to nuclear-charge pickup is due to electromagnetic processes of − production by virtual photons.…”

“…At relativistic energies, however, the Fermi spheres of projectile and target are totally nonoverlapping, preventing any transfer of a target proton to the projectile. Instead, we can assume ⌬-resonance formation and decay in NN collisions to be the most likely elementary processes in which a projectile neutron can be converted into a proton, e.g., by n → ⌬ This holds for different projectiles with energies between 0.5A and 10A GeV [46,48,49].…”

Nuclear and electromagnetic fragmentation of 2.25-TeV197Au nuclei

“…In the strict sense, the concept of limiting fragmentation implies that thepartial cross sections, rather than the total cross section, become independent of energy above some limiting energy. In their study of fragmentation of Au in CH 2, C, A1, and Cu, Binns et al [25] found changes in partial cross sections of up to a factor 3 for A Z--1, 2, and 3 in the energy interval from 555 to 915 A MeV, and Cummings et al [26] found smaller changes for larger values of AZ. Our partial cross sections for Au in C, A1, and Cu at 11.4 A GeV differ by occasionally as much as 30% from those of Binns et al and Cummings et al There may be a trend for the partial cross sections at highest energy to be smaller for small A Z and larger for large A Z than those at low energy.…”

Heavy fragment production cross sections from 1.05 GeV/nucleon 56Fe in C, Al, Cu, Pb, and CH2 targets

“…The heaviest ion present in significant numbers in the GCR is 56 Fe; the measurements described in this paper were made with iron ions at an energy of 1.05 GeV/nucleon, which is near the peak of the solar-modulated GCR iron energy spectrum [3]. While many results have been published on iron fragmentation between several hundred MeV/nucleon and several GeV/nucleon [4][5][6][7][8][9][10], previously-reported fragment production cross sections [4,7,9] show significant discrepancies which we believe are resolved by the present measurements.…”