J. B. Wilhelmy

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.

Nuclei far from stability using exotic targets

The meson factories such as the Los Alamos Meson Physics Facility have made possible high fluence medium energy proton beams that can be used for spallation reactions to produce macro quantities of unstable isotopes. Targets of over 10 g/cm/sup 2/ can be exposed to total fluence approaching 1 A-hour resulting in spallation yields in the 0.01-10 mg range for many isotopes of potential interest for nuclear structure studies. With the use of hot cell facilities, chemical processing can isolate the desired material and this coupled with subsequent isotope separation can result in usable quantities of material for nuclear target application. With off-stable isotopes as target materials, conventional nuclear spectroscopy techniques can be employed to study nuclei far from stability. The irradiation and processing requirements for such an operation, along with the isotope production possibilities, are discussed. Also presented are initial experiments using a /sup 148/Gd (t/sub 1/2/ = 75a) target to perform the (p,t) reaction to establish levels in the proposed double magic nucleus /sup 146/Gd.

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.