Low-energy Capture Research Articles

Charge exchange collisions involving highly stripped ions: Distribution and anisotropy of final state angular momenta

In this paper, physical effects responsible for l and m distributions in low energy capture process are discussed and a review of the physical content of various theories is given. Experimental data are reported for l, m capture cross sections for 4 keV u Ne 9+ → H 2 collisions and compared to theoretical predictions for the F 9+ → H case.

On the difference between the effective charges used for bound states of29Si and for low-energy neutron radiative capture by28Si

The neutron effective charges used in the analysis of low-energy neutron radiative capture and in nuclear spectroscopy differ by several orders of magnitude. This is illustrated by a quantitative analysis of the28Si(n, γ) reaction; this difference reflects the dominance of external capture.

Atomic orbital expansion study of electron capture in H++Li and He2++Li collisions

A modified two-centre atomic orbital expansion is used in an investigation of electron capture in collisions of H+ and He2+ ions with Li atoms. The calculated total and partial transfer cross sections constitute the first published origin-independent results in the energy range 0.5-20 keV for H++Li and in the range 0.1-2.0 keV amu-1 for He2++Li collisions. Total capture cross sections agree well with experimental data wherever the measurements have led to a consistent picture among themselves. For He2++Li collisions, low-energy capture cross sections are predicted to be much larger than is indicated by results from two-state molecular orbital calculations without translational factors.

Neutron Capture and Total Cross Section of Thorium-232 from 0.006 to 18 eV

The neutron total cross section and the shape of the neutron capture cross section of /sup 232/Th have been measured in the energy range from 0.006 to 18 eV at the Rensselaer Polytechnic Institute Gaerttner Linac Laboratory. The neutron total cross section was obtained from transmission measurements using metallic /sup 232/Th samples and a /sup 6/Li glass neutron detector. The first goal of this work is to determine the total cross section to an accuracy of a few percent. The second goal is to measure the shape of the low-energy capture cross section and to resolve the rather large discrepancy between the results of the two previous measurements. 23 refs.

Energy dependence of the differential cross sections for simple models of ion-induced dipole capture collisions

At low relative kinetic energies, the product angular distributions characteristic of the short range part of a reactive scattering event may become distorted by a long range attractive force. We examine this behavior for several different simple models of direct, short range encounters, each of which is coupled at long range to an attractive potential term proportional to r−4. The long range attraction does not generally lead to symmetric angular distributions for low-energy capture collisions. The anisotropy of the differential cross section which is observed at high energies may be preserved at extremely low kinetic energies, or it may be substantially altered toward either more symmetric or less symmetric distributions. It is even possible for a distribution which is forward-peaked at high energy to become backward-peaked at low energy, and vice versa. These results suggest that caution is warranted when one wishes to interpret a change in the product angular distribution, in going from high kinetic energies to low kinetic energies, as due to a change in the short range reaction mechanism.

The dynamics of the reaction D+2+O(3P) →OD++D, and the influence of the atomic quadrupole moment on the cross section at very low kinetic energies

We report the results of a merged-beam study of the reaction D+2+O(3P) →OD++D over the range of relative kinetic energy from 0.002 to 27 eV. The data include accurate absolute values of the total reaction cross section and also high-resolution measurements of the product ion laboratory energy distributions, which are deconvoluted to obtain estimates of the product energy and angle distributions in c.m. coordinates. The reaction mechanism is direct, with the OD+ product scattered preferentially in the direction of the incident O atom, and with large average internal excitation. The fact that O(3P) possesses an electrostatic quadrupole moment has important consequences for the interpretation of the low-energy data in terms of the adiabatic state correlations of reactants, intermediates, and products. Our major conclusions are (1) that the average probabilities of reaction for low-energy capture collisions are about 87% for approaches on Σ−–A2 potential energy surfaces and about 53% for approaches on Π–B1, B2 surfaces and (2) that the data are not consistent with the assumption of electronic adiabaticity.

Non-statistical aspects of resonance neutron capture in103Rh

Measurements have been made of high-energy neutron capture gamma ray spectra from the 103Rh(n, gamma )104Rh reaction for discrete resonances up to 850 eV and for unresolved regions up to 6 keV, with the aim of investigating the reaction mechanism. Spins of stronger resolved s-wave resonances up to 1272 eV were assigned using low-energy capture gamma rays, and in some cases also using high energy gamma rays. A value was obtained for the neutron binding energy, and a level scheme was constructed for 104Rh states up to 1 MeV populated by primary transitions. The distribution of a sample of 1938 reduced partial radiation widths in spin 1 resonances were found. The averaged gamma -ray spectra up to 6 keV showed an enhancement in the region 6.0-6.2 MeV, confirming previous observations. No correlations were found between resonance reduced neutron widths and reduced partial radiation widths in any part of the gamma -ray spectrum.

In-beam neutron activation analysis of stainless steel and iron ore

Neutron capture gamma-ray activation analysis technique has been used for the non-destructive analysis of Fe, Cr, Ni, Mn and B in stainless steel and iron ore samples. It has been shown that the use of low energy capture gamma-rays, ranging from 0.2 to 1.4 MeV, helps considerably in reducing the time of analysis. The problem of congestion of peaks due to compton continuum and the double and single escape peaks in this region of the spectrum has been overcome by using a Ge(Li) detector in conjunction with a 15.25 cm thick bifurcated NaI(Tl) annulus in anticompton mode. The results obtained by this technique have been compared with those of the chemical analysis.

Measurement of the linear polarization of low-energy capture γ-rays from the 35Cl(n, γ) reaction

The 0.79 and 1.17 MeV levels of 36C1 and the associated γ-transitions following thermal neutron capture have been studied. From measurements of the correlation between direction and linear polarization of γ-rays, the following spins and E2/M1 mixing ratios δ 1 (for primary transitions) and δ 2 (for secondary transitions) have been found: for the 0.79 MeV level J φ = 3 +, δ 1 = 0.210±0.004, δ 2 = -1.1±0.4 and for the 1.17 MeV level J φ = 1 +, δ 1, = -0.47±0.10, δ 2 = 0.32±0.06.

Method for Determining Spins of Neutron Resonances

The proposed method for measuring the spin of $S$-wave neutron resonances is based on the detailed properties of the low-energy capture $\ensuremath{\gamma}$-ray spectrum. Measurements on nuclei with resonances of known spin show that this method gives reliable spin assignments. It is also applied to unassigned resonances in $^{167}\mathrm{Er}$ and $^{187,189}\mathrm{Os}$.

Low-Energy Nuclear Level Scheme ofRh104

Investigations of the low-energy level properties (level energies, spins, and parities) of ${\mathrm{Rh}}^{104}$ have been undertaken from studies of the coincidence relationships existing between the low-energy capture gamma rays produced by thermal neutron capture in ${\mathrm{Rh}}^{103}$ using NaI(Tl) scintillation crystals as detectors. It is known from the decay scheme of the 4.4-min ${\mathrm{Rh}}^{104m}$ isomer that ${\mathrm{Rh}}^{104}$ has energy levels at 52, 96, and 129 keV with spins and parities of 2-, 2+, and 5+, respectively. The data obtained in these investigations have been combined with the isomeric level data in order to determine the properties of several additional levels. Additional levels in ${\mathrm{Rh}}^{104}$ have been determined at the following energies, with the level spin and parity in parenthesis after the energy; 184 keV (1\ifmmode\pm\else\textpm\fi{}), 192 keV (3+), 269 keV (3\ifmmode\pm\else\textpm\fi{}), 450 keV, and either 229 keV (3+) or 325 keV (4+). These spin and parity assignments were made on the basis of a $K$ internal conversion coefficient analysis of the coincidence data together with consideration of the relative cascade intensities. On the basis of the possible odd-proton and odd-neutron configurations open to the 184- and 269-keV levels, and considering the transition intensities to the lower levels, it was determined that the negative-parity assignment is most probable for both of these levels, with the levels having configuration assignments of $({p}_{\frac{3}{2}})({d}_{\frac{5}{2}})$. The 192-keV level together with the 229- or 325-keV level most probably have either ${[{({g}_{\frac{9}{2}})}^{5}]}_{\frac{7}{2}}{({d}_{\frac{5}{2}})}^{n}$ or ${({g}_{\frac{9}{2}})}^{5}{({d}_{\frac{5}{2}})}^{n}$ configurations. In fact, if it is the 229-keV level which does exist, as the available evidence might seem to indicate, then, since they both have spins and parities of 3+, the 192-keV level would have one of these configurations while the 229-keV level would have the other.

Low-Energy Capture Gamma Rays ofEu152andEu154

The low-energy capture gamma-ray spectra of ${\mathrm{Eu}}^{152}$ and ${\mathrm{Eu}}^{154}$ have been examined up to an energy of 300 kev by the use of a scintillation spectrometer. ${\mathrm{Eu}}^{152}$ was found to exhibit gamma lines at 81\ifmmode\pm\else\textpm\fi{}4 kev and 92\ifmmode\pm\else\textpm\fi{}3 kev while ${\mathrm{Eu}}^{154}$ exhibited gamma lines at 75\ifmmode\pm\else\textpm\fi{}3 kev and 91\ifmmode\pm\else\textpm\fi{}3 kev. Coincidence measurements were made on a composite spectrum produced by thermal neutron capture in natural Eu. The data are consistent with the interpretation that the ${\mathrm{Eu}}^{154}$ lines are members of a rotational band while the ${\mathrm{Eu}}^{152}$ lines are not.

Negative Ion Formation in Hydrogen Chloride by Electron Impact

The energy dependence for the formation of Cl— from HCl vapor by dissociative attachment of electrons is studied with a mass spectrometer. Within experimental error the low-energy onset for the capture process occurs at the same energy as that for the maximum capture cross section which is determined to be at 0.66 ev. The ion pair formation process, HCl+e→H++Cl—, is found to have a linear onset at 14.5 ev. The maximum yield of negative ions by this process is found to be only a few percent of that from the low-energy capture process. The energy distribution of the electron beam and the calibration of the energy scale is obtained by comparison with SF6—. It is observed that when a low-energy electron capture process is possible, spurious effects may be obtained at higher electron energies due to low-energy secondary electrons ejected from electrode surfaces by the primary beam.

Low-Energy Gamma Radiation from the Bombardment of Carbon by Protons

Weak, low-energy capture radiation has been observed when ${\mathrm{C}}^{12}$ is bombarded by protons of energy 1-3 Mev. From the observed dependence of gamma-ray energy on proton bombarding energy, it is concluded that the radiation arises from a transition to the 2.369-Mev level in ${\mathrm{N}}^{13}$. Since the latter level is unstable to proton emission a second gamma ray is not observed. The excitation curve for this reaction shows an anomaly in the neighborhood of 1.7 Mev, which can be explained as resulting from the interference of a nonresonant $p$-wave radiation with the radiation from the 3.511-Mev, ${P}_{\frac{3}{2}}$ level in ${\mathrm{N}}^{13}$.