Measurement of the branching ratio related to the internal pair production of Y-90.

The aim of the work is to determine the number of positron-electron pair creation in the E0 transition between the 1760.7 keV level and the ground level of the Zr-90 nucleus at the Y-90 decay. The number of conversions is determined from the number of 511 keV photons originating from positron annihilation corrected for the annihilation of positrons in flight. Emission of annihilation photons was determined from the measurements of 511 keV full-energy peak on two calibrated high-purity germanium detectors. The measurements were performed with two sources of a different construction. The first source was a 1 ml ampoule filled with Sr-90 solution (in equilibrium with Y-90) with an activity of 38.041 MBq inserted into an aluminum absorber. The other source was the evaporation residue of the Sr-90 solution (in equilibrium with Y-90) in a polyethylene absorber. In both cases, the annihilation of positrons occurred in the source materials. The efficiency of 511 keV photon detection was determined by Monte Carlo calculation, where the source was defined as a theoretical continuous positron spectrum with a maximum energy of 738 keV. The branching ratio related to the internal pair production during Y-90 decay was determined to be (3.26 ±â€¯0.04) × 10-5 pairs/decay.

Emission probability measurement of γ- and X- rays in Ra-226 and Pb-210 decay.

The emission intensities of 186.21keV, 46.54keV, XL(Bi) and XK(Rn) photons were measured with calibrated HPGe detectors. The efficiency was computed with the MCNP Monte Carlo code and validated using experimental points. Sources of Ra-226 were prepared from two different radioactive materials. The X-ray emission intensities in Ra-226 decay were determined without X-rays from the daughter decay products using a radon emanation source. The standard CMI source with Pb-210 was used and compared with a source prepared from the NPL solution delivered under the EMRP project "Metrology for processing materials with high natural radioactivity - MetroNORM".

(60)Co in cast steel matrix: A European interlaboratory comparison for the characterisation of new activity standards for calibration of gamma-ray spectrometers in metallurgy.

Two series of activity standards of (60)Co in cast steel matrix, developed for the calibration of gamma-ray spectrometry systems in the metallurgical sector, were characterised using a European interlaboratory comparison among twelve National Metrology Institutes and one international organisation. The first standard, consisting of 14 disc shaped samples, was cast from steel contaminated during production ("originally"), and the second, consisting of 15 similar discs, from artificially-contaminated ("spiked") steel. The reference activity concentrations of (60)Co in the cast steel standards were (1.077±0.019) Bqg(-1) on 1 January 2013 12h00 UT and (1.483±0.022) Bqg(-1) on 1 June 2013 12h00 UT, respectively.

Activity standardization, photon emission probabilities and half-life measurements of (177)Lu.

Activity standardization of (177)Lu and measurement of two nuclear parameters were done. Activity standardization of (177)Lu was done utilizing the 4πß-γ coincidence method with a combined standard uncertainty of 0.28%. Emission probability of 112.95keV and 208.37keV was measured by calibrated spectrometer with HPGe detector. The efficiency was computed with MCNP code and validated using experimental points. Half-life was derived from prolonged measurement of peak area by three different spectrometer systems and also from measurement with ionization chamber.

Disease activity is an important factor for indeterminate interferon-γ release assay results in children with inflammatory bowel disease.

BACKGROUND: Interferon-γ release assay (IGRA) is widely used for screening of latent tuberculosis (TB) before and during biological therapy (BT). An indeterminate result of IGRA represents a limitation in the management of inflammatory bowel disease (IBD). Data on factors influencing IGRA results are scarce in children. The aim of the study was to identify factors influencing IGRA results in children with IBD. METHODS: Seventy-two children with IBD (59 Crohn disease, 11 ulcerative colitis, 2 IBD-unclassified) indicated for BT were tested for TB infection (history, TB skin test, chest radiograph, IGRA; QuantiFERON-TB Gold in tube [QFT]) and consecutively retested using QFT in 1-year intervals. RESULTS: We recorded 165 results of QFT (3% positive, 87% negative, and 10% indeterminate results). During follow-up we identified 4 conversions of negative QFT to positivity (3%) and 4 reversions (4%). Patients with indeterminate results of QFT had significantly lower actual weight-for-height z score (P = 0.022), higher platelet count (P = 0.00017), and lower levels of serum albumin (P = 0.015) compared with patients with positive or negative QFT. Indeterminate QFT was associated with corticosteroid treatment, BT, and disease activity, but not with treatment by immunomodulators. In a subanalysis of patients with Crohn disease alone, Pediatric Crohn's Disease Activity Index was identified as single independent risk factor for indeterminate results (P = 0.00037). CONCLUSIONS: Although corticosteroid treatment is traditionally considered to be the main risk factor for indeterminate results of IGRA, the disease activity of IBD has even more profound effects on the results.

Comparison of properties of digital spectrometer systems.

We have tested two digital spectrometer systems, the DSP 9660 and Lynx(®) modules, connected to a HPGe detector. Lynx(®) is a fully integrated 32K channel signal analyzer based on digital signal processing techniques, which offers advanced digital stabilization. The model DSP 9660 digitalizes the signal directly at a very high sampling rate. The evaluated properties were integral nonlinearity, differential linearity, channel profiles, resolution and throughput. We found that the DSP system has slightly inferior resolution and throughput in comparison with the Lynx(®) system.

Calibration of stack monitors for measurement of noble gases in nuclear facilities.

In nuclear facilities stack monitors are used for the measurement of the volumetric activity of noble gases. Spectrometric measurement is needed because the content of stack effluents is always a mixture of radionuclides. In some nuclear power plants new types of monitors were installed based on HPGe detectors. For efficiency calibration a standard with the radionuclide Xe-127 was developed and calibration curve constructed in the energy range 81 keV-1293 keV. Experiental efficiencies were checked using an MC model.

Total efficiency of GE detectors--dead layer signal effect.

Two types of detectors (GC 4018 and BE 5030) were compared regarding the signal from the outer dead layer of the detector. Gamma-spectra of Am-241 were acquired with various delays against the starting signal from an alpha LS probe. Coincidence spectra from both detectors were different. The dead-layer signal does not increase the full-energy peak efficiency but it increases the total efficiency, as it was demonstrated by the reconstruction of Am-241 spectra for both detectors.

Gaseous standards preparation with the radionuclide Ar-41 for stack monitors calibration and verification in nuclear facilities.

The Czech Metrology Institute performs calibration and verification of noble gases stack monitors in nuclear power plants and nuclear research facilities. Together with Kr-85 and Xe-133, the radionuclide Ar-41 is measured using HPGe detectors and its activity is determined using a gamma-ray peak at 1293keV. The counting efficiency used in these measurements was calculated by the Monte Carlo method using the MCNP code. Radioactive gas standard is prepared by irradiation of argon in a high-pressure vessel by a Cf-252 neutron generator. The inner shape and thickness of the cylinder walls were determined by radiography. The argon volume under normal conditions is determined from the high-pressure vessel volume and by a precise gas pressure measurement. As a result, the activity concentration of Ar-41 at normal conditions is certified.

Experimental and MC determination of HPGe detector efficiency in the 40-2754 keV energy range for measuring point source geometry with the source-to-detector distance of 25 cm.

A precise model of a 40% relative efficiency p-type HPGe detector was created for photon detection efficiency calculation using the MCNP code. All detector parameters were determined by different experiments. No experimental calibration points were used for the modification of detector parameters. The model was validated by comparing calculated and experimental full energy peak efficiencies in the 40-2754 keV energy range, for point-source geometry with the source-to-detector distance of 25 cm.

Testing of properties of digital modules used in gamma-ray spectrometry.

The properties of digital modules (analog-to-digital converters (ADC), digital signal processor (DSP)) in spectrometric chain are the decisive factors which affect the quality of spectrometric measurements. Several properties, integral and differential linearity, channel profiles and throughput, of various ADC and DSP models by CANBERRA were tested.

Determination of corrections to true summations of photons for measurements in Marinelli beakers.

This paper describes a method of determination of correction factors for the true summation effect of photons for measurement of activity of radionuclides emitting gamma radiation. The method was tested with Marinelli beakers samples measured with coaxial germanium detectors. The advantage of this method is its simplicity since it is not necessary to determine the curves of total efficiency for each detector. The correction factor for the particular peak is determined by means of a detector index which is calculated from one of the measurements with a calibration standard.