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Mass measurements of highly neutron-excess nuclei in the light elements

Description: The $sup 26$Mg($sup 7$Li,$sup 8$B)$sup 25$Ne reaction at 78.9 MeV was used to measure the mass-excess of $sup 25$Ne (-2.18 +- 0.10 MeV) and several low- lying excited states. Mass-excesses for $sup 43$Ar (-31.98 +- 0.07 MeV), $sup 45$Ar (-29.727 +- 0.06 MeV), and $sup 46$Ar (-29.732 +- 0.07 MeV) were determined from the $sup 48$Ca($alpha$,$sup 9$,$sup 7$Be)$sup 43$,$sup 45$Ar reactions at 77.7 MeV and the $sup 48$Ca($sup 6$Li,$sup 8$B)$sup 46$Ar reaction at 80.1 MeV. Several excited states of $sup 43$Ar and $sup 45$Ar were observed. These and the excited states of $sup 25$Ne are compared with theoretical predictions. Ground state differential cross sections are given for all reactions, ranging from 0.1 to 1 $mu$b/sr at forward angles. Upper limits of about 1 to 25 nb/sr were determined for the ground state cross sections of the reactions $sup 48$Ca($alpha$,$sup 8$,$sup 10$,$sup 11$B)$sup 44$,$sup 42$,$sup 41$Cl and $sup 48$Ca($alpha$,$sup 10$-$sup 13$C)$sup 42$-$sup 39$S at 110 MeV. Recoil coincidence techniques were used to measure the mass-excess of the particle- unbound nucleus $sup 10$Li(33.83 +- 0.25 MeV) by the $sup 9$Be($sup 9$Be,$sup 8$B)$sup 10$Li reaction at 121 MeV; the ground state cross section was 30 nb/sr. The $sup 14$C($sup 9$Be,$sup 8$B)$sup 15$B reaction at 120 MeV was also investigated using coincidence techniques. Contamination problems only permitted determining a ground state cross section upper limit of 50 nb/sr. A simple mass relation is derived, similar in approach to the Garvey-Kelson method but taking more explicit account of shell effects. Comparison is made with the Garvey- Kelson relation, and predictions of masses and of the stability of neutron-excess light nuclei are given for both methods. The modified mass relation is shown to offer better account for highly neutron-excess nuclei, including the values reported here for $sup 25$Ne and $sup 43$,$sup 45$,$sup 46$Ar. (26 figures, 2 ...
Date: May 1, 1975
Creator: Wilcox, K.H.
Partner: UNT Libraries Government Documents Department