F. W. Prosser

Vanishing spin alignment: Experimental indication of a triaxial {sup 28}Si+{sup 28}Si nuclear molecule

Fragment-fragment-{gamma} coincidences have been measured for {sup 28}Si+{sup 28}Si at an energy corresponding to the population of a conjectured resonance in {sup 56}Ni. Fragment angular distributions as well as {gamma}-ray angular correlations indicate that the spin orientations of the outgoing fragments are perpendicular to the orbital angular momentum. This differs from the {sup 24}Mg+{sup 24}Mg and the {sup 12}C+{sup 12}C resonances, and suggests two oblate {sup 28}Si nuclei interacting in an equator-to-equator molecular configuration. {copyright} {ital 1999} {ital The American Physical Society}

Complete fusion of /sup 16,18/O with /sup 24,26/Mg

Total fusion cross sections for /sup 16/O + /sup 24/Mg, /sup 16/O + Pu2/sup 6/Mg, and /sup 18/O + /sup 24/Mg have been measured in the energy range 18 MeV < or = E/sub c.m./ < or = 50 MeV by detection of the evaporation residues. In addition, elastic scattering angular distributions have been measured and analyzed with the optical model. The fusion cross section for /sup 16/O + /sup 24/Mg saturates at approx. 1100 mb, while that for /sup 16/O + /sup 26/Mg and /sup 18/O + /sup 24/Mg reaches approx. 1200 mb. The fusion cross section excitation functions can be well described by the model of Glas and Mosel using reasonalbe parameters; the model of Bass reproduces the data well above E/sub c.m./ approx. = 25 MeV but overpredicts the cross section below this energy.

Fusion evaporation-residue cross sections for sup 28 Si+ sup 40 Ca at E ( sup 28 Si)=309, 397, and 452 MeV

Velocity distributions of mass-identified evaporation residues produced in the {sup 28}Si+{sup 40}Ca reaction have been measured at bombarding energies of 309, 397, and 452 MeV using time-of-flight techniques. These distributions were used to identify evaporation residues and to separate the complete-fusion and incomplete-fusion components. Angular distributions and upper limits for the total evaporation-residue and complete-fusion evaporation-residue cross sections were extracted at all three bombarding energies. The complete-fusion evaporation-residue cross sections and the deduced critical angular momenta are compared with earlier measurements and the predictions of existing models. The ratios of the complete-fusion evaporation-residue cross section to the total evaporation-residue cross section, along with those measured for the {sup 28}Si+{sup 12}C and {sup 28}Si+{sup 28}Si systems at the same energies, support the entrance-channel mass-asymmetry dependence of the incomplete-fusion evaporation-residue process reported earlier.

Prompt compound nuclear K X-rays in fusion reactions induced by a heavy projectile

Abstract Prompt K X-rays were studied in compound nuclear reactions induced by a heavy projectile. Total production cross sections and multiplicities of K X-rays were measured for the systems 32 S + 116, 120, 124 Sn by determining X-ray singles, X-ray—X-ray coincidence, and direct evaporation residue yields over the incident energy range 130 MeV ⩽ E lab ⩽202 MeV. We find a slow dependence of the multiplicities and cross sections on target mass and incident energy, establishing the prompt K X-ray yields as a useful indicator of the complete fusion cross section behavior induced by a heavy projectile in this mass region.

A large-acceptance Bragg curve spectrometer with a longitudinal electric field and a segmented anode

Abstract A large-acceptance Bragg curve spectrometer with a longitudinal electron collection field and a segmented anode has been constructed and tested. The effects on the charge resolution of the entrance angle and entrance position of the incident particle have been studied. Simulations have been done in order to isolate the contribution to the overall detector performance of the signal-shaping electronics from that of the intrinsic design of the detector.

Fusion-evaporation cross sections for sup 24 Mg+ sup 24 Mg at 5 lt E sub lab lt 9 MeV/nucleon

The evaporation residue cross sections for the fusion of the {sup 24}Mg+{sup 24}Mg system have been obtained at laboratory energies of 111, 160, and 206 MeV. Angular distributions of the evaporation residues were measured and used to determine the cross sections. These cross sections decrease at the higher energies, characteristic of a limiting angular momentum. Results are compared with the predictions of fusion-evaporation models and to the systematics known from other light heavy-ion systems. Evidence is presented for a contribution from incomplete fusion and for a possible contribution from the evaporation of ejectiles heavier than {alpha} particles to the fusion-evaporation cross section at 206 MeV.