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تسجيل مستخدم جديد(n,$gamma$) Cross Sections of Light p Nuclei -- Towards an Updated Database for the p Process
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The nucleosynthesis of elements beyond iron is dominated by the s and r processes. However, a small amount of stable isotopes on the proton-rich side cannot be made by neutron capture and are thought to be produced by photodisintegration reactions on existing seed nuclei in the so-called p process. So far most of the p-process reactions are not yet accessible by experimental techniques and have to be inferred from statistical Hauser-Feshbach model calculations. The parametrization of these models has to be constrained by measurements on stable proton-rich nuclei. A series of (n,$gamma$) activation measurements on p nuclei, related by detailed balance to the respective photodisintegrations, were carried out at the Karlsruhe Van de Graaff accelerator using the $^7$Li(p,n)$^7$Be source for simulating a Maxwellian neutron distribution of kT= 25 keV. We present here preliminary results of our extended measuring program in the mass range between A=74 and A=132, including first experimental (n,$gamma$) cross sections of $^{74}$Se, $^{84}$Sr, $^{120}$Te and $^{132}$Ba, and an improved value for $^{130}$Ba. In all cases we find perfect agreement with the recommended MACS predictions from the Bao et al. compilation.
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The total cross sections for the $^{152}$Gd(p,$gamma$)$^{153}$Tb and $^{152}$Gd(p,n)$^{152}$Tb reactions have been measured by the activation method at effective center-of-mass energies mbox{$3.47 leq E_mathrm{c.m.}^mathrm{eff}leq 7.94$ MeV} and mbox
{$4.96 leq E_mathrm{c.m.}^mathrm{eff} leq 7.94$ MeV}, respectively. The targets were prepared by evaporation of 30.6% isotopically enriched $^{152}$Gd oxide on aluminum backing foils, and bombarded with proton beams provided by a cyclotron accelerator. The cross sections were deduced from the observed $gamma$-ray activity, which was detected off-line by a HPGe detector in a low background environment. The results are presented and compared with predictions of statistical model calculations. This comparison supports a modified optical proton+$^{152}$Gd potential suggested earlier.
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