V. Valković

Trace element analysis using proton-induced x-ray emission spectroscopy

Abstract A system for trace element analysis by proton-induced X-ray emission spectroscopy developed at the T. W. Bonner Nuclear Laboratories at Rice University is presented. Some characteristic problems are discussed and applications to the study of trace element concentrations in environmental and biological targets are described.

NEUTRON--CHARGED PARTICLE COINCIDENCE MEASUREMENTS FROM 14.4 MeV NEUTRON INDUCED REACTIONS.

Abstract A method for measuring neutron-proton coincidences in reactions induced by neutrons has been described. The possibility of measuring neutron-proton bremsstrahlung and neutron-deuteron breakup processes been discussed.

Proton-induced X-ray emission: Applications in medicine☆

Abstract Fourteen elements have been recognized as essential trace elements for higher animals. Only fluorine and silicon are below 20 in atomic number; in addition, the list includes V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Mo, Sn, and I. Proton-induced X-ray emission spectroscopy allows simultaneous determination of the concentrations of all biologically essential trace elements. Correlations of trace element levels in different tissues and blood with disease activities have been studied. Trace element levels in hair appear to be very useful. Of special interest are the variations of concentrations along the length of hairs.

Nucleon-nucleon quasi-free scattering in the p+d → p+p+n reaction at low bombarding energies

Abstract Proton-proton and proton-neutron quasi-free scattering (QFS) contributions in the p+d → p+p+n reaction have been measured for proton bombarding energies 4.5–13.0 MeV. The impulse approximation gives a good description of the measured spectral shapes for θ 1 = − θ 2 = 30°, and when normalized (with a factor ≈ 0.2 for p-p QFS and a factor ≈ 0.3 for n-p QFS) describes the peak cross-section energy dependence surprisingly well. The ratio of the peak cross sections ( σ np / σ pp ) exp is ≈ 2.0 for most of the bombarding energies, while the simple impulse approximation predicts ( σ np / σ pp ) imp ≈ 1.3. Coulomb effects are found not to be significant. The influence of the final-state interaction on the measured spectra has been discussed.

Three-body break-up in the d + d → d + p + n reaction

Abstract Neutron-charged-particle and charged-particle-charged-particle coincidence spectra from the d + d → d + p + n reaction were measured for θ 1 = −θ 2 = 20° at bombarding energies 6–13 MeV. Deuteron-neutron and deuteron-proton spectra for θ 1 = −θ 2 are dominated by a broad peak associated with deuteron-nucleon quasi-free scattering. The measured data were interpreted using the quasi-free scattering model. The constructed model describes the general behavior of the coincidence spectra rather well, although the calculated spectral shapes are broader than the measured ones. The limitations of the simple quasi-free scattering model are shown also by the fact that the model predicts an order of magnitude too high cross section and that the normalization constant to the measured peak cross section is energy dependent.

Three-body break-up in 7 Li(d, n α) 4 He and 7 Li(d, αα)n reactions

Abstract The reaction 7 Li(d, n α) 4 He has been studied detecting neutron-alpha coincidences. The energies of the detected particles were determined by means of time-of-flight measurement for neutrons and a silicon, surface-barrier detector for alphas. Simultaneously alpha-alpha coincidences from 7 Li(d, αα)n were detected using two solid-state detectors. The measurements were performed at bombarding energies from 2.6 to 4.0 MeV in steps of 0.2 MeV. In addition the reaction 7 Li(d, αα)n was studied separately at 4.0 and 9.0 MeV for several angular settings of the two solid-state detectors. The most important reaction mechanism is found to be sequential decay through intermediate 5 He and 8 Be states.

Trace element concentrations in tree rings as indicators of environmental pollution

Abstract Proton induced X-ray emission spectroscopy has been successfully used to measure variations in relative and absolute trace element concentration levels in tree rings. Valuable information on past concentration levels, stored in the tree rings have been obtained. Peaks associated with 15 elements have been identified in all X-ray spectra. Variations of trace elements levels in the tree rings reflect the variations in their availability from the environment.

ANGULAR DISTRIBUTIONS OF QUASI-FREE SCATTERING CONTRIBUTIONS IN DEUTERON BREAK-UP BY PROTONS AND DEUTERONS.

Abstract Proton-proton and proton-neutron coincidence spectra from the p + d → p + P + n reaction were measured simultaneously for E p = 12.5 MeV and θ = θ 1 = − θ 2 in the interval 15° + = θ ≦ 60°. Deuteron-proton and deuteron-neutron coincidence spectra from the d + d → d + p + n reaction were measured also for E d = 12.5 MeV and θ = θ 1 = − θ 2 in the interval 15° ≦ θ ≦ 40°. Measured spectra are discussed in terms of the quasi-free scattering model. The shape of measured spectra and the angular dependence of the peak cross sections are fairly well reproduced. It was found that the ratio of the peak cross section for n-p and p-p quasi-free scattering in the p + d → p + p + n reaction varied from 1.3 at θ = 15° to 4.3 at θ = 42.5°. The ratio of the peak cross section for n-d and p-d quasi-free scattering in the d + d → d + p + n reaction was found to be constant and close to one. The variation of the σ np σ pp peak ratio in the p + d → p + p + n reaction can be attributed to the influence of n-p and p-p final-state interactions.

Rescattering effects in reactions with three particles in the final state

Abstract The rescattering effect in reactions with three particles in the final state is discussed. The kinematic conditions for the observation of the contribution from the rescattering effect are given. The experimental results of the d+ 7 Li → n+ α + α reaction at deuteron bombarding energies E d = 3.0, 3.2 and 5.9 MeV are presented. The experimental conditions were chosen in such a way that neutron-alpha particle rescattering after the decay of the 8 Be ∗ (16.63 and 16.9 MeV states) and the 5 He ∗ (16.70 MeV state) could be observed. An upper limit of ≦ 1 % has been established for the ratio of the neutron-alpha-particle rescattering contribution through an intermediate 8 Be ∗ or 5 He ∗ state to the sequential decay contribution through that state. This rescattering effect is so small that it cannot be confused with any “new” resonance levels.

METHOD FOR NEUTRON DETECTION EFFICIENCY MEASUREMENTS AND NEUTRON--CHARGED PARTICLE COINCIDENCE DETECTION.

A simple and straightforward method for experimentally determining neutron time-of-flight detector threshold and efficiency as a function of neutron energy is presented. A procedure for neutron-charged particle coincidence studies is included also.