Monte Carlo codes have been widely used at the Laboratoire national Henri Becquerel (LNE-LNHB) for the last twenty years. They contribute to the establishment of national dosimetric references. In this paper, two main dosimetric quantities are calculated using Monte Carlo modelling in the field of medical physics: the absorbed dose and the kerma. Further discussions of the problems encountered are also presented.

The manganese bath technique is the reference method for the calibration of neutron source emission rates. It is used to calibrate neutron sources using radionuclides in terms of neutron emission rate under 4p sr. The neutron source to be measured is immersed in a manganese sulphate solution where the emitted neutrons interact with the elements of the bath. In a typical configuration, approximately half of the neutrons lead to the creation of ⁵⁶Mn via the ⁵⁵Mn(n, γ) capture reaction. This radionuclide has a half-life of approximately 2.6 h and the bath reaches saturation when the number of nuclei decaying is equal to the number of nuclei created per unit time. The neutron emission rate from the source can then be deduced from the ⁵⁶Mn activity at saturation, assuming proper modelling of the nuclear reactions occurring within the bath. The manganese bath facility has been recently refurbished in order to comply with appropriate safety and radioprotection regulations. This has lead to the upgrading of both the measurement methodology and the modelling of the bath, and a study on the development of a new detector for the on-line measurement of the manganese activity was developed. This new detector uses the 4πß-γ coincidence measurement method. The beta channel consists of photomultipliers tubes for the detection of Cerenkov light, and the γ channel uses a scintillation detector. The advantage of this measurement method is that it allows the determination of the bath activity without any prior calibration. A detector has been built and the results obtained have been compared to those from a primary measurement method already in use at LNE-LNHB. Furthermore, a comparison of the Monte-Carlo simulation results using GEANT4, MCNPX and FLUKA has been undertaken. This comparison revealed some discrepancies between the codes and uncertainty factors, such as the modeling of the neutron emission and the choice of the cross-section library.

In this paper we present the developments conducted at LNE-LNHB with the aim of improving the knowledge of the shapes of beta spectra, concerning the theoretical calculation of the spectra as well as their experimental determination by means of cryogenic detectors. The theoretical calculation comprises a screening correction that avoids the non-physical discontinuity present in the standard correction, as well as a correction of the exchange effect that is usually not taken into account and has a strong impact on the spectra of ⁶³Ni and ²⁴¹Pu. These calculations are compared with experimental spectra obtained with metallic magnetic calorimeters, a class of cryogenic detectors. The beta emitter is enclosed in the absorber of these detectors which offer high detection efficiency, high energy resolution and a very low energy detection threshold. The measured spectra of ⁶³Ni and ²⁴¹Pu confirm the correctness of the theoretical spectra, in particular the calculation of the exchange effect down to very low energies that have been explored for the first time.

Nowadays, the absorbed dose to water for kilovoltage X-ray beams is determined from standards in terms of air-kerma by application of international dosimetry protocols. New standards in terms of absorbed dose to water have just been established for these beams at the LNELNHB. A specific calorimeter was developed to do measurements at low depth in water, in order to fulfill the reference conditions required by the international dosimetry protocols for medium-energy X-ray. This new calorimeter was used to measure the absorbed dose rate in water at a depth of 2 cm for six medium-energy X-ray reference beams with a tube potential from 80 kV to 300 kV. The relative standard uncertainty obtained on the absorbed dose rate by water calorimetry is lower than 0.8%, whereas the one given by application of protocols based on airkerma is around 2.5%.

The monitoring of environmental radioactivity is important for public health protection. In France, environmental radioactivity is specifically monitored by a network of certified laboratories. Indeed the Nuclear Safety Authority (ASN) delivers three to five year governmental agreements to each laboratory provided that it succeeds in proficiency tests (PTs) organized by the Institute for Radiological Protection and Nuclear Safety (IRSN). To ensure a direct traceability chain in radioactivity measurements, the Laboratoire National Henri Becquerel (LNE-LNHB), as the French national laboratory for radionuclide metrology, has been organizing national PTs for more than 40 years. LNE-LNHB also regularly realizes specific PTs to train the laboratories to the regulatory tests of IRSN. Most tests are based on aqueous solutions but there is a growing demand for tests on solid matrices to be measured by γ-spectrometry. Measurement of radionuclides from environmental samples includes a wide variety of matrix compositions and densities. Since 2009, LNE-LNHB is working on the production of suitable calibration reference materials to improve the traceability of environmental radioactivity measurements in France. To address this issue, LNELNHB intends to produce mixed γ-ray reference materials with a known mass activity and a composition as representative as possible of real environmental samples. The use of such materials will also improve the calibration of γ-spectrometry measurement systems due to a more accurate determination of the self-attenuation correction by measuring a known sample whose composition is close to the real one. This paper describes the development of the preparation protocol and the characterization of traceable matrices, spiked with various γ-ray emitters. A PT exercise has been organized with a low density matrix produced. The results of the participants are mentioned in this article.

For radioprotection, the reference quantity is air kerma. For an cobalt-60 beam, the reference dosimeter is a cavity ionization chamber whose volume is measured. The new LNE-LNHB reference is based on six different chambers instead of one as was done previously. Although every new ionization chamber was treated as much as possible in the same way (manufacturing, measurements of volumes, wall effect calculations, current corrections), a maximum discrepancy of 0.2% was observed between the final measurement results from each chamber. The final value of the air kerma rate in reference conditions was determined as the mean value of the measurement results from all six chambers. Among the different factors whose determination is necessary to calculate the air kerma rate, some are considered independent of or common to all the graphite-walled ionization chambers (for example, mean energy expended by an electron to produce an ion pair in dry air), while others vary for each chamber (for example, air cavity ionic collection volume). Considering that the uncertainties of the individual ionizationchamber measurement results seem slightly underestimated, the uncertainty on the mean of the six chamber-dependent factors products was taken equal to the standard deviation of the sample composed of the six chamber-dependent factors products (0.08%). Compared to the previous standard, the air kerma rate of the ⁶⁰Co photon beam would then increase by 0.09% and the air kerma rate uncertainty would drop from 0.38% to 0.31%. This article describes the procedure used to establish the primary standard in terms of absorbed dose to tissue of LNE-LNHB.

For the last four years, the LNE-LNHB/LMD has been developing methods and material to measure the X-ray spectra of its X-ray tubes used to perform primary standards and transfers in medical or industrial fields. Two different measuring devices have been built. They include the possibility to use three different semiconductor detectors (Si-PIN, GeHP, CdTe) equipped with tungsten collimators with small apertures. Two rotation and translation stages were included to these benches for an automatic and precise alignment of the couple detector/collimator on the beam axis. Correction methods were developed for each detector, to take into account all the detection artefacts taking place into the semi-conductor crystal. They were included in specific spectrum correction programs. Characterization of 28 LNE-LNHB/LMD reference beams was carried out. It allows testing and validating all the different algorithms of spectrum correction developed at the laboratory. These results were compared to the calculated spectra obtained with the XCOMP5r and SpekCalc V1.0 software.

Molecular radiotherapy consists in the injection of a therapeutic agent with known activity in order to deliver a high-dose radiation directly to the tumors while sparing healthy tissues. The Euramet/EMRP project MetroMRT "Metrology for Molecular Radiotherapy" was intended to bring together national metrology laboratories and nuclear medicine services in order to give them metrological support in the field of molecular radiotherapy. In particular, LNE-LNHB was involved in the project for the standardization of ⁹⁰Y-labelled resin microspheres (SIR-Spheres). This therapeutic agent produced by Sirtex (Sydney, Australia) for selective internal radiotherapy is dedicated to the treatment of unresectable hepatic tumors by radioembolization. The primary activity measurement of ⁹⁰Y microspheres was carried out after their complete dissolution in the Sirtex vial. Two types of measurements using the TDCR method were used, one based on liquid scintillation and the other on the Cherenkov effect. An original method for the dissolution was developed at LNE-LNHB to optimize the homogeneity of the radioactive solution dedicated to primary measurements. A comprehensive description of the dissolution protocol implemented is reported in this article. The calibration of the ionization chambers at LNE-LNHB for the reference transfer of ⁹⁰Y-microspheres to end-users is also addressed. The influence of the inhomogeneity of the vial geometry on the uncertainty associated with calibration factors in the case of pure β ^- emitters such as ⁹⁰Y is presented. The standardization of SIR-Spheres was also aimed at lowering the 10% relative uncertainty given by Sirtex on the ⁹⁰Y-microspheres activity (3 GBq).

In this work we present the results of the first part of a research project aimed at offering a complete response to dosimeter manufacturers and users of the nuclear industry demand for high energy (6 MeV–9MeV) photon radiation beams for radiation protection purposes. Classical facilities allowing for the production of high energy photonic radiation (proton accelerators, nuclear reactors) are very rare and need large investment for development and use. We thus propose a novel solution, consisting in the use of a medical linear accelerator, allowing for a significant decrease of all costs. Using Monte-Carlo simulations (MCNP5 and PENELOPE codes), we have built a specifically designed electron-photon conversion target allowing for obtaining a high energy photon beam (with an average energy weighted by fluence of 6.17 MeV) for radiation protection purposes. Due to the specific design of the target, this “realistic” radiation protection high energy photon beam presents a uniform distribution of air kerma at a distance of 1 m, over a (30 × 30) cm² area. Two graphite cavity ionization chambers for ionometric measurements have been built. For one of these chambers we have measured the charge collection volume allowing for its use as a primary standard. The second ionization chamber is a transfer standard, as such it has been calibrated in a 60Co source, and in the high energy photon beam for radiation protection. The measurements with these ionization chambers allowed for an evaluation of the air kerma rate in the high energy photon beam for radiation protection: the values cover a range between 80 mGy·h^-1 and 210 mGy·h^-1, compatible with radiation protection purposes. Finally, we have calculated using Monte-Carlo simulations conversion coefficients from air kerma to dose equivalents in the range between 10 keV and 22.4 MeV, in specific geometrical set-ups, and for the spectral distribution of the fluence in the beam produced by the linear accelerator of LNE-LNHB.