The absolute value of ($n,p$) reaction cross sections, as given by the pre-equilibrium exciton model is estimated using Fermi gas approximation.A general agreement with experimental data, particularly in the gross $A$ dependence is obtained. The energy range considered is 10-20 MeV, and the nuclei are those with $Ag100$: In these ranges evaporation is negligible and the analysis is rather easy. The approximate life-time of one single-particle exciton in nuclear matter is also deduced.

Analysis of the Total ( n , p ) Cross Sections Around 14 MeV with the Pre-Equilibrium Exciton Model

New empirical and semi-empirical formulae have been suggested for the (n, 3He) reaction cross-sections with dependent on asymmetry parameter, S = (N − Z)/A. The (n, 3He) reaction cross-sections at the energy of 14–15 MeV have been investigated for two different parameters groups by the classification of nuclei into 31 ≤ A ≤ 103 and 133 ≤ A ≤ 181. The obtained results have been compared with the other systematics and experimental data for the (n, 3He) reaction cross-sections. Some improvement has been got in describing the (n, 3He) reaction cross-sections compared with the existing relations.

A New Comparison of Empirical and Semi-empirical Formulae for the (n, 3He) Reaction Cross-sections at 14–15 MeV

A vast knowledge of nuclear data is available and is grouped under three headings, namely, nuclear structure, nuclear decay and nuclear reaction data. Still newer aspects are under continuous investigation. Data measurements are done using a large number of techniques, including the radiochemical method, which has been extensively worked out at Julich. This method entails preparation of high-quality sample for irradiation, isolation of the desired radioactive product from the strong matrix activity, and preparation of thin source suitable for accurate measurement of the radioactivity. It is especially useful for fundamental studies on light complex particle emission reactions and formation of low-lying isomeric states, both of which are rather difficult to describe by nuclear model calculations. The neutron induced reaction cross section data are of practical application in fusion reactor technology, particularly for calculations on tritium breeding, gas production in structural materials and activation of reactor components. The charged particle induced reaction cross section data, on the other hand, are of significance in medicine, especially for developing new production routes of novel positron emitters and therapeutic radionuclides at a cyclotron. Both neutron and charged particle data also find application in radiation therapy. A brief overview of advances made in all those areas is given, with major emphasis on nuclear reaction cross section data.

Radiochemical determination of nuclear data for theory and applications

The activation cross-sections for sixteen (n, p) and (n, α) reactions on rare earth nuclides were measured at 14.8 MeV neutron energy. A Ge(Li) detector was used for the radioactivity measurements. The measured cross-sections are compared with the semi-empirical predictions of LEVKOVSKII3 and BAYHURST and PRESTWOOD.16

14.8 MeV neutron activation cross-sections for (n, p) and (n, α) reactions of some rare earth nuclides

Neutron activation cross sections for zirconium isotopes

The activation cross sections for 18 ($n, p$), ($n, \ensuremath{\alpha}$), and ($n, 2n$) reactions have been measured with 14.8-MeV neutrons. The radioactivity measurements were carried out with a Ge(Li) detector. The cross sections measured, in millibarns, are $^{27}\mathrm{Al}(n, p)^{27}\mathrm{Mg}$, 73\ifmmode\pm\else\textpm\fi{}5; $^{85}\mathrm{Rb}(n, 2n)^{84m}\mathrm{Rb}$, 714\ifmmode\pm\else\textpm\fi{}50; $^{85}\mathrm{Rb}(n, 2n)^{84g}\mathrm{Rb}$, 621\ifmmode\pm\else\textpm\fi{}75; $^{85}\mathrm{Rb}(n, p)^{85m}\mathrm{Kr}$, 6\ifmmode\pm\else\textpm\fi{}1; $^{87}\mathrm{Rb}(n, 2n)^{86m}\mathrm{Rb}$, 584\ifmmode\pm\else\textpm\fi{}40; $^{87}\mathrm{Rb}(n, 2n)^{86g}\mathrm{Rb}$, 833\ifmmode\pm\else\textpm\fi{}60; $^{87}\mathrm{Rb}(n, p)^{87}\mathrm{Kr}$, 7\ifmmode\pm\else\textpm\fi{}1; $^{84}\mathrm{Sr}(n, 2n)^{83}\mathrm{Sr}$, 395\ifmmode\pm\else\textpm\fi{}75; $^{86}\mathrm{Sr}(n, 2n)^{85m}\mathrm{Sr}$, 360\ifmmode\pm\else\textpm\fi{}30; $^{86}\mathrm{Sr}(n, p)^{86m}\mathrm{Rb}$, 9\ifmmode\pm\else\textpm\fi{}1; $^{88}\mathrm{Sr}(n, 2n)^{87m}\mathrm{Sr}$, 344\ifmmode\pm\else\textpm\fi{}30; $^{88}\mathrm{Sr}(n, p)^{88}\mathrm{Rb}$, 20\ifmmode\pm\else\textpm\fi{}2; $^{90}\mathrm{Zr}(n, 2n)^{89m}\mathrm{Zr}$, 143\ifmmode\pm\else\textpm\fi{}15; $^{90}\mathrm{Zr}(n, 2n)^{89g}\mathrm{Zr}$, 342\ifmmode\pm\else\textpm\fi{}25; $^{90}\mathrm{Zr}(n, p)^{90m}\mathrm{Y}$, 13\ifmmode\pm\else\textpm\fi{}1; $^{90}\mathrm{Zr}(n, \ensuremath{\alpha})^{87m}\mathrm{Sr}$, 4.6\ifmmode\pm\else\textpm\fi{}0.5; $^{93}\mathrm{Nb}(n, 2n)^{92m}\mathrm{Nb}$, 455\ifmmode\pm\else\textpm\fi{}25; and $^{93}\mathrm{Nb}(n, \ensuremath{\alpha})^{90m}\mathrm{Y}$, 5.8\ifmmode\pm\else\textpm\fi{}0.5. The measured cross sectons are compared with those calculated by evaporation theory. The ($n, 2n$) measured cross sections agree well with the calculated values but the agreement between calculated and measured values for ($n, p$) reactions is poor.

A. Bari

Papers

Neutron Activation Cross Sections at 14.8 MeV for Rubidium, Strontium, Zirconium, and Niobium

14·8 MeV neutron cross-sections for (n, 3He) and other rare nuclear reactions on 103Rh