R. Pretorius

A study of the Ca(p, n)Sc reactions: (I). Energy levels in scandium isotopes

Abstract Time-of-flight measurements have been made on the neutrons emitted from enriched targets of 43, 44, 48 Ca bombarded by 4.0 to 5.5 MeV protons. Two additional levels have been found in 43 Sc at 1347±10 and 1424±10 keV in agreement with recent work on the 40 Ca(α, p) reaction; in 48 Sc, knowledge of the level structure has been extended up to 4169 keV with the observation of 34 additional levels; and the measurements for the low-lying states in 44 Sc agree with previous work. The measured (p, n 0 ) Q -values for 43 Ca, 44 Ca and 48 Ca are −2998±10, −4447±10 and −534±15 keV, respectively.

Activation cross sections for proton-induced reactions on calcium isotopes up to 5·6 MeV

Calcium fluoride, of natural isotopic composition and isotopically enriched, was activated with proton beams up to 5·6 MeV using a Van de Graaff accelerator. Activation cross sections were determined by γ-ray spectrometry for the reactions: 43Ca(p,n)43Sc;44Ca(p,n)44Scand48Ca(p,n)48Sc . The relative accuracy of the excitation functions is ±5 per cent except for the reaction 43Ca(p, n)43Sc, where the accuracy is ±8 per cent.

The isotopic analysis of boron by the coincident measurement of complementary particles

The coincident measurement of both nuclear reaction products at their complementary angles was used for the isotopic analysis of boron by the reactions10B(d,p)11B and11B(d,α)9Be. Both isotopes were determined simultaneously with a relative standard deviation of ±2.5%.

A study of the Ca(p, n)Sc reactions: (II). Fluctuation analysis of the reaction 48Ca(p, n)48Sc

Abstract The 48Ca(p, n)48Sc reactions to the first 11 excited states in 48Sc have been studied as a function of angle and proton energy from 4.03 to 5.63 MeV. Absolute cross sections (±25%) have been obtained using a calibrated, time-of-flight detection system. The cross sections are observed to have random fluctuations in accordance with the Ericson fluctuation theory. There is no indication of any direct reaction contributions to the cross sections. The average angular distributions are symmetric about 90°. The coherence energy Γ is observed to be ≦ 9 keV at 15 MeV excitation in 49Sc. Autocorrelation analysis of the cross sections for exciting the third to 11th excited states of 48Sc leads to probable spins of (3,4), (1,2), 2, (1,2), 1, (2,3), 2 and 0, respectively.

The determination of carbon, nitrogen and oxygen in gases by neutron time-of-flight spectrometry

Carbon, nitrogen and oxygen were determined in gases by time-of-flight spectrometry of prompt neutrons from the respective reactions12C(d, n)13N,14N(d, n)15O and16O(d, n)17F, produced by a pulsed beam of deuterons of 2 MeV (for nitrogen) or 3 MeV. The analysis is non-destructive and requires about 15 min. per sample. The relative standard deviation for all three elements was about ±3%. Detection limits, using a total irradiation current of 20 millicoulombs, for carbon, nitrogen and oxygen, respectively, were 6·10−8 g, 2·10−7 g and 1.7·10−7 g per cm2 cross-sectional area of irradiating beam.

Deuteron activation analysis of geological samples

Deuteron activation was found to be suitable for analysing geological samples, as no interfering activities are formed from oxygen, silicon and aluminium, which together make up more than 80% by weight of the earths crust. To test the applicability of this method to geological samples, the mineral tourmaline was activated with 5.5 MeV deuterons obtained from the 6 MV van de Graaff accelerator at the Southern Universities Nuclear Institute. The induced activities were measured and analysed by gammaray spectrometry and the elements Al, Mg, B, Mn, Na, Fe and Li could readily be determined.

Analysis of glass by simultaneous spectrometry of scattered alpha particles and prompt protons.

The energy spectrum of alpha particles scattered from a beam of 4 MeV was used to determine heavy elements and oxygen and silicon in glass. Simultaneously, but with a separate detector, the energy spectrum of prompt protons from (α, p) reactions were used to determine boron, sodium and aluminium. Both detectors were placed at 135° to the direction of the beam, but the proton detector was covered with an absorber to stop backscattered alpha particles, Glass samples analysed by other methods and standard glass powders from the U. S. Bureau of Standards were used as references.

Isotopic analysis of lithium by prompt alpha measurement during deuteron irradiation

Charged particle spectrometry was used to determine the isotopic concentration of lithium in lithium fluoride targets irradiated with a deuteron beam of 4.0 MeV. Alpha particles emitted by the6Li(d, α)4He and7Li(d, α)5He reactions were used as a measure of6Li and7Li, respectively. From the6Li/7Li α-count ratio the isotopic concentration of6Li was determined for isotopic concentrations over the range 7.42 (natural) to about 30 atom%6Li, with a relative standard deviation of±4.1%. Alpha particles from the19F(d, α)17O reaction could also be measured as an internal standard, extending the measurements from natural to 100 atom%6Li and giving a relative standard deviation of ±1.9%. The effect of target thickness on the accuracy of the determinations was investigated.

Experimental criteria for light nuclide analysis by coincident measurement of complementary particles

Abstract Experimental parameters affecting the use of the technique of coincidence measurement of complementary particles (CMCP) for analytical purposes, have been investigated. Expressions describing the measured coincident count rate in terms of angular positioning of the detectors, their size and distance from the target and the size of the beam spot, have been derived and verified by experimental measurements. The effect of these parameters on the precision of the method is also discussed.

Charged particle analysis of light elements by total energy coincident measurement of complementary particles

Abstract An extension to the technique of coincident measurement of complementary particles (CMCP) is described in which the energies of the complementary particles are electronically summed. Increased precision and sensitivity can thus be attained without loss of energy resolution through kinematic broadening. The technique has been used to determine the isotopic composition of lithium by means of the reaction 6 Li(p, α) 3 He and 7 Li(p, α) 4 He.