Exemption Clauses in Contracts: Historical and Comparative Law Analysis

"In general, exemption clauses are stipulations according to which one or both parties to a contract will not be liable in the case of breach1 of one or more of its (their) obligations. These clauses are also known as exculpatory, exoneration, limitation, or exclusion clauses. In the present paper I will use these words interchangeably. Exemption clauses aim to modify the rules of liability otherwise applicable in the case of breach, placing the obligor in a better position. The doctrine of freedom of contract (and the related doctrine of autonomy of will) is considered to be a fundamental principle of the law of contracts.2 Autonomy of will is, in addition, a justification of the presence of exemption clauses in contracts. But also in this field of the law of contracts a considerable movement towards the limitation of contractual freedom can be seen."(...

Testing and Calibration of CDs as Radon Detectors at Highly Variable Radon Concentrations and Temperatures

The application of the compact disk (CD) method for radon measurements at mines, caves and other workplaces needs testing under highly variable exposure conditions. We present the results from a blind comparison of CDs exposed in the Laboratory of Natural Radiation (Saelices el Chico, Spain). During the exposure the temperature varied from 6.5 to 24.9 °C (average 12.6 °C) and the 222Rn activity concentrations varied from <10 Bq m-3 to 147 kBq m-3. Good correspondence was observed between the integrated 222Rn activity concentration determined by the reference instruments in the laboratory (122,500 ± 6100 kBq h m-3) and that assessed by analysis of the CDs at a depth 80 µm beneath the front surface (118,000 ± 12,000 kBq h m-3) and at a depth of 120 µm (106,000 ± 12,000 kBq h m-3). The theoretical modeling of the CD response under variable temperature and radon concentration suggested that the small bias is probably due to the time variation of the calibration factor because of the time variations of the temperature.Funding: This research was funded by the European Metrology Programme for Innovation and Research (EMPIR), JRP-Contract 16ENV10 MetroRADON (http://www.euramet.org). The EMPIR initiative is co-funded by the, European Union’s Horizon 2020 research and innovation programme and the EMPIR Participating States

Approaches for reduction of the temperature bias on radon detectors packed in anti-thoron polymer membranes

International audiencePassive and active detectors used for radon ($^{222}$Rn) measurements can be influenced by thoron ($^{220}$Rn). Polyethylene membranes are very appropriate diffusion barriers for anti-thoron protection of such detectors. However, if not properly chosen, these membranes may not reduce efficiently the thoron influence or could introduce temperature bias in the radon sensitivity of the detectors. In this work three approaches are proposed dealing with the thoron influence and the temperature bias introduced by packing in polymer membranes. The approaches exploit a model of the radon and thoron diffusion transport through the membranes and the already known diffusion properties of the membranes to estimate the thoron influence and the temperature bias and to take them into account. The approaches are experimentally verified. It is shown that, in some cases, with the proper choice of membrane the thoron influence could be reduced down to few percents introducing only a few percents temperature bias. Additionally, in the cases when temperature bias is significant and cannot be avoided (the thoron bias in that cases is shown to be below 1%), the proposed approaches allow to estimate and to correct that bias

In quest of the optimal coincidence resolving time in TDCR LSC

International audienceThis paper presents studies of the influence of the coincidence resolving time on the activity calculated by the Triple-to-Double Coincidences Ratio (TDCR) method in Liquid Scintillation (LS) counting. Recently, published methods for the correction for accidental coincidences in TDCR counting open the possibility to use resolving times up to several µs, long enough not to miss true coincidences and to study the effects of delayed fluorescence.3H, 14C, 55Fe and 63Ni LS-sources in UltimaGold (UG), UG LLT and Toluene+PPO cocktails were measured using a TDCR counter connected to a digitizer working in list-mode. The necessary resolving time to include 99.9% of the logical sum of double (D) coincidences was found to be 1.2 µs for 3H, 1 µs for 55Fe and 500 ns for 63Ni in UG. The activity of all LS-sources was calculated using the TDCR method for resolving times from 10 ns to 2 µs and a significant dependence between the calculated activity and resolving time was observed. A dedicated Monte Carlo (MC) code was used to simulate list-mode data from TDCR measurements. The simulation results suggest that the 3H activity calculated by the TDCR method is overestimated regardless of the used resolving time if delayed fluorescence is present which is not described by the used ionization quenching function.Efficiency variation measurements of 3H in UG LLT show a strong dependence of the optimal kB parameter on the used resolving time: 85 µm/MeV at 40 ns and 110 µm/MeV at 200 ns, leading to 2.5% difference in calculated activity. In the framework of this study the efficiency variation methods by chemical quenching and gray filters were compared and a difference of 60 µm/MeV between the two was observed. The results from this article demonstrate that regardless of the available corrections for accidental coincidences, it is not advisable to increase the resolving time beyond what is necessary to register all prompt fluorescence events. Moreover, even for short coincidence resolving times, delayed fluorescence could have a significant influence on the activities calculated by the TDCR method

Evaluation of the accidental coincidence counting rates in TDCR counting

International audienceThis paper presents analytical and experimental methods to evaluate the accidental coincidence counting rates in a Triple-to-Double Coincidence Ratio (TDCR) Liquid Scintillation (LS) measurement. The experimental method we propose is based on the analysis of the distribution of the time delays between the first detected events in each photomultiplier tube. The underlying assumption is that events separated by several microseconds in time are not correlated, thus the accidental coincidence counting rates could be determined from the time interval distribution of uncorrelated events. The analytical evaluation of the accidental coincidence counting rates is based on the conditional probabilities for the occurrence of uncorrelated events within the same coincidence resolving time. The analytical and experimental evaluations of the rate of accidental coincidences give consistent results for TDCR measurements of H, 55Fe and 14C. The two methods were used to evaluate corrections for accidental coincidences for Monte Carlo (MC) generated list-mode files of H measurements with increasing activities. The counting rates, corrected for accidental coincidences using the analytical method, are within 0.29% of the MC reference up to 100 kBq and the corrected, using the experimental method, are within 0.21% up to 200 kBq

Time-domain based evaluation of detection efficiency in liquid scintillation counting

International audienceThis work explores the distribution of time intervals between signals from the photomultiplier tubes (PMTs) of a liquid scintillation counting (LSC) system when a scintillation burst caused by an ionizing particle is detected. This distribution is termed the cross-correlation distribution and it is shown that it contains information about the probability to detect a scintillation event. A theoretical model that describes the cross-correlation distribution is derived. The model can be used to estimate the mean number of detected photons in a LSC measurement, which allows the calculation of the detection efficiency. The theoretical findings are validated by Monte Carlo simulations and by experiments with low-energy beta-emitting and electron-capture radionuclides ($^3H$, $^{14}C$, $^{63}Ni$, $^{55}Fe$), with dedicated LSC systems and several commercial LSC cocktails. The results show that some of the parameters of the cross-correlation distribution such as the peak height or the kurtosis can be used as detection efficiency estimators or quenching indicators in LSC. Thus, although the time domain and the cross-correlation distribution have received little to no attention in the practice of LSC, they have the capacity to bring significant improvements in almost all LSC applications related to activity determination of low-energy beta-emitting and electron-capture radionuclides. The results also suggest concepts for the development of innovative LSC systems

Significance of the correction for accidental coincidences in liquid scintillation counting measurements

International audienceMethods for the evaluation of the accidental coincidences counting rates in Triple-to-Double Coincidences Ratio (TDCR) Liquid Scintillation (LS) measurements have been proposed recently [1]. The methods were used in this study where the corrections for accidental coincidences are applied to TDCR measurements of different radionuclides with a wide range of activities and in different measurement conditions. The contribution of the accidental coincidences to the true coincidences counting rates is evaluated. The corrections for accidental coincidences are also applied to TDCR measurements of 18F with counting rates from 430000 s-1 to 150 s-1. The contribution of the accidental coincidences for each order of magnitude of the counting rate is presented. The effect of the accidental coincidences to the evaluated half-life of 18F is presented and discussed.This study also shows how the corrections can be extended to a four-detector system as used in the Compton Source Efficiency Tracing (CSET) method [2] or the Zombies method [3]. For such detector systems, employing an external gamma-ray source and a Compton spectrometer, the counting rate in the LS must be very high to observe a reasonable counting rate in the gamma-ray detector. In this case the correction for accidental coincidences is far from negligible

Performance of portable TDCR systems developed at LNE-LNHB

International audienceThe triple to double coincidence ratio (TDCR) liquid scintillation measurement technique is commonly used in national metrology institutes (NMIs) to perform standardization of pure beta emitters. The LNE-LNHB historical device, RCTD1, is a quite large device, which has been developed and commonly used over the past 30 years with its associated electronics for measurements of various radionuclides. During the last 4 years LNE-LNHB has developed two new portable TDCR devices. Such portable instrumentation gives end-users access to a reference measurement method that can be used for a large number of radionuclides. It addresses a wide range of industrial and medical applications for radionuclide metrology, including calibrations of solutions containing short-lived radionuclides, avoidance of radioactive source transportation, and performing on-site comparison to promote radionuclide metrology harmonization. In this paper, we will present the newly developed portable TDCR liquid scintillation measurement systems. Two kinds of devices have been developed and designed at LNE-LNHB and built using fused deposition modelling (FDM) 3D printing: a mini-TDCR (25 cm diameter, 10 cm height) and a micro-TDCR (16 cm diameter, 10 cm height). After a detailed discussion of the design and the possibilities offered by 3D printing for their conception, this paper will present the performance of the devices obtained for several radionuclides. The results will be compared with the RCTD1 in order to validate the performance of the new devices. They exhibit improved performance, such as higher detection efficiency, and include various useful tools for proper on-site metrology. The first tests, which were performed in Orsay Hospital (CEA/SHFJ) and in another laboratory (IRSN), allowed us to show the very good overall performance of the systems including their outstanding linearity, which was tested in the range from 430 000 s$^{−1}$ down to 160 s$^{−1}$ in the double coincidences channel. Applications of the developed systems for high and low activity measurements are also discussed. Finally, the portable device has been used for half-life measurements in order to check for impurities in a radio-pharmaceutical solution

Measurement of the half-life of excited nuclear states using liquid scintillation counting

International audienceThis work presents measurements of the half-lives of excited nuclear states of 237Np and 57Fe using a liquid scintillation (LS) spectrometer and a gamma detector. A novel approach for the determination of the half-lives of some excited states is presented which uses only LS counting data from a detector with two PMTs. The lifetime of the 1st and 2nd excited states of 57Fe were obtained without the use of a gamma detector. The obtained value for the 59.54 keV level of 237Np is 67.60(25) ns. The obtained values for the 14.4 keV and 136.5 keV levels of 57Fe are 97.90(40) ns and 8.780(36) ns, respectively. The half-life results from this study are consistent with the average value found in the reference decay data tables and have a lower uncertainty

Investigation of the possible effect of the accidental coincidences correction on the determination of optimal kB value by efficiency variation with gray filters

International audienceRecently, analytical and experimental methods for evaluating accidental coincidences in TDCR measurements were proposed. It was shown that the correction for accidental coincidences depends on the experimental counting rates and that it is significant not only for measurements of high-activity sources but also in low-level LSC measurements. The efficiency variation by optical grey filters, on the other hand, is widely used for determining the optimal value of the Birks’ ionization quenching parameter kB, which has the major contribution to the uncertainty in the TDCR standardization of low-energy β-emitters like 3H.Since there is a change in the counting rates between measurements of a sample with different grey filters, it is interesting to investigate the effect of accidental coincidences on the choice of the proper kB value. This question is of practical relevance because it is interesting to assess the correctness of the estimates of kB applied in the past when no accidental coincidence corrections have been applied.To achieve this goal, we have re-analyzed a large set of experimental data of kB determinations by applying and not applying analytical accidental coincidence corrections. Examples of the obtained results are shown in Fig. 1. Overall, at this point, we do not see a statistically significant effect of the accidental coincidence correction on the optimal kB value. These results verify the choices of kB by efficiency variation by grey filters made in the past. More results for different nuclides and TDCR systems will be presented