The relative abundances of Sn, Te, Xe, Ba, and Ce in the cosmic radiation

Elements with even atomic number (Z) in the interval 50 ≤ Z ≤ 58 have been resolved in the cosmic radiation using the Heavy Nuclei Experiment on the HEAO-3 satellite. Their relative abundances have been compared with the results expected from pure r-process material, pure s-process material, and solar system material, both with and without a modification due to possible first ionization potential effects. Such effects may be the result of the preferential acceleration, and hence enhancement in the cosmic rays, or those elements having low first ionization potentials. We find that our measurements are inconsistent with pure r-process material at the greater than 98% confidence level whether or not the first ionization potential adjustments are made.

In addition, we have compared our results with mixtures having varying ratios of pure r-process material to pure s-process material. We find that, if no first ionization potential effects are included,

(r/s)CRS/(r/s)SS = 0.20^+0.18_-0.14

where CRS refers to the cosmic ray source and SS refers to the solar system, consistent with having an almost pure s-process source. If the first ionization potential adjustments are applied

(r/s)CRS/(r/s)SS = 1.5^+1.1_-0.7

consistent with a solar system mixture.

Isotope shift measurements using k x-rays in Sn, Sm, and W

Electronic Kαl x-ray isotope shifts have been measured for Sn 116-124, Sm 148-154, W 182-184, W 184-186, and W 182-186 using a curved crystal Cauchois spectrometer. The analysis of the measurements has included the electrostatic volume effect, screening by the transition electron as well as the non-transition electrons, normal and specific mass shifts, dynamical nuclear qudrupole polarization, and a radiative correction effect of the electron magnetic moment in the nuclear charge radii are obtained. Where other experimental data are available, the agreement with the present measurements is satisfactory. Comparisons with several nuclear model predictions yield only partial agreement.

Supernovae explosions induced by pair production instability

Stars with a core mass greater than about 30 M_⊙ become dynamically unstable due to electron-positron pair production when their central temperature reaches 1.5-2.0 x 10^{9 0}K. The collapse and subsequent explosion of stars with core masses of 45, 52, and 60 M_⊙ is calculated. The range of the final velocity of expansion (3,400 – 8,500 km/sec) and of the mass ejected (1 – 40 M_⊙) is comparable to that observed for type II supernovae.

An implicit scheme of hydrodynamic difference equations (stable for large time steps) used for the calculation of the evolution is described.

For fast evolution the turbulence caused by convective instability does not produce the zero entropy gradient and perfect mixing found for slower evolution. A dynamical model of the convection is derived from the equations of motion and then incorporated into the difference equations.