Fast determination of 9°Sr/9°Y activity in milk by Cherenkov counting.

Cherenkov counting of the 9°Sr/9°Y pure beta emitters is an attractive method for 9°Sr activity determination, but the color quenching effect may be significant, especially for strongly colored or semi-opaque media. A quench correction method based on the external source of some liquid scintillation systems (named ESAR - external source area ratio) was proposed and checked for aqueous solutions and was proved to be effective also for urine samples. In the present work, the application of the ESAR method for fast determination of 9°Sr/9°Y activity in milk samples is described.

Can scintillation detectors with low spectral resolution accurately determine radionuclides content of building materials?

The current paper makes an attempt to check whether the scintillation NaI(Tl) detectors, in spite of their poor energy resolution, can determine accurately the content of NORM in building materials. The activity concentrations of natural radionuclides were measured using two types of detectors: (a) NaI(Tl) spectrometer equipped with the special software based on the matrix method of least squares, and (b) high-purity germanium spectrometer. Synthetic compositions with activity concentrations varying in a wide range, from 1/5 to 5 times median activity concentrations of the natural radionuclides available in the earth crust and the samples of popular building materials, such as concrete, pumice and gypsum, were tested, while the density of the tested samples changed in a wide range (from 860 up to 2,410 kg/m(3)). The results obtained in the NaI(Tl) system were similar to those obtained with the HPGe spectrometer, mostly within the uncertainty range. This comparison shows that scintillation spectrometers equipped with a special software aimed to compensate for the lower spectral resolution of NaI(Tl) detectors can be successfully used for the radiation control of mass construction products.

Determination of 90Sr-90Y activity in urine samples by using Cherenkov counting.

Cherenkov counting of the (90)Sr-(90)Y pure beta emitters in aqueous samples is an attractive method; but color quenching correction is needed, this being especially significant for urine which is characterized by a strong coloration. A quench correction method based on the external source of some liquid scintillation systems (named ESAR-External Source Area Ratio) was proposed for aqueous solutions. In the present work, the application of the ESAR method for determination of (90)Sr-(90)Y in human urine samples is described.

Measurement of ²²²Rn diffusion through sandy soil with solar cells photodiodes as the detector.

An experimental system was developed to study the diffusion rate of radon (²²²Rn) gas through porous media as a function of soil porosity/grain size and soil water content. Columns with different grain sizes, soil water content and soil depths were used. The system used solar cells photodiodes as alpha (α) detectors. This new detector is highly efficient and low cost compared to other known detectors. Soil water content was found to be the most dominant factor affecting the ²²²Rn diffusion rate. A maximum diffusion rate value of (6.5 ± 0.07) × 10⁻6 m²/s was found in dry conditions. The minimum diffusion value of less than (3.9 ± 0.14) × 10⁻7 m²/s was found in 2% soil water content. The experimental results were compared with theoretical calculations done with the "GREEN equation". Two discrepancies were observed: the time to equilibrium state in the measurements was longer compare to the calculated values and the α count rates were lower in the experiment compared with the theoretical calculations. These results can be explained by the differences in the system geometry.

A comparative study of color quenching correction methods for Cerenkov counting.

The color quenching correction for Cerenkov counting is normally based on indexes defined for liquid scintillation spectra. Because of the differences in the spectrum shapes, these indexes are not optimal, and a different method was proposed based on the integral counting of the external (152)Eu source spectra of a 1200 Quantulus system. We have shown that this method, named ESAR (external source area ratio), is superior to all the other correction methods, offering the highest sensitivity and the widest range of application.

Measurement of the radiation dose and assessment of the risk in mammography screening for early detection of cancer of the breast, in Israel.

The mean glandular doses to samples of women attending for mammographic screening are measured routinely at screening centres in Israel. As at present, no detailed and systematic data have been collected regarding the average glandular dose in mammography screening procedures carried out in Israel for the last 20 y. Especially data are lacking related to the glandular dose (GD) involved in mammography with the new digital mammography systems. In this work, partial results of the measurements are presented to asses the radiation dose to the breast and to the glandular tissue within the Israeli national mammography programme updated to year 2009.

Color quench correction for low level Cherenkov counting.

The Cherenkov counting efficiency varies strongly with color quenching, thus correction curves must be used to obtain correct results. The external (152)Eu source of a Quantulus 1220 liquid scintillation counting (LSC) system was used to obtain a quench indicative parameter based on spectra area ratio. A color quench correction curve for aqueous samples containing (90)Sr/(90)Y was prepared. The main advantage of this method over the common spectra indicators is its usefulness also for low level Cherenkov counting.

An improved method for Organic Bound Tritium (OBT) determination in urine samples.

The Organic Bound Tritium (OBT) amount in the body may induce changes in the evaluation of the internal exposure to tritium, due to its different retention time relative to HTO. OBT measurements for urine are not performed routinely, mainly because of the lengthy work needed in preparation of the samples, when using the standard oxygen combustion method. A simpler and more rapid method based on liquid scintillation counting (LSC) was employed, and an evaluation was performed to check its suitability for urine samples. The principle of the proposed method is based on subtracting the LSC counts of the water phase sample (HTO) from the total activity of the urine sample (OBT+HTO). A good correlation was found between the results obtained when applying the proposed direct method and the Gold standard method. The minimum detectable activity when using this method was determined.

Determination of a neutron source position in an unknown homogeneous medium; the 2D case.

The localisation of an unknown neutron source in various bulky homogeneous media was studied. For the planar case two (3)He detectors on the opposite faces of a box were used. It is shown that the location of a single small neutron emitting source in a large box can be found to a better than 7% by using two neutron detectors positioned on parallel faces of the box, coplanar with the source. The localisation requires measurement of the count rate of both the unknown source (ratio of the count rates of the two detectors is R(x)) and an extra source positioned on one of the faces of the box (ratio of the count rates of the two detectors R(0)). The location of the neutron source is found according to the equation. (formula see text). The localisation is based on the finding that the ratio of the count rates of the two detectors is an exponential function of the distance of the source from one of the detectors.

Pre- and post-irradiation fading of 6LiF:Mg,Ti (TLD-600) exposed to thermal neutrons.

The results of (6)LiF:Mg,Ti (TLD-600) glow peaks fading after irradiation by thermal neutrons, as a function of pre- and post-irradiation times up to 3 months, are presented. The measured glow curves were analysed using the computerised glow curve deconvolution and region of integration methods, to study the decay characteristics of each individual peak and the sum of selected peak areas in the glow curve. The results confirm a high stability for the sum of peaks 4 + 5 and 6 + 7, whereas peaks 2 and 3 have a dominant contribution to the fading effect.

On the reassessment of thermal neutron doses in TLD-100 by measuring the residual dose.

By employing second readouts and the Phototransferred thermoluminescence (PTTL) method, high doses may be reassessed on the basis of residual dose information. It was shown in the past that for TLD-100, gamma doses can be reassessed by using a simple and efficient method, which consists of expanding the heating time to 30 s. In the present study, the 'extended time' method and the PTTL residual dose evaluations are used for reassessing thermal neutron doses when using TLD-100 crystals. Reassessment characteristics are presented for relatively low thermal neutron doses, in the range between approximately 1 and 18 mSv gamma dose equivalent.

Optimisation of the readout parameters when evaluating thermal neutron doses by TL dosimetry with LiF:Mg,Ti.

The location of the glow peaks depends on the heating rate. It takes some time until the crystal reaches the heater temperature, and this time lag has a direct effect on the shift of peaks towards higher temperatures. Some information on the high-temperature peaks may be lost if the readout conditions (mainly length of time) are not properly chosen. Step heating profiles to a varying final temperature between 300 degrees C and 125 degrees C were used to study the time dependence of the collected information in the glow curves of (6)LiF:Mg,Ti crystals, and the minimal heating time for evaluation of thermal neutron doses was determined.

The determination of a neutron source position in an unknown homogeneous medium; the 3D case.

The possibility of localisation of an unknown neutron source in various bulky homogeneous media (box) was studied. Previous study showed that for the planar case, neutron source could be localised with accuracy better than 7%, by using the count rates ratio of two (3)He detectors, positioned on the opposite faces of the box. The influence of the deviation of the source from the virtual plane connecting the two (3)He detectors was studied. It was found that for detectors placed on the centres of the sample faces, larger distance of the source from the central line leads to larger error, up to 15%. It was found that while using the measurement of the ratio R(0) of external source placed on the box face coplanar with unknown source, accuracy does not depend on the distance from central line. Different ways to determine the plane of the unknown source were investigated. It was found that it is impossible to determine it by looking for maximum count rate of one detector or geometric mean of a pair of detectors. The experimental results were confirmed with Monte-Carlo N-particle (MCNP) simulations.

On the reassessment of doses in TL-dosimetry by measuring the residual dose.

Second readouts and the photo-transferred thermoluminscence (PTTL) method are sometimes used to reassess high doses. When using the common LiF:Mg,Ti, if the second readout is performed by a regular readout cycle of 13.3 s, its efficiency is low and the estimations cannot be obtained with acceptable accuracy for low doses in the 10-100 mSv range. By applying the PTTL method, the efficiency is much higher, but a high background is also present, deteriorating the quality of the reassessment. A simple and efficient method was studied, which consists of expanding the heating time to 30 s. Although the efficiency relative to a standard readout is improved by only a factor of 3, the low background enables to obtain results with the same uncertainty as the more complicated PTTL method. By applying region of integration discrimination, the errors can be further diminished.

Improved localization of a 'hot spot' in the lungs for an array of four HPGe detectors--the isotopic ratio effect.

Considerable errors in the determination of radioactivity in lungs are caused by the usual assumption of homogeneous distribution, while actually the radioactive contamination can be distributed, and even in the form of a 'hot spot'. Modern lung counter systems use several HPGe detectors, and the ratio of the different count rates of the detectors can be used to locate a 'hot spot' and apply correction algorithms for activity calculation. In the present work it is shown that the variability of the isotopic composition of the uranium source has a major effect on the process of localization of the 'hot spot' in the lungs. A way to eliminate this effect is proposed by separate normalization of the count rates of each energy peak.

HPGe virtual point detector for radioactive disk sources.

Validity of the model of a virtual point detector (implying existence of a point where all interactions virtually occur) was confirmed for measurements of radioactive disk sources with HPGe detectors. The existing correlation of the count rates with the distance between the virtual plain detector and the detector face makes it possible to inter- and extrapolate calibration curves for disk radioactive sources for use at different source-detector face distances. The dependence of the distance between the virtual plane detector and the detector face on the photon energy was studied for sources of various radii.

On neutron-gamma mixed field dosimetry with LiF:Mg,Ti at radiation protection dose levels.

The possibility of using the specific responses of the high temperature Peaks 6 and 7 and Peaks 4 and 5 to different LET radiations was mentioned in the past mainly for very high doses. The applicability of the two regions method for thermal neutrons--gamma ray mixed field dosimetry was investigated by analysing the response of LiF:Mg,Ti dosemeters irradiated to different ratios of thermal neutrons and gamma rays at radiation protection dose levels encountered in routine work conditions, up to approximately 50 mSv. The Region of Interest method was used to define the areas of the Peaks 4 + 5 and 6 + 7. We found that a simple algorithm can be used to determine with good accuracy the separate contributions of neutron and gamma doses.