Double differential cross sections of all prominent transfer channels have been measured in the systems 338+9~ at two energies close to the nominal Coulomb barrier. In addition the fusion excitation functions of these systems have been measured below and around the barrier. The angular-and Q-distributions of the most important transfer reactions have been analysed in the framework of a simple semiclassical formalism. Particularly the two-nucleon transfer angular distributions exhibit strong multi step coupling effects which manifest themselves in reduced cross sections at large angles corresponding to close distances. From the angular distributions at forward angles, where a single step character of the transfer reaction can be assumed, approximate form factors have been extracted employing a first order perturbation theory. Within the uncertainties of a schematic coupled channels calculation the isotopic differences of the sub-barrier fusion enhancement can be understood on the basis of the isotopic differences of the transfer form factors and Q-values.

No abstract

No abstract

We carried out measurements of the excitation function for the reaction 45 Sc(p,2n) 44 Ti from 16 to 55 MeV. The results show a discrepancy with the only previous work on the subject. It was also possible to measure the cross sections for the reactions ( p,pn) 44 Sc m from 16 to 55 MeV, ( p, pn) 44 Sc g and (p,n) 45 Ti from 16 to 22 MeV, and (p,3pn) 42 K and (p,3p) 43 K from 40 to 55 MeV. ͓S0556-2813͑96͒03010-5͔ PACS number͑s͒: 25.40.Hs, 26.30.ϩk, 27.40.ϩz The long-lived radioisotope 44 Ti has a significant astrophysical interest. The decay chain 44 Ti ⇒ ͑EC͒ 44 Sc ⇒ (ECϩ␤ ϩ ) 44Ca yields the 1157 keV line that was recently observed by the COMPTEL telescope in the young supernova remnant Cas A ͓1͔ and also contributes to the diffuse 511 keV line in the galaxy through ␤ ϩ annihilation ͓2͔. 44 Ti can also be produced in meteorites through cosmic-ray interactions providing information on solar activity from the cosmic-ray exposure of such objects ͓3͔. Furthermore, the abundance of 44 Ca is believed to be determined by the nucleosynthesis of 44 Ti and its subsequent decay ͓4͔.One of the important production mechanisms of 44 Ti is the 45 Sc(p,2n) reaction. There is only one account of the cross sections for this reaction in the literature ͓5͔. In the present work, we show the results of our measurements of the excitation function for the reaction 45 Sc( p,2n) in the energy range 16-55 MeV. Above 25 MeV, our results are in disagreement with the ones of ͓5͔ and lead to a much faster decrease of the excitation function at high energies. We also measured the cross sections for the following reactions resulting from the bombardment of protons on 45 Sc at the corresponding energies: (p,pn) 44 Sc m from 16 to 55 MeV, (p,pn) 44 Sc g from 16 to 22 MeV, ( p,n) 45 Ti from 16 to 22 MeV, ( p,3pn) 42 K from 40 to 55 MeV, and (p,3p) 43 K from 40 to 55 MeV.The irradiations were performed in two different cyclotrons. For the lower energies, the cyclotron at IPEN in São Paulo was used. The targets consisted of about 50 mg of Sc 2 O 3 enclosed in a 1.2ϫ1.2 cm 2 holder of Al foil. They were then fixed to a water-cooled target holder. Irradiations at the energies 16, 18, 20, and 22 MeV at the target were performed with duration of 10 min and at a current of 0.8 A. The irradiated material was then placed inside a lucite ampoule which was put in front of a HPGe detector for activity measurement. The distance between the source and the detector was kept constant at 8 cm for the longer-lived isotope measurements and 13 cm for the shorter-lived ones. The detector efficiencies were measured in the experimental geometry with standard calibrated sources. We verified that corrections due to the fact that the material under investigation was not as pointlike as the calibration sources and due to self-absorption and absorption in the lucite were negligible ͓6͔.At higher energies, the 88'' cyclotron at the Lawrence Berkeley National Laboratory ͑LBNL͒ was used. There were two different runs at proton energies of 55 MeV and 36 MeV. For each...

No abstract