[en] Californium 252 presents itself as a Neutron source whose nuclear characteristics: flux, average energy of neutrons, dose of gamma radiation are likely to be used in hospitals. The authors present the achieved results that have permitted to determine the physical characteristics of a block, which allows homogeneous irradiation of thick animal or human biological targets (hands) thanks to 252 Cf. The variations of the thermal flux measured by means of irradiated manganese (with or without cadmiumscreen) and samples of calcium, show that a homogeneousness superior to +-5% is obtained for a depth of field ranging about 6 cm. The screen used, is chosen with a density superior to 1, so as to reduce the rate of thermal neutron production in comparison with a more hydrogenized material. The quantitative and qualitative study of spectra induced 'in vivo' obtained with a Ge (Li) junction compared with those obtained thanks to 2 crystals (6x4 inch) allows to justify the use of detectors. The results obtained on a group of 40 normal patients and of 70 patients in chronic renal deficiency show the possibilities and the limits of such a measure in clinical routine

[en] Owing to the recent commercialisation of californium 252 it is now possible to obtain neutron fluxes strong enough for precise activation of the calcium content of biological targets. After the preliminary measurements necessary to establish the most suitable conditions for irradiating 3 to 5cm thick targets, two parallel sets of experiments were developed. In the first the medium-term total calcium variation was studied in 20 rats, 16 suffering from chronic kidney deficiency. In the second the precision expected as a function of the calcium content of the irradiated target was examined, using 3 sets of tissue equivalent standards of calcium contents 5, 20 and 50g respectively. The first results obtained on calcium 49 in vivo show that a calcium content variation can be followed with a sensitivity threshold below that obtained by conventional methods

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[en] With californium-252 it is easy to obtain a high neutron flux of the order of 10⁹n/s. The mean energy of this radiation, which is close on 2 MeV, activates calcium very well. The authors describe a storage and irradiator unit with a 100 μg californium source, with which it will henceforth be possible to develop this technique of measuring the calcium of the hand in a hospital. The test programme has three distinct phases: (1) irradiation of the biological target for 10 min; (2) after a transfer period of 30 s, detection of the radiation emitted by the ⁴⁹Ca for 600 s; (3) processing of the numerical data received, which are transmitted on line to a T 1600 calculator. The weight is found by comparing the activity induced in the unknown calcium mass with that induced in a phantom chosen as the activity standard. The reproducibility of the method is of the order of 3% (5% at the worst). The gross standardized result is edited automatically. For physical and clinical reasons, the hand is chosen as the reference part of the body in 70 control subjects. The local irradiation dose is less than 2 rem. The bone calcium content is 14.3+-1.9 g in men and 10.1+-1.3 g in women. In clinical application of the technique it is necessary to differentiate between the normal calcium content and the calcium content found with a pathological state. This makes it necessary to express the measurement in the form of a volume mass (rho). The volume of the hand skeleton (V in cm³) is calculated from the corresponding bone surface (S in cm²) measured by planimetry with the relationship V=8.925 exp 0.0205.S, found after studying 80 hand skeletons. In our control subjects the calcium bone volume mass was 0.288 g/cm³ in men and 0.282 g/cm³ in women. There is a very significant difference (p<0.001) in a population of 88 subjects with chronic renal insufficiencies at the terminal stage: rho=0.233 in men and 0.235 in women