Haluk Yücel

Measurement of thermal neutron cross-sections and resonance integrals for and by using –Be isotopic neutron source

Abstract Thermal neutron cross-sections and resonance integrals for the 71 Ga ( n , γ ) 72 Ga and 75 As ( n , γ ) 76 As reactions were measured by the activation method. The experimental samples with and without a cylindrical Cd shield case in 1 mm wall thickness were irradiated in an isotropic neutron field of the 241 Am –Be neutron source. The induced activities in the samples were measured by high-resolution γ-ray spectrometry with a calibrated reverse-electrode germanium detector. Thermal neutron cross-sections for 2200 m/s neutrons and resonance integrals for the 71 Ga ( n , γ ) 72 Ga and 75 As ( n , γ ) 76 As reactions have been obtained relative to the reference values, σ 0 =13.3±0.1 b and I 0 =14.0±0.3 b for the 55 Mn ( n , γ ) 56 Mn reaction as a single comparator. The necessary correction factors for gamma attenuation, thermal neutron and resonance neutron self-shielding effects were taken into account in the determinations. By defining Cd cut-off energy 0.55 eV , the results obtained were: σ 0 =4.41±0.18 b and I 0 =32.3±2.3 b for 71 Ga ( n , γ ) 72 Ga , and σ 0 =4.15±0.24 b and I 0 =63.5±3.8 b for 75 As ( n , γ ) 76 As . These results are discussed and compared with previous measurements and the evaluated data in ENDF/B-VI and JENDL-3.2. Thermal neutron cross-sections for 71 Ga ( n , γ ) 72 Ga and 75 As ( n , γ ) 76 As reactions are in good agreement with the recent measurements. However, the discrepancies between present results and some of old experimental data for resonance integrals for both reactions are within about 8–58%.

Use of the 1001 keV peak of 234mPa daughter of 238U in measurement of uranium concentration by HPGe gamma-ray spectrometry

Abstract For the direct gamma-ray spectrometric measurements of uranium concentrations in the samples, the use of 1001xa0keV peak of 234m Pa, second daughter of 238 U is emphasized. This “clean” peak is well resolved by HPGe detectors and gives accurate indication of uranium concentration in the samples without any self-absorption correction. The 1001xa0keV peak of 234m Pa in the 238 U chain is selected because it does not include any contribution from any other gamma emissions and does not have any interference with other peaks in the high-energy region even if the samples contain high amounts of thorium. The activity of 234m Pa is determined by calibrating a HpGe detector with uranium standards. The measurement of 1001xa0keV gamma-ray emission from 234m Pa by high-resolution gamma-ray spectrometry provides the basis for a reliable determination of 238 U in the samples. The results obtained from the 63.3xa0keV peak of 234 Th and those of the 1001xa0keV peak from 234m Pa in the 238 U chain for the uranium standards are compared with the certified values of the same samples. The results obtained from the measurements of 1001xa0keV peak from 234m Pa agreed to within 2–5% with the certified activity values of 238 U in the samples with uranium content ranging from 0.014 to 1.02xa0wt%. The results indicate that the uranium concentrations in the samples can be determined to within 5% error by about 14xa0h counting in a HpGe detector system.

Spectral interference corrections for the measurement of 238U in materials rich in thorium by a high resolution γ-ray spectrometry

In this study, the spectral interferences are investigated for the analytical peaks at 63.3 keV of (234)Th and 1001.0 keV of (234m)Pa, which are often used in the measurement of (238)U activity by the gamma-ray spectrometry. The correction methods are suggested to estimate the net peak areas of the gamma-rays overlapping the analytical peaks, due to the contribution of (232)Th that may not be negligible in materials rich in natural thorium. The activity results for the certified reference materials (CRMs) containing U and Th were measured with a well type Ge detector. The self-absorption and true coincidence-summing (TCS) effects were also taken into account in the measurements. It is found that ignoring the contributions of the interference gamma-rays of (232)Th and (235)U to the mixed peak at 63.3 keV of (234)Th ((238)U) leads to the remarkably large systematic influence of 0.8-122% in the measured (238)U activity, but in case of ignoring the contribution of (232)Th via the interference gamma-ray at 1000.7 keV of (228)Ac to the mixed peak at 1001 keV of (234m)Pa ((238)U) results in relatively smaller systematic influence of 0.05-3%, depending on thorium contents in the samples. The present results showed that the necessary correction for the spectral interferences besides self-absorption and TCS effects is also very important to obtain more accurate (238)U activity results. Additionally, if one ignores the contribution of (232)Th to both (238)U and (40)K activities in materials, the maximum systematic influence on the effective radiation dose is estimated to be ~6% and ~1% via the analytical peaks at 63.3 and 1001 keV for measurement of the (238)U activity, respectively.

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.

Dependence of photon interaction depth on linear attenuation coefficient in high pure germanium detectors

Abstract The present work is concerned with the construction of a semiempirical function d e ( μ , E γ ) of the effective photon interaction depth depending upon both the linear attenuation coefficient of Ge and γ-ray energy. The interaction depth results obtained from the measurements in two high purity germanium crystals, which are nearly equal in volume, have been fitted by using a function. The semiempirical function agrees with the measured interaction depth values on the average to within 3–4%. The knowledge of effective interaction depth of γ-rays in germanium detector is a useful parameter in order to calculate the absolute efficiency for any source-to-detector distance on the particular detector.

Uranium enrichment measurements using the intensity ratios of self-fluorescence X-rays to 92* keV gamma ray in UXKα 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.

Measurement of absolute intensity of 1001 keV gamma-ray of 234mPa

The 1001 keV γg-ray emission from 234mPa as an analytical peak has ever increasing importance in direct γg-ray spectrometric measurements of 238U content in samples with the development of high pure Ge detectors of larger crystal volumes and higher efficiency. In this study, γ-ray spectrometric measurement for the determination of the absolute intensity, Pγ, of 1001 keV γ-rays of 234mPa was carried out using powdered uranium samples and a new experimental value of 0.861±0.015% for Pγ of the 1001 keV γ-ray of 234mPa has been obtained. The present measured value is greater than most of the recent experimental results and the newly recommended value of 0.835±0.004% for Pg by 2.5 to 4%. The present result differs from the latest experimental value of 0.92±0.02% by 7%.

Automation of a pneumatic system by controlling a microcomputer equipped with a custom add on board for neutron activation analysis

Abstract An automated sample transfer system associated with a 3 × 592 GBq Amue5f8Be neutron source has been constructed at the Ankara Nuclear Research and Training Center (ANRTC) for Instrumental Neutron Activation Analysis (INAA) and Cyclic Instrumental Neutron Activation Analysis (CINAA). The pneumatic transfer system is controlled by an IBM PS/1 personal computer which is equipped with a custom add-on board for relevant hardware and control software written in Turbo Pascal. The system computer interactively works with a Multichannel Analyzer (MCA) for proper data acquisition. The sample transfer system also runs manually. The design and performance of the hardware and software are discussed.

Correction methodology for the spectral interfering γ-rays overlapping to the analytical peaks used in the analysis of 232Th

In the γ-ray spectrometric analysis of the radionuclides, a correction factor is generally required for the spectral interfering γ-rays in determining the net areas of the analytical peaks because some interfering γ-rays often might contribute to the analytical peaks of interest. In present study, a correction methodology for the spectral interfering γ-rays (CSI) is described. In particular, in the analysis of (232)Th contained in samples, the interfering γ-rays due to (226)Ra, (235)U, (238)U and their decay products often overlap to the peaks of interest from (232)Th decay products, and vise versa. For the validation of the proposed CSI method, several certified reference materials (CRM) containing U and Th were measured by using a 76.5% efficient n-type Ge detector. The required correction factors were quantified for spectral interference, self-absorption and true coincidence summing (TCS) effects for the relevant γ-rays. The measured results indicate that if one ignores the contributions of the interfering γ-rays to the analytical peaks at 583.2 keV of (208)Tl and 727.3 keV of (212)Bi, this leads to a significantly systematic influence on the resulted activities of (232)Th. The correction factors required for spectral interference and TCS effects are estimated to be ∼13.6% and ∼15.4% for 583.2 keV peak. For the 727.3 keV peak, the correction factor is estimated to be ∼15% for spectral interference, and ∼5% for the TCS effects at the presently used detection geometry. On the other hand, the measured results also indicate that ignoring the contribution of the interfering γ-rays to the areas of the analytical peaks at 860.6 keV of (208)Tl, 338.3 and 911.2 keV of (228)Ac does not lead to any significant systematic influence on the (232)Th analysis. Because these factors are remained generally less than ∼5%, i.e., within overall uncertainty limits. The present study also showed that in view of both the spectral interference and TCS effects, the cleaner analytical peaks are seen at 338.3 keV (11.25%) and 911.2 keV (26.13%) of (228)Ac when high resolution γ-rays spectrometry was used in the (232)Th activity measurements. Therefore, they can be adopted as the reference peaks in the (232)Th analysis.

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 40-100u2009kVp, 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 40-80u2009kVp and then showed a flat behavior at about 80 to 120u2009kVp. 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.