RESUMO
We report the first measurement of low-energy proton-capture cross sections of ^{124}Xe in a heavy-ion storage ring. ^{124}Xe^{54+} ions of five different beam energies between 5.5 and 8 AMeV were stored to collide with a windowless hydrogen target. The ^{125}Cs reaction products were directly detected. The interaction energies are located on the high energy tail of the Gamow window for hot, explosive scenarios such as supernovae and x-ray binaries. The results serve as an important test of predicted astrophysical reaction rates in this mass range. Good agreement in the prediction of the astrophysically important proton width at low energy is found, with only a 30% difference between measurement and theory. Larger deviations are found above the neutron emission threshold, where also neutron and γ widths significantly impact the cross sections. The newly established experimental method is a very powerful tool to investigate nuclear reactions on rare ion beams at low center-of-mass energies.
RESUMO
Penicillium chrysogenum strains were constructed which express a mutant acyltransferase lacking the putative targeting signal for microbody proteins. The mutated enzyme was located in vacuoles and in neighbouring cytoplasm. Although acyltransferase was expressed in vivo and was active in vitro, the mutants did not produce penicillin. The results demonstrate the involvement of microbodies in penicillin production.