Intramedullary melanotic schwannoma

We present a case of an intramedullary melanotic schwannoma (IMS) of the thoracic spinal cord. To our knowledge, this is the seventh reported case of an IMS of the central nervous system. Schwannomas are benign nerve sheath tumors of neural crest origin composed entirely of well differentiated Schwann cells that typically occur in peripheral nerves. Both the intramedullary location and the melanotic component of the reported lesion make it exceedingly rare. We will present our case, theories as to the origin of these tumors, clues in radiographic identification, and current clinical follow-up recommendations

Improvement of 93mNb and 103mRh activity measurement methodology for reactor dosimetry

Reactor dosimetry is based on the analysis of the activity of irradiated dosimeters, such as 93mNb and 103mRh. The activity measurement of these dosimeters is conventionally performed by X-ray spectrometry, but the low-energy of emitted photons makes it difficult to derive reliable results with low uncertainties. Approaches to improve these characterisations are presented: they include high accuracy efficiency calibration of a HPGe detector using both experiments and Monte Carlo simulation, calculation of corrective factors for the geometry (selfabsorption) and self-fluorescence effects. Improvement of the knowledge of the 103mRh decay scheme is also required and a specific experiment is proposed, including activity measurement of a 103mRh solution by liquid scintillation, and measurement of the photon emission intensities by X-ray spectrometry. A method for calculating coefficients to take into account the self-fluorescence effects in dosimeters is also suggested to improve the uncertainties on activity measurements

Improvement of

Reactor dosimetry is based on the analysis of the activity of irradiated dosimeters, such as 93mNb and 103mRh. The activity measurement of these dosimeters is conventionally performed by X-ray spectrometry, but the low-energy of emitted photons makes it difficult to derive reliable results with low uncertainties. Approaches to improve these characterisations are presented: they include high accuracy efficiency calibration of a HPGe detector using both experiments and Monte Carlo simulation, calculation of corrective factors for the geometry (selfabsorption) and self-fluorescence effects. Improvement of the knowledge of the 103mRh decay scheme is also required and a specific experiment is proposed, including activity measurement of a 103mRh solution by liquid scintillation, and measurement of the photon emission intensities by X-ray spectrometry. A method for calculating coefficients to take into account the self-fluorescence effects in dosimeters is also suggested to improve the uncertainties on activity measurements

Improvement of the activity measurement method for solid dosimeters emitting X-rays

21st International Conference on Radionuclide Metrology and its Applications (ICRM), Argentinian Comis Nacl Energia Atomica, Buenos Aires, ARGENTINA, MAY 15-19, 2017. Organizer: Argentinian Comission Nacional Energia AtomicaInternational audienceToday, there is growing interest for neutrons in the intermediate energy range between 100 keV and 1 MeV, which are responsible for damaging materials in reactor. To improve this deficiency, we use rhodium and niobium which, through the inelastic neutron scattering reaction, leads to the formation of Rh-103m and Nb-93m low-energy X-emitters. This paper describes the improvements and validation made on this type of complex measurement by X spectrometry: self-attenuation, fluorescence correction, and emission intensity were poorly known previously

Recent improvements in the nuclear reactor dosimetry techniques for the epithermal neutron flux measurement

International audienceReactor dosimetry techniques are commonly used for the characterization of neutron spectra (both shape and level) encountered in nuclear reactors. One can derive neutron flux and fluences integrated on a specific energy domain such as thermal, epithermal or fast flux, from radioactivity measurements of a set of dedicated irradiated dosimeters. Neutron flux and fluences are calculated from activity measurements using Bateman equation, irradiation history and nuclear data (cross sections), neutron modelling codes and unfolding codes if necessary. For thermal and low epithermal energies (E1MeV), nuclear reactions are numerous and well known as for example radiative captures (n, $\gamma$) and thermal fission for the first domain and inelastic (n,n'), (n,p) and (n, $\alpha$) reactions for high energies. In addition, fission reactions can also give information, depending of the target isotope, either on the thermal and low energy epithermal neutrons, where resonance peaks of the cross section contribute significantly, or on the high energy epithermal and fast neutrons. Unfortunately there are no dominant reactions identified for the medium epithermal spectrum part (1keV-1MeV) that could give de-correlated information from thermal or fast energy contributions. The characterization of the intermediate energy region, in particular for neutron spectrum shape, relies then mainly on neutron modelling codes, such as TRIPOLI4®, and presents higher uncertainties than the other zones of the spectrum. This is an issue for reactor dosimetry, knowing that epithermal area constitutes the main neutron population in GEN-IV reactors and is also of first importance for material embrittlement evaluation of both internals and reactor vessel (displacement per atoms).Therefore, several studies have been launched in the recent years at the Cadarache CEA center in order to enhance reactor dosimetry techniques for the epithermal neutron flux measurement in nuclear reactors. The first aspect explored concerns the upgrade of activity measurement techniques of the niobium and rhodium dosimeters which are X-ray emitters. Indeed, both of them have relevant (n,n') reactions for characterization of the upper part of the epithermal spectrum (E>700keV) but their activities measurement presents relatively high uncertainties. In parallel with the improvement of these measurement techniques, nuclear data are under study for lowering their associated uncertainties. The second aspect consists in searching new reactions or developing new irradiation and measurement techniques for having information integrated on the 1keV 1MeV domain. The zirconium dosimeter has been identified as a good candidate for this purpose and a new measurement process has been developed.Besides, studies have been performed concerning the $^{117}$Sn(n,n')$^{117m}$Sn reaction for upper neutron energy domain (E>300keV) as well as the optimization of the neutron filter used during irradiation to de-correlate thermal neutrons from low energy epithermal neutrons. After a synthetic review of the reactor dosimetry principle and issues concerning epithermal neutron spectrum, this paper will present the status of the different improvements listed above. Gains and limitations associated to these new techniques are then discussed and prospects about futures studies are listed