Cross Sections Of Threshold Reactions Research Articles

Alpha induced reactions on natCd up to 38.5MeV: Experimental and theoretical studies of the excitation functions

Abstract The energy dependence of the cross sections of threshold reactions induced by alpha particles on targets of natural cadmium is studied in the energy range from threshold up to 38 MeV. Using a stacked foil irradiation technique and classical gamma-spectroscopy the formation of the radioisotopes 110,113m+g,117m Sn, 108m,g,109g,110m,g,111cum,113m,114m,115m,116m,117m,g In and 111m,115g Cd was assessed. The newly obtained excitation functions were compared with earlier published values, measured either on enriched or natural Cd targets. The results of calculations based on theoretical models of nuclear reactions obtained by the codes ALICE–IPPE, EMPIRE and GNASH are presented. Thick target yields and production routes for some medically relevant radioisotopes are discussed.

Fission neutron spectrum averaged cross sections for threshold reactions on arsenic

We have measured the cross sections, averaged over a 235U fission neutron spectrum, for the two high threshold reactions: 75As(n,p)75mGe and 75As(n,2n)74As. The measured averaged cross sections are 0.292±0.022 mb, referred to the 3.95±0.20 mb standard for the 27Al(n,p)27Mg averaged cross section, and 0.371±0.032 mb referred to the 111±3 mb standard for the 58Ni(n,p)58m+gCo averaged cross section, respectively. The measured averaged cross sections were also evaluated semi-empirically by numerically integrating experimental differential cross section data extracted for both reactions from the current literature. The calculations were performed for four different representations of the thermal-neutron-induced 235U fission neutron spectrum. The calculated cross sections, though depending on analytical representation of the flux, agree with the measured values within the estimated uncertainties.

Threshold Reaction Cross Sections of Nickel Isotopes, Averaged Over a 235U Fission Neutron Spectrum

We have measured, for nickel isotopes, several threshold reaction cross sections averaged over a 235U fission neutron spectrum. The measured reactions, and corresponding averaged cross sections found, are the following: 60Ni(n,p)60mCo, 1.499 ± 0.083 mb; 61Ni(n,p)61Co, 1.632 ± 0.096 mb; 58Ni(n,2n)57Ni, 4.72 ± 0.26 μb; 58Ni(n, d+np+pn)57Co, 275 ± 15 μb; 58Ni(n,p)58gCo, 74.8 ± 2.3 mb; and 58Ni(n,p)58mCo, 36.6 ± 1.2 mb; all referred to the well-known standard of 111 ± 3 mb for the 58Ni(n,p)58m+gCo-averaged cross section. The measured cross sections are of interest in nuclear engineering for the characterization of the fast neutron component in the energy distribution of reactor neutrons.

An empirical formula for (n, 2n) reaction cross sections in the neutron energy range of about 14.5 MeV

The (n,2n) threshold reaction cross-sections, available in the literature are analysed for nuclei with 20≤Z≤92 in the neutron energy range of about 14.5 MeV. An empirical formula based on multiple regression technique is proposed for quick estimation of the (n,2n) reaction cross sections. The results obtained are compared with experimental data and those from other empirical formulae as long as byN-Z systematic. The validity of this formula is discussed.

Experimental and Calculated Scandium Threshold Reaction Cross Sections Averaged over a 235U Fission Neutron Spectrum

The reaction cross sections averaged over a 235U fission neutron spectrum have been measured for the 45Sc(n,α)42K, 45Sc(n,2n)44Scg, and 45Sc(n,2n)44Scm threshold reactions. The values found for these cross sections are, respectively: 308 ± 16 μb, 27.3 ± 1.3 μb, and 22.0 ± 2.7 μb, using 111 ± 3 mb as the averaged cross section for the 58Ni(n,p)58Com+g reaction that was used as a standard. To the authors’ knowledge, these are the first experimental determinations of the 45Sc(n,2n)44Scg and 45Sc(n,2n)44Scm spectrum-averaged cross sections, which were measured using a new method for the case when both the ground and an isomeric state are generated.By fitting with a suitable function the experimental differential cross sections found in the EXFOR data file for each of these reactions, the corresponding spectrum-averaged cross sections have been calculated for nine different analytical representations of the 235U fission neutron spectrum. This calculation was also performed for the representation based on the Madland-Nix model of prompt fission neutrons. The agreement between calculated and measured values is in general excellent for the 45Sc(n,α)42K low-threshold reaction. However, the agreement is rather poor for the 45Sc(n,2n) high-threshold reactions, except for two, Maxwellian-type, representations tried. Since it is well known that Watt-type representations, rather than the Maxwellian type, produce an overall better description of the 235U fission spectrum, the recommended analytical representations to be used are the Watt type. Taking into account their poor performance for high-threshold reactions and recognizing the practical importance of having an analytical representation that agrees with experimental data in the whole energy range, two new representations are presented, based on the one recommended for the ENDF/B-V file, for the 235U fission neutron spectrum, whose main merit is better agreement with experimental results.

Measurement of Gamma-Ray Spectra and Heating Rates in Iron and Stainless Steel Shields Bombarded by Deuterium-Tritium Neutrons and Validation of Secondary-Gamma-Ray Data in Evaluated Nuclear Data Libraries

Benchmark experiments for the validation of secondary-gamma-ray data are conducted for iron and Type 316 stainless steel (SS316) shield assemblies bombarded by deuterium-tritium neutrons. Gamma-ray spectra and heating rates for both threshold and capture gamma rays are measured. With the present experimental data for gamma rays, a set of benchmark data for iron and SS316, including neutron energy spectra in entire energies and various dosimetry reaction rates, is completed for the first time. Secondary-gamma-ray data in JENDL-3.1, JENDL-3.2, JENDL-Fusion File, and FENDL/E-1.0 are tested by benchmark calculation of the experiments. As a result, larger gamma-ray-production cross sections for threshold reactions in JENDL-3.1 and JENDL-3.2 and an inconsistent energy balance of the (n, γ) reactions in JENDL-3.1 are found. From the viewpoint of fusion engineering, the first priority in evaluating secondary-gamma-ray data should be conserving the energy balance. A rigid energy balance in both the JENDL Fusion File and FENDL/E-1.0 is confirmed for both threshold and capture gamma rays. The JENDL Fusion File and FENDL/E-1.0 provide the highly accurate secondary-gamma-ray data for iron and SS316 needed for fusion reactor nuclear design.

Measurements of U-235 Fission Neutron Spectrum Averaged Cross Sections for Threshold Reactions

Measurements of U-235 Fission Neutron Spectrum Averaged Cross Sections for Threshold Reactions

Analytic approximation of neutron physics data

The method presented above for constructing rational approximants and obtaining their statistical characteristics is fairly convenient and universal. When it is considered that exponential-harmonic analysis also reduces to rational approximation, not of the function itself but of the application of the Fourier and Laplace transforms to the function [15a, b], the range of application of this method encompasses practically all the major systems of approximating functions. The existence of pole singularities in the Pade approximant is an extremely valuable analytic property, substantially expanding the region of convergence and increasing its speed as compared with the polynomial approximation. The Pade approximation is particularly a natural instrument for processing resonance curves since the resonances correspond to complex poles of the approximant. But in the general case as well analytic representation of data in this form is convenient and compact. Thus, representation of data on the cross sections for threshold reactions under the action of neutrons (BOSPOR library [14h]) in the form of rational functions resulted in a 20-fold reduction of the numerical information subject to storage as compared with the pint-by-point assignment with the same accuracy of description. All of this enables the Pade approximation to be considered as a promising method of representing neutron and nuclear data.

Fission spectrum averaged cross sections of threshold reactions of threshold reactions

Measurements of some (n, p) and (n, α) reaction cross sections have been made in a 235U fission neutron spectrum. The neutron spectrum used was that obtained from a neutron converter. The measured values are compared with the results from other workers.

Cross Sections of Threshold Reactions for Fission Neutrons: Nickel as a Fast Flux Monitor

Measured values of effective cross sections for fission neutrons obtained for n,p reactions on Ni58, Fe54, Zn64, Mg24, Fe56, Zn67, and Cu65 are 92, 54, 28, 1.2, 0.82, 0.57, and 0.36 mb, respectivel...