Search

241Americium–beryllium neutron sources are used in a variety of applications, spanning from the civil engineering to the oil industry, and to the radiation dosimetry. The ISO 8529-1 Standard reports a reference distribution for the energy of the emitted neutrons, which extends from 0.1 to 11 MeV. Nevertheless every source exhibits a slightly different spectrum, depending on the material and dimension of the capsule, and on the amount of active material. This source-to-source variability is expected to mainly affect the energy region below 0.1 MeV. As these differences can be important in the fields of neutron dosimetry and metrology, some relevant source formats have been investigated with spectrometric methods. The neutron calibration laboratory of the Politecnico di Milano recently acquired a CZ/1003/S — 96 type 241 Am–Be source (nominal emission rate 2.2E+6 s−1). As this type of source is in use in a number of European laboratories, its spectrum was determined through a neutron spectrometry experiment, involving two Bonner sphere spectrometers with well-known responses. The experimental spectrum is compared to that published for a similar source and to the ISO-recommended one.

This report documents measurements of cosmic ray induced background neutrons using a new Bonner sphere spectrometer (BSS) based on a 3 He thermal neutron counter (SP9 type). Three spheres with a lead or copper layer were added to a BSS to enhance its sensitivity in the high-energy range above 20 MeV and enable the spectrometer to cover the entire energy range from thermal to multi-GeV. The response function of the spectrometer was calculated using the Monte Carlo code MCNP6. Below 20 MeV, the responses of polyethylene spheres were experimentally verified with 6 mono-energetic neutron sources . A neutron spectrum was measured near the ground at one location in Beijing. Also deduced from the spectrum were the rates of neutron fluence , ambient dose equivalent, and effective dose.

It is well to known that in different knowledge´s areas as research, application and development neutrons are involved either, whether as a product of secondary reactions or applied it to a specific purpose. The Bonner Sphere Spectrometer actually is widely used to detect neutrons using active or passive detectors in health physics and research arenas. The Monte Carlo Code in radiation transport is an effective way to predict absorbed dose distributions and neutron spectra. The aim of this work is design and build a spectrometer as a cubic moderators with the versatility to use passive and active detectors, using Monte Carlo Code to obtain the response matrix, compare the results with SEEB used by others authors. En diversas áreas del conocimiento como investigación, desarrollo o aplicación, los neutrones se encuentran inmersos ya sea como producto secundario de otras reacciones o aplicados con un propósito en particular. El espectrómetro de esferas Bonner es actualmente el sistema más empleado para determinar la energía de los neutrones, usando detectores activos o pasivos, en diferentes ámbitos como la nucleoelectricidad, los rayos cósmicos y la física médica. El uso del código Monte Carlo en el transporte de la radiación nos permite estimar de forma precisa dosis, fluencias y espectros. El objetivo de este trabajo es diseñar un espectrómetro con moderadores cúbicos con la versatilidad de poder emplear tanto detectores pasivos como activos, usando el Código Monte Carlo para obtener las matrices de respuesta, se compararán los resultados con los obtenidos con el SEEB empleado por otros autores.

International audience; This paper discusses an instrument intercomparison performed in the high-energy field at the CERF facility at CERN between 2015 and 2017 (October 2015, May 2016, November 2016 and June 2017). Measurements were performed in several reference exposure locations with the CERN extended-range Bonner Sphere Spectrometer (BSS), a Berthold LB4611, the LINUS rem counter from CERN, the LUPIN rem counter from ELSE Nuclear, the FHT 762 Wide Energy Neutron Detection Instrument (WENDI-II) from Thermo Scientific, the LUDLUM MODEL 42–41 PRESCILA NEUTRON PROBE and two models of Tissue-equivalent proportional counters (TEPCs) from Far West Technologies. All results are compared with the latest FLUKA reference values from simulations performed in 2017.

Radiation therapy is one of the most used treatment modalities of cancer. While most patients receive photon-therapy, a growing number of patients are treated with particles, mainly protons. Protons offers a more localized dose deposition compared to photon-therapy. This allows to reduce the dose that is applied by the primary beam to the healthy tissue outside the target volume. At the same time, the use of protons leads to a change in the composition of the secondary radiation field, when compared to photons. In most locations, the out-of-field dose is dominated by secondary neutrons. The out-of-field dose varies significantly in shape and size. Currently, there is no established procedure to monitor the secondary neutron dose to the patients. This paper describes the simulation and measurement of the secondary neutron radiation field at the University Dresden Proton Therapy. The simulation uses a detailed model of the beam delivery system, an IBA universal nozzle. The simulations have been validated by a comprehensive set of extended range Bonner sphere spectrometer measurements, with the NEMUS spectrometer operated by the Physikalisch-Technische Bundesanstalt. The set of measurements covers all possible machine configurations for the double scattering mode. An excellent agreement between unfolded measurements and simulation predictions is achieved. The data shows that the neutron field is varying strongly on the scale of a human body. This indicates that the use of fluence to dose conversion tables is not justified for neutron dose calculation in patients. Therefore, the presented data is of high importance for future studies of the organ doses in different treatment scenarios.

The spectrum weighted responses of various detectors were calculated to provide guidance on the proper selection and use of survey instruments on the basis of their energy response characteristics on the neutron fields. To yield the spectrum weighted response, the detector response functions of 17 neutron-measuring devices were numerically folded with each of the produced calibration neutron spectra through the in-house developed software ‘K-SWR’. The detectors’ response functions were taken from the IAEA Technical Reports Series No. 403 (TRS-403). The reference neutron fields of 21 kinds with 2 spectra groups with different proportions of thermal and fast neutrons have been produced using neutrons from the 241Am-Be sources held in a graphite pile, a bare 241Am-Be source, and a DT neutron generator. Fluence-average energy (Eave) varied from 3.8 MeV to 16.9 MeV, and the ambient-dose-equivalent rate [H*(10)/h] varied from 0.99 to 16.5 mSv/h.

Experimental activities are underway at INFN Legnaro National Laboratories (LNL) (Padua, Italy) and Pisa University aimed at angular-dependent neutron energy spectra measurements produced by the 9 Be(p,xn) reaction, under a 5 MeV proton beam. This work has been performed in the framework of INFN TRASCO-BNCT project. Bonner Sphere Spectrometer (BSS), based on 6 LiI (Eu) scintillator, was used with the shadow-cone technique. Proper unfolding codes, coupled to BSS response function calculated by Monte Carlo code, were finally used. The main results are reported here.

Measurements performed with the High Energy Range Multisphere Extended IRSN System (HERMEIS) acquired by the French Aerospace Lab are presented and discussed. The detectors were calibrated at the Low Noise Underground Laboratory of Rustrel. Atmospheric neutron spectra were obtained at three altitudes ( ${+}500$ m, ${+}1000$ m and ${+}2885$ m) and the first results about the continuous measurements of the Natural Radiative Environment at the Pic du Midi are presented with a discussion about the uncertainties.

"In this work we describe the design and construction of an extended range Bonner Sphere Spectrometer (BSS) intended to be used in the measurement of the energy spectra of neutrons produced by cosmic radiation. A single BSS spectrometer designed and constructed by us, has been used for a long time as neutron monitor at the tandem accelerator of the National Institute for Nuclear Research (ININ, México). The extended spheres added are 10 and 6 inch diameters with copper, bismuth and lead as inner shells. The measurements are to be initiated at the Physics Institute UNAM México (IFUNAM) and at the Mexican Nuclear Center, near 3000 meters high."

cited By 8; In the present work, the general purpose radiation transport MCNPX code (version 2.5.0) was used to evaluate the neutron fluence response matrix of the passive Bonner sphere spectrometer recently developed in our laboratory. The calculations were performed for an extended neutron incidence energy range (from 10-9 MeV to 1 GeV). Afterward, a sensitivity analysis of the main parameters affecting the neutron fluence response of each detector-sphere assembly has been undertaken and complementary MCNPX simulations of bare gold foils considering normal, parallel and isotropic neutron incidence directions are also presented. Finally, the simulated response matrix was experimentally validated with a252Cf standard radioactive source available in our facilities. © 2010IOP Publishing Ltd and SISSA.

The neutron emission from 50 mm thick copper, silver and lead targets bombarded by a mixed proton/pion beam with momentum of 40 GeV/c were measured at the CERN Super Proton Synchrotron. The neutron yield and spectral fluence per incident particle on target were measured with an extended range Bonner sphere spectrometer in the angular range 30–135° with respect to the beam direction. Monte Carlo simulations with the FLUKA code were performed to provide a priori information for the unfolding of the experimental data. The spectral fluences show two peaks, an isotropic evaporation component centred at 3 MeV and a high-energy peak sitting around 100–150 MeV. The experimental neutron yields are given in four energy bins