V. N. Potapov

The design and performance of a large-volume spherical CsI(Tl) scintillation counter for gamma-ray spectroscopy

This paper presents details of the design and performance of a prototype large-volume scintillation detector used for gamma-ray spectroscopy. In this detector, a spherical CsI(Tl) scintillation crystal having a diameter of 5.7 cm was polished and packed in dry MgO powder. The scintillation light from the crystal was viewed using a single 1 � 1c m 2 silicon PIN diode. A low-noise preamplifier was also integrated within the detector housing. The measured noise level was equivalent to B800 electrons (FWHM). Such a configuration provided a very good light collection efficiency, which resulted in an average of 20 electrons being generated per keV of energy deposited in the crystal. One of the key features of the detector design is that it minimises spatial variations in the light collection efficiency throughout the detector. Compared with a standard 3 in. NaI scintillation counter, this feature leads to a much-improved energy resolution, particularly for photon energies above 1 MeV. The results presented in this paper clearly demonstrate that a spherical CsI-photodiode detector could be used as an ideal replacement for the standard 3 in. NaI detectors in many applications, but especially when the incident gamma-ray spectra extend up to B10 MeV as in neutron-activated gamma-ray analysis. r 2001 Elsevier Science B.V. All rights reserved.

Determination of surface activity and radiation spectrum characteristics inside buildings by a gamma locator

Abstract A gamma locator designed to conduct contamination survey inside buildings connected with nuclear production is developed. The device consists of a detector head and a remote control unit connected with a cable (>150 m). The detector head (200 × 200 × 250 mm 3 ; the weight is nearly 40 kg) is a collimated scintillated gamma detector installed on a scanning unit. The gamma detector is placed in a lead shielding with the collimator having an entrance angle near 10°. The detector head contains a TV camera and laser distance device. The remote control unit provides operation and processing of the acquired information. The gamma detector is based on a system of CsI(Tl) scintillators and an Si photodiode. The detector energy resolution (nearly 9% for radiation of 137 Cs) provides identification of gamma radiating isotopes such as 57 Co, 137 Cs, 40 K, 60 Co, 131 I and 154 Eu. The gamma locator threshold of determination is 250 Bq/cm 2 for a 10 cm 3 scintillator and 137 Cs radiation. The system allows one to measure the effective surface activity density (for 137 Cs radiation) of all building surfaces and to reconstruct an exposed dose rate distribution within the volume of the investigated space.

A combined spectrometric detector of fast neutrons

A combined spectrometric detector consisting of two subdetectors for fast and thermal neutrons has been developed. The fast neutron detector is a total absorption detector with a polystyrene-based scintillator generating a signal proportional to the absorbed energy of a fast neutron. The thermal neutron detector based on a 6LiF/ZnS(Ag) scintillator in the form of a thin screen detects neutrons that have lost almost all their energy in the first detector and have been thermalized. The electronics of the combined detector operates in coincidence: if a neutron has been detector by the thermal neutron detector, the signal from the fast neutron detector participates in the formation of the amplitude spectrum within a predetermined time interval (fast neutron moderation time). The methods for reconstructing the neutron spectrum by the spectrum recorded using the combined detector are considered. The measured neutron spectra from various sources are presented.

Computational and experimental justification of a method for determining the137Cs contamination density and depth in soil

For decontamination and to make well-founded decisions concerning the rehabilitation of populated points subjected to radioactive contamination after the Chernobyl accident, it was necessary to develop a method that would make it possible to determine reliably the density distribution of the Cesium-137 contamination at the populated points with a spatial resolution of approximately 1-2 meters. The method must be efficient and it must provide tens of thousands of measurements for one field season. Each measurement must be inexpensive so that the inspection of the territory would be economically viable. It is extremely important to estimate also the penetration depth of Cesium-137 in the soil. In this paper, we present a computational and experimental method for this method.

Experience of Application of New Remote Controlled Instruments for Scanning of Distribution of Radioactive Contamination in Rooms With High Dose Rate

When carrying out the decommissioning of nuclear facilities is necessary to measure the distribution of radioactive contamination in the rooms and the equipment at high levels of background radiation. In the decommissioning of the reactor in the MR NRC “Kurchatov Institute” for such problems is developed and applied a few special systems with remote control. For a survey of high-level objects used mounted on the robot radiometric system. To determine the composition of pollutants and use a portable collimated spectrometric system. To obtain a detailed distribution of contamination of used remote-controlled gamma camera.Copyright

A gamma locator for remote radioactivity mapping and dose rate control

The automatic system for remote measurements of radiological conditions at territories of rehabilitation activity was developed. The apparatus is realized as computer controlled collimated gamma-locator. The methods of exposure dose rate (EDR) calculation in 3-D space around territory of activity and analysis of relative input of main gamma-sources into EDR are developed. The results of application of the system during rehabilitation activity at RRC Kurchatov Institute for exposure dose rate monitoring and control are presented and discussed.

Calculation of the Equivalent Dose Rate Distribution Using Data Obtained with a γ Locator

A method is presented for calculating the equivalent dose rate for the interior spaces in enclosures. The method uses the results of remote measurements, performed with a γ locator, of radioactive contamination levels. The spectral characteristics of photon radiation are taken into account. The results of a calculation of the equivalent dose rate in the reactor room of the No. 4 unit of the Chernobyl nuclear power plant, which are based on measurements performed in the fall of 1996, are presented as an example.

Parameters of the new scintillation detectors

The parameters of two types of scintillation detectors—LGSO + solid state photomultiplier and LaBr3 + ΦЭУ-184 photomultiplier tube—are experimentally estimated. These detectors are interesting from the standpoint of γ-ray measurements.

Neutron detectors based on silicon photomultipliers

Neutron detectors comprising a new type of photosensors—silicon photomultipliers—coupled to a single-crystal LiI(Eu) scintillator and a 6LiF/ZnS(Ag) scintillation screen are described. These detectors are compact, which improves their usability. Some parameters of the detectors are presented, their sensitivity to thermal neutrons and γ rays is estimated, and their possible applications are proposed.

Measurements of photon ionizing radiation fields in the reactor room of the 4th power-generating unit of the chernobyl nuclear power plant

A radiation examination of the reactor room of the damaged fourth unit of the Chernobyl nuclear power plant was performed. The most strongly radiating surfaces were determined. Digital maps of the distribution of the effective surface activity on the inner surfaces of the room were constructed from the measurement results. 4 figures, 1 table, 10 references.