LIGHT FRAGMENT CHARACTERISTICS FROM THE INTERACTION OF MULTI-GEV C-12 IONS AND PROTONS WITH A RANGE OF TARGET ELEMENTS

GEORGE DOUGLAS COLE, Purdue University

Abstract

Comparative studies of the interaction of high energy ('12)C ions and protons with complex nuclei serve to elucidate the mechanisms of nuclear reactions induced by the former, a novel and not well understood projectile. The current experiment was designed to broadly explore the properties of light products using a thick-target, thick-catcher technique. Target packets were constructed using foils of Cu, Ag, Gd, Ta, Au and U metal, each surrounded by thick plastic catchers. Targets were irradiated by 400-GeV protons and 18.5-GeV ('12)C heavy ions (HI). Gamma-ray analysis of the foils allowed the determination of cross sections ((sigma)) and recoil properties associated with products of ('24)Na, ('28)Mg, ('42)K, ('44)Sc('m), ('48)Sc, ('48)V and ('52)Mn from each target for each projectile. Use of the recoil properties and the velocity-vector representation of the two-step model gave corresponding recoil parameters. These include the forward velocity, (beta)(,(PARLL)) (in units of c), imparted to the target residue, and the average kinetic energy, , of the recoiling product of the residue's breakup. The results have been used to test the factorization hypothesis, which predicts that the product cross sections from target-fragmentation reactions depend on the identity of the projectile only via a factorable total cross-section term. Comparisons of (sigma) from different projectiles must be made at the same bombarding energy and, consequently, slight adjustments were required in our proton data on the basis of lower energy results from the literature. All the (HI-to-proton) comparative-(sigma) results from Cu are consistent with factorization, as are those for the heavier products from Ag targets. For the heavier targets, departures from factorization range from 30% to 100%, indicating heavy ion effects beyond the larger HI total cross section. The HI enhancement suggests that the observed products result from a central-collision mechanism, leading to the destruction of both target and projectile, instead of the more peripheral target-fragmentation process. The behavior of the (beta)(,(PARLL)) values with target mass (A(,T)) is found to vary with product mass. The difference in behavior is most pronounced in the region of heaviest targets. The lightest products show increasing forward velocities, while the five heavier products have values decreasing to nearly zero. The chief production mechanism in this A(,T) region thus imparts a considerable range of forward momenta to the products. The HI irradiations generally produce larger (beta)(,(PARLL)) values than do the proton bombardments. The recoil kinetic energies for both mass groups behave independently of projectile and increase monotonically with target mass. Reaction models are used to correlate calculated and experimental values to show that fissionlike breakup is predominant at larger A(,T). The recoil kinetic energies do not exhibit the departures from factorization shown by the other properties. This suggests that the kinetic energy alone is not a sensitive measure of the difference between peripheral and central collisions between projectile and target.

Degree

Ph.D.

Subject Area

Nuclear chemistry

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