Nuclear Astrophysics with Radioactive Beams

Abstract

Radioactive beams, either at low or high energy, can be very useful for understanding violent events which are encountered in nuclear astrophysics.The main aim of the field of nuclear astrophysics is to understand the produc tion of energy and the synthesis of ele ments in stars and during stellar events. Both processes occur through nuclear reactions [1]. In "quiet" stars like our sun, and in general during non-violent stellar events, the rate of these nuclear reactions is much smaller than the average decay rate of the radioactive nuclei which are often produced by the reactions. In conse quence, these radioactive nuclei have ample time to decay before becoming involved in other nuclear reactions, so that mostly reactions between stable nuclei are important.It is believed that, during "violent" stellar events, examples of which will be given below, the opposite situation pre vails, i.e. the average time between succesFig· 1 . Schematic model of a novae phenomenon. Matter ejected from a (large) red giant is attracted by a (small) white dwarf, and splashes onto Its surface. sive nuclear reactions is much shorter than the average decay time of the radio active nuclei. These nuclei do not have time to decay before participating in new nuclear reactions, so that reactions in which at least one of the two partners is radioactive (the other one often being a proton or an a α-particle) then become very important. It is thus essential, in order to fully understand these violent events, to know the decay properties of the radioactive nuclei produced (half-lives, decay modes etc.) and the cross sections for nuclear reactions in which they are involved. In the present article, we will show that radioactive beams are very use ful for the determination of these decay properties and nuclear reaction cross sec tions.