[en] Aside from the great disparity in fluxes, neutron activation analysis with a ²⁵²Cf source differs in two ways from the more traditional methods with a reactor. Firstly, in situ analyses require that the bombarding source and detector conform to the requirements of the sample, e.g. material on a conveyor belt or minerals in a bore hole, and hence frequently use ²⁵²Cf sources; secondly, prompt capture gamma rays, the photons produced virtually simultaneously with the capture of a neutron by the nucleus, are frequently used for detection in californium activation analysis. They are rarely used in activation analysis with a reactor. This review discusses the major 'field' applications of ²⁵²Cf activation analysis - on-stream analysis, well logging, terrestrial mineral exploration, in vivo analysis, oceanography, studies of inland waters and sediments, and for nuclear safeguards. This is followed by a discussion of more conventional laboratory activation analysis with the isotope source. (author)

[en] On-line analysis techniques are constantly gaining ground in the mineral processing industry. The use of a ²⁵²Cf neutron source makes on-stream neutron activation analysis possible in this field. A review of currently applied on-line activation analysis is given. An irradiation loop has been built at the Laboratorium fuer Isotopentechnik which will make it possible to develop industrial process control techniques using ²⁵²Cf. The loop uses a 1 mg²⁵²Cf for continuous irradiation of the liquids to be analysed. The design and operation of the loop are described. Any given loop can be characterized by an optimum flow rate, that at which the maximum activity is obtained in the liquid. This flow rate is a function of the half-life of the radioisotopes generated. For aqueous solutions containig various elements, this dependence was determined experimentally. In addition, the loop volume was experimentally optimized. The experiments required the design of irradiation and detector measuring cells, which enabled a step by step increase of the loop volume to be made. Detection sensitivities have been determined for approximately 20 elements in aqueous solutions for both single stage and cyclic irradiation and a number of elements could be excellently determined. To demonstrate a possible industrial application, a method of analysis for vanadium in crude oil was worked out in detail. (author)

[en] The relative biological effectiveness (RBE) is defined as the ratio of doses of a standard radiation to a test radiation required to produce equal biological effect. When comparing acute exposures of a high LET radiation, such as neutrons, with a low LET radiation, such as gamma rays, the RBE varies with the dose. As the dose is decreased the RBE is increased. This is the inevitable consequence of the difference in survival curve shape between high and low LET radiations; the high LET radiations are characterized by having a survival curve with a smaller initial shoulder than those corresponding to low LET radiations. At low dose rate all radiations, of both high and low LET, have survival curves which are exponential functions of dose; consequently RBE no longer varies with dose. Instead, RBE varies with dose rate, because the slope of the dose response curve for gamma rays varies much more rapidly than the corresponding slope of the survival curve for neutrons. As the dose rate is reduced, the RBE of neutrons relative to gamma rays increases. The picture is complicated in the case of californium-252 because the radiation emitted is a mixture of neutrons and gamma rays. The effectiveness of the gamma-ray component of the californium-252 varies, as well as the effectiveness of the radium gamma rays with which they are compared. Experimental data are available for RBE measurements over a wide range of dose rates which confirm the theoretical prediction that RBE should increase as the dose rate is reduced. There is also a tendency for RBE to vary with the type of biological system used to measure it. (author)

No abstract available

[en] Californium-252 neutron sources are already being used in various fields including cancer therapy, industrial radiography, radiobiological research, and education and training programmes all over the world. However, one should not lose sight of the fast neutron hazard associated with them. This paper outlines the salient radiobiological data for protection purposes and discusses in detail radiation protection measures that are to be scrupulously followed. Although built-in safety can go a long way to minimizing risks in the industrial application of these sources, special situations involving exposure to the staff and public arise in brachytherapy departments at various stages of their use, storage, source preparation, transportation, application of the sources into patients, segregation and nursing care of patients. Other aspects such as leak-testing, damage to needles and tackling emergency situations arising out of loss or misplacing of needles are also discussed. Experience gained over the past 20 years in the use of radium-226 and, recently, cobalt-60 in various hospitals in India is extended to encompass the special problems encountered with ²⁵²Cf. Details of the layout, structural shielding and other safety features in the use of large activity ²⁵²Cf sources are also presented. Finally, the necessity for providing special training of personnel who intend to use ²⁵²Cf sources is stressed. (author)

[en] The radiation field of a ²⁵²Cf source in free space is described in terms of kerma, absorbed dose and dose equivalent with respect to dose measurements made for radiation protection purposes. The application of various detectors and the calibration technique are discussed and compared with the ionization chamber method. Results of fluence and dose measurements are presented which were obtained with activation and threshold detectors, and with very sensitive dose-rate meters placed in the radiation field; the source was positioned in free air, behind shielding and in a glove box. The use of track etching detectors and albedo neutron detectors in field and personnel dosimetry, and measurements on ²⁵²Cf sources with low emission rates are also discussed. (author)

[en] An activation facility was designed to accommodate up to 50 mg of ²⁵²Cf; it contains at present a 500 μg source. The absolute values of thermal, epithermal and fast neutron fluxes were determined by the foil activation method using In, Dy, Au, Al and Fe detectors. Cross-sections averaged for unmoderated ²⁵²Cf neutrons were determined for 22 different reactions for elements with atomic weights lying between A=27 and 204. The sensitivity for determination of Al, Ti, Cu, As, Sr, Mo, In, Cd, Ba, Au, Hg and Pb was calculated for NaI(Tl) and Ge(Li) detectors. Average (n,2n) cross-sections for ²⁵²Cf spectrum were calculated for 49 nuclei lying between A=14 and 204. Angular distributions and cross-sections for the fragments from ²⁵²Cf neutron-induced fission of ²³²Th and ²³⁸U were measured. Titanium in bauxite and manganese in aluminium alloys were determined with a ²⁵²Cf source. The applicability of solid-state track detectors for neutron dosimetry, radiography and for the determination of fuel burn-up were investigated using ²⁵²Cf neutron and fragment sources. Characteristics of a jumping spark counter for counting fission fragments were studied with ²⁵²Cf sources. (author)

[en] Three experiments designed to demonstrate and measure several properties of the neutron radiation emitted by a 3μg ²⁵²Cf source are described. The experiments constitute a special project carried out by a third-year undergraduate student at the Institute of Physics of the University of Neuchatel. The ²⁵²Cf source is enclosed in a shield which allows a pencil of fast neutrons to pass through a central tube, while reducing the ambient radiation below the tolerance level. The shield consists of layers of borated paraffin wax, iron and cadmium. The first experiment uses an air-alcohol diffusion cloud chamber for the demonstration of tracks of recoil protons produced by the neutrons. Semi-quantitative measurements of track lengths give the correct order of magnitude of the proton energies. In the second experiment a liquid scintillator detector is used to scan the beam profile across the radiation shield enclosing the source. A pulse-shape-discrimination system discriminates between neutrons and gamma photons. The third experiment makes use of the nuclear emulsion technique to study the neutron energy distribution of ²⁵²Cf. Preliminary results are compared with published values. (author)

[en] Californium-252 is potentially of use in medicine as a replacement for radium in interstitial and intracavitary applications. The expected advantage is based on the lower oxygen enhancement ratio (OER) characteristic of the mixture of neutrons and gamma rays emitted by ²⁵²Cf, compared with the pure gamma-ray emission from radium. OER values have been measured over a wide range of dose-rates from 10 rads per hour up to several hundred rads per hour. At the lower dose-rates, the OER of the mixed neutron and gamma-ray emission from ²⁵²Cf is found to be approximately 1.5, which is indistinguishable from that characteristic of fission spectrum neutrons alone. This is explained by the fact that, at these exceedingly low dose-rates, the gamma-ray component has a negligible biological effect. As dose-rate is increased to approximately 100 rads per hour, the biological effectiveness of the gamma rays can no longer be ignored, and the OER that is obtained is a compromise between the 1.5 characteristic of fission spectrum neutrons, and the 2.5 to 3 characteristic of gamma rays. This increase of OER with dose-rate has some bearing on the range of applications of ²⁵²Cf in radiotherapy. The OER for this mixture of neutrons and gamma rays emitted by ²⁵²Cf can be calculated and predicted from values for neutrons and gamma rays alone. (author)

[en] The Division of Radiological Protection of the Bhabha Atomic Research Centre has been conducting, with the active collaboration of the World Health Organization, a one-year post-graduate training course in Hospital Physics and Radiological Physics since l962. Californium-252 needle sources procured on loan from the International Atomic Energy Agency have been used since January l974 in this course, both for laboratory experiments and for short-term research projects. The laboratory experiments include sorting of californium needles according to their strengths using a neutron flux meter, testing them for leakage, checking the uniformity of ²⁵²Cf distribution in the needles, etc. The short-term projects consist of studies of the gamma ray and neutron dose distribution around the needles, of shielding materials suited to californium radiations and of related safety aspects. Additional experiments, planned for the future, are also described. At least three hospitals in India have shown interest in obtaining ²⁵²Cf sources for use in therapy. The Division has been advising these hospitals in clinical dosimetry, and on the safe storage, transport and handling of ²⁵²Cf sources. Radiobiological studies at low dose rates using a diploid yeast mutant cell have also been planned. Details of the faculty-student oriented research in a teaching programme, with special reference to the facilities available within the Division, are presented. (author)