Measurement of cross sections for 14 MeV neutron capture

Activation cross sections for neutron capture have been measured at an energy of 14.6 ± 0.2 MeV relative to $\text{σ(}{}^{27}\text{Al}\text{(}\text{n}\text{,α)}{}^{24}\text{Na}\text{) = 114.2}\text{mb}\text{± 1.2\%}$ for the nuclei ³⁷Cl, ¹⁴K, ⁵⁰Ti, ⁵¹V, ⁵⁵Mn, ⁷¹Ga, ⁸⁷Rb, ⁸⁹Y, ¹²⁷I, ¹³⁰Te, ¹³⁸Ba, ¹³⁹La, ¹⁴²Ce, ¹⁸⁶W, ¹⁹⁸Pt,¹⁹⁷Au. Gamma-ray spectra of the product nuclei were measured with a Ge(Li) detector. Special attention was paid to taking into account all possible sources of error, especially contributions of lower energy neutrons. It seems to be shown that consistent results can be obtained for the cross sections for 14 MeV neutron capture if one properly takes into account the influence of lower energy neutrons even in cases where the relevant correction is large. In particular results from activation measurements agree well with results obtained by the method of integrated γ-spectra.     

Total cross sections for two off shell photons

The EVDM and factorization technique are extended to the case of two tagged photons. The results obtained from both methods are remarkably close, and in very good agreement with the recent measurements made by the PLUTO collaboration at PETRA. Predictions are made for higher values ofQ ² andP ², where future experiments are planned, and these are compared with the relevant QCD calculations.     

Total Born cross sections for positronium and helium atom scattering

A thorough and systematic study has been performed for positronium (Ps) and helium (He) atom scattering using the first Born approximation. As a first step, the direct scattering has been studied. Here excitations of both the Ps atom and He atom, the ionization of the Ps atom with all the excitations of the He atom, the ionization of the He atom with all the excitations of the Ps atom and the ionizations of both the Ps and He atoms are taken into consideration. For the different states of the He atom, the wavefunctions suggested by Winter and Lin [Phys. Rev. A 12 (1975) 434] are used. For the ionization channels the continuum Coulomb wavefunctions have been taken for the ionized electrons.     

Total cross sections for electron scattering from sulfur compounds

The original additivity rule method cannot give good results for electron scattering from SO,SO2,SO2Cl2,SO2ClF,and SO2F2 molecules at low energy,because the electron-molecule scattering is simply reduced to electron-atom scattering.Considering the difference between the bound atom in a molecule and the corresponding free atom,the original additivity rule is revised.With the revised additivity rule,the total cross sections for electron scattering from these molecules are calculated over a wide energy range below 3000 eV and compared with the available experimental and theoretical data.A better agreement between them is obtained.     

Total cross sections for electron scattering from well-known and exotic molecules

In this review paper, scattering of intermediate to high energy electrons on well-known as well as exotic molecular targets is considered. The ‘additivity rule’ and its modifications for calculating various total cross sections are discussed against the background of an extensive experimental data. The theory succeeds at high impact energies (E _i>100 eV). Tentative upper and lower limits of e-molecule ionization cross sections are identified. Fitting formulas to represent total cross sections as functions of energy are also given.     

Total nuclear photon absorption cross sections for some light elements

Absolute nuclear photon absorption cross sections have been measured for the elements Li, Be, C, O, Al, Si and Ca from 10 MeV up to photon energies beyond the meson production threshold. Magnetic Compton spectrometers and a bremsstrahlung spectrum with fixed end-point energy were used. The cross sections show structure in the region of the giant resonance and fall off smoothly towards higher energies. In the giant resonance region recent 1p-1h calculations are in poor agreement with these measurements except for one calculation for carbon, which included low lying excited states of the residual mass-11 system. The cross section in the intermediate region (40 to 140 MeV) can be described by the quasideuteron model with the density of deuteron-like structures taken as 8 NZ/A. The moments of the measured cross sections are compared with sum rule predictions. The integrated cross sections from 10 MeV up to the meson production threshold (140 MeV) exceed the classical dipole sum by a factor of 1.4 to 2.     

Mass number dependence of activation capture cross sections for 14 MeV neutrons

Radiative capture cross sections of 14.5 MeV neutrons have been measured for several nuclei with an essentially improved activation method. The results agree with those from the spectrum method, which confirms that “shell effects” exhibited by earlier activation data are due to experimental errors.     

Total and partial capture cross sections in reactions with deformed nuclei at energies near and below the Coulomb barrier

Within the quantum diffusion approach, the capture of a projectile nucleus by a target nucleus is studied at bombarding energies above and below the Coulomb barrier. The effects of deformation of interacting nuclei and neutron transfer between them on the total and partial capture cross sections and the mean angular momentum of the captured system are studied. The results obtained for the ¹⁶O + ¹¹²Cd, ¹⁵²Sm, and ¹⁸⁴W; ¹⁹F +¹⁷⁵Lu; ²⁸Si +^94,100Mo and ¹⁵⁴Sm; ⁴⁰Ca +⁹⁶Zr; ⁴⁸Ca+ ⁹⁰Zr; and ⁶⁴Ni +^58,64Ni, ^92,96Zr, and ¹⁰⁰Mo reactions are in good agreement with available experimental data.     

Exciton capture cross sections of indium and boron impurities in silicon

Measurements have been made of the decay rates and intensity ratios of photoluminescence lines from Si:In, B. We deduce values for the In and B exciton capture cross sections in the temperature range 3.6 ? 5.9 K. The large difference between the In and B cross sections is discussed in terms of excited states of the In bound exciton.     

keV Neutron capture cross sections of 134Ba and 136Ba

The neutron capture cross sections of ¹³⁴Ba and ¹³⁶Ba have been measured in the energy region 3 to ¹⁰⁰keV. The following average quantities were deduced from the extracted resonance parameters: 〈D〉 = 127±10eV, 10⁴S₀ = 0.85±0.3, 10⁴S₁ = 0.8, 〈Γ_γ〉 = 120±20 meV for ¹³⁴Ba. Analysis of the ¹³⁶Ba data gave 〈Γ_γ〉 = 125±30meV for s-wave neutrons. The average 30 keV capture cross sections for these two s-process nuclei were found to be $\text{225±35}\text{mb}\text{for}{}^{134}\text{Ba and}\text{61±10}\text{mb}\text{for}{}^{136}\text{Ba}$.     

Total ionisation cross sections for chlorofluoromethanes and CClx radicals by electron impact

We report here the total ionisation cross section for chlorofluoromethanes, namely CCl₃F (Freon 11), CCl₂F₂ (Freon 12), CClF₃ (Freon 13), CHCl₂F (Freon 21), CHClF₂ (Freon 22), CH₂ClF (Freon 31), CCl₄ and CCl_x (x = 1–3), radicals by electron impact from ionisation threshold to 2 keV. The total inelastic cross section is obtained employing a complex optical potential formalism and solving the Schrödinger equation through partial wave analysis. Using the complex scattering potential-ionisation contribution method, the total ionisation cross section is derived from the inelastic cross section for these targets. The results obtained are then compared with the existing experimental and theoretical data, wherever available. The present result shows reasonable agreement with previous data. For the CCl_x radicals, the ionisation cross section is predicted for the first time. The data reported here have immense interest to atmospheric and technological plasma modelling.     

Total charge-changing cross sections for neutron-deficient isotopes from58Ni fragmentation

At the projectile-fragment separator FRS of GSI, relativistic secondary beams of about 520 MeV/nucleon were produced by fragmentation of a primary beam of⁵⁸Ni at 650 MeV/nucleon in a beryllium target. By means of aΔE—Bρ—TOF measurement, the fragments have been identified and their charge-changing probabilities in targets of CH₂, C, Al, and Pb have been determined. We describe the results for the total charge-changing cross sections in this first paper, whereas a second article deals with the partial charge-changing cross sections. At the drip line, the measured charge-changing cross sections exhaust close to 100% of the total interaction cross sections as calculated with semiempirical models. The measurements at the proton drip line with low-Z targets indicate that only a very small increase of the cross sections may be observed, whereas the measurements with a lead target show that no significant increase of the total charge-changing cross sections is present which would be a hint for low-lying dipole strength. Our experimental data are compared to Glauber-type calculations.     

Total cross sections for fission of heavy nuclei by intermediate-energy protons

The results of measuring total cross sections for proton-induced fission of ^natPb, ²⁰⁹Bi, ²³²Th, ²³³U, ²³⁵U, ²³⁸U, ²³⁷Np, and ²³⁹Pu nuclei at proton energies from 200 to 1000 MeV are reported. The measurements were carried out in steps of ≈100 MeV. Complementary fission fragments were detected in coincidence by two parallel-plate avalanche gas counters placed in the beam line on both sides of the thin target close to it. Energy and isotope dependences of the fission cross sections are analyzed.     

The neutron total and capture cross sections of 92, 94Zr

The neutron total and capture cross sections of^92,94Zr have been measured at the 80 and 40 m flight stations, respectively, on the Oak Ridge Electron Linear Accelerator (ORELA). Resonance analysis of the total cross sections gave values of s, $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ strength functions. Strong intermediate structure was observed in the $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ cross section of ⁹²Zr. Significant single particle transitions identified in the p-wave capture cross section indicate the importance of the valence process for both nuclei. It is noted that the intermediate structure in the $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ total cross section leads to enhanced valence effects in the capture cross section. The effects of non statistical E1 transitions following particle-hole annihilation in the compound states were not observed in either the ⁹²Zr or ⁹⁴Zr capture cross sections as they had been in that for ⁹⁰Zr.