J. Mahoney

Determination of Y40 and Y60 components in the shapes of rare earth nuclei

Abstract Differential cross sections for 50 MeV alpha particles of members of the ground state rotational band up to the 6 + or 8 + state were measured in a number of even nuclei of the rare earth region. The data were analyzed under the assumption of a perfect rotor description for the nucleus and a deformed optical interaction between alpha and nucleus by solving the resulting coupled equations. Higher order components Y 4 and Y 6 in the nuclear shapes were determined with precision. A systematic variation of B 4 from positive values in the light rare earths to negative values in the heavy ones is established.

Energy dependence of peripheral reactions induced by heavy ions

Abstract Collisions of 16 O ions on targets of 94 Zr, 197 Au, 208 Pb, and 232 Th are investigated at incident energies of 140 and 315 MeV and compared to published data on peripheral collisions at 33.6 GeV. At 140 MeV, the isotope-production cross sections resemble the ground-state Q -value systematics characteristic of a partially-equilibrated, di-nuclear system formed in deeply-inelastic scattering. The yields are independent of shell and pairing effects in the target and residual nuclie. These Q -value systematics fail at 315 MeV, where the relative element yields are similar to those at 33.6 GeV. A theory of projectile fragmentation accounts for the shapes of the inclusive energy spectra as well as for the isotope yields at both energies. The relative cross sections are target independent (i.e., factorize) for the data at 315 MeV incident energy, but limiting fragmentation (i.e. isotope yields independent of energy) applies only at higher energies. The differential cross sections peal at the grazing angle or decrease exponentially, depending on the incident energy and the mass of the ejectile; the distributions are described by classical trajectories and diffraction models for which the reaction time is estimated to be typical of direct reactions. The kinetic energies of the reaction products depend primarily on their charge and only slightly on their mass number. For the 315 MeV results, the velocities of the reaction products at the maximum of the spectrum and the grazing angle are slightly less than the beam velocity and decrease rapidly for larger scattering angles. The results are interpreted with simple fraction and fragmentation models, and are compared to observations at 33.6 GeV.

A SPECTROMETER FOCAL PLANE DETECTOR FOR HEAVY IONS

Abstract A resistive-wire position-sensitive proportional transmission counter has been built for the detection of heavy ions in the focal plane of a magnetic spectrometer. The 45 × 6 cm2 counter measures position and energy loss with a resolution of 0.7 mm and 8–10% respectively. Time-of-flight is measured with a plastic scintillator behind the proportional counter. The position, time and energy loss signals are used to identify heavy ions with unit mass and atomic number resolution up to about A = 20, Z = 10.

INFLUENCE OF INTRINSIC NUCLEON MOTION ON ENERGY SPECTRA AND ANGULAR DISTRIBUTIONS FOR 16O-INDUCED REACTIONS AT 20 MEV/A

Abstract Energy spectra and angular distributions for peripheral reactions induced by 16 O on 208 Pb at 20 MeV/ A can be explained in terms of the intrinsic nucleon motion of the excited projectile, in a manner similar to the interpretation of projectile fragmentation reactions at 2.1 GeV/ A .

Coherent and incoherent processes in projectile breakup

Abstract We have studied the breakup of 140 MeV 16 O into 12 C + α by targets of 12 C, 13 C and 28 Si. At least two mechanisms contribute. One can be identified as the coherent excitation of the 16 O projectile to components of the giant resonance states. Another dominant mechanism may be the quasi-free scattering of the α or 12 C constituents of the projectile by the target.

Response of pilot U scintillator to heavy ions

Abstract The light output response of Pilot U scintillator for stopped charged particles has been measured for 4He, 6Li, 12C, 16O, 20Ne and 40Ar ions incident at various energies up to 20 MeV/nucleon. From these we derived a systematic description of the variation of the scintillation parameters with the charge and energy of the projectile. The suitability of such a detector for the focal plane of a heavy ion magnetic spectrometer is discussed.

Particle-particle angular correlations in peripheral heavy-ion reactions☆

Abstract Angular correlations between fast α-particles and outgoing heavy reaction products have been measured for the reactions ( 16 O, 12,13,14 Cα) and ( 16 O, 14 Nα) on 208 Pb and 197 Au targets at 140 and 310 MeV laboratory energy. For a wide range of energy losses, coincident particles are preferentially emitted on the same side of the beam axis. The results are compared with recent qualitative predictions.

High energy proton emission in reactions induced by 315 MeV 16O ions

Abstract Inclusive proton spectra have been measured for the reaction 197Au(16O, p)X at 315 MeV. The data, which are consistent with emission from a moving source, are compared with the fireball model and with models preequilibrium emission.

Improvements to resistive-wire focal-plane detector

Abstract A resistive-wire spectrometer focal-plane proportional-counter system has been improved by the addition of a thin-foil scintillation timing detector near the spectrometer entrance and of a second proportional counter with larger energy loss and hence better resolution.

Trends of isotope yields observed in reactions induced by 16O ions of 140, 315 and 33600 MeV

Abstract Isotope yields from reactions induced by 16 O ions of 140 and 315 MeV on 94 Zr, 197 Au, 208 Pb and 232 Th targets are measured and compared with published data at 33.6 GeV. The previously reported similarity of cross sections at 315 MeV and 33.6 GeV is augmented by the fact that the relative isotope yields are essentially target independent at 315 MeV (as has been established at 33.6 GeV). Significant differences are observed between cross sections at 140 and 315 MeV.