The new measuring possibilities of 6-crystal gamma-rays spectrometers of “Pripyat” type are reported. Distinctive features of these spectrometers are the 4π registration geometry and large sensitive volume (up to 5 l). Principle of operation of the new registration system and the processing methods of spectra using the corresponding software are described. The minimal volume activities measured by using modernized spectrometers of “Pripyat” type are presented (137Cs, 226Ra, 232Th < 1 Bq/l, 40К < 10 Bq/l).

Spectra-angular distribution of the orthopositronium 3γ-decay was investigated for the first time in an asymmetric geometry of annihilation, using multidetector spectrometer ARGUS. In order to analyse the experimental data, a method for selection of the three-photon annihilation events and background reduction, built on the well-known algorithm of Dalitz plane, was developed. The experimentally obtained distribution is found to be in a good agreement with prediction of quantum electrodynamics, calculated by the computer Monte-Carlo modelling. The technique realised in this experiment is going to be used for testing quantum electrodynamics of bound state.

Uranium content in bauxite is generally several times higher than its average occurrence in the Earth’s crust. Bauxite deposits in Montenegro are widespread in the Niksich region. Some settlements are built above these deposits, and some detached family houses have basements directly in bauxite ground. Indoor radon measurements in this region were performed in such places, and in places where there is no presence of bauxite. Radon was measured on the ground floor, using cellulose nitrate detectors exposed 3 months during the winter season. The results show that bauxite ground produces a high indoor radon level. However, all measured concentrations are below the tolerance of 400 Bq/m3 adopted in Yugoslavia, except in two houses built directly on bauxite ground, where indoor radon concentration reached 540 Bq/m3 and 676 Bq/m3.

Se midieron las concentraciones de radon en suelo de la ciudad de Podgorica, capital de Montenegro, utilizando radiometrospasivos. Los radiometros se colocaron a una profundidad de 70-80 cm, en pozos perforados, y se expusieron detectores de nitratode celulosa durante 14 dias. La media aritmetica de las concentraciones de radon en 17 sitios fue de 37 kBq/m 3 , con una desviacionestandar de 16 kBq/m 3 . La distribucion de frecuencias de los niveles de radon en el suelo fue casi simetrica. Esta investigacionmuestra que los niveles de radon en suelo sobre la falla geologica, en una situacion asismica, no son mayores que los niveles enotras areas de la ciudad. Las concentraciones de radon en suelo en una zona de contacto entre el terreno plano y la zona montanosano fueron en general mayores que en otros sitios de la ciudad.

A method for event selection takes into account all features of orthopositronium-atom annihilation. The spectral and angular distributions of positronium three-photon decay was investigated with the 4π-spectrometer ARGUS. The filtration program for the events corresponding to the three-photon positronium decay was developed, and positronium 3γ-annihilation was simulated by the Monte Carlo method. The measured spectra agree well with the simulation. The technique developed will be used to test the quantum electrodynamics of bound state.

We describe a setup for experimental testing of the CPT-invariance by observing the angular correlations in the decay of polarized orthopositronium atoms. Annihilation events are detected by five NaI(T1) sensors of 150-mm diameter and 100-mm thickness, located at the vertices of a regular pentagon. The sensor signals are detected in the double-coincidence circuits gated by signals with different time delays from the positron escape. The setup has a time resolution of 8.0 ns. In order to reduce the effect of the long-term instability and the instrumental asymmetry on the experimental results, the direction of positron incidence on a SiO 2 target was reversed with a program-driven period during data acquisition. The value of the asymmetry, measured with due account of statistical and systematic errors, is 0.0008±0.00091, which is twice better as compared with the previous experiment.

In the paper we describe the capabilities of the multidimensional (multidetector) spectroscopy of photon cascades. Attention is paid to a considerable increase in the resolution of multidetector spectrometers compared to one-detector spectrometers. We give a derivation of the radiation intensity detection limit, which relates all the basic characteristics of a multidetector spectrometer, and present examples of calculation of spectrometer characteristics.