Authors:C. Vandecasteele, R. Kieffer, and J. Hoste
Fast neutrons produced by irradiation of a thick beryllium target with 20–50 MeV deuterons are used for activation analysis.
The spatial neutron flux distribution around the target is measured. A rotating sample holder is used for the simultaneous
irradiation of samples and standards. Instrumental analysis can be applied for a number of elements. As an example, results
for calcium and strontium in some reference materials are given. The19F(n, 2n)18F reaction is used for the radiochemical determination of fluorine in rocks with a fluorine concentration ranging from 9 to
The triple comparator method is used for the analysis of impurities of high purity silicon by neutron activation. The ratios
of the specific photopeak activities of the isotopes investigated to the specific photopeak activities of the gold, indium
and cobalt comparators were determined. The triple comparator method avoids some tedious problems in the multi-element activation
analysis and it is very well suited for the determination of ‘non-expected’ elements.
An analysis has been elaborated to determine the long-living γ-emitting fission products of uranium. It consists of a sodium
bisulphate melt of the fission product solution or the U-fuel, followed by liquid-liquid extractions. Afterwards the isotopes
are absolutely counted with a standardized 3″×3″ NaI crystal. The total γ-spectrum of the original fission product solution,
taken with a NaI crystal or a Ge−Li detector, is also analyzed mathematically by mixed γ-spectrometry. From a short post-irradiation
of the fission product solution the concentrations of both235U and238U are determined. The absolute amount of fission products related to the U-concentration allows the calculation of the percent
atomic burn-up, the irradiation time, the cooling period, the flux of the reactor and the original degree of enrichment of
A quantitative separation procedure for210Po in lead has been developed by cupferron and dithizone extraction. The210Po activity is plated on a silver foil for counting with a ZnS(Ag) scintillator, or by α-spectrometry with a surface barrier
semiconductor. Different lead samples were analyzed ranging from very old lead with a negligible210Po content to recently manufactured lead samples showing up to 9100 disintegrations per hour and per gram of lead. The reproducibility
and the accuracy of the analyses are satisfactory.
A method was developed for the determination of 15 trace elements in tin. High-purity tin samples (99.9999% and 99.999%) as
well as tin of technical quality were analysed. Reactor neutron activation of the tin samples was followed by distillation
of the matrix activities from a HBr−H2SO4 medium and Ge(Li) gamma-ray spectrometry of the distillation residue. The sensitivity of the method is generally high. For
the high-purity samples the detection limits vary from 0.02 ppb (scandium) to 200 ppb (iron) for irradiation of 1 g of tin
for 1 week at a thermal flux of 5·1012n·cm−2. ·sec−1. To decontaminate the surface of the tin samples, pre- and post-irradiation etching procedures were applied. The efficiency
of these etching techniques was studied.
Electrophoretic focussing of ions was applied to the separation of fission products present in solutions of nuclear uranium
fuel irradiated in various European reactors. By combining two separation methods, all the long-lived fission products could
be determined individually and quantitatively by counting with a NaI(T1) and a GM detector of known detection efficiency.
Radiography and autoradiography were used for semi-quantitative purposes. The concentrations of235U and238U were determined from a short post-irradiation of the fuel solution and counting of140Ba−140La and239Np, respectively. An iterative calculus method is presented which allows calculation of the irradiation history of the fuel
solution from the above analyses. without any a priori knowledge.
For the determination of very low concentrations of copper in tin, an analytical method involving reactor neutron activation
was developed whereby the copper activity was separated from the tin matrix by extraction of the Cu(I) cuproin complex in
n-amyl alcohol. A new decontamination technique was sought in order to remove the copper contamination present on the tin
surface. Pre-irradiation removal of the tin surface combined with post-irradiation etching appeared to be the most efficient.
The neutron flux distribution in the vicinity of 30, 20 and 10 mm diameter targets is measured by irradiating concentric ring-type
iron monitors at different distances from the target and counting the induced56Mn activity. Considering the many uncertainties, satisfactory agreement was found between theory and experiment.
The effects of inaccurate sample sizes and sample positioning on 14 MeV neutron activation analysis results are estimated
for 30, 20 and 10 mm diameter targets. It appears that axial positioning is the most critical parameter and that using a larger
tritium target will yield an overall improvement of the reproducibility.