Bunched release of gases from oxide targets

Targets made out of oxides of the alkaline earth metals have been shown at ISOLDE to be among the fastest targets for production of radioactive beams of the rare gas elements. In addition oxide target materials release nitrogen and seem to be the only ones which may release the element carbon due to its oxidation to the high temperature stable CO gas. Thick targets of MgO and CaO have been studied in connection with their use at the 1GeV pulsed proton beam from the PS-BOOSTER synchrotron. It is shown that the 2.4$\mu$s short proton pulse causes a pronounced bunched release with short delay of these elements which gives rise to 100-200 ms wide pulses of radioactive ion beams. Pulse shapes and overall yields of ion beams of He, Ne and Ar isotopes are studied as function of temperature and proton pulse intensity. For carbon and nitrogen also the release as function of the observed ionic species C$^+$, CO$^+$, N$^+$ and N$_2^+$ is discussed.