Calibration of surface contamination monitors for the detection of iodine incorporation in the thyroid gland

In Switzerland, individuals exposed to the risk of activity intake are required to perform regular monitoring. Monitoring consists in a screening measurement and is meant to be performed using commonly available laboratory instruments. More particularly, iodine intake is measured using a surface contamination monitor. The goal of the present paper is to report the calibration method developed for thyroid screening instruments. It consists of measuring the instrument response to a known activity located in the thyroid gland of a standard neck phantom. One issue of this procedure remains that the iodine radioisotopes have a short half-life. Therefore, the adequacy and limitations to simulate the short-lived radionuclides with so-called mock radionuclides of longer half-life were also evaluated. In light of the results, it has been decided to use only the appropriate iodine sources to perform the calibratio

Variability of radioiodine measurements in the thyroid

Monte Carlo simulations were carried out to study the response of a thyroid monitor for measuring intake activities of 125I and 131I. The aim of the study was 3-fold: to cross-validate the Monte Carlo simulation programs, to study the response of the detector using different phantoms and to study the effects of anatomical variations. Simulations were performed using the Swiss reference phantom and several voxelised phantoms. Determining the position of the thyroid is crucial for an accurate determination of radiological risks. The detector response using the Swiss reference phantom was in fairly good agreement with the response obtained using adult voxelised phantoms for 131I, but should be revised for a better calibration for 125I and for any measurements taken on paediatric patient

Activity standardisation of 177Lu.

<sup>177</sup> Lu decays through low-energy β <sup>-</sup> - and γ-emissions in addition to conversion and Auger electrons. To support the use of this radiopharmaceutical in Switzerland, a <sup>177</sup> Lu solution was standardised using the β-γ coincidence technique, as well as the TDCR method. The solution had no <sup>177m</sup> Lu impurity. Primary coincidence measurements, with plastic scintillators for beta detection, were carried out using both analogue and digital electronics. TDCR measurements using only defocusing were also made. Monte Carlo calculations were used to compute the detection efficiency. The coincidence measurements with both analogue and digital electronics are compatible within one standard uncertainty, but they are lower than (and discrepant with) the TDCR measurements. An ampoule of this solution was submitted to the BIPM as a contribution to the Système International de Référence

Silane depletion dependent ion bombardment and material quality of microcrystalline silicon deposited by VHF-PECVD

Microcrystalline silicon is a composite material embedding silicon nanocrystals in an amorphous matrix [1]. It has attracted much research efforts in the photovoltaic domain [2], because of its potential for integration in a tandem cell concept as bottom cell with an amorphous silicon top cell. Efficiencies of micromorph tandem cells and modules well above 10% have thus been demonstrated [3]. However, due to its complex structure that depends on deposition conditions [1, 4] and substrate properties [5], and due to the difficulty of characterizing plasma deposition regimes, the impact of these parameters on the microcrystalline material quality is still an open field of research. In this paper, microcrystalline silicon thin films are deposited in different conditions of silane depletion following a recent publication [6] and the material quality is investigated. It is shown that by simply reducing the hydrogen flow, the microcrystalline material quality can be greatly improved. This improvement is correlated with the reduced ion bombardment energy in high depletion regimes, leading to lower defect densities in the microcrystalline intrinsic layer

Activity standardisation of ³²Si at IRA-METAS.

This work explores the primary activity standardisation of <sup>32</sup> Si as part of the SINCHRON project that aims at filling the geochronological dating gap by making a new precise measurement of the half-life of this nuclide. The stability of some of the radioactive test solutions, providing <sup>32</sup> Si as hexafluorosilicic acid (H <sub>2</sub> <sup>32</sup> SiF <sub>6</sub> ), was monitored over long periods, pointing to the adequate sample composition and vial type to ensure stability. These solutions were standardised using liquid scintillation counting with the triple to double coincidence ratio (TDCR) technique and the CIEMAT-NIST efficiency tracing (CNET) method. Complementary backup measurements, using 4πβ-γ coincidence counting with <sup>60</sup> Co as a tracer, were performed with both liquid and plastic scintillation for beta detection. While <sup>60</sup> Co coincidence tracing with a liquid scintillator predicted activities in agreement with the TDCR and CNET determinations, using plastic scintillation turned out to be unfeasible as the addition of lanthanum nitrate and ammonia to fix the silicon during the drying process generated large crystals that compromised the linearity of the efficiency function

Influence of pressure and silane depletion on microcrystalline silicon material quality and solar cell performance

Hydrogenated microcrystalline silicon growth by very high frequency plasma-enhanced chemical vapor deposition is investigated in an industrial-type parallel plate R&D KAI (TM) reactor to study the influence of pressure and silane depletion on material quality. Single junction solar cells with intrinsic layers prepared at high pressures and in high silane depletion conditions exhibit remarkable improvements, reaching 8.2% efficiency. Further analyses show that better cell performances are linked to a significant reduction of the bulk defect density in intrinsic layers. These results can be partly attributed to lower ion bombardment energies due to higher pressures and silane depletion conditions, improving the microcrystalline material quality. Layer amorphization with increasing power density is observed at low pressure and in low silane depletion conditions. A simple model for the average ion energy shows that ion energy estimates are consistent with the amorphization process observed experimentally. Finally, the material quality of a novel regime for high rate deposition is reviewed on the basis of these finding

Calibration of the Politrack® system based on CR39 solid-state nuclear track detectors for passive indoor radon concentration measurements

Swiss national requirements for measuring radon gas exposures demand a lower detection limit of 50 kBq h m−3, representing the Swiss concentration average of 70 Bq m−3 over a 1-month period. A solid-state nuclear track detector (SSNTD) system (Politrack, Mi.am s.r.l., Italy) has been acquired to fulfil these requirements. This work was aimed at the calibration of the Politrack system with traceability to international standards and the development of a procedure to check the stability of the system. A total of 275 SSNTDs was exposed to 11 different radon exposures in the radon chamber of the Secondary Calibration Laboratory at the Paul Scherrer Institute, Switzerland. The exposures ranged from 50 to 15000 kBq h m−3. For each exposure of 20 detectors, 5 SSNTDs were used to monitor possible background exposures during transport and storage. The response curve and the calibration factor of the whole system were determined using a Monte Carlo fitting procedure. A device to produce CR39 samples with a reference number of tracks using a 241Am source was developed for checking the long-term stability of the Politrack system. The characteristic limits for the detection of a possible system drift were determined following ISO Standard 1192

Effect of conventional and ultra-high dose rate "FLASH" irradiations on preclinical tumour models: A systematic analysis: Tumour response to CONV and UHDR irradiation.

When compared to conventional dose rate irradiation (CONV), ultra-high dose rate irradiation (UHDR) has shown superior normal tissue sparing. However, a clinically relevant widening of the therapeutic window by UHDR, termed "FLASH effect", also depends on the tumour toxicity obtained by UHDR. Based on a combined analysis of published literature, the current study re-examines the hypothesis of tumour isoefficacy for UHDR versus CONV and aims to identify potential knowledge gaps to inspire future in vivo studies. A systematic literature search identified publications assessing in vivo tumour responses comparing UHDR and CONV. Qualitative and quantitative analyses were performed, including combined analyses of tumour growth and survival data. We identified 66 data sets from 15 publications that compared UHDR and CONV for tumour efficacy. The median number of animals per group was 9 (range: 3-15) and the median follow-up period was 30.5 (range: 11-230) days after the first irradiation. Tumour growth assays were the predominant model used. Combined statistical analyses of tumour growth and survival data are consistent with UHDR isoefficacy compared to CONV. Only one study determined tumour-controlling dose (TCD <sub>50</sub> ) and reported statistically non-significant differences. The combined quantitative analyses of tumour responses support the assumption of UHDR isoefficacy compared to CONV. However, the comparisons are primarily based on heterogeneous tumour growth assays with limited numbers of animals and short follow-up, and most studies do not assess long-term tumour control probability. Therefore, the assays may be insensitive in resolving smaller response differences, such as responses of radio-resistant tumour sub-clones. Hence, tumour cure experiments, including additional TCD <sub>50</sub> experiments, are needed to confirm the assumption of isoeffectiveness in curative settings