Optimization of krypton yields for rp-process studies at ISOLDE(CERN) ∗ A. Kankainen a , M. Santana Leitner b† , L.M. Fraile b , A. Jokinen abc , M. Oinonen c , K. Per¨aj¨ arvi b‡ , H. Ravn b , J. ¨ Ayst¨ o a and The ISOLDE Collaboration a Department of Physics, P.O. Box 35, FIN-40014 University of Jyv¨ askyl¨ a, Finland b CERN, CH-1211 Geneva, Switzerland c Helsinki Institute of Physics, P.O. Box 64, FIN-00014 University of Helsinki, Finland The production of neutron-deficient krypton isotopes having astrophysical importance has been studied at the ISOLDE PBS facility at CERN. To investigate several effects on the yield a Monte Carlo code has been extensively applied. 1. MOTIVATION The neutron-deficient krypton isotopes play an important role in the studies of rapid proton capture process (rp-process), a nucleosynthetic process occurring at high stellar temperatures and hydrogen densities, for example in accreting neutron stars [1]. The rp- process proceeds as a sequence of rapid proton capture reactions and β + decays through proton-rich nuclei. The region near the neutron-deficient krypton isotopes is of particular interest due to the two waiting-point nuclei 68 Se and 72 Kr. At these points the rp-process is inhibited because of the long beta-decay half-lives of the waiting-point nuclei and the proton-unbound nature of proton capture daughter nuclei, 69 Br and 73 Rb [2,3]. The situation changes if the daughter nucleus lives long enough to capture another proton. Then the rp-process can continue via 2p-capture and the effective lifetime of the waiting- point can be remarkably reduced. The proton capture Q-value for 68 Se can be inversely determined by measuring the decay energy of the ground state proton decay of 69 Br. 69 Br is proton-unbound by at least 450 keV [2], but it can be produced via the beta decay of 69 Kr (T 1/2 = 32 ms [4]). In addition to the β -delayed protons from the 69 Br ground state, β -delayed protons with an energy of about 4 MeV are also expected [4]. The production of neutron-deficient Kr isotopes was studied at ISOLDE PSB facility at CERN. The isotopes were produced in spallation reactions in a dedicated Nb foil target irradiated by a 1.4 GeV proton beam. A Ta target container was filled with 10 Nb-foil rolls, each made by turning a 25- m-thick dimpled stripe over 100 times. These rolls were evenly spaced using 3-mm-long spacers. Filling was started from the both ends of the ∗ Supported by the EU RTD project EURISOL (HPRI-CT-1999-50001). † The present address: Pantechnik, Alfred Kastler 12, 14000 Cedex, Caen, France ‡ The present address: Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA Nuclear Physics A 746 (2004) 433c–436c 0375-9474/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysa.2004.09.121