Fission spectrum averaged cross-section of 94Zr(n, α)91Sr

The fission spectrum averaged cross-section of ⁹⁴Zr(n, α)⁹¹Sr reaction was obtained by comparing that of ²⁷Al(n, α)²⁴Na reaction as reference. Highly enriched ⁹⁴ZrO₂ and ²⁷Al samples were irradiated with fast neutrons having a fission-like spectrum above about 5.6 MeV. After the neutron irradiation, the produced ⁹¹Sr was chemically separated from the irradiated sample. Gamma-rays from ⁹¹Sr and ²⁴Na were measured with a Ge(Li) detector. The obtained value is 5.37 ± 0.43 μb assuming the averaged cross-section of the reference reaction to be 0.61 mb.     

Measurements of Double-Differential Neutron Emission Cross Sections of 6Li, 7Li and 9Be for 11.5 MeV and 18.0 MeV Neutrons

Double-differential neutron emission cross sections (DDXs) of ⁶Li, ⁷Li and ⁹Be were measured for 18.0 MeV and 11.5 MeV incident neutrons produced by the T(d, n) and ¹⁵N(d, n) reactions respectively, using the Tohoku University Dynamitron time-of-flight (TOF) spectrometer. The data were obtained at 13 laboratory angles, and angular-differential cross sections (ADXs) of elastic and inelastic scattering neutrons were derived from the DDXs. For 11.5 MeV neutrons, we obtained the neutron emission spectra over the secondary neutron energies by newly employing the double TOF method as well as the conventional one. In the measurements at 18.0 MeV, we achieved better energy resolution than in our previous studies by using a neutron detector that has a larger solid angle and a thinner tritium target. The experimental results of DDXs and ADXs were compared with our previous results and the evaluated data given in JENDL-3.2, JENDL Fusion File and ENDF/B-VI. It is found that the JENDL data reproduce the experimental ones very well.     

Photo-Neutron Production in Heliotron-E

Photo-neutron emission in H₂ and He discharges was observed in the initial ohmic heating experiments of the Heliotron-E. Typical total neutron yield was 10⁹ neutrons per pulse under high level of runaway electrons (≧10 MeV). Neutron flux was localized near the limiters. Energy spectrum of neutrons was continuous up to about 2 MeV. The radioactive nuclides in the limiters and the vacuum chamber irradiated by runaway electrons showed that ⁵⁸Ni(γ, n) ⁵⁷Ni and ⁵³Cr(γ, n)⁵¹Cr reactions had occurred, proving that the photo-disintegration process was the source of neutron flux.     

The 10B(n, αγ)7Li cross-section between 0.1 and 2.2 MeV

The shape of the excitation function for the standard neutron reaction ¹⁰B(n, αγ)⁷Li in the energy range from 0.1 to 2.2 MeV has been determined relative to the angular distribution of the neutron source reaction T(p, n)³He at 1.6, 2.3, and 3.0 MeV proton energy. The 478 keV γ's produced in a 3-mm thick boron carbide sample were observed in a Ge(Li)-detector. The time-of-flight method was used to discriminate against events from neutrons of degraded energy.     

Measurement of cross sections for (n, 2n), (n, p) and (n, α) reactions on germanium isotopes induced by 14 MeV neutrons

Activation cross sections at the neutron energy about 14 MeV on germanium isotopes have been measured, employing the activation technique and γ-ray spectrometry. The data of the cross section are reported for the (n, 2n), (n, p) and (n, α) reactions. The neutron flux was determined using the monitor reactions ²⁷Al (n, α) ²⁴Na and the neutron energies were measured by the method of cross section ratios for ⁹⁰Zr (n, 2n) ⁸⁹Zr to ⁹³Nb (n, 2n) ^92mNb reactions. The measured results were compared with the other measurements.     

Evaluation of neutron nuclear data for Technetium-99

Neutron nuclear data of ⁹⁹Tc was evaluated, considering cross-sections and spectra provided from recent experiments. The evaluation was made in the incident neutron energy range from 1 keV to 20 MeV, using the optical model and nuclear reaction models. The optical model calculation based on the coupled-channels method was performed for the interaction of neutrons with ⁹⁹Tc, and potential parameters appropriately chosen reasonably explain the measured data of total cross-section. The cross-section of inelastic scattering, capture, (n, 2n), (n, p), (n, α) and (n, n′α) reactions, and γ-ray emission spectra were calculated on the basis of statistical model with preequilibrium and direct components, and they were compared with available experimental data. It is found that the presently evaluated cross-sections and γ-ray emission spectra well reproduce those experimental values and that there is a large discrepancy among the present result and evaluated data for neutron emission spectra. The obtained capture cross-section increases at the energies below 1 MeV, relative to that in JENDL-4.0. This makes the transmutation efficiency of ⁹⁹Tc into stable ¹⁰⁰Ru by accelerator driven system enhanced. The production cross-section of ⁹⁹Mo important for the medical use of nuclear diagnostics reduces by 5–30% at the energies above 12 MeV, compared with JENDL-4.0.     

Measurements and model calculations of activation cross sections for 232Th(n,2n)231Th reaction between 13.57 and 14.83 MeV neutrons

In this study, activation cross sections were measured for the reaction of ²³²Th(n,2n)²³¹Th (T_1/2 = 25.5 h) by using neutron activation technique at six different neutron energies from 13.57 and 14.83 MeV. Neutrons were produced via the ³H(²H,n)⁴He reaction using SAMES T-400 neutron generator. Irradiated and activated high purity Thorium foils were measured by a high-resolution γ-ray spectrometer with a high-purity Germanium (HpGe) detector. In cross section measurements, the corrections were made for the effects of γ-ray self-absorption in the foils, dead-time, coincidence summing, fluctuation of neutron flux, low energy neutrons. For this reaction, statistical model calculation, which the pre-equilibrium emission effects were taken into consideration, were also performed between 13.57 and 14.83 MeV energy range. The cross sections were compared with previous works in literature, with model calculation results, and with evaluation data bases (ENDF/B-VII, ENDF/B-VI, JEFF-3.1, JENDL-4.0, JENDL-3.3, and ROSFOND-2010).     

Measurement and analysis of the energy–angular distribution of secondary neutrons for Be at 5.9 and 6.4 MeV incident neutrons

The energy-angle double-differential neutron emission cross-sections of beryllium have been measured using the time of flight technique for 5.9 and 6.4 MeV incident neutrons, respectively, at 10 laboratory angles between 25° and 150°. The measured results are compared with model calculations based on the LUNF code and those of other authors and the ENDF/B-VII data. The estimation of the inelastic scattering neutron cross-sections leaving ⁹Be^∗ at the low-lying level states are also theoretically analyzed by the LUNF code. The experimental and calculated results indicated that the lowest (1.68 MeV) level still contributes to the (n, 2n) reaction with cross-sections of several 10 mb. The angular distributions and the angle-integrated elastic scattering cross-sections are also presented in comparison with other ones, these being in good agreement with the ENDF/B-VII data.     

Measurement and analysis of reaction rates in a large spherical depleted uranium pile surrounding a 14-MeV neutron source

Measurement was made of the reaction rate distributions for ²³⁸U(n, f), ²³⁵U(n, f), ²³⁸U(n, γ), ²⁷Al(n, α) and ⁵⁸Ni(n, p) in a large depleted uranium (DU) pile. The pile consisted of DU blocks forming a spherical shell of 45.72 cm radius and 40.64 cm thick. 14-MeV neutrons were generated at the center. Fast neutron leakage spectrum was also measured by an NE-213 spectrometer. In order to assess the ²³⁸U neutron cross sections of JENDL-2, the experiment was analyzed using the Monte-Carlo transport code MCNP with continuous energy cross sections. The agreement between the calculation and the experiment is generally unsatisfactory. The ratios of calculation to experiment of low energy reactions decreased with the thickness of the DU layer. The analysis of the Livermore pulsed sphere experiment for the small DU sphere revealed underestimation of leakage neutron spectrum around 10 MeV. The ²³⁸U cross sections of JENDL-2 should be improved for 14-MeV neutronics calculation.     

Alpha Production Cross Sections for Some Target Fusion Structural Materials up to 35 MeV

In the next century, because of the worldwide energy shortage, human life will badly be affected. Nuclear fusion energy is the remarkable solution to the rising energy challenges because it has the great potential for sustainability, economic and reliability. There have been many research and development studies to get energy from fusion. Moreover, the neutron induced reaction cross section data around 14–15 MeV are need to the design and development of nuclear fusion reactors. Thus, the working out the systematics of (n,α) reaction cross sections is very important and necessary for the definition of the excitation curves at around 14–15 MeV energy. In this study, neutron induced reaction cross sections for structural fusion materials such as Sc (Scandium), Co (Cobalt), Ni (Nickel), Cu (Copper), Y (Yttrium), Mo (Molybdenum), Zr (Zirconium) and Nb (Niobium) have been investigated for the (n,α) reactions. The new calculations on the excitation functions of ⁴⁵ Sc(n,a) ⁴² K, ⁵⁹ Co (n,a) ⁵⁶ Mn, ⁶² Ni(n,a) ⁵⁹ Fe, ⁶³ Cu(n,a) ⁶⁰ Co, ⁶⁵ Cu(n,a) ⁶² Co, ⁸⁹ Y(n,a) ⁸⁶ Rb, ⁹² Mo(n,a) ⁸⁹ Zr, ⁹⁸ Mo(n,a) ⁹⁵ Zr, ⁹² Zr(n,a) ⁸⁹ Sr, ⁹⁴ Zr(n,a) ⁹¹ Sr and ⁹³ Nb(n,a) ⁹⁰ Y reactions have been carried out up to 35 MeV incident neutron energies. In these calculations, the pre-equilibrium and equilibrium effects have been investigated. The pre-equilibrium calculations involve the new evaluated the geometry dependent hybrid model, hybrid model and the cascade exciton model. The equilibrium effects of the excitation functions for the investigated reactions are calculated according to the Weisskopf-Ewing model. Additionaly, in the present work, the (n,α) reaction cross sections have calculated by using evaluated empirical formulas developed by Tel et al. at 14–15 MeV energy. The calculated results have been discussed and compared with the available experimental data taken from EXFOR database.     

Cross section measurements of the 23Na(n, 2n)22Na, 58Ni(n, 2n)57Ni and 115In(n,n′)115mIn reactions

Cross sections for two high energy threshold reactions ²³Na(n, 2n)²²Na and ⁵⁸Ni(n, 2n)⁵⁷Ni were measured by the activation method in the neutron energy range from 14 to 18 MeV. Inelastic scattering cross section for ¹¹⁵In was measured in the threshold region, i.e. from 0.5 to 1.3 MeV. The results of measurements are compared with scarce and divergent earlier data.     

Evaluation of Neutron Nuclear Data for Sodium-23

Neutron nuclear data of ²³Na have been evaluated in the neutron energy region up to 20 MeV. Evaluated are the elastic and inelastic scattering, capture, (n, 2n), (n, p), (n, α), (n, np), (n, nα) reaction and γ-ray production cross sections, and the angular and energy distributions of neutrons and γ-rays. The evaluation is mainly based on nuclear model calculations. The pre-equilibrium and direct-reaction processes were taken into account in addition to the compound process. The evaluated data have been compiled into the latest version of JENDL, JENDL-3.3.     

The 232Th(n, f) cross-section for thermal and 2.44 MeV neutrons

The thermal neutron induced fission cross-section of ²³²Th was measured at an intense and very pure thermal neutron beam of the Grenoble High Flux Reactor, yielding a value of (3 ± 1) μbarn. For control purposes, the same targets were used at the VandeGraaff accelerator of the CBNM (Geel), where a ²³²Th (n, f) cross-section value of (0.12 ± 0.02) barn was obtained with 2.44 MeV neutrons, in agreement with other published data.     

Cross-section measurements for the (n,p) and (n,α) reactions on 23Na and for the (n,p) reaction on 26Mg at the neutron energies from 13.6 to 14.9 MeV

Cross sections were measured at neutron energies from 13.6 to 14.9 MeV for the reactions ²³Na(n,p)²³Ne and ²³Na(n,α)²⁰F, and ²⁶Mg(n,p)²⁶Na leading to short-lived products. The production of short-lived nuclei and the spectra accumulation have been carried out by cyclic activation method. Corrections were made for the effects of gamma ray attenuation, coincidence summing, pulse pile-up, dead time, neutron flux fluctuations and scattered low energy neutrons.     

Tables of thermonuclear-reaction-rate data for neutron-induced reactions on heavy nuclei

The results of statistical model calculations of (n,γ), (n,p), and (n,α) cross sections and reaction-rate factors are presented in tabular form for over 500 target nuclei in the range 36 ≤ Z ≤ 83 (krypton to bismuth). Included in these tables is information on (i) the reaction cross section as a function of energy for the exoergic channel in the range 0.01 ≤ E(MeV) ≤ 3.0; (ii) the thermally averaged reaction-rate factor, N_A〈σv〉 and the nuclear partition function G(T) for temperatures in the range 10⁸ ≤ T(^oK) ≤ 3 × 10⁹; (iii) analytic fits to the reaction-rate factors and partition functions as functions of temperature; and (iv) nuclear level-density parameters and formulas for their extrapolation. Two types of reaction-rate factors have been computed. One, which may be called the “laboratory rate factor,” is based on the assumption that the target nuclei occupy only their ground states. The other, which shall be termed the “stellar rate factor,” is based on the more realistic assumption that the target nuclei occupy a thermal distribution of excited states at temperature T. A brief discussion of theory and instructions for usage of the tables are included. New fitting forms for statistical-model thermonuclear reaction rates are presented and justified.     

Geometrical Interpretation of Mutual Relatonship between Ordinary Coherence and Noise Power Contribution Ratio

Angular neutron fluxes leaking from the surface of lithium-oxide and graphite slab assemblies have been measured with irradiation of D-T neutrons. The spectrum measurement was performed using the time-of-flight technique with an NE213 scintillation detector. The thicknesses of the slabs were 0.6 to 5 mean free path for 14.8 MeV neutrons, and the measured leaking angles of the angular fluxes were 0.0°, 12.2°, 24.9°, 41.8° and 66.8°. The experimental results have been compared with the results calculated by the continuous energy Monte Carlo transport code MCNP, using the data in the JENDL-3PR1, ?3PR2, and ENDF/B-V nuclear data files. The comparisons between the experimental and calculated results show that the data of ⁷Li in JENDL-3PR2 is improved for the secondary emission spectra of the 4.63 MeV level and (n, 2n) reactions; the angular distributions of 3rd-and 4th-level inelastic reactions of C in the JENDLs are questionable. The thickness dependences for high energy neutrons also suggest that the total cross section of ⁷Li and the elastic cross sections of C are slightly inadequate.     

Triton Emission Spectra in Some Target Nuclei Irradiated by Ultra-Fast Neutrons

High-current proton accelerator technologies make use of spallation neutrons produced in (p,xn) and (n,xn) nuclear reactions on high-Z targets. The produced neutrons are moderated by heavy water. These moderated neutrons are subsequently captured on ³He to produce tritium via the (n,p) reaction. Tritium self-sufficiency must be maintained for a commercial power plant. So, working out the systematics of (n,t) reaction cross sections and triton emission differential data are important for the given reaction taking place on various nuclei at different energies. In this study, triton emission spectra by using ultra-fast neutrons (incident neutron energy >50 MeV), the (n,xt) reactions for some target nuclei as ¹⁶O, ²⁷Al, ⁵⁶Fe, ⁵⁹Co, ²⁰⁸Pb and ²⁰⁹Bi have been investigated. In the calculations, the pre-equilibrium and equilibrium effects have been used. The calculated results have been compared with the experimental data taken from the literature.     

Systematics studies of (n, α) reaction cross sections at 14.5 MeV neutrons energy

A new semi-empirical formula for the calculation of the (n, α) cross-section at 14.5 MeV neutron energy is obtained. It is based on the pre-equilibrium exciton and evaporation models and uses the Droplet model of Myers and Swiatecki to express the reaction energy Q(n, α). The systematics behavior of the different terms of the Droplet model involved in Q(n, α) was checked individually before choosing the pertinent terms and setting up the formula. Fitting this formula to the existing cross-section data, the adjustable parameters have been determined and the systematics of the (n, α) reaction have been studied. The predictions of this formula are compared with those of the existing formulae and with the experimental data. The formula with five parameters is found to give a better fit to the data than the previous comparable formulae.     

High Resolution Measurements of Double Differential (n, α) Cross Sections of 58Ni and natNi between 4.2 and 6.5 MeV Neutrons

Double differential (n, α) reaction cross sections of ⁵⁸Ni and ^natNi were measured for 4.2–6.5 MeV neutrons with energy resolution good enough to separate α-particles from the low-lying levels of residual nuclei by using a gridded ionization chamber. Angular distribution and excitation functions were derived for α₀, α₁ and α_i≥2 components (α-particles to the ground level, the 1st level and levels higher than the 2nd level, respectively). The experimental results were compared with these obtained from calculation based on Hauser-Feshbach model employing the optical potential and the level density parameters derived to reproduce the experimental values of total, (n,p) and (n,α)cross sections. The calculation showed fair agreement with the experimental data while it underestimated the (n,α)cross section above 6 MeV.