S. M. Ignatov

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 scintillation γ-ray detector based on a solid-state photomultiplier

A scintillation detector based on a silicon photodetector of a new type—a solid-state photomultiplier—and a single-crystal CsI(Tl) scintillator was investigated. The effect of temperature on the low-energy detection threshold and the energy resolution of the detector and the influence of the radiation level on the detector efficiency (i.e., the influence of the counting rate of the distortion in the recorded spectrum shape) were estimated. A mathematical model of the detector was developed in order to assess its parameters.

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.

A dip detector for in situ measuring of /sup 137/Cs specific soil activity profiles

A field method for measurement of Cs-137 contamination depth profiles is described. The method is based on the use of a collimated dip detector created as a gamma-ray probe: CsI(Tl) scintillating crystal + PIN photodiode + front-end electronics. The presented method allows determination of specific activity distribution with vertical spatial resolution of 5 cm. Exposure time for one point in the distribution profile is less than 180 s if the level of specific activity is more than 50 Bq/kg. This method may be applied for efficient and quick inspection of a contaminated rivers flood planes in areas with leakage of radioactive wastes. Application of the method for such a task gives an effective solution to obtain qualitative and quantitative characteristics of contamination.

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.

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.

Environmental monitoring using large-volume CsI(Tl) scintillation counters

The new scintillation detectors, CsI(Tl) + Si PIN photodiode, were developed in the Kurchatov Institute. The current state of the developed spectrometric probes are large volume (10-300cm3) scintillation detectors intended for gamma-ray spectroscopy. These detectors consist of a spherical CsI(Tl) crystal packed in MgO powder within a cylindrical aluminum housing and a Hamamatsu photodiode. Environmental devices based on the above probes uses methods of field spectrometry. They include spectrometric electronics and algorithms for spectra processing to obtain particular characteristics of environmental radioactivity or radioactive contamination. The description of measurement techniques used with devices, their performance parameters and results of their practical applications are presented.

Experience of Gamma-Locator System Using for Radiation Monitoring During Rehabilitation Works at Temporal Radwaste Storage Area of Kurchatov Institute

Remote monitoring of radiological conditions on large areas is important task during large-scale activity with radioactive contamination/materials. We present results of application of an automatic system for remote measurements of radiological conditions at territory of rehabilitation activity. The system is scanning collimated spectrometric detector, its construction and main performance characteristics are shortly described. System, including two different measurement heads was used during three years for radiological monitoring of area rehabilitation works at temporal radwaste storage area of RRC Kurchatov Institute. The results of its application for exposure dose rate monitoring at particular control points from separate strong sources located in the territory of activity are presented and special cases are studies in details. The method of EDR calculation in 3-D space around territory of activity and analysis of relative input of main gamma-sources into EDR are presented. The results of application of the system during rehabilitation activity at territory of temporal storage of radioactive wastes of RRC Kurchatov Institute have shown high efficiency of this system for such operations.Copyright