High precision gamma spectrometry measurements have been made on five sets of uranium isotope abundance reference materials for nondestructive assay (NDA). These sets are intended for international safeguards use as primary reference materials for the determination of the235U abundance in homogeneous uranium bulk material by gamma spectrometry. The measurements were made to determine the count rate uniformity of the235U 185.7 keV gamma-ray as well as the235U isotope abundance for each sample. Since the samples were packaged such that the U3O8 is infinitely thick for the 185.7 keV gamma-ray, the measured count rate was not dependent on the material density. In addition, the activity observed by the detector was collimated to simulate calibration conditions used to measure bulk material in the field. The sample-to-sample variations observed within the 5 sets of samples ranged between 0.005–0.11% (1s) with standard deviations of the mean ranging from 0.01–0.02%. This observed variation appears to be due predominantly to counting statistics and not to material inhomogeneity and/or packaging. The results of this study indicate that accuracy of235U determinations via gamma spectrometry, in the range of few hundredths of a percent (2), is achievable. The main requirement for achieving this level of accuracy is a set of standards whose235U isotope abundances are known to within 0.01% (2).
Isotopic correlation analysis is believed to make possible quick and accurate determinations of nuclear fuel parameters for
reactor operation, reprocessing, fuel management and nuclear safeguards. Correlation dependencies have been found between
ratios of fission products on the one hand and isotope ratios of the heavy elements on the other hand. The use of the154Eu/155Eu ratio in correlation analysis was proposed by SMULEK. The scope of useful applications of this isotopic ratio has been
further investigated. A quick and time-saving method to measure the154Eu/155Eu ratio has been elaborated. The atomic ratios have been found by internal calibration using the computer programme ABSINT.
Beside this the atomic ratios of154Eu/155Eu as a function of nuclear fuel burn-up have been calculated using the computer programme ISOTOP.
The correlation between the154Eu/155Eu ratio and nuclear fuel burn-up is best approximated by a quadratic function. Up to a burn-up of 1% fima a linear function
can be used.
Authors:R. Jakopič, A. Verbruggen, R. Eykens, F. Kehoe, H. Kühn, Y. Kushigeta, U. Jacobsson, J. Bauwens, S. Richter, R. Wellum, and Y. Aregbe
In nuclear safeguards, precise and accurate isotopic analyses are needed for two major elements from the nuclear fuel cycle:
uranium and plutonium. This can be achieved by Isotope Dilution Mass Spectrometry (IDMS), which is one of the most reliable
analytical techniques for the determination of plutonium amount content to a high level of accuracy. In order to achieve reliable
isotope measurements isotopic reference materials with certified amount of plutonium and isotopic composition are required.
At the Institute for Reference Materials and Measurements (IRMM) various plutonium spike reference materials for isotopes
239Pu, 240Pu, 242Pu and 244Pu are available. This enabled the setup of an inter-calibration campaign inter-linking selected plutonium spikes on a metrological
basis applying state-of-the-art measurement procedures. The aim of this campaign is threefold: firstly to perform measurements
on selected plutonium spike isotopic reference materials for quality control purposes, secondly to verify the amount content
and the isotopic composition of the recently produced IRMM-1027m large sized dried (LSD) spikes and thirdly to demonstrate
IRMM’s measurement capabilities for plutonium analysis via external quality tools. The obtained results using various spike
isotopic reference materials will be presented and discussed in this paper. The measurement uncertainties of the IDMS results
were calculated according to the guide to the expression of uncertainty in measurement (GUM).
Authors:B. Srinivasan, K. Mathew, U. Narayanan, W. Guthrie, and T. Sampson
The calorimetry exchange (CALEX) program is administered by New Brunswick Laboratory (NBL). The main objective of the program
is to provide an independent verification of the internal quality control practices in nuclear material safeguards facilities
making plutonium accountability measurements by non-destructive calorimetry/gamma spectrometry techniques. Facilities measure
the calorimetric power, and plutonium and 241Am isotope abundances of CALEX program standards using routine accountability procedures. The measurement results as well
as two other quantities (effective specific power and plutonium mass) calculated from these results are evaluated for accuracy
(or bias) and precision. In this paper, a limited number of measurement results of a CALEX program standard (identified as
Calex I) are evaluated with specific goals to identify a suitable method for uncertainty estimation and to identify the major
contributors to the uncertainties. In order to achieve the goals, the Calex I measurement results were evaluated using two
different methods: the first method confined to uncertainty estimation from random variations of the measurement results alone,
and the second method providing a more comprehensive evaluation of uncertainties from both the measurements and the characterized
values of the measured standard according to the Guide to the Expression of Uncertainty in Measurement (GUM). The results
of this study, and a subsequent study extended to a larger number of results in the CALEX program database, are expected to
provide relevant input for developing the International Target Values for plutonium measurements by the calorimetry/gamma
A direct simple and fast method was established, to overcome the influence of low and high level impurities on the measurement
of 235U/238U isotopic ratio in nuclear spent fuel safeguard by thermal ionization mass spectrometry (TIMS), by using refractory metal
oxide. The addition of refractory metal oxides forming solution (RMOFS), in certain proportions alongside with the spent fuel
solution on the sample filaments were found to be useful during the analysis of uranium isotopic ratio by TIMS. RMOFS (with
oxide melting point exceeding 2,000 °C), and particularly that of magnesium, were found to be very effective in improving
the quality of the ion signal of 235U and 238U, when added without the need for prior purification. Solutions of chromium, cerium, thorium, and magnesium were investigated,
to select the more convenient one, and it was found that magnesium was very useful to start with. The method was very simple,
improve both the accuracy and precision of the collected data, reduce the time required to achieve steady uranium pilot signal,
and hence the over all time of the analysis, regardless of the level of impurities present.
Neutron multiplicity analysis has been a valuable technique for safeguards measurements of plutonium oxide and mixed oxides.
Historically, most of these measurements have been performed using shift register based electronics. The shift register data
acquisition lacks certain flexibility because the basic coincidence parameters (e.g., pre-delay, gate width, and long delay)
must be fixed prior to the start of the measurement and the values may potentially, therefore, be sub optimal. List mode or
time stamped data acquisition records the arrival time of each pulse thereby preserving the history of the pulse stream and
allowing analysis and reanalysis using software analogs to the shift register circuit with adjustable parameters. Until recently,
the data rates encountered in the assay of modest amounts of plutonium using efficient multiplicity counters were beyond the
capacity of readily available personal computers. The calibration of the large epithermal neutron multiplicity counter (LEMC)
for assay of plutonium scrap materials is used as a vehicle to compare the performance of the multiplicity shift register
and a commercially available list mode acquisition module.
Authors:M. Addo, J. Gbadago, H. Affum, T. Adom, K. Ahmed, and G. Okley
The concentration of thirty-four elements each in Ghanaian dried tobacco leaves and snuff (powdered tobacco) have been determined
using instrumental neutron activation analysis (INAA). The concentration of Hg, Cr, As and Cd in both set of samples were
found to be in excess of WHO limits for drinking water, thus indicating potential toxicity of the samples. Cr, Cd, Sb and
Cu were two to eight times high, whilst As and Hg were comparable in powdered tobacco and tobacco leaves. The aim of the study
was to determine the pattern of elemental concentrations and the toxicological strengths in both tobacco leaves and tobacco
powder. The results indicated that the toxicity of the snuff was higher than the tobacco. This indicated strongly that from
the medical point of view, the level of toxic accumulation in users might be potentially high in the tobacco powder compared
to the leaves. Thus, education of the Ghanaian public on the threshold value of toxic elements contained in both set of samples
was suggested to safeguard users against these addictives.
Authors:Dao-Xing Sun, Xiao Miao, Chuan-Xin Xie, Jing Gu, and Rong Li
There is a single oxygen–oxygen (O–O) bonding easy to brake in the BPO molecule. It makes BPO sensitive to shock, heat, and friction, so safeguards should be taken to protect against the possibility of its exposure to ignition