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The responses of the three photomultiplier tubes (PMTs) in a triple-to-double coincidence ratio (TDCR) liquid scintillation (LS) system are often not identical. Such asymmetries can have a significant influence on activity determinations. The problem is often solved by means of a minimization algorithm which can easily be applied when analytical methods are used for the efficiency calculation, as is usually done for pure beta emitters. However, for radionuclides with more complex decay schemes, the counting efficiencies are often calculated with stochastic methods and the computation of the required corrections becomes very challenging. This paper presents a new numerical method to overcome the asymmetry problem for such complex decays and a comprehensive study on 55Fe is described in detail. For the measurements, the asymmetry was varied by means of grey filter films which were placed in front of one of the photomultiplier tubes. In the case of the pure electron-capture (EC) radionuclide 55Fe, the asymmetry can also be taken into account with a very simple correction which is derived assuming monoenergetic emissions. This work is also of great importance for the planned extension of the International Reference System (SIR) at the BIPM which will be used for international comparisons in radionuclide metrology.

CEA LIST is working of the development of a high-sensitivity thermal neutron counter, based on the insertion of gadolinium in spherical plastic scintillators. As the radiation sensor comprises one or several volumes of scintillating polymers, it is, by nature, sensitive to both neutron and gamma radiations. This property allows the development of a versatile detector, provided that it is possible to algorithmically separate the signature of both types of radiations. The technologically building brick is, moreover, to be implemented in a transportable ( 15 kg) system, handled by a first intervention task force in an exposed area. The aim of this paper is to study, both through Monte Carlo simulation and experimentally, an algorithmic architecture of the measurement chain discriminating neutron and gamma events. The presentation is subdivided in three main sections. First, we detail a comparative study between the outputs of a numerical modeling tool, developed to simulate the total response of the sensor to varying radiation sources and the results of a series of experiments carried out in a controlled environment. Second, we describe the building and numerical pre-validation of a simulation code dedicated to the study of consolidated algorithmic architecture, namely γ – γ quasi-coincidence on two adjacent plastic scintillators. Third, we comment on an experimental study of γ – γ quasi-coincidence, Gd-based neutron detection and a comparison between the results and the estimated of the numerical study. We conclude with the presentation of first estimates of neutron sensitivity), gamma-background vulnerability, and n/ γ discrimination ratio for the scaled and assessed, material and algorithmic architectures.

A general view of spectroscopic phenomena of intermolecular collisions is presented together with the present directions of research in this field. A bibliography of about 600 references has been established, completing up to 1981 that of N.H. RICH and A.R.W. Mc KELLAR given in 1975.

Influences of various parameters on the apparatus function of a F.I.R. grid Fabry-Perot spectrometer are analysed. A pseudo-deconvolution method allowing an improvement of experimental results is tested by simulation and then applied to data concerning the isotopic HCl doublet at 41 cm−1.

We describe a mounting fitted to select a narrow frequency band between 20 and 100 cm−1 in the far infrared; it consists of a coupling of a grating monochromator with a plane scanning Fabry-Perot interferometer (F. P.).

The aim of this study is the frequency shift measurement of pure rotation lines for three strongly dipolar molecules: HF, HCl and HBr, each of them successively perturbed by one of the two others, under low pressure (1 to 2 bar). Measurements are made with a grid Fabry-Perot interferometer in the 16–100 cm−1 region.

In order to develop a coherent optical source intended for very low frequency laser spectroscopy, we have studied, manufactured and then tested (calibrated) a device for generating submillimetric waves by frequency difference in a non linear crystal. The mounting is made of two single mode and single line T E A CO2 lasers which, by means of an AsGa crystal, allows the difference f3=f1−f2 of the two near frequencies f1 and f2 emitted by each laser to be obtained. We present a system using two CO2 atmospheric lasers with a simple and efficient pre-ionization and an original treatment of the electrodes. Manufacturing characteristics of the primary sources are detailed and then the obtained Far Infra Red (F I R) emission is studied.

Resume On decrit un spectrometre de laboratoire, equipe de reseaux de petites dimensions (68,6 x 68,6 mm), pour l'etude des gaz dans l'infrarouge lointain. Cet instrument comporte deux systemes de filtrage distincts: l'un utilisant des pastilles par transmission, l'autre, des grilles metalliques par reflexion. Pour donner les performances de l'appareil, dont la resolution suivant l'intervalle spectral analyse varie de 1-0,5 cm -1 , des spectres de la vapeur d'eau et de l'ammoniac sont presentes. On obtient la mesure directe de l'elargissement par effet de pression du a l'Argon, de la raie de rotation pure (0-1) de l'acide fluorhydrique anhydre.

A short review is made of the general characteristics of electromagnetic and corpuscular radiations to which man can be exposed. Following some considerations on the action of ionizing radiations and the radiobiological factors governing their effects on health, the overall characteristics of pathological effects differentiating stochastic from non-stochastic effects are summarized. The uncertainties remaining as to low-level exposures are stated as well as the cautious assumptions usually madein this field. The various sources of exposure to which the population is submitted are considered, i.e. exposures from natural, medical, domestic, industrial sources or from fallout from nuclear weapon tests; the present or predictable levels of exposure and their variations are given for each source. But for medical irradiation, all the exposures connected to human activities are much lower than natural exposure variations; such exposures should modify the incidence of certain affections but quite insignificantly as compared with the regional or local variations observed.