J. van der Plicht

Giant quadrupole resonance in /sup 24,26/Mg: A comparison of inelastic-scattering and. cap alpha. -capture experiments

The distribution of giant quadrupole resonance strength in /sup 24,26/Mg obtained from inelastic ..cap alpha..- and proton-scattering experiments and ..cap alpha..-capture experiments have now been shown to be compatible. The results show that the giant quadrupole resonance strength in /sup 24/Mg and /sup 26/Mg is fragmented into several states or clusters of states and suggest that the giant quadrupole resonance states have very different ..cap alpha../sub 0/-decay strength.

The Masses of 51Ca and 47Ar

Transfer reactions with beams of 14C on a target of 48Ca were used to measure the masses of 51Ca and 47Ar. A natural Ca target was used to estimate the background due to impurities in the 48Ca target. In the case of 47Ar this is the first reported measurement, but in the case of 51Ca the results do not corroborate a previous experiment.

Fission ofEs255,256,Fm255−257, andMd258at moderate excitation energies

The fission of /sup 255,256/Es, /sup 255en-dash257/Fm, and /sup 258/Md has been studied in the excitation energy range from threshold to 25 MeV. A target of /sup 254/Es was used in the direct reaction studies; (d,pf), (t,pf), (/sup 3/He,df), (/sup 3/He,pf), and in the compound induced fission reactions formed with p, d, t, and ..cap alpha.. particle projectiles. Coincident fission fragment energies were recorded along with (in the direct reaction studies) the outgoing light charged particle. The mass and kinetic energy distributions were studied as a function of nuclear excitation energy. The observed bulk properties were consistent with established systematics in that they exhibited an asymmetric mass distribution and a phenomenologically consistent total kinetic energy. However, the systems demonstrated a fission decay mode which we ascribe to high energy symmetric fission decay. This component, though somewhat arbitrary in its definition, showed a general decrease in yield as a function of increasing nuclear excitation energy. This observed rapid change in fission properties between normal and high energy symmetric fission probably points to the important observable consequences that can occur from small variations in the potential energy surface.

The study of the (α, α'f) reaction at 120 MeV on 232Th and 238U (II): Fission barrier properties deduced from fission probabilities and angular distributions

Abstract The fission probabilities and angular distributions of the fission fragments for the (α, αf) reaction on 232 Th and 238 U at a bombarding energy of 120 MeV have been measured from about 4 to 14 MeV excitation energy. Evidence for sub-barrier resonances has been found, the negativeparity ones occurring at the same excitation energy where photofission resonances have been observed. The data are analyzed with the two-humped barrier model. For 238 U the data are reasonably well fitted with barriers similar to those known from the literature. For 232 Th though, the outer barrier parameters are quite different: the height E B = 6.6 MeV and the width ( khω ) B = 1.2 MeV. Also for 232 Th, introducing an additional mass symmetric and axially asymmetric outer barrier, as was previously found necessary for 238 U, does not result in a good fit to the data at higher excitation energies.

Proton emission in La + La collisions at E/A = 138 and 246 MeV

Abstract Proton cross sections with associated multiplicities have been measured in 139 LA + 139 La collisions at E / A = 138 and 246 MeV. Data were taken at center of mass angles between 40° and 90°. At both energies the inclusive proton cross section is approximately isotropic over the range of CM angles covered. At E / A = 246 MeV the angular distribution of protons depends strongly on the associated multiplicity. We discuss the possibility that hydrodynamic flow of nuclear matter is manifested in the semi-inclusive cross section.

Fission of Es-255, Es-256, Fm-255-257, and Md-258 at moderate excitation energies

The fission of /sup 255,256/Es, /sup 255en-dash257/Fm, and /sup 258/Md has been studied in the excitation energy range from threshold to 25 MeV. A target of /sup 254/Es was used in the direct reaction studies; (d,pf), (t,pf), (/sup 3/He,df), (/sup 3/He,pf), and in the compound induced fission reactions formed with p, d, t, and ..cap alpha.. particle projectiles. Coincident fission fragment energies were recorded along with (in the direct reaction studies) the outgoing light charged particle. The mass and kinetic energy distributions were studied as a function of nuclear excitation energy. The observed bulk properties were consistent with established systematics in that they exhibited an asymmetric mass distribution and a phenomenologically consistent total kinetic energy. However, the systems demonstrated a fission decay mode which we ascribe to high energy symmetric fission decay. This component, though somewhat arbitrary in its definition, showed a general decrease in yield as a function of increasing nuclear excitation energy. This observed rapid change in fission properties between normal and high energy symmetric fission probably points to the important observable consequences that can occur from small variations in the potential energy surface.

Fission of /sup 255,256/Es, /sup 255en-dash257/Fm, and /sup 258/Md at moderate excitation energies

The fission of /sup 255,256/Es, /sup 255en-dash257/Fm, and /sup 258/Md has been studied in the excitation energy range from threshold to 25 MeV. A target of /sup 254/Es was used in the direct reaction studies; (d,pf), (t,pf), (/sup 3/He,df), (/sup 3/He,pf), and in the compound induced fission reactions formed with p, d, t, and ..cap alpha.. particle projectiles. Coincident fission fragment energies were recorded along with (in the direct reaction studies) the outgoing light charged particle. The mass and kinetic energy distributions were studied as a function of nuclear excitation energy. The observed bulk properties were consistent with established systematics in that they exhibited an asymmetric mass distribution and a phenomenologically consistent total kinetic energy. However, the systems demonstrated a fission decay mode which we ascribe to high energy symmetric fission decay. This component, though somewhat arbitrary in its definition, showed a general decrease in yield as a function of increasing nuclear excitation energy. This observed rapid change in fission properties between normal and high energy symmetric fission probably points to the important observable consequences that can occur from small variations in the potential energy surface.