No abstract available

[en] Modern scientific technology now plays an increasingly important role in the process of law enforcement. Neutron activation, as developed for elemental analysis offers, in many cases, the suitable answer to forensic problems. The author discusses the use NAA has been put to in forensic science. (Auth.)

[en] Developing solutions for complex safe guards problems in close cooperation with Operators is becoming more common, especially as the IAEA continues to operate under zero-growth limitations. This has in practice taken on various forms; from the extreme case of very specific equipment developed and constructed by the State/Operator for use in only one facility, to the more normal case where only the development is carried out by the State/Operator. This practice has advantages and disadvantages. For example, to ensure that Agency inspections will be carried out in a predictable manner, it will be in the Operator's interest to ensure that any equipment he provides is of the highest quality, meets all national safety requirements, and is installed and maintained in such a manner that it will provide years of service. Agency equipment performs its intended function in a reliable manner, but with very specific, limited applications in mind, improvements in reliability over that obtained with normal Agency equipment are to be expected. Also, the authors experience is that reaching acceptable arrangements for the use of State- of Operator-supplied equipment is often far more straightforward than when arranging to apply Agency equipment

[en] The removal of interfering radiations from a radioactive nuclide is usually essential for the measurement of its radiation. The present paper aims at a discussion of some of the very rapid radiochemical separation techniques used in research with reactors, with emphasis on instantaneous and continuous flow methods. (author). 31 refs

[en] The programme of the Soreq-On-Line Isotope Separator (SOLIS) aimed at the study of very short-lived nuclides produced in thermal and 14 MeV neutron-induced fission is outlined. The use of appropriate chemical separation methods in conjunction with the isotopic separation facilitates the observation, at steady state conditions, of individual rapidly decaying nuclides. This system will be used for a systematic investigation of delayed neutron emission, viz. identification and characterization of precursors followed by a detailed study of nuclear structure and independent yields. At present, techniques for the rapid separation of rare gas and halogen fission products, suitable for on-line isotopic separation, are being developed. For rare gas studies, a uranium-barium stearate emanation source swept by a stream of nitrogen gas is being used. The decontamination factor with respect to halogen is ∼10⁵, and higher for other activities. Separation time of ∼2 seconds is routine. With this system (without isotopic separation), it was possible to establish delayed neutron emission from both ⁹³Kr (T_1/2 = 1.19 t 0.05 sec, P_n = 3.9%) and ⁹³Rb(T_1/2 = 5.60 ± 0.05 sec, P_n = 2.6%). The half-life of ⁹⁴Kr is estimated as 0.4 ± 0.1 sec. For bromine and iodine, selective recoil labelling is used (for extraction of independently produced species while the same nuclides produced by beta decay are discriminated against) followed by fast gas chromatography. Using empirical P_n-values and fission yields for 14 known precursors, good fits to experimental total delayed neutron yields of groups 1-4 were obtained for a series of fission reactions. Systematic deviations indicate unidentified precursors. The inconsistencies between expected and reported results on delayed neutron yield variations with the energy of the fission-inducing neutrons are being checked by high resolution γ-ray spectrometry in conjunction with neutron counting, with the aim of determining these relations with neutrons of various energies (thermal, fission and 14 MeV). A technique for obtaining data on the masses and half-lives of delayed neutron precursors, based on selective collection, through a bias potential, of recoils from neutron emission, is being studied. The energies of delayed neutrons from gross and separated elements produced in fission are being studied with an improved ³He spectrometer and time-of-flight techniques. (author)

[en] The programme of the Soreq-On-Line Isotope Separator (SOLIS) aimed at the study of very short-lived nuclides produced in thermal and 14 MeV neutron-induced fission is outlined. The use of appropriate chemical separation methods in conjunction with the isotopic separation facilitates the observation, at steady state conditions, of individual rapidly decaying nuclides. This system will be used for a systematic investigation of delayed neutron emission, viz. identification and characterization of precursors followed by a detailed study of nuclear structure and independent yields. At present, techniques for the rapid separation of rare gas and halogen fission products, suitable for on-line isotopic separation, are being developed. For rare gas studies, a uranium-barium stearate emanation source swept by a stream of nitrogen gas is being used. The decontamination factor with respect to halogen is ≈ 10⁵ , and higher for other activities. Separation time of ∼2 seconds is routine. With this system (without isotopic separation), it was possible to establish delayed neutron emission from both ⁹³Kr (T_0.5 = 1.19 t 0.05 sec, P_n = 3.9%) and ⁹³Rb (T_0.5 = 5.60 ±0.05 sec, P_n = 2.6%). The half-life of ⁹⁴Kr is estimated as 0.4 ± 0.1 sec. For bromine and iodine, selective recoil labelling is used (for extraction of independently produced species while the same nuclides produced by beta decay are discriminated against) followed by fast gas chromatography. Using empirical P_n-values and fission yields for 14 known precursors, good fits to experimental total delayed neutron yields of groups 1-4 were obtained for a series of fission reactions. Systematic deviations indicate unidentified precursors. The inconsistencies between expected and reported results on delayed neutron yield variations with the energy of the fission-inducing neutrons are being checked by high resolution γ-ray spectometry in conjunction with neutron counting, with the aim of determining these relations with neutrons of various energies (thermal, fission and 14 MeV). A technique for obtaining data on the masses and half-lives of delayed neutron precursors, based on selective collection, through a bias potential, of recoils from neutron emission, is being studied. The energies of delayed neutrons from gross and separated elements produced in fission are being studied with an improved ³He spectrometer and time-of-flight techniques. (author)

[en] The ARC/SPAR sealing system, based on an ultra-sonic signature and designed for sealing CANDU-type spent fuel, has been undergoing field evaluation at Gentilly-2 600 MW Reactor for the last ten months. The test was designed to evaluate the hardware and software of the system, the effort required for the application and verification of the containment and seals, the interference with operator, the procedures and the false- and missed alarm rates. Routine use conditions were emphasized throughout the test. In the course of the trial the entire content of the spent fuel in the pond was sealed. Preliminary results indicate that the system is acceptable. Hardware, software and procedures except for the transducer worked well. Transducer failure occurred too frequently at an unacceptable rate. The problem was identified and will hopefully be overcome. Level of intrusion with operations could be considered acceptable. Inspectors carrying out seal application and verification were adequately trained and performed satisfactorily. Auto- and crosscorrelations are reported. Recommendations are made for the improvement of equipment and procedures. The test will continue until the end of this year

[en] We describe a simple method for determining the neutron-absorption cross sections of radioactive nuclides and its application to ²²Na and ¹²⁶I. These nuclides are produced by fast-neutron reactions in cadmium-wrapped and unshielded samples simultaneously irradiated with cobalt flux wires. Values for the thermal cross section, sigma₀, the resonance integral, Σ', and s₀ are calculated from the data using the Westcott convention. The results are as follows: for ²²Na, sigma₀ = (5.11 +- 0.31) x 10⁴ b, s₀ = 2.3 +- 0.1, and Σ' = (1.0 +- 0.1) x 10⁵ b; for ¹²⁶I, sigma₀ = (9.0 +- 5.0) x 10³ b. 1 figure, 4 tables

[en] The determination of yields of individual nuclides formed in fission and the measurement of their nuclear properties is being carried out with the aid of an electromagnetic mass separator. The separator is connected in an on-line mode with a target placed at an external neutron beam of a nuclear reactor. The measurements are performed by controlled neutron irradiations, very rapid chemical separations and transfer of a specific element for subsequent isotopic separation. Overall times of transfer and separation are of the order of one second. The experimental arrangement permits direct measurements of separated isotopes over a wide range of masses, on both sides of the Z_p line. Of great advantage is the possibility provided by this technique of obtaining in a single time-controlled irradiation a simultaneous determination of independent and fractional yields of an isotopic series. The elements Br, I, Kr and Xe have been studied. Yields were determined by the assay of the individual isotopes or their descendents collected at various positions on an aluminium strip. These measurements were supplemented by direct on-line measurements of very short-lived activities to determine the half-lives of the isotopes in question, their daughters and their precursors, and to evaluate the corrections required to compensate for decay and build-up during extraction, chemical separation, transfer and ion-source residence time. Selective recoil labelling was also employed in the determination of the independent yields. The results for the independent fission yields of isotopes of elements at the asymmetric mass yield peaks in the thermal neutron fission of ²³⁵U are presented. The shape of the independent isotopic distribution curves obtained in the present experiments points to the importance of nuclear structure effects in the yields from low-energy fission. The results are discussed in the light of the available experimental data on isobaric charge dispersions at various masses and the existing models of mass and charge distributions in fission. Data relevant to the fission yields and nuclear properties of some nuclides for which little or no information has been published are given as well. (author)

[en] The International Atomic Energy Agency, with the assistance of the Canadian Safeguards Support Programme and Hydro Quebec, have carried out a 16-month intensive field trial, under routine use conditions, of a sealing system for irradiated fuel in an operating CANDU 600 MW(e) power reactor. The sealing system evaluated was composed of the ARC (AECL Random Coil) ultrasonic seal, a micro-processor-based interrogator called the SPAR (SEAL PAttern Reader), and a suitable containment structure. The test evaluated the hardware and software of the system, the effort required for the application, verification and maintenance of the seals, and the containment structure. Also evaluated were the sealing procedures, role of the facility operator, the need for training of both inspectors and facility personnel, interference with routine activities at the facility, and the overall logistics of the system from procurement of components to management of a seal information database. The stability of the seal signatures over the long term was examined. False and missed alarm rates were calculated. The feasibility of verification of the underwater containment structure was demonstrated. The overall results are good, and the system was demonstrated to be a workable and reliable one