科研之友
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摘要
Background: Uncertainties in adopted models of particle + nucleus optical-model potentials directly influence the accuracy in the theoretical predictions of reaction rates as they are needed for reaction-network calculations in, for instance, gamma-process nucleosynthesis. The improvement of the alpha + nucleus optical-model potential is hampered by the lack of experimental data at astrophysically relevant energies especially for heavier nuclei. %26lt;br%26gt;Purpose: Measuring the Re-187(alpha,n)Ir-190 reaction cross section at sub-Coulomb energies extends the scarce experimental data available in this mass region and helps understanding the energy dependence of the imaginary part of the alpha + nucleus optical-model potential at low energies. %26lt;br%26gt;Method: Applying the activation method, after the irradiation of natural rhenium targets with alpha-particle energies of 12.4 to 14.1 MeV, the reaction yield and thus the reaction cross section were determined via gamma-ray spectroscopy by using the Cologne Clover Counting Setup and the method of gamma gamma coincidences. %26lt;br%26gt;Results: Cross-section values at five energies close to the astrophysically relevant energy region were measured. Statistical model calculations revealed discrepancies between the experimental values and predictions based on widely used alpha+nucleus optical-model potentials. However, an excellent reproduction of the measured cros-ssection values could be achieved from calculations based on the so-called Sauerwein-Rauscher alpha + nucleus optical-model potential. %26lt;br%26gt;Conclusion: The results obtained indicate that the energy dependence of the imaginary part of the alpha + nucleus optical-model potential can be described by an exponential decrease. Successful reproductions of measured cross sections at low energies for alpha-induced reactions in the mass range 141 %26lt;= A %26lt;= 187 confirm the global character of the Sauerwein-Rauscher potential.
- 出版日期2014-12-22
