Beta Particle Counting Research Articles

A low-noise current-sensitive amplifier-discriminator system for beta particle counting

NPL has developed a low-noise current amplifier/discriminator system for radionuclides that emit low-energy electrons and X-rays. The new beta amplifier is based on the low-noise Amptek A-250 operational amplifier. The design has been configured for optimum signal to noise ratio. The new amplifier is described and results obtained using primarily electron-capture decaying radionuclides are presented. The new amplifier gives rise to higher particle detection efficiency than the previously used Atomic Energy of Canada Limited-designed amplifier. This is shown by measurements of 54Mn and 65Zn. The counting plateaux are significantly longer and have reduced gradients.

Temperature variation of indoor and outdoor radon progeny

Abstract The indoor and outdoor radon progeny concentrations were investigated at a semi-hilly area of Pathankot in Punjab using the method of beta particle counting of aerosol samples collected on a glass micro-fiber filter. A linear relation was found between indoor and outdoor equilibrium equivalent concentrations of radon-222 (EECRn) with correlation coefficient of R = 0.9 . The indoor and outdoor EECRn levels were also studied as a function of outdoor temperature. The variations with temperature in both cases showed negative correlation with correlation coefficient of R = - 0.66 and R = - 0.73 , respectively. The ratio of outdoor to indoor EECRn investigated as a function of absolute difference of indoor and outdoor temperatures (|Tin–Tout|) resulted in a correlation coefficient of R = 0.52 , which is positive. The indoor EECRn was also estimated from an empirical relation based on transport of inside and outside radon progeny through ventilation. The measured inside EECRn agrees well with the computed value.

Beta particle counting of sediments from Lac du Bouchet and Meerfelder Maar

A plastic scintillator system for beta particle counting, with automatic sample changer, has been employed to determine the depth dependence of radioactivity at approx. 2 cm intervals along a 6.5 sediment core from Lac du Bouchet in France. The reliability and reproducibility of measurements from the system are assessed. The data are compared with detailed alpha particle measurements made previously on the same samples as used in the present work and with an earlier smaller set of beta activity measurements from a different core from the same lake. Fifty two out of the 222 samples from the core were also subject to gamma ray spectrometry to aid the discussion. The relative merits of alpha particle counting, beta particle counting and gamma ray spectrometry to assess the depth dependence of radioactivity in a sediment core are considered. The interpretation of the activity distribution down the Lac du Bouchet core and in some sediment samples from Meerfelder Maar in Germany is discussed, particularly in relation to possible climatic influence.

Optimum scintillator thickness for beta dosimetry

Beta particle counting by plastic scintillation counter is a convenient method of determining the beta dose rate from the natural radioactivity in soils, as required for example in the process of luminescence dating of sediments or sherds. Data is presented to establish the optimum thickness of plastic scintillator for such beta dosimetry, found to be about 6 mm.

Determination of 89Sr and 90Sr in highly radioactive water from a nuclear power plant

The main criterion in assaying strontium radionuclides is to obtain radiochemically pure strontium sources for beta-particle counting. Nuclear power plant waters contain both 89Sr and 90Sr accompanied by many beta-particle and gamma-ray emitting fission and neutron-activation products. The latter activities can sometimes exceed those of strontium by a factor of 10 7. Efficient purification procedures must be used to remove these products, preferably at an initial stage of analysis to reduce the radiation risk to personnel. A method has been developed in which a water sample is passed through a prefilter installed on top of an ion-exchange column filled with Dowex-50 resin in H + form. This prefilter is impregnated with ferrocyanides and manganese dioxide and retains most of the interfering radionuclides while the underlying cation-exchanger takes up strontium ions. A few additional purification steps result in a strontium salt that is free from other radioactivity.

Design and operation of an automated beta-particle counting system for the measurement of 220Rn (and 222Rn) progeny

A fully automated system of the continuous (active) type has been designed for the unattended quantification of 222Rn progeny and 220Rn progeny in calibration and test facilities, as well as working and living environments. The system uses a β-particle detector and associated electronic circuitry, in conjunction with an in-house microprocessor-based processing interface card and a personal computer, operated by specially developed in-house software. The system represents a significant improvement over systems using α-particle detectors because of its enhanced flexibility of design and virtual elimination of plate-out effects in the sampling head, and of self-absorption phenomena in the sampling filter. The β-particle system was tested and calibrated in a Radon and Thoron Test Facility of the walk-in type under a variety of experimental conditions. For the geometry used for this system, the Potential Alpha-Particle-Energy Concentration (PAEC), in μJ m −3, in air can be calculated by the expression PAEC ∼4.4 N β (s −1/μJ m −3), where N β is the β-particle-system count rate in counts per second (s −1).

Scattering correction in beta dosimetry by beta particle counting

An assessment is made of the importance of scattering within the sample for beta dose rate determination from beta counting by an NE102A plastic scintillator. Convenient methods of source preparation, calibration and interpretation of the measurements are described which can take account of widely varying sample composition. The dependence of the scattering effect on the mean atomic number of the sample is discussed.

Analysis of 228Ra and 226Ra in Public Water Supplies by a Gamma-ray Spectrometer

Methods for measuring 228Ra were reviewed to select a brief and simple screening procedure under NIPDW Regulations for public water supplies. A two-step method was considered to concentrate Ra by evaporation or co-precipitation and to count it with a gas ionization detector, a liquid-scintillation detector, or a Ge detector with multichannel analyzer. Gross beta particle counting appears to be feasible for screening to meet the 0.04 Bq L-1 detection limit. One can utilize the same sample volume as currently collected and measure radiation with commonly available equipment in reasonable time. The required sample volumes were estimated on the basis of known counting efficiencies and background count rates. Gamma-ray spectral analysis is the recommended option, however, because 226Ra and 228Ra can be determined directly and simultaneously. Several aspects of the method were examined to assure that the concentration procedure is nearly quantitative and that the detection limit can be reached with a 3.8-L sample in a 6000-s counting period. The method was tested with Ra tracer solutions and EPA intercomparison samples over the range of 0.04 to 1 Bq L-1. It was found appropriate for 228Ra and 226Ra analyses.

Calculation of liquid-scintillation detector efficiency

Definitions of basic notions are given and dependence of counting probabilities of different kinds of scintillation pulses upon energy of beta particles interacting with scintillator are derived. Efficiency of beta-particle counting in liquid-scintillation coincidence detectors is determined. Calculated and experimental counting efficiencies are compared for double and triple detectors.

Calculation of beta-particle counting efficiency for liquid-scintillation systems with three phototubes

Formulae are derived for the computation of the β-particle counting efficiencies for three-phototube liquid-scintillation counting systems. It is shown that the counting efficiency for double and triple coincidences may be computed by considering the probabilities for secondary-electron production at the first dynodes. Effects due to asymmetry of the phototubes are also evaluated. The computed efficiencies are compared with experimental values obtained by Pochwalski et al. ( Appl. Radiat. Isot. 39, 165, 1988).

4π low background measurement of alphas and betas with four silicon detectors

An apparatus for low-level alpha and beta-activity measurements is described. Semiconductor detectors mounted in holders made of carefully selected materials are used for particle registration. The two measurement detectors between which the investigated sample is placed, can work in parallel or in anticoincidence. The anticoincidence shield of the measurement counter is provided by two thick Si(Li) detectors. The passive shield and the detector chamber are make of mercury and plexi, respectively. The samples are in the form of discs of up to 20 mm in diameter and up to 1 mm in thickness. The materials under investigation can be placed in a small container of the given dimensions. A very low background rate was achieved. It was of the order of 0.017 cpm/cm 2 at an 80 keV discriminator level and 0.5 mm detector thickness. The beta-particle counting efficiency was 65% for 50 mg KCl and for a 4π-measurement geometry. The low and constant (over a long period of time) background and high registration efficiency enabled measurements to be made of an activity of 40K at the level of 0.11 pCi in 1000 min and within 10% standard deviation.

Distribution of Fission Yields for Fission Spectrum Neutron-Induced Fission of Uranium-238

The mass-yield distribution for the neutron-induced fission of /sup 238/U by degraded fission spectrum neutrons with an average energy of 1.52 MeV has been measured radiochemically for 26 mass chains in the region A = 89 to 153. Germanium-lithium gamma-ray spectroscopy coupled with beta-particle counting techniques was used to determine the absolute activities of each nuclide measured. The absolute cumulative fission yield of mass chain 140 (/sup 140/Ba--/sup 140/La) was determined to be 6.07 +- 0.24 percent, and all other reported yields were measured relative to that value. Measured yields ranged from a maximum of 6.33 +- 0.55 percent for /sup 103/Ru on the light mass wing and 6.54 +- 0.28 percent for /sup 133/I on the heavy mass wing to a minimum of 0.030 +- 0.007 percent for /sup 121/Sn in the valley region. Results from this investigation provide a consistent set of cumulative mass yields from /sup 238/U fission induced by a well-characterized neutron spectrum.

Scintillation Counters for Radioactive Sample Measurement

A gamma-ray counter for liquid or solid samples is described. It uses an RCA 5819 phototube at room temperature with a thallium activated sodium iodide crystal in the shape of an annular ring. The gamma-ray counting efficiencies of this counter for 2-milliliter samples of Fe59, Co60, and I131 are about equal to the beta-particle counting efficiency of a mica-window G-M counter when counting thin samples. When the counter is heavily shielded, the background is about 160 counts per minute. The phototube operating voltage is not critical since over a wide range of operating voltage the counting efficiency and background count change only slightly. A directional gamma-ray counter is also described.

A secondary-emission electron multiplier tube for the detection of high energy particles.

The requirements of high gain and low background current in an electron-multiplier tube for the direct detection of high energy particles are considered. The design and construction of an experimental electron-multiplier tube with a stable over-all gain of at least 108 and a background at room temperature corresponding to three or four electrons per minute released at the input is described. An 0.0008-inch thick nickel window is provided in the tube envelope to admit the high energy particles to the multiplier. The efficiency of this device is compared quantitatively with that of a Geiger tube as a detector of beta-particles. It is found that the over-all beta-particle counting efficiency of the tube is of the order of 1.3 percent, and that the efficiency of the oxidized silver magnesium target surface is 4.9 percent for a uranium source and 6.0 percent for a strontium source.