Eric B. Norman

On the Conditions Required for the r-PROCESS

The astrophysical site for the production of the r-process nuclei is not presently known. Part of the reason for this lack of knowledge is that the range of conditions which enable the production of these nuclei has not been accurately determined. Dynamic r-process nucleosynthesis calculations provide a means by which limits can be placed on the range of initial conditions that can produce r-process nuclei. Such calculations have several important time scales inherent to them. By requiring the time scales for neutron captures, ..beta..-decays, hydrodynamic expansion, and seed-nucleus production to be mutually compatible, it has been found that constraints can be placed on the initial temperatures, densities, neutron/proton ratios, and chemical compositions that can produce the r-process nuclei. The allowed ranges of these parameters are presented along with the results of r-process calculations performed for several different sets of initial conditions.

Conditions required for the r-process

The astrophysical site for the production of the r-process nuclei is not presently known. Part of the reason for this lack of knowledge is that the range of conditions which enable the production of these nuclei has not been accurately determined. Dynamic r-process nucleosynthesis calculations provide a means by which limits can be placed on the range of initial conditions that can produce r-process nuclei. Such calculations have several important time scales inherent to them. By requiring the time scales for neutron captures, ..beta..-decays, hydrodynamic expansion, and seed-nucleus production to be mutually compatible, it has been found that constraints can be placed on the initial temperatures, densities, neutron/proton ratios, and chemical compositions that can produce the r-process nuclei. The allowed ranges of these parameters are presented along with the results of r-process calculations performed for several different sets of initial conditions.

β− Decay and Cosmic-Ray Half-Life of 54Mn

A superconducting solenoid electron spectrometer operated in the lens mode was adapted to search for the β- decay of 54Mn. The Compton electron and other instrumental backgrounds were largely reduced by special shielding of the absorber system. An improved procedure was developed to select the events by momenta. An upper limit of less than 3.9 × 10-5 has been established for the intensity of the β- branch. This would define the partial half-life of the 54Mn β- decay to be greater than 2.2 × 104 yr. The implications of this result for the 54Mn cosmic-ray chronometry problem are discussed.