Activation Capture Cross Section Research Articles

Cross sections for fast neutron capture on the Se, Pd, Cd, Os and Pt isotopes

Activation capture cross sections are measured for Se, Pd, Cd, Os and Pt isotopes in the neutron energy range from 0.5 MeV to 1.3 MeV. The results of measurements are tested against the compound nucleus cross sections. The role of the width fluctuation corrections is examined.

Interaction of deep-level traps with the lowest and upper conduction minima in InP

Deep-level electron traps in bulk, vapor-phase epitaxial (VPE) and liquid-phase epitaxial (LPE) undoped InP crystals are investigated by an extensive method of capacitance measurement. Eight different traps are found in bulk and VPE crystals, and on the other hand no traps are found in LPE crystals. Characteristics of three traps with emission activation energies of ΔEe=0.43, 0.59, and 0.63 eV are analyzed in detail. The absolute energy levels for these traps measured from the lowest Γ conduction minimum are ET=0.34, 0.20, and 0.24 eV, respectively. It is shown that the 0.43-eV trap is coupled to the Γ minimum and that the 0.59- and 0.63-eV traps are coupled to the upper L minima. The capture of Γ electrons by the 0.43-eV trap is found to exhibit a thermally activated capture cross section σ with a barrier energy of ΔEB=0.09 eV. On the contrary, the temperature dependence of capture of L electrons by the 0.59-eV trap is found to be dominated by the temperature dependence of electron density in the L minima and to exhibit a negligible ΔEB for σ. The intervalley energy separation ΔELΓ?0.39 eV is derived and found consistent with the observed emission and capture properties of both of the L-coupled traps. Reasonable agreements are obtained between the capture cross sections derived from capture and from emission experiments, for both the Γ-coupled and L-coupled traps, respectively.

The effect of non-exponential transients on the determination of deep-trap activation energies by deep-level transient spectroscopy

The deep-level transient spectroscopy technique is now well established for the characterisation of deep traps in semiconductors. Gross errors may appear in the trap activation energy and capture cross section, however, when non-exponential capacitance transients are present. This paper describes the mechanism which gives rise to this effect and an example of its observation in experimental data. An analysis of the transient shape is found to be necessary if such errors are to be avoided.

Deep-level traps and the conduction-band structure of InP

Three traps found in n-type InP with emission activation energies ΔEe=0.43, 0.59, and 0.63 eV are analyzed. The position of the energy levels for these traps, relative to the lowest conduction-band minimum Γ, are ET=0.34, 0.20, and 0.24 eV, respectively. It is shown that the 0.43-eV trap emits to and captures electrons from the Γ minimum and exhibits a thermally activated capture cross section with a barrier energy of 0.09 eV. Very good agreement is found between the capture cross sections derived from capture and from emission experiments: σ∞=3.4×10−15 and 5.8×10−15 cm2, respectively. It is concluded from detailed emission and capture studies that the 0.59- and 0.63-eV traps emit and capture carriers via the higher-lying L minima. A value of 0.39 eV for the intervalley L-Γ energy separation is consistent with the observed emission and capture properties of both centers.

Multiple Reaction Correction to 15 MeV Neutron Capture Cross Section in 115In

The cross section of the 115In(n,γ)116m In reaction at an incident neutron energy of 15 MeV has been determined by measuring the γ-rays following the decay of the metastable (T1/2=54 min) first excited state of 116In. By systematically varying the geometrical arrangement the corrections due to secondary low-energy neutrons could be determined. Numerical estimates of the multiple reaction corrections have been made and a comparison with the experimental results indicates a good agreement. The corrected activation capture cross section at 15 MeV is 0.7±0.3 mb which is an order of magnitude lower than previous activation measurements on the same reaction.

Calculations on the scattering of keV neutrons from the 7Li ( p, n) 7Be reaction in a typical target assembly

The angular distributions and energy spectra of keV neutrons scattered from a typical target assembly employing the 7Li ( p, n) 7Be reaction have been calculated by the Monte Carlo method for several proton energies, target backing and beam tube wall thicknesses and target radii. A brief discussion is given of possible errors due to scattering in the experimental measurements of neutron activation capture cross-sections, dose equivalents and angular distributions.

The role of target geometry in 14 MeV neutron capture cross-section measurements

Some activation capture cross sections of 14.5 MeV neutrons have been measured by systematically varying the target geometry. In all cases, the results are found to strongly depend on the geometrical conditions, which implies that a large part of the activation capture cross sections reported earlier are in error. An investigation of a number of materials shows that aluminium gives rise to a fairly small fraction of secondary low-energy neutrons and is, therefore, suitable material for target holders. A thin air-cooled target head specially designed for reliable activation cross-section measurements has been constructed and tested.

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.