Stopping cross sections and backscattering factors for 4He ions in matter Z = 1–92, E(4He) = 400–4000 keV

A table is presented of semiempirical values of stopping cross sections [expressed in eV/(atom/cm²)] for ⁴He ions in every element (1 ≤ Z ≤ 92) for ion energies from 400 to 4000 keV. The semiempirical results have been fitted with polynomial expansions whose coefficients are also tabulated. The stopping cross sections provide parameters for the interpretation of backscattering experiments, for example factors for converting backscattering-peak widths to areal density (atoms/cm²). The semiempirical results are based on recent experimental measurements and on theoretical values calculated in the Lindhard-Winther formalism with Hartree-Fock-Slater elemental wavefunctions. Comments are included on combining the specific energy loss tables for compound backscattering analysis by using Bragg's Rule, and also on the effects on backscattering of target tilt and of the finite thicknesses of targets.     

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.     

Total cross sections for the 40Ca(n,p) and (n, α) reactions between 2.7 and 5.5 MeV

Measurements have been made of the ⁴⁰Ca(n,p), ⁴⁰Ca(n,α), ⁴⁰Ca(n,n′) ⁴⁰Ca(3.35) cross sections in the energy range 2.7–5.5 MeV. Neutron flux measurements are made using the associated particle technique. The data are compared to previous data and the recent Hauser-Feshbach calculations made by Fu (1979).     

Transport properties of U0.7Ce0.3O2 − x

We have determined a number of transport properties of $\text{U}{}_{0.7}\text{Ce}{}_{0.3}\text{O}{}_{\mathrm{2-x}}$ at 1273 K for various deviations from stoichiometry and compared them with available results on $\text{(UPu)O}{}_{\mathrm{2\; ?\; x}}$. They are: the electrical conductivity, Seebeck coefficient, effective charge number and chemical diffusion coefficient.A very characteristic behaviour is observed for the electronic properties of $\text{(UCe)O}{}_{\mathrm{2\; ?\; x}}$. A p-type conduction for all the studied deviations from stoichiometry (up to $\text{x = 3 × 10}{}^{\mathrm{?2}}$) is interpreted in terms of a high electronic disorder in the stoichiometric compound. Electronic disorder at stoichiometry is probably less important in $\text{(UPu)O}{}_{\mathrm{2\; ?\; x}}$, which presents a sharp p-n transition at $\text{x = 5 × 10}{}^{\mathrm{?3}}$.Ionic transport properties obtained on $\text{(UCe)O}{}_{\mathrm{2\; ?\; x}}$ indicate an approximate proportionality between the ionic conductivity resulting from oxygen ions transport and the deviation from stoichiometry. Results available on $\text{(UPu)O}{}_{\mathrm{2\; ?\; x}}$ do not appear to be compatible with ours and some arguments are presented which cast doubt on their validity.     

Phase relation and defect structures of nonstoichiometric U4O9±y and UO2+x at high temperatures

Phase relations in the composition range from $\text{UO}{}_{\mathrm{2+x}}$ to $\text{U}{}_3\text{O}{}_{\mathrm{8?z}}$ were studied by electrical-conductivity measurements and X-ray diffraction in the ranges $\text{1025°C ? T ? 1140°C}$ and . The plot of log σ versus log showed straight lines with distinct slopes, which corresponded to four regions ($\text{UO}{}_{\mathrm{2+x}}$, $\text{U}{}_4\text{O}{}_{\mathrm{9?y}}$, $\text{U}{}_4\text{O}{}_{\mathrm{9+y}}$ and $\text{U}{}_3\text{O}{}_{\mathrm{8?z}}$). The existence of the hyperstoichiometric $\text{U}{}_4\text{O}{}_{\mathrm{9+y}}$ phase was suggested in the temperature range from 1025 to 1126°C. The peritectoid temperature ($\text{U}{}_4\text{O}{}_{\mathrm{9\pm y}}\text{= UO}{}_{\mathrm{2+x}}\text{+ U}{}_3\text{O}{}_{\mathrm{8?z}}$) was estimated to be present between 1126 and 1131°C. The partial free enthalpies and entropies for the two-phase equilibrium ($\text{U}{}_4\text{O}{}_{\mathrm{9+y}}\text{+ U}{}_3\text{O}{}_{\mathrm{8?z}}$, and $\text{U}{}_4\text{O}{}_{\mathrm{9?y}}\text{+ UO}{}_{\mathrm{2+x}}$) were calculated and compared with previous results. From the dependence of the electrical conductivity on the oxygen partial pressure the nonstoichiometric defect structures of $\text{UO}{}_{\mathrm{2+x}}$ and $\text{U}{}_4\text{O}{}_{\mathrm{9\pm y}}$ were interpreted as consisting of doubly charged oxygen interstitials (O_i'') and doubly charged oxygen vacancies (V_O''). At room temperature, the homogeneity range of the U₄O₉ phase was investigated with a Debye-Scherrer camera.     

Activation cross sections for Os(n,p)Re, Os(n,p)Re and Os(n,n′)Os reactions from 13.5 to 14.8 MeV

Cross sections for (n,p) and (n,n′) reactions have been measured on osmium isotopes at the neutron energies from 13.5 to 14.8 MeV using the activation technique in combination with high-resolution gamma-ray spectroscopy. Neutrons were produced via the ³H(d,n)⁴He reaction using solid TiT. The neutron fluences were determined using the monitor reaction ⁹³Nb(n,2n)^92mNb. Data are reported for the following reactions: ¹⁹⁰Os(n,p)^190mRe, ¹⁹⁰Os(n,p)^190gRe, ¹⁹⁰Os(n,p)¹⁹⁰Re, ¹⁸⁸Os(n,p)¹⁸⁸Re and ¹⁹⁰Os(n,n′)^190mOs. Nuclear model calculations using the code HFTT, which employs the Hauser-Feshbach (statistical model) and exciton model (precompound effects) formalisms, were undertaken to describe the formation of the products. The cross sections were discussed and compared with experimental data found in the literature, with values of model calculations including the pre-equilibrium contribution, and with evaluation data of JEFF-3.1/A.     

The average number of prompt neutrons v̄p, from neutron induced fission of 235U between 0.2 and 1.4 MeV

For the clarification of existing discrepancies in the energy dependence of $\text{v}\text{?}{}_{\mathrm{p}}$ for ²³⁵U an experiment was performed which was based on a method independent of current techniques. A considerable reduction of background and correction problems was achieved by renouncing on an absolute measurement. Thus the resulting systematic uncertainty was 0·6%. In the energy range between 0·2 and 1·4 MeV the shape of $\text{v}\text{?}{}_{\mathrm{p}}$ was measured at 22 points in steps of 50 keV with an average energy resolution of 3·3%. Repetition of several runs with modified experimental conditions ensured the consistent reproduction of the results. It was found that $\text{v}\text{?}{}_{\mathrm{p}}$ of ²³⁵U shows distinct deviations of up to 2% from a linear energy dependence.     

Measurement of the 239Pu(n,f) cross section from thermal up to 30 keV neutron energy

At GELINA measurements of the ²³⁹Pu fission cross-section were performed covering the neutron energy region from thermal up to 30 keV. Fission fragment as well as fission neutron detection techniques were used. Also for the neutron flux determination different methods were applied. From the σ_f-data, several fission integrals were calculated and compared with other results.     

Solid state transport as a mechanism of oxygen thermomigration in (U,Pu)O2±x

A general account is given of the theory of thermomigration as it applies to oxygen redistribution via the solid state in non-stoichiometric mixed uranium-plutonium oxide. This predicts that oxygen redistributes down the temperature gradient in hypostoichiometric material and up in hyperstoichiometric material. Some previous treatments are criticised. The evidence from laboratory experiments suggests that solid state transport is the dominant mechanism. A treatment, such as the cluster model, based on the manner in which oxygen deficiency or excess is accommodated in the structure, accounts naturally for the observed behaviour. The CO₂/CO route may be limited because of sluggish transfer of oxygen between the solid and the gas mixture. The H₂O/H₂ route could be important in reactor fuel pins during service, the behaviour then being different from that found in the out-of-pile work.     

A method for measuring the muon capture ratio A(HZ) in a H2 + Z gas mixture

A method is proposed for measuring the $\text{A(}\text{H}\text{Z}\text{)}$ capture ratio of muons in a H₂ + Z gas mixture making use of the transfer of muons captured in hydrogen to the heavier element Z.     

Absorber material cladding chemical interaction in vented fast breeder reactor absorber pins. B4C/stainless steel chemical interaction in sodium environment and effect of metallic Nb and Cr4 layers

Out-of-pile tests were performed to study the chemical interaction between B₄C and cladding material (stainless steel) in sodium environment as components of a “Fast Breeder” absorber pin. The results of isothermal capsule tests (873–1073 K and 750–8600 h) show a chemical attack on the cladding. The penetration depth amounted to 50 microns within one year at 873 K and increased parabolically in the course of time. The test results indicate that diffusion of boron through the reaction layer is determinative for the kinetics of chemical interaction. Carbon diffusion is inhibited by the formation of metal boride layers. Metallic niobium or chromium layers on the inner surface of the cladding material reduce definitely the process of boronation. The tests show that chemical interaction in the B₄C-Na-stainless steel system is sufficient low at conditions foreseen for high absorber pins in SNR-300 reloads and SNR-2.     

Parametric determination of a Si(Li) detector efficiency curve using KβKα branching ratios

The efficiency curve of a Si(Li) detector was determined with the parametric model of Gallagher and Cipolla which considers the parameters to be free, being determined by a least-squares fit to experimentally measured points. A least-squares fit can strongly correlate the physically uncorrelated parameters. In this paper, we do an energy analysis of the parametric expression and we propose a method to calculate the low energy parameters independently of those of the high energy region.     

Experimental cross sections for two-electron capture into nitrogen autoionising states in Nq+ (q = 6, 7) on He and H2 collisions at 10.5q keV

Singly differential cross sections for two-electron capture into autoionising states (nl, n'l') with n = 2, 3, 4 and n′≥ in N^q+ (q = 6, 7) on He and H₂ collisions have been measured at 10.5q keV collision energy and an observation angle θ_lab =11.6°Total cross sections are estimated assuming isotropic angular distributions.     

Ionization of He,Ne and Ar atoms by 1.05 MeVamuCq+(q = 2–6) and Arq+(q = 4–14) ion impact

Total “apparent” ionization cross sections and partial cross section of the production of highly ionized recoil ions of He, Ne and Ar in 1.05 MeV/amu highly charged C^q+(q = 2–6) and Ar^q+(q = 4,6,10–14) ion impact have been measured and compared with theoretical prediction and other experimental data. The total ionization cross sections have been found to scale as the square of the effective charge of projectile ions $\text{q}{}^1$, as predicted by theories.     

He+ (np) cross sections for 2, 3, 4 and 5 MeV C4+ ions colliding with He atoms

The cross sections of ionization plus excitation of He are measured by the C⁴⁺ + He prototype reaction with energies ranging from 2 to 5 MeV. Theoretically the independent electron approximation is used to calculate the HeII (np) ionization plus excitation cross sections. The results of the calculations are compared with our experimental data.