The Laboratory for Neutron Metrology and Dosimetry of the Institute for Radiation Protection and Nuclear Safety has undertaken a study related to the optimization of the geometry of a long counter to ...determine the neutron fluence reference values at the AMANDE facility. This study was performed on the basis of a De Pangher long counter design. The materials, the dimensions and the geometry were varied and the consequences on the response function were studied. Different parameters were optimized to flatten the neutron response energy distribution, over a wide energy range, from a few eV’s to a few MeV’s. The aim of this paper is to present the results of the study performed by using intensive Monte-Carlo simulations which helped in the design of the new IRSN long counter.
A review on radiation sources, calibration facilities and realistic fields is presented and examples are given. The main characteristics of the fields are shortly described together with their domain ...of applications. New emerging fields are also mentioned and the question of needs for additional calibration fields is raised.
A neutron spectrometry campaign was carried out in the AMANDE accelerator control room. These measurements had several objectives, one of which was to verify the possibility of determining, with the ...HERMEIS Bonner sphere system, very low fluence and ambient dose equivalent rates. These measurements were also expected to provide comparison values with calculations, performed with MCNPX 2.6.0, used for modeling the whole facility and to verify the radiological zoning implemented. Neutrons of 3.3 MeV then 15 MeV were produced in the experimental hall of AMANDE and measurements were made in the control room, behind a 40 cm thick concrete wall. The ambient dose equivalent rates derived from the measured spectra are respectively of the order of 0.2 and 10 μSv/h, which are in agreement with a LB6411 surveymeter data also involved.
A Bonner sphere spectrometer extended to high energies (HERMEIS) was set up at the summit of the Pic du Midi de Bigorre in the French Pyrenees (altitude: +2,885 m; geomagnetic cutoff: 5.6 GV) in May ...2011. The spectral fluence rate distribution of the cosmic ray induced neutrons was continuously measured over a broad energy range from meV up to several GeV and with a 1 h time resolution. While the Sun's activity was increasing and reaching its 24th maximum in the 11 year solar cycle, some Forbush decreases were observed in the atmospheric secondary radiation at mountain altitude. We investigated the evolution of the cascade fluence rate (i.e., neutrons with energy greater than 20 MeV) during the March 2012 events with a series of strong coronal mass ejections hitting the Earth's magnetosphere. The amplitude of the greatest Forbush decrease peaked at 10%. Then, a simulation work based on the GEANT4 toolkit was carried out to quantify the solar modulation induced on the galactic cosmic ray transportation during these events. We performed calculations of extensive air showers generated by monoenergetic primaries (Hydrogen and Helium nuclei) for several zenith incidences. Hence, a complete database was built and validated. We derived an analytical model to estimate the atmospheric neutron spectrum at the Pic du Midi according to primary spectra which only depend on the solar modulation potential (force field approximation). We compared the solar modulation potentials obtained in March 2012 with the ones derived by the neutron monitor yield method. Finally, a satisfying agreement was found.
Key Points
A neutron spectrometer is operating at the Pic du Midi de Bigorre
Extensive air shower simulations were performed with GEANT4 toolkit
Solar modulation potential is derived with two methods
Monte Carlo calculations are increasingly used to assess stray radiation dose to healthy organs of proton therapy patients and estimate the risk of secondary cancer. Among the secondary particles, ...neutrons are of primary concern due to their high relative biological effectiveness. The validation of Monte Carlo simulations for out-of-field neutron doses remains however a major challenge to the community. Therefore this work focused on developing a global experimental approach to test the reliability of the MCNPX models of two proton therapy installations operating at 75 and 178 MeV for ocular and intracranial tumor treatments, respectively. The method consists of comparing Monte Carlo calculations against experimental measurements of: (a) neutron spectrometry inside the treatment room, (b) neutron ambient dose equivalent at several points within the treatment room, (c) secondary organ-specific neutron doses inside the Rando-Alderson anthropomorphic phantom. Results have proven that Monte Carlo models correctly reproduce secondary neutrons within the two proton therapy treatment rooms. Sensitive differences between experimental measurements and simulations were nonetheless observed especially with the highest beam energy. The study demonstrated the need for improved measurement tools, especially at the high neutron energy range, and more accurate physical models and cross sections within the Monte Carlo code to correctly assess secondary neutron doses in proton therapy applications.
The neutron metrology and dosimetry laboratory has developed a long counter, on the basis of optimization work using Monte-Carlo simulations. The calibration of this new device was performed at the ...IRSN standard radionuclide source facility. Measurements were also realized at the monoenergetic neutron fields facility, AMANDE, to determine the dead time correction, the effective center and efficiency as a function of neutron energy. A good agreement was observed between the long counter results and the monoenergetic neutron fluence values determined with proton recoil counters. The results of the experimental characterization of the IRSN long counter are presented in this paper.
Cervical cancer is the second most frequent cancer in women in French Guiana. Studies have shown that populations living in the remote areas of the interior have early sexual debut and that multiple ...sexual partnerships are common. The objective of the present study was thus to determine the prevalence of human papillomavirus (HPV) infection in these areas. A study was conducted in women aged 20–65 years with previous sexual activity. Women were included on a voluntary basis after using local media and leaders to inform them of the visit of the team. HPV infection was defined by the detection of HPV DNA using the Greiner Bio-One kit. In addition to HPV testing cytology was performed. The overall age-standardized prevalence rate was 35%. There was a U-shaped evolution of HPV prevalence by age with women aged >50 years at highest risk for HPV, followed by the 20–29 years group. Twenty-seven percent of women with a positive HPV test had normal cytology. Given the high incidence of cervical cancer in French Guiana and the high prevalence of HPV infections the present results re-emphasize the need for screening for cervical cancer in these remote areas. Vaccination against HPV, preferably with a nonavalent vaccine, also seems an important prevention measure. However, in this region where a large portion of the population has no health insurance, this still represents a challenge.
In this paper, a Bonner Sphere Spectrometer extended to high energies (HERMEIS) was employed to measure continuously the cosmic-ray-induced neutron spectra over a long-term period (2 y) at mountain ...altitude and medium geomagnetic latitude (Pic du Midi de Bigorre in the French Pyrenees, +2885 m, 5.6 GV). The results showed 1-y sinusoidal oscillations in the integrated fluence rates. The amplitude of these oscillations depends on the neutron energetic domain. The fluence rate of thermal neutrons was 53 % higher in August than that in February. Those of epithermal neutrons with energies between 0.4 eV and 0.1 MeV and evaporation neutrons (from 0.1 to 20 MeV) were ∼25 % higher in the summer than those in the winter. Finally, the cascade neutron fluence rate (>20 MeV) remained quite the same (<10 % variation). To understand the effects of local and seasonal changes in the measurement environment, GEANT4 simulations were performed. The nature of rock and thickness of the snow cover during the winter period (given by meteorological data) were investigated. A reasonable agreement between experiments and calculations was found.
In this paper, high-altitude measurements of both radiation environment and effects are described. Measurements are made using a neutron spectrometer and CCD camera. MUSCA SEP3 software is used to ...correlate both measurement approaches. Analyses of the charge levels in pixels induced by radiation events are proposed. Then, cross-comparison analyses based on a CCD camera and HERMEIS neutron spectrometer are performed to investigate radiation dynamic properties, including neutron/proton and muon contributions.
The production of unwanted neutrons by electron linear accelerators (LINACs) has attracted a special attention since the early 50s. The renewed interest in this topic during the last years is due ...mainly to the increased use of such machines in radiotherapy. Specially, in most of developing countries where many old teletherapy irradiators, based on
60Co and
137Cs radioactive sources, are being replaced with new LINAC units. The main objective of this work is to report the results of an experimental characterization of the neutron spectra generated by a high-energy clinical LINAC. Measurements were carried out, considering four irradiation configurations, by means of our recently developed passive Bonner sphere spectrometer (BSS) using pure gold activation foils as central detectors. This system offers the possibility to measure neutrons over a wide energy range (from thermal up to a few MeV) at pulsed, intense and complex mixed n–γ fields. A two-step unfolding method that combines the NUBAY and MAXED codes was applied to derive the final neutron spectra as well as their associated integral quantities (in terms of total neutron fluence and ambient dose equivalent rates) and fluence-averaged energies.
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