ESTIMATION OF RADIOLOGICAL EXPOSURE LEVELS IN A MINING AREA BASED ON 238U, 226Ra, 232Th and 40K ACTIVITY MEASUREMENTS: A CASE STUDY FOR BEYLIKOVA-SIVRIHISAR COMPLEX ORE SITE IN TURKEY

The study estimated the radiological exposure levels in a mining area for miners in the Beylikova-Sivrihisar (Turkey) complex ore site containing 238U, 226Ra and 232Th. Sixty samples were collected from the study area based on a geologic map. The radionuclide activities were measured using a 78.5% efficient n-type HPGe detector. The measured mean activities were 1871 ± 38 Bq kg-1 for 238U, 1749 ± 5 Bq kg-1 for 226Ra, 3467 ± 9 Bq kg-1 for 232Th and 309 ± 2 Bq kg-1 for 40K. From the measured results, the external effective dose was calculated to be max. 3.80 ± 0.03 mSv y-1 (mean: 2.04 ± 0.03 mSv y-1) for inside gallery and max. 7.59 ± 0.05 mSv y-1 (mean: 4.08 ± 0.05 mSv y-1) for outdoor. Additionally, the external exposure index was calculated to be Hex = 33.5 ± 0.2(mean: 18.2 ± 0.3) and internal exposure index to be Hin = 45.9 ± 0.3 (mean: 22.9 ± 0.4). The results indicate that additional radiation protection measures should be taken during the mining process if an opencast mining is implemented in Beylikova complex ore deposit.

Determination of the energy dependence of the BC-408 plastic scintillation detector in medium energy x-ray beams

The energy dependence of the response of BC-408 plastic scintillator (PS), an approximately water-equivalent material, has been investigated by employing standardized x-ray beams. IEC RQA and ISO N series x-ray beam qualities, in the range of 40-100 kVp, were calibrated using a PTW-type ionization chamber. The energy response of a thick BC-408 PS detector was measured using the multichannel pulse height analysis method. The response of BC-408 PS increased gradually with increasing energy in the energy range of 40-80 kVp and then showed a flat behavior at about 80 to 120 kVp. This might be due to the self-attenuation of scintillation light by the scintillator itself and may also be partly due to the ionization quenching, leading to a reduction in the intensity of the light output from the scintillator. The results indicated that the sensitivity drop in BC-408 PS material at lower photon energies may be overcome by adding some high-Z elements to its polyvinyltoluene (PVT) base. The material modification may compensate for the drop in the response at lower photon energies. Thus plastic scintillation dosimetry is potentially suitable for applications in diagnostic radiology.

Measurements on the spectroscopic performance of CdZnTe coplanar grid detectors

A performance study was performed for CdZnTe coplanar grid (CPG) detectors when used as γ-ray spectrometers. The detectors have the crystal volumes of 1, 1.6875 and 2.25 cm(3), respectively. Time stability of each CdZnTe CPG detector was investigated in a long-term operation (time span of 0.25 to about 100 h). The spectroscopic performances were measured at different bias voltages and at various photon energies ranging from 59.6 keV ((241)Am) to 1332.5 keV ((60)Co) for each detector, and evaluated by using the following parameters: energy resolution in FWHM, peak tailing in peak-to-valley (P/V) ratio and in FWHM/FW.25 M ratio, and photofraction using the acquired γ-ray spectra. No polarization effect was observed in terms of count rate, energy resolution and peak centroid shift. The obtained results indicate that better time stability and excellent spectroscopic performances of the present CdZnTe CPG detectors are shown for a room temperature γ-ray spectroscopy.

Methods for spectral interference corrections for direct measurements of 234U and 230Th in materials by gamma-ray spectrometry

When the high-resolution gamma-ray spectrometry was used in the analysis of (234)U and (230)Th in samples, there is a much more need to correct for the measured activity results of (234)U and (230)Th mainly due to self-absorption effects and the interfering lines from (226)Ra, (235)U, (238)U and their decay products that often might be present in the samples. Therefore, in the present study, the methods for the spectral interference corrections for the analytical peaks of (234)U and (230)Th are suggested to take into account the contributions of the overlapping gamma rays to these peaks. For the method validation, direct gamma-ray spectrometric measurements were carried out using certified reference materials (CRM) by use of a 76.5 % n-type Ge detector. The activities measured for the CRM samples were corrected for spectral interferences, self-absorption and true coincidence-summing (TCS) effects. The obtained results indicate that ignoring of the contribution of the interference gamma rays to the main analytical peak at 53.2 keV of (234)U leads to a lager systematic error of 87.3-90.4 % for the measured activities of (234)U, and similarly if one ignores the contributions of the interference gamma rays to the main analytical peak at 67.7 keV of (230)Th, this leads to a much smaller systematic error of 2.1-2.7 % for the activities of (230)Th. Therefore, the required correction factors for spectral interferences to the analytical peaks of (234)U and (230)Th are not negligible and thus they should also be considered besides necessary self-absorption factors to determine more accurate activities in the samples. On the other hand, it is estimated that although the TCS effects on the main analytical peaks of both (234)U and (230)Th are negligibly small, those TCS correction factors for their interference gamma rays to these peaks should be taken into account when direct measurements are performed in a close-counting geometry condition. Otherwise, the resulted activities can have serious erroneous results for both (234)U and (230)Th while using gamma-ray spectrometry, thereby leading to inaccuracies in their derived quantities, for instance, the corresponding age determinations of the samples.

Uranium enrichment measurements using the intensity ratios of self-fluorescence X-rays to 92* keV gamma ray in UXK alpha spectral region

In this paper, the known multigroup gamma-ray analysis method for uranium (MGAU) as one of the non-destructive gamma-ray spectrometry methods has been applied to certified reference nuclear materials (depleted, natural and enriched uranium) containing (235)U isotope in the range of 0.32-4.51% atom (235)U. Its analysis gives incorrect results for the low component (235)U in depleted and natural uranium samples where the build-up of the decay products begins to interfere with the analysis. The results reveal that the build-up of decay products seems to be significant and thus the algorithms for the presence of decay products should be improved to resulting in the correct enrichment value. For instance, for the case of (235)U analysis in depleted uranium or natural ore samples, self-induced X-rays such as 94.6 keV and 98.4 keV lying in UXK(alpha) spectral region used by MGAU can be excluded from the calculation. Because the significant increases have been observed in the intensities of uranium self-induced X-rays due to gamma-ray emissions with above 100 keV energy arising from decay products of (238)U and (235)U and these parents. Instead, the use of calibration curve to be made between the intensity ratios of self-fluorescence X-rays to 92(*)keV gamma-ray and the certified (235)U abundances is suggested for the determination of (235)U when higher amounts of decay products are detected in the gamma-ray spectrum acquired for the MGAU analysis.

The applicability of MGA method for depleted and natural uranium isotopic analysis in the presence of actinides (232Th, 237Np, 233Pa and 241Am)

The multi-group analysis (MGA) method for the determination of uranium isotopic abundances in depleted uranium (DU) and natural uranium (NU) samples is applied in this study. A set of non-destructive gamma-ray measurements of DU and NU samples were performed using a planar Ge detector. The relative abundances of 235U and 238U isotopes were compared with the declared values of the standards. The relative abundance for 235U obtained by MGA for a "clean" DU or NU sample with a content of uranium>1wt% is determined with an accuracy of about +/-5%. However, when several actinides such as 232Th, 237Np, 233Pa and 241Am are present along with uranium isotopes simulating "dirty" DU or NU, it has been observed that MGA method gives erroneous results. The 235U abundance results for the samples were 6-25 times higher than the declared values in the presence of above-mentioned actinides, since MGA is utilized the X-ray and gamma-ray peaks in the 80-130 keV energy region, covering XKalpha and XKbeta regions. After the least-squares fitting of the spectra, it is found that the increases in the intensities of the X-ray and gamma-ray peaks of uranium are remarkably larger in the complex 80-130 keV region. On the other hand, it is observed that the interferences of the actinide peaks are relatively less dominant in the higher gamma-ray region of 130-300 keV. The results imply the need for dirty DU and NU samples that the MGA method should utilize the higher energy gamma-rays (up to 1001 keV of (234m)Pa) combined with lower energies of the spectra, which may be collected in a two detector mode (a planar Ge and a high efficient coaxial Ge).

Natural radioactivity measurement in pumice samples used raw materials in Turkey

The activity concentrations of 232Th, 226Ra, and 40K in different pumice samples have been determined by high-resolution gamma-ray spectrometry using a 110% HpGe detector. The radium equivalent activities (Raeq), external hazard index (Hex), and internal hazard index (Hin) associated with the natural radionuclides and representative level index (Igamma r) are calculated to assess the radiation hazard of the natural radioactivity in the pumice samples. The mean values of the measured radioactivity concentrations of 232Th, 226Ra, and 40K for pumice samples from the region of lakes (ROL) are 232.4+/-8.0, 196.9+/-7.8, and 1325.8+/-20.4 Bqkg(-1) and for pumice samples from Cukurova region (CR) 16.3+/-4.0, 16.1+/-4.9, and 479.7+/-170.4 Bqkg(-1), respectively. The calculated Raeq values vary from 435.9+/-12.5 to 883.6+/-41.5 Bqkg(-1) with a mean of 630.9+/-20.2 Bqkg(-1) for the ROL samples and from 49.7+/-3.3 to 101.9+/-7.2 Bqkg(-1) with a mean of 76.3+/-23.7 Bqkg(-1) for the CR samples. For the ROL samples, Raeq are above the limit of 370 Bqkg(-1), equivalent to external gamma dose of 1.5 mSv yr(-1), recommended for the safe use of construction materials by NEA-OECD, while for the CR samples, Raeq values are lower than the limit.

Pharmacological study of the chicken's monocular optokinetic nystagmus: effects of GABAergic agonist and antagonists

When injected into the chicken open eye, the GABA-agonist THIP and the GABA-antagonists bicuculline and picrotoxin induced spontaneous eye movements in nasal-temporal (N-T) and in temporal-nasal (T-N) direction, respectively. These spontaneous movements were scarcely modulated by optokinetic stimulation, irrespective of the direction of stimulation. It is suggested that they are due to the suppression of directional selectivity of retinal ganglion cells. When injected into the closed eye, GABAergic drugs did not produce spontaneous nystagmus. THIP provoked a reduction of the N-T component, without modifying the T-N one, while GABA antagonists induced a significant increase in OKN performance, especially for the N-T direction of stimulation. In these conditions, picrotoxin also provoked an increase in the duration of both components of optokinetic after nystagmus, indicating a direct effect of the drug upon the velocity-storage system.

Pharmacological study of the chicken's monocular optokinetic nystagmus: involvement of the ON retinal channel evidenced by the glutamatergic separation of ON and OFF pathways

The chicken's monocular optokinetic nystagmus (OKN), recorded by the magnetic search coil technique, displays a directional asymmetry, the temporal-nasal (T-N) stimulation being more efficient than the nasal-temporal (N-T) one to evoke the reflex. The intravitreal administration of APB, a glutamate agonist which selectively blocks the ON retinal channel strongly reduced the eye monocular OKN; it also induced spontaneous eye movements in the T-N direction. The intravitreal injection of PDA another glutamate analog, which reduces the OFF channel, while increasing the activity of the ON channel, induced a large increase in OKN velocity gain, especially for a N-T stimulation at the lowest drum speeds. These results indicate the main involvement of the ON retinal channel in the OKN genesis and the inhibitory effect of the OFF channel upon this oculomotor reflex.

Glutamatergic separation of ON and OFF retinal channels: possible modulation by glycine and acetylcholine

When intravitreally injected into the frog in vivo, 2-amino-4-phosphonobutyrate (APB) and cis-2,3-piperidine dicarboxylic acid (PDA) showed opposite effects on ON and OFF retinal channels: APB abolished the ON responses in the electroretinogram and in ganglion cell activity, and increased OFF responses. At the same time the receptive field area was enlarged, and the inhibition exerted by the surround was suppressed. A cholinergic/glycinergic loop involving amacrine cells was suggested to be the pathway of the inhibitory ON input upon the OFF channel. PDA abolished the OFF responses in the ERG and in ganglion cell activity, while increasing the ON response in the ERG and decreasing the ganglion cell sensitivity at ON. The receptive field area was not modified, but the inhibition exerted by the surround was suppressed, probably by a blockade of horizontal cell glutamate receptors.