Electron capture and loss cross sections for U 28+ colliding with H 2 , N 2 and Ar were measured at 3.5 and 6.5 MeV/u. These data were used to benchmark n-body calculations using the classical trajectory Monte Carlo method. The n-body calculations include electrons on both nuclear centres and all electronelectron and electron-nuclear interactions between each centre. For the U 28+ ion, 36 electrons were incorporated in the calculations (4s 2 4p 6 4d 10 4f 14 5s 2 5p 2 ), while for the H, N and Ar targets all electrons were used except those for the Kshell of Ar, leading to 39-, 45-and 54-body calculations, respectively. Projectile electron loss was predicted for U 28+ at energies from 2 to 150 MeV/u. Only for the H-target did the projectile electron loss cross section decrease approximately as E −1 . The heavier targets exhibited slower energy dependences, contrary to the E −1 prediction of one-electron theories. Moreover, the collisional interactions are quite strong with an average of 1.64 and 2.88 electrons removed from the U 28+ ion at 10 MeV/u in each collision with N and Ar, respectively. These data and calculations were used to assess the vacuum requirements for the SIS-100 synchrotron ring under construction at GSI-Darmstadt. For the residual gases expected to be in the ring, the U 28+ lifetime was found to be essentially constant as a function of projectile energy, leading to very stringent vacuum requirements.

Experimental cross sections are presented for single and multiple electron stripping from Xe18+ projectiles in collisions with N2 at energies 2.0-9.3 MeV u-1. The data are compared to 2-30 MeV u-1 n-body classical trajectory Monte Carlo calculations that explicitly include electrons on both centres. Two-centre electron-electron (e-e) and electron-screened nuclear interactions contribute to the ionization reactions. The computations are in reasonable accord for the total stripping cross section but underestimate the higher stages of multiple electron loss. An energy deposition model gives improved agreement with experiment. The energy dependence of the total stripping cross section is close to E-0.5. Calculations are also presented for target ionization by Xe+, Xe8+ and Xe18+ at 10 and 20 MeV u-1. Projectile and target ionization cross sections are found to be comparable. Cross sections for projectile stripping by ionized targets are also calculated and found to be relatively insensitive to the ionization stage of the target. This latter observation is attributed to the compensating contributions between the two-centre e-e and electron-screened nuclear interactions.

We report the first branching-ratio measurement of the superallowed 0+→0+β transition from Ca38. The result, 0.7728(16), leads to an ft value of 3062.3(68) s with a relative precision of ±0.2%. This makes possible a high-precision comparison of the ft values for the mirror superallowed transitions, Ca38→38mK and K38m→Ar38, which sensitively tests the isospin symmetry-breaking corrections required to extract Vud, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, from superallowed β decay. The result supports the corrections currently used and points the way to even tighter constraints on CKM unitarity.

No abstract

We have measured the K-shell internal conversion coefficient, αK , for the 65.7-keV M 4 transition in 119 Sn to be 1621(25). This result agrees well with Dirac-Fock calculations in which the effect of the K-shell atomic vacancy is accounted for, and disagrees with calculations in which the vacancy is ignored. This extends our precision tests of theory to Z = 50, the lowest Z yet measured.