Transfer cross sections for58Ni+58

Abstract

Transfer cross sections have been measured for 58 Ni + 58 ' 64 Ni in the energy range £ cm . = IOC-107 MeV with use of time of flight in a magnetic spectrograph. The direct reactions are dominated by one-neutron transfer, with other transfer cross sections being smaller by a factor of 3-4 or more. The average kinetic energy loss is -2 MeV. Over the measured energy range the total transfer cross section for 58 Ni + 58 Ni is smaller than that observed for 58 Ni + 64 Ni by a factor of 4.PACS numbers: 25.70.CdMuch of the recent interest in heavy-ion reactions at energies near the Coulomb barrier follows from the large subbarrier fusion cross sections 1 " 9 observed in reactions induced by heavy projectiles {A > 40). Particularly striking are the results for the systems 58 Ni + 58>64 Ni (Ref.3) which revealed a strong isotope dependence in the subbarrier fusion yield. A number of theoretical models have been put forth recently, 10 "" 15 mainly invoking the coupling of quasielastic channels in order to explain the large enhancements of the fusion cross section observed for many systems. While fusion cross sections have now been measured for a variety of heavy systems, only little experimental information is available on the strength of quasielastic reaction channels at energies in the vicinity of the Coulomb barrier. 16 "" 19 It has been argued 11,12 that for 58 Ni + 64 Ni the two-neutron transfer reaction 64 Ni( 58 Ni, 60 Ni) could be responsible for the large enhancement of the subbarrier fusion cross section because of its positive ground state Q value. This paper reports on measurements of the transfer cross sections for the systems 58 Ni + 58 Ni and 58 Ni + 64 Ni at energies in the vicinity of the Coulomb barrier.Attempts to measure the energy dependence of the total strength of heavy-ion transfer reactions at low incident energies have been mainly performed by detection of characteristic y rays of the final nuclei. 16 ' 18 This technique allows the measurement of relative yields in an excitation function, but for the extraction of absolute cross sections a detailed knowledge of the decay scheme of the final nuclei is necessary. In addition, transfer to ground states can in principle not be observed and weak channels are difficult to detect because of background problems. Indeed, a recent y-ray measurement of the reaction 64 Ni( 58 Ni, 59 Ni) 63 Ni encounters these difficulties. When the strength of these transitions, which are easily observed in the y-ray spectra, is extrapolated to deduce the total transfer cross section the results are in disagreement with our charged-particle measurements, as discussed below. The direct detection of the outgoing particles requires a detector capable of detecting and identifying lowenergy beamlike particles at backward angles. For reactions between nuclei with comparable masses one can detect targetlike fragments at forward angles which correspond to beamlike particles scattered backwards. The problem in this case is the large background of elastically scattered beam particle...

Competition between binary reactions and fusion in heavy-ion collisions at the Coulomb barrier

“…We will show this in our magnetospectroscopic study [15]. Here we mention the Q-value spectrum measured by Rehm et al [50] for 64Ni(SaNi, 59Ni). In contrast to the CRC calculations of Esbensen et al [60] which were limited to states with Q > -3 MeV, the true experimental spectrum shows (despite the finite resolution) remarkable strength for Q < -3 MeV.…”

“…This saturation seem to be generally reached (with some rest-fluctuations left, see later) for heavy systems, but not for light systems, where both very large (e.g. the Ni + Ni system [50,54]) and very low cross sections (e. g. the neutron pickup in the reaction 36S + 64Ni [55]) can occur. In the previous sections we have seen that the complex-channel reactions are able to explore the full multi-dimensional potential-energy surface of the merging dinuclear system, reseparating in part with total kinetic energies expected after a passage close to the conditional saddlepoint.…”

Fusion reactions ofNi58,64+Sn124

“…Its importance was first emphasized by Broglia et al [4,5] and the first indications were observed experimentally in transfer measurements of 58 Ni + 58,64 Ni [6]. A coupledchannels model of this effect was developed early on [7] in an attempt to make a consistent description of the fusion, transfer, and elastic scattering data that had been obtained in the 58 Ni + 64 Ni collisions.…”

Contribution of nucleon transfer to the elastic scattering of+5828,64Ni near the Coulomb barrier

“…a=s 54. 8 The outgoing particles were momentum analyzed in the magnetic spectrograph ENMA and detected in the focal plane 13 opened 2.2° horizontally and vertically which corresponded to a solid angle of 1.6 msr. From a measurement of total energy E, energy loss SE, and position Bp an unambiguous determination of mass, atomic number, Q value, and atomic charge state q were possible.…”