NEUTRON DOSE ASSESSMENT USING SAMPLES OF HUMAN BLOOD AND HAIR.

The unique feature of nuclear accidents with neutron exposure is the induced radioactivity in body tissues. For dosimetry purposes, the most important stable isotopes occurring in human body, which can be activated by neutrons, are 23 Na and 32 S. The respective activation reactions are as follows:23Na(n,γ)24Na and32S(n,p)32P. While sodium occurs in human blood, sulfur is present in human hair. In order to verify the practical feasibility of this dosimetry technique in conditions of our laboratory, samples of human blood and hair were irradiated in a channel of a training reactor VR-1.24Na activity was measured by gamma-ray spectrometry.32P activity in hair was measured by means of a proportional counter. Based on neutron-spectrum calculation, relationships between neutron dose and induced activity were derived for both blood and hair.

EMERGENCY PREPAREDNESS OF GAMMA SPECTROMETRY LABORATORIES.

Currently, the territorial Radiation Monitoring Network (RMN) of the Czech Republic consists of seven laboratories equipped with gamma spectrometry High Purity Germanium (HPGe) detectors. From 2007 to 2018, five emergency exercises were carried out to test the sample throughput of these facilities and their staff. The main objective was to identify weaknesses and problem areas in the whole process from the moment of obtaining the samples to logging the results into the central RMN database. The long-term aim of these exercises is to optimize emergency response procedures. The most important factor limiting laboratory capacity is the lack of qualified personnel. The exercises showed that in the current state, these laboratories would be able to operate in 12-hour shifts for 14 days and analyze 1700 samples per day. Emergency exercises have highlighted the fact that this type of exercise should be repeated periodically in order to monitor the performance and analytical capabilities of RMN.

238U CONTENT IN URINE OF URANIUM MINERS AND ITS MODELED VALUES.

The aim of the study is to make a comparison of daily 238U excretion in urine among 115 active uranium miners and its modeled values obtained from inhalation intake of long-lived alpha emitters as measured by personal dosemeters and assessed by biokinetic models for different absorption parameters settings for inhaled uranium. A total of 144 spot samples of urine were collected. The 238U content was measured using high-resolution inductively coupled plasma mass spectrometry method. To obtain estimates of the daily excreted values, the daily values were calculated according to the expected daily excretion of creatinine assessed individually for each miner. When determining the relation between the experimentally found data and the modeled data, a high emphasis was placed on uncertainty of the both compared quantities. All the tested absorption parameters settings produced in average 1.4-4.7-fold higher values than the experimentally found values in the urine.

Size distribution of aerosol particles produced during mining and processing uranium ore.

The aerosol particle size distributions of uranium and its daughter products were studied and determined in the area of the Rozná mine, which is the last active uranium mine in the Czech Republic. A total of 13 samples were collected using cascade impactors from three sites that had the highest expected levels of dust, namely, the forefield, the end of the ore chute and an area close to workers at the crushing plant. The characteristics of most size distributions were very similar; they were moderately bimodal, with a boundary approximately 0.5 µm between the modes. The activity median aerodynamic diameter (AMAD) and geometric standard deviation (GSD) were obtained from the distributions beyond 0.39 µm, whereas the sizes of particles below 0.39 µm were not differentiated. Most AMAD and GSD values in the samples ranged between 3.5 and 10.5 µm and between 2.8 and 5.0, respectively. The geometric means of the AMADs and GSDs from all of the underground sampling sites were 4.2 µm and 4.4, respectively, and the geometric means of the AMADs and GSDs for the crushing plant samplings were 9.8 µm and 3.3, respectively. The weighted arithmetic mean of the AMADs was 4.9 µm, with a standard error of 0.7 µm, according to the numbers of workers at the workplaces. The activity proportion of the radon progeny to (226)Ra in the aerosol was 0.61.

Urinary excretion of uranium in adult inhabitants of the Czech Republic.

The main aim of this study was to determine and evaluate urinary excretion of uranium in the general public of the Czech Republic. This value should serve as a baseline for distinguishing possible increase in uranium content in population living near legacy sites of mining and processing uranium ores and also to help to distinguish the proportion of the uranium content in urine among uranium miners resulting from inhaled dust. The geometric mean of the uranium concentration in urine of 74 inhabitants of the Czech Republic was 0.091 mBq/L (7.4 ng/L) with the 95% confidence interval 0.071-0.12 mBq/L (5.7-9.6 ng/L) respectively. The geometric mean of the daily excretion was 0.15 mBq/d (12.4 ng/d) with the 95% confidence interval 0.12-0.20 mBq/d (9.5-16.1 ng/d) respectively. Despite the legacy of uranium mines and plants processing uranium ore in the Czech Republic, the levels of uranium in urine and therefore, also human body content of uranium, is similar to other countries, esp. Germany, Slovenia and USA. Significant difference in the daily urinary excretion of uranium was found between individuals using public supply and private water wells as a source of drinking water. Age dependence of daily urinary excretion of uranium was not found. Mean values and their range are comparable to other countries, esp. Germany, Slovenia and USA.

Monitoring radionuclides in the atmosphere over the Czech Republic after the Fukushima Nuclear Power Plant accident.

This paper presents the results of atmospheric radioactivity monitoring over the Czech Republic, as obtained by the Radiation Monitoring Network, following the Fukushima Dai-Ichi Nuclear Power Plant accident. Maximum values for (131)I were 5.6 mBq m(-3) in aerosol form and 13 mBq m(-3) in gaseous form. The maximum values for (134)Cs and (137)Cs were 0.64 and 0.72 mBq m(-3), respectively. The estimated effective half-time for removing the activity from the atmosphere was 6-7 d and 3.5 d for caesium and iodine, respectively. The gaseous-to-total activity ratios of (131)I ranged between 0.3 and 0.9, with an arithmetic mean value of 0.77. The mean value for the (134)Cs/(137)Cs ratios was close to 1.0. The effective inhalation dose due to the accident for an adult living in the Czech Republic was estimated at <4 × 10(-5) mSv, out of which the proportion of (131)I was 88%.

Particle size distribution of radioactive aerosols after the Fukushima and the Chernobyl accidents.

Following the Fukushima accident, a series of aerosol samples were taken between 24th March and 13th April 2011 by cascade impactors in the Czech Republic to obtain the size distribution of (131)I, (134)Cs, (137)Cs, and (7)Be aerosols. All distributions could be considered monomodal. The arithmetic means of the activity median aerodynamic diameters (AMADs) for artificial radionuclides and for (7)Be were 0.43 and 0.41 µm with GDSs 3.6 and 3.0, respectively. The time course of the AMADs of (134)Cs, (137)Cs and (7)Be in the sampled period showed a slight decrease at a significance level of 0.05, whereas the AMAD pertaining to (131)I increased at a significance level of 0.1. Results obtained after the Fukushima accident were compared with results obtained after the Chernobyl accident. The radionuclides released during the Chernobyl accident for which we determined the AMAD fell into two categories: refractory radionuclides ((140)Ba, (140)La (141)Ce, (144)Ce, (95)Zr and (95)Nb) and volatile radionuclides ((134)Cs, (137)Cs, (103)Ru, (106)Ru, (131)I, and (132)Te). The AMAD of the refractory radionuclides was approximately 3 times higher than the AMAD of the volatile radionuclides; nevertheless, the size distributions for volatile radionuclides having a mean AMAD value of 0.51 µm were very close to the distributions after the Fukushima accident.

Twelve years of follow up of cases with old 241Am internal contamination.

A group of workers internally contaminated with Am have been followed for about 12 years. The source of contamination was AmO2 powder used for production of AmBe neutron sources and other applications. The production of some radionuclide sources included chemical treatment of the original material, which transformed the americium into the nitrate, but mostly powder metallurgy was used for production of sources for smoke detectors. In vivo measurement of the workers was performed with two LEGe detectors placed near the head of the measured person. Calibration was performed with four different physical skull phantoms of different origin and a voxel phantom with Monte Carlo simulation, which was developed to fit the head sizes of individual persons. Samples of urine and feces were analyzed by means of radiochemical separation followed by alpha-spectrometry. Separation of 241Am from mineralized excreta was performed by combined anion exchange and extraction chromatographic techniques. As a tracer, 243Am was used. When the measured data (83 data on skeletal activity, activity in 389 bioassay samples) were compared with International Commission on Radiological Protection's and Leggett's biokinetic models of americium, it was found that in most cases, after more than 15 y since the intake, the excretion rate was lower (or skeletal activity higher) than predicted. On the other hand, the ratio of excreted activity in urine and feces agrees well with model predictions.

Dissolution behaviour of 238U, 234U and 230Th deposited on filters from personal dosemeters.

Kinetics of dissolution of (238)U, (234)U and (230)Th dust deposited on filters from personal alpha dosemeters was studied by means of a 26-d in vitro dissolution test with a serum ultrafiltrate simulant. Dosemeters had been used by miners at the uranium mine 'Dolní Rozínka' at Rozná, Czech Republic. The sampling flow-rate as declared by the producer is 4 l h(-1) and the sampling period is typically 1 month. Studied filters contained 125 +/- 6 mBq (238)U in equilibrium with (234)U and (230)Th; no (232)Th series nuclides were found. Half-time of rapid dissolution of 1.4 d for (238)U and (234)U and slow dissolution half-times of 173 and 116 d were found for (238)U and (234)U, respectively. No detectable dissolution of (230)Th was found.