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The Neutron Standards Laboratory (LPN) at CIEMAT serves as the national reference for calibrating neutron measurement devices and conducts research on measuring different neutrons fields, arising the necessity of neutron spectrometry. There are different neutron fields which are attracting interest in the recent years, for example ambient neutron spectra, generated basically by cosmic rays in the atmosphere or secondary neutrons on the surroundings of accelerators, for instance in protontherapy centres. These neutrons spectra are characterized by having an important component of high energy neutrons up to hundreds MeV or even GeV. In order to do spectrometry in this kind of neutron fields, a Bonner Sphere Spectrometer extended range was designed, constructed and tested. • Response Matrix simulations for Bonner Sphere Spectrometer wit Monte Carlo code. • Digital electronics implementation to the extended Bonner Sphere Spectrometer. • Ambient neutron measurements with an extended range BSS. [ABSTRACT FROM AUTHOR]

There are usually two kinds of experiment methods for neutron spectrum measurement by Bonner sphere spectrometer (BSS). The first is to use only one Bonner sphere (BS) at a time to complete the neutron experiment by repeated measurements; The other is to measure multiple Bonner spheres (BSs) together, and this multi-sphere simultaneous measurement method can complete the neutron experiment only once. The single sphere measurement method cannot guarantee that the measurement environment is completely consistent every time, which leads to inevitable measurement errors. The multi-sphere simultaneous measurement method can ensure the same experimental environment for each sphere, but there will be cross-talking. This paper studies the influence of cross-talking on BSS. Firstly, we use Geant4 to simulate the corresponding neutron response function with and without cross-talking, and analyze the error between the two neutron response functions. Secondly, the neutron count of ▪ neutron source experiment is simulated. Considering that the BSS is close to the floor, the neutron counting error of BS with and without cross-talking and floor scattering is calculated. Finally, we actually measure the ▪ neutron source using a BSS and obtain 8 neutron counts. The spectrum of ▪ neutron source is obtained by calibrating the influence of cross-talking. The results show that the scattered neutrons which affect the count of BS are mainly the primary scattered neutrons, which account for more than 90% of all scattered neutrons. The scattered neutrons mainly affect the neutron response function of the large BS in the high energy domain and the small BS in the low energy domain. The cross-talking has a great influence on the neutron count of large and small BS, while the floor scattering has a great influence only on the small BS. The ▪ neutron spectrum obtained by calibrated neutron counts is more accurate than that obtained by the original experiment counts. Especially in the range of 1 ∼ 5 MeV, the calibrated ▪ neutron spectrum is much closer to the international standard spectrum. The mean square error (RMSE) of calibrated ▪ neutron spectrum is reduced by 3.86%. In this paper, by analyzing the influence of cross-talking, the neutron count of BSS is calibrated, and the accuracy of ▪ neutron spectrum is improved, which provides a strong basis for unfolding neutron spectrum. [ABSTRACT FROM AUTHOR]

This report documents measurements of cosmic ray induced background neutrons using a new Bonner sphere spectrometer (BSS) based on a 3He 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. • A Bonner sphere spectrometer with three extended spheres was employed to measure cosmic ray induced background neutrons at Beijing. • The MCNP6 code was used for the response function calculation. • Each count rate of the BSS was obtained after neutron flux variation correction. • A neutron spectrum was unfolded, and the deduced flux and dose rate values were also compared with other works. [ABSTRACT FROM AUTHOR]

Abstract 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. [ABSTRACT FROM AUTHOR]

Abstract In order to undertake further studies on neutron spectra deconvolution in radiotherapy LinAc bunkers after using high megavolts treatment beams, it has been calculated the theoretical Response Function for a widespread neutron Bonner Sphere Spectrometer (BSS) exposed to arbitrary neutron sources. The neutron response function of the Bonner spectrometer is of essential importance for its neutron spectrum unfolding procedure and is directly related to the quality of the unfolded spectrum. Response detector curves from 10 keV to 20 MeV have been obtained by Monte Carlo (MC) simulation with MCNP6.1.1, where the use of unstructured mesh geometries is introduced as a novelty. In order to validate the accuracy of the MCNP6 simulation, we have used the detector model to measure an 241Am-Be neutron source, and the obtained neutron counts of the spectrometer and simulated counts are found to be very consistent, with a relative error below 10%. This comparison shows that the estimation of the Bonner sphere neutron response by MCNP6 is highly precise. Highlights • The Response Function for a neutron Bonner Spectrometer has been calculated. • The response function of the spectrometer is important for the spectrum unfolding procedure. • Response detector curves have been obtained by Monte Carlo (MC) simulation with MCNP6.1.1. • To validate results an 241Am-Be neutron source has been used and compared with simulations. • The obtained neutron counts of the spectrometer and simulation are very consistent, with a relative error below 10%. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • The BSS , WENDI II, LINUS and LUPIN agree amongst them and with the FLUKA simulations within one sigma of uncertainty. • The LB6411 underestimates up to 35% as compared to FLUKA and the extended rem counters. • The PRESCILA overestimates the high-energy component and underestimate the evaporation part. Therefore, the PRESCILA overestimates the H*(10) on the CT and underestimates it on the IT. • Concerning the two TEPC , they agree within their range of uncertainty for all positions. The agreement with FLUKA is satisfactory on the CT/CS but the TEPCs show underestimation on the IT. [ABSTRACT FROM AUTHOR]

The neutron field measurement was performed in the Experimental Advanced Superconducting Tokamak (EAST) experimental hall using a Bonner sphere spectrometer (BSS) based on a 3 He thermal neutron counter. The measured spectra and the corresponding integrated neutron fluence and dose values deduced from the spectra at two exposed positions were compared to the calculated results obtained by a general Monte Carlo code MCNP5, and good agreements were found. The applicability of a homemade dose survey meter installed at EAST was also verified with the comparison of the ambient dose equivalent H*(10) values measured by the meter and BSS. [ABSTRACT FROM AUTHOR]

The response functions (RFs) of a Bonner Sphere Spectrometer (BSS) with a 6LiI thermal neutron detector were calculated using the Monte Carlo codes PHITS (version 3.26) and MCNPX (version 2.7.0), with their own default nuclear data libraries, and physics models. RFs were compared with other published data, obtained for the same spectrometer using the MCNP6.1 code with its own physics models. A discussion on the influence of using different nuclear data libraries and physics models using these codes/versions is analyzed. • Response functions (RFs) of a BSS with a 6LiI thermal neutron detector were calculated with the codes PHITS and MCNPX. • Use of the default nuclear data libraries, and physics models of the codes. • RFs were compared with other published data. • RFs obtained can be used for neutron spectrometry in workplaces. [ABSTRACT FROM AUTHOR]

In this study, a conventional Bonner sphere spectrometer, together with 6 LiI(Eu) inorganic scintillator used as the central detector, was used to obtain the neutron energy spectrum of an 241 Am–Be source. To achieve this, we calculated the response matrices corresponding to eight different sizes of polyethylene spheres for the neutron energies ranging from about 10 −7 to 15 MeV in 54 energy groups by using the MCNPX2.6 code, and the 241 Am–Be neutron spectrum was obtained using a modified version of the neutron spectrum unfolding code, AFITBUNKI. In a feasibility study, similar calculations were performed with different sizes of polyethylene cylinders. A comparison between the unfolded spectra of a typical 241 Am–Be neutron source with those of Bonner spheres, cylinders of similar sizes, and standard 241 Am–Be neutron energy spectra shows that the spectrometer with polyethylene cylinders can be used as a potential alternative for conventional Bonner spheres. [ABSTRACT FROM AUTHOR]

The neutron spectral fluence of an accelerator-based neutron source facility for boron neutron capture therapy (BNCT) based on a proton linac and a beryllium target was evaluated by the unfolding method using a Bonner sphere spectrometer (BSS). A 3 He-proportional-counter-based BSS was used with weak beam during the development of the facility. The measured epithermal neutron spectra were consistent with calculations. The epithermal neutron intensity at the beam port was estimated and the results gave a numerical target for the enhancement of the proton beam intensity and will be used as reference data for measurements performed after the completion of the facility. [ABSTRACT FROM AUTHOR]

Neutron spectrometry measurements with an extended-range Bonner Sphere Spectrometer (BSS), as well as neutron H*(10) measurements using an extended-range rem meter WENDI-2, a conventional rem meter LB 6411 and a tissue-equivalent proportional counter, were performed inside and around the Fixed-Beam Treatment Room at the proton therapy facility of Essen, in Germany. The WENDI-2 stood out as the easiest detector for making accurate neutron H*(10) measurements, since its direct measurements were equivalent to the H*(10) rates obtained with the BSS. The measurements were also compared to simulation results obtained with MCNPX 2.7.0 using two different selections of physics models for the hadron interactions above 150 MeV: the Bertini & Dresner models and the CEM03 model. For neutron H*(10) rates outside the treatment room, factors of 1.6–1.8 were obtained between the results of the two simulations, the Bertini & Dresner models yielding the largest values in all positions. The comparison of the simulation results with the WENDI-2 and BSS measurements for positions inside the treatment room showed that the Bertini & Dresner models reproduce the global neutron production in the water phantom relatively well, whereas the CEM03 model underestimates it by a factor of ∼1.3. At the most-forward angle, however, the Bertini model (unlike the CEM03 model) seemed to overestimate the production of neutrons with energies above 100 MeV. Outside the shielding, the simulated H*(10) overestimated the WENDI-2 measurements by factors of 2–3 with the Bertini & Dresner models, and 1.1–1.7 with the CEM03 model. Both simulations were thus conservative with respect to the neutron fluxes transmitted through the concrete walls. This conservative behaviour is probably caused by a combination of several uncertainties, including for instance uncertainties on the proton and neutron interaction cross-sections and uncertainties on the concrete composition and density. [ABSTRACT FROM AUTHOR]

For neutron spectrometry of the D 2 O-moderated 252Cf source with a Bonner sphere spectrometer (BSS), it is difficult to use the large and heavy shadow cone to correct the neutron scattering effect. To overcome this problem, Monte Carlo (MC) simulation method was applied to calculate the neutron scattering ratio and to establish the BSS response functions. The simulated response functions were verified by experimental measurements in reference mono-energetic neutron fields. MC simulation based scattering-correction was validated by measurement of 252Cf neutron field. The measured and simulated values of the neutron scattering ratio were very close with relative errors within ±6%. Finally, the neutron spectrum and the spectrum averaged conversion coefficients of the D 2 O-moderated 252Cf were measured using BSS after scattering-correction by MC simulation, and the results agreed with the values recommended by ISO 8529–1:2021. It shows that the MC simulation can be a useful substitute to shadow cones method for neutron scattering-correction. • D 2 O-moderated 252Cf spectrum was measured by a Bonner sphere spectrometer. • The response functions were verified in reference mono-energetic neutron fields. • MC simulation based scattering-correction was validated in 252Cf field. [ABSTRACT FROM AUTHOR]

In this work a calibrated Bonner Sphere Spectrometer (BSS), together with ISO shadow cones, was used to quantify the total and scattered components of bare and heavy water moderated 252 Cf neutron fields. All measurements were performed with a BSS that was calibrated at the National Physical Laboratory (NPL), Teddington, UK, which is a global primary standard laboratory and world-leading facility for neutron metrology and neutron instruments calibration. The fields were characterized for source-spectrometer distances of 80, 100, 150 and 200 cm; and at heights of 103 and 200 cm from the facility floor. As expected, the scattered contribution was greatest at the farthest distance from the source and closer to the floor. Hence, at a distance of 200 cm and a height of 103 cm, the scatter added to the direct field up to 162% of the total neutron fluence and up to 61% of the ambient dose equivalent, while at the same distance and height of 200 cm above the floor, these values were up to 146% and 52%, respectively. In the case of heavy water moderated 252 Cf neutron fields, a shadow cone subtraction technique could not be implemented, however Monte Carlo simulations were utilized in order to differentiate between the direct and scatter components of the neutron fields. In this case, at a source–detector distance of 200 cm and a height of 103 cm, the scatter added to the direct field up to 148% of the total neutron fluence and up to 45% of the ambient dose equivalent, while at the same distance and a height of 200 cm above the floor, these values were up to 134% and 42%, respectively. [ABSTRACT FROM AUTHOR]

The measurements of neutron energy spectra and neutron dose rates were performed using the KN Van de Graaff accelerator, located at the McMaster University Accelerator Laboratory (MAL). Protons were accelerated on the thin lithium fluoride (LiF) target and produced mono-energetic neutrons which were measured using three different spectrometers: Bonner Sphere Spectrometer (BSS), Nested Neutron Spectrometer (NNS), and Rotational Proton Recoil Spectrometer (ROSPEC). The purpose of this work is (1) measurement and quantification of low energy accelerator neutron fields in terms of neutron fluence and dose, (2) comparison of results obtained by three different instruments, (3) comparison of measurements with Monte Carlo simulations based on theoretical neutron yields from 7 Li(p,n) 7 Be nuclear reaction, and (4) comparison of results obtained using different neutron spectral unfolding methods. The nominal thickness of the LiF target used in the experiment was 50 μ g / cm 2 , which corresponds to the linear thickness of 0.19 μ m and results in approximately 6 keV energy loss for the proton energies used in the experiment (2.2, 2.3, 2.4 and 2.5 MeV). For each of the proton energies, neutron fluence per incident proton charge was measured and several dosimetric quantities of interest in radiation protection were derived. In addition, theoretical neutron yield calculations together with the results of Monte Carlo (MCNP) modeling of the neutron spectra are reported. Consistent neutron fluence spectra were obtained with three detectors and good agreement was observed between theoretically calculated and measured neutron fluences and derived dosimetric quantities for investigated proton energies at 2.3, 2.4 and 2.5 MeV. In the case of 2.2 MeV, some plausibly explainable discrepancies were observed. [ABSTRACT FROM AUTHOR]

Americium–beryllium neutron sources are certainly the most widely used in neutron dosimetry laboratories, basically due to their long half-life and their energy distribution, which covers the energy domain of interest for many applications in ambient and personal dosimetry. Nevertheless, the spectrum of this source depends on the materials and dimension of the capsule and on the amount and physical–chemical properties of the active material, thus affecting relevant quantities such as the spectrum-averaged fluence-to-dose equivalent conversion coefficient. A EURAMET (European Association of National Metrology Institutes) project (n. 1104) was initiated to experimentally investigate how the neutron spectrum changes for different source sizes and encapsulations with a view to providing improved data for a planned revision of the ISO 8529 Standard Series. The experimental campaign was carried out in the low scatter facility at NPL. Here three different Bonner sphere spectrometers, BSSs, were exposed to the neutron fields produced by three different neutron sources formats: one X3 capsule (1 Ci) and two X14 capsules (10 Ci and 15 Ci). The specific advantage of the BSS is the large sensitivity to low-energy neutrons ( E <0.1 MeV) which is the component expected to be most affected by the capsule-to-capsule variations and the component which is least well known. This paper summarises the results of the campaign with emphasis on (1) estimating the low-energy component of the Am–Be neutron spectrum, according to the encapsulation type; (2) evaluating the coherence between the Bonner spheres data and the previous studies performed with high-resolution spectrometers but limited in energy to E >0.1 MeV; (3) understanding whether the ISO-recommended Am–Be spectrum needs to be amended, and for which source formats. [ABSTRACT FROM AUTHOR]

Abstract: 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 9Be(p,xn) reaction, under a 5MeV proton beam. This work has been performed in the framework of INFN TRASCO-BNCT project. Bonner Sphere Spectrometer (BSS), based on 6LiI (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. [Copyright &y& Elsevier]

The neutron spectra have been measured in two beam ports, one radial and another tangential, of the TRIGA Mark III nuclear reactor from the National Institute of Nuclear Research in Mexico. Measurements were carried out with the reactor core loaded with high enriched uranium fuel. Two reactor powers, 5 and 10 W, were used during neutron spectra measurements using a Bonner sphere spectrometer with a 6 LiI(Eu) scintillator and 2, 3, 5, 8, 10 and 12 in.-diameter high-density polyethylene spheres. The neutron spectra were unfolded using the NSDUAZ unfolding code. For each spectrum total flux, mean energy and ambient dose equivalent were determined. Measured spectra show fission, epithermal and thermal neutrons, being harder in the radial beam port. [ABSTRACT FROM AUTHOR]

The spectrum of photoneutrons produced by a 15 MV VARIAN iX linac working in Bremsstrahlung mode was measured a 100 cm from the IC located 5 cm-depth of a solid water phantom. The spectrum was measured with a Bonner spheres spectrometer with pairs of TLDs as thermal neutron detector. The measurements were carried out using the spectrometer in planetary method mode where a single shoot of the LINAC was required. [ABSTRACT FROM AUTHOR]

Abstract: We measured the background neutron spectrum using a Bonner sphere spectrometer at the YangYang underground laboratory, where the vertical earth overburden is approximately 700m. The neutron fluence rate and the energy spectrum were determined through the unfolding procedure. The measured neutron fluence rate was (0.242±0.008)ncm−2 h−1 for k=1, and most of the neutrons were below 20MeV. [Copyright &y& Elsevier]

Abstract: In this study, shadow cones were examined with Bonner sphere spectrometer (BSS) for the measurement of neutron spectrum of an 241Am–Be source. The BSS consists of a set of nine polyethylene spheres with a central 6LiI(Eu) scintillator sensitive to thermal neutrons. The energy response matrix of the BSS was determined by Monte Carlo simulations for the neutron energies from 10−8 to 100MeV. A crucial problem in neutron measurements is determining the contribution of scattered neutrons coming from the structures and materials surrounding a source. For this purpose two shadow cones were manufactured and positioned between the source and the detector. Experiments were performed to select the optimal source-to-shadow cone distance. An unfolding code was used to obtain the neutron spectrum. The difference between the unfolded spectrum obtained by using the shadow cones and the ISO reference spectra was considered as a parameter to select the optimum condition in the shadow cone technique application. [Copyright &y& Elsevier]

Abstract: A measurement campaign has been carried out recently to provide the source intensity and the reference spectra around a neutron irradiation facility based on 241Am-Be radionuclide source, using the UAB Bonner Sphere Spectrometer. This facility, which consists of a bunker, a container/shielding for the source and an irradiation device that uses an automated remote-controlled system for the source positioning and rotating during the dosimeter irradiation, is intended to be routinely used to check the response of passive dosimeters, namely those based on photo-stimulated imaging plates and solid-state nuclear track detectors. The measurement results, in terms of neutron spectra and global dosimetric quantities (i.e., fluence and ambient dose equivalent rates) at different distances with respect to the 241Am-Be source, were compared with Monte Carlo simulations using the MCNPX code and a good agreement was observed. An estimation of the un-scattered neutron spectrum directly emitted from the 241Am-Be source is given as well. [Copyright &y& Elsevier]

Abstract: Neutrons constitute an important component of the radiation environment in hadron therapy accelerators. Their energy distribution may span from thermal up to hundred of MeV. The characterization of these fields in terms of dosimetric or spectrometric quantities is crucial for either the patient protection or the facility design aspects. To date, the Extended Range Bonner Sphere Spectrometer (ERBSS) is the only instrument able to simultaneously determine all spectral components in such workplaces. With the aim of providing useful data to the scientific community involved in neutron measurements at hadron therapy facilities, a measurement campaign was carried out at the Centro di AdroTerapia e Applicazioni Nucleari Avanzate (CATANA) of INFN-LNS (Laboratori Nazionali del Sud), where a 62AMeV carbon ion is available. The beam was directed towards a PMMA phantom, simulating the patient, and two neutron measurement points were established at 0° and 90° with respect to the beam-line. The ERBSSs of UAB (Universidad Autónoma de Barcelona-Grup de Física de les Radiacions) and INFN (Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali di Frascati) were used to measure the resulting neutron fields. The two ERBSSs use different detectors and sphere diameters, and have been independently calibrated. The FRUIT code was used to unfold the results. [Copyright &y& Elsevier]

Abstract: The LVR-15 research reactor''s horizontal channel with its epithermal neutron beam is used mainly for boron neutron capture therapy. Neutrons from the reactor core pass through a special filter before the collimator and the beam outlet. Neutron fluence and spectrum are the basic characteristics of an epithermal neutron beam. Three methods used to measure the beam''s neutron spectrum are described: the activation method, a Bonner sphere spectrometer with gold activation detectors and a Bonner sphere spectrometer with LiI(Eu) scintillation detector. Examples of results are compared and discussed. [Copyright &y& Elsevier]

Abstract: A photo-neutron irradiation facility is going to be established at the Frascati National Laboratories of INFN on the base of the successful results of the n@BTF experiment. The photo-neutron source is obtained by an electron or positron pulsed beam, tuneable in energy, current and in time structure, impinging on an optimized tungsten target located in a polyethylene–lead shielding assembly. The resulting neutron field, through selectable collimated apertures at different angles, is released into a 100m2 irradiation room. The neutron beam, characterized by an evaporation spectrum peaked at about 1MeV, can be used in nuclear physics, material science, calibration of neutron detectors, studies of neutron hardness, ageing and study of single event effect. The intensity of the neutron beam obtainable with 510MeV electrons and its fluence energy distribution at a point of reference in the irradiation room were predicted by Monte Carlo simulations and experimentally determined with a Bonner Sphere Spectrometer (BSS). Due to the large photon contribution and the pulsed time structure of the beam, passive photon-insensitive thermal neutron detectors were used as sensitive elements of the BSS. For this purpose, a set of Dy activation foils was used. This paper presents the numerical simulations and the measurements, and compares their results in terms of both neutron spectrum and total neutron fluence. [Copyright &y& Elsevier]

Abstract: This work evaluated the neutron spectra induced by a medical used cyclotron. The neutrons were induced during the 18F-radioisotope productions due to the 9.6 MeV proton beam hit 18O-water target and induced (p, n) reactions in this SK Cyclotron. To evaluate the induced neutron doses in the cyclotron room, dual-TLD chips and gold foils with bare and 113Cd covered were used separately to measure thermal neutron doses and fluence rates at positions outside the self-shielding of cyclotron, in the cases of using different targets. Besides, a 6LiI (Eu) detector with Bonner spheres were used and were placed at the specific locations in the cyclotron room to estimate the neutron spectra of using different operation parameters. In the results, the thermal neutron doses at the locations outside the self-shielding of cyclotron in the case of using target 1 were less than that using target 2. However, thermal neutron doses inside the self-shielding in the case of using target 1 were higher than that using target 2. The evaluated neutron spectra inside and outside the self-shielding confirmed the dose results. The impact of the volume of 18O-water target was discussed in this study. In conclusion, the large target volume (target 1) caused the higher production yield of 18F-radioisotope and induced lower dose and softer spectra of neutrons than the small target, under the same operation parameters which were adopted for validation in this study. [Copyright &y& Elsevier]

Abstract: The Neutron Measurements Laboratory of the Technical University of Madrid (LMN) has an automated panoramic irradiator with a 111 GBq 241Am–Be neutron source installed in a bunker-type large room. This facility is going to be used for calibration purposes. Recently, a spectrometry campaign involving four research groups working with different Bonner Sphere Spectrometers (BSS) and using different spectral unfolding codes was carried out. As part of these measurements the emission rate, B(t), was estimated. The application of the generalized fitting method to account for the scattering contribution is difficult due to specific characteristics of the neutron installation. A reduced fitting method, which includes room-return and in-scatter, has instead been used to overcome this problem. Detailed Monte Carlo simulations (with MCNPX code) were also performed to estimate the fluence rate using the measured source strength value. This was performed at different points. Results were then compared with measurements. Finally, the ambient dose equivalent rate measured with a neutron monitor (LB6411) was compared with results using the BSS. [ABSTRACT FROM AUTHOR]

Abstract: Since many decades, Bonner sphere spectrometers (BSSs) are routinely used for assessment of neutron spectra over a wide energy range from some meV to GeV. Typically, a spectrometer consists of a neutron detector sensitive to thermal neutrons located inside moderating polyethylene (PE) spheres of various sizes. Based on the response functions of the detector/sphere systems that must be calculated by Monte Carlo codes, an unfolding procedure is applied to deduce the present neutron spectrum from the count rates of the detectors. To start the unfolding procedure, a guess spectrum is required that includes some prior information on the physics of the investigated neutron spectrum, and that is iteratively modified to match the measured count rates. For the present investigation, a BSS-system consisting of an 3He proportional counter and seventeen spheres containing PE or a combination of PE and lead is used. The system is used for example to measure secondary neutrons from cosmic radiation at mountain altitudes, or from high-energy accelerators outside the radiation shielding. A systematic study was performed to quantify the influence of the chosen guess spectrum and the number of iteration steps on the unfolded neutron spectrum, and on integral quantities deduced such as total neutron fluence or ambient dose equivalent. It turned out that none of these changes resulted in dose quantities that were more than a few percent different to those deduced when the optimised start spectrum was used. Similarly, use of the two different response matrices available for our BSS system provided similar values for the ambient dose equivalent. [Copyright &y& Elsevier]

Abstract: The neutron emission from 50mm thick copper, silver and lead targets bombarded by a mixed proton/pion beam with momentum of 40GeV/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 3MeV and a high-energy peak sitting around 100–150MeV. The experimental neutron yields are given in four energy bins: <100keV, 0.1–20MeV, 20–500MeV and 0.5–2GeV. The total yields show a systematic discrepancy of 30–50%, with a peak of 70% at the largest angles, with respect to the results of the Monte Carlo simulations, which it is believed to be mainly due to uncertainties in the beam normalization factor. Analytic expressions are given for the variation of the integral yield as a function of emission angle and of target mass number. [Copyright &y& Elsevier]

The space distribution of the epithermal neutron flux was determined for the epithermal neutron beams of several NCT facilities in USA (FCB at MIT), Europe (HFR at JRC, Petten; FiR at VTT, Espoo; LVR-15 at NRI, Rez) and Japan (JRR-4 at JAERI, Tokai). Using p–n diodes with 6Li radiator and the set of Bonner sphere spectrometer (BSS) the beams were quantified in-air. Axial beam profiles along the beam axes and the radial distributions at two distances from the beam aperture were measured. Except for the well-collimated HFR beam, the spatial characteristics of the other studied beams were found generally similar, which results from their similar designs. [Copyright &y& Elsevier]

The neutron emission from 5, 10 and 20 mm thick lead and 10 and 20 mm thick copper targets bombarded by a lead ion beam with momentum of 158 GeV/c per nucleon were measured at the CERN Super Proton Synchrotron. The neutron yield and spectral fluence per incident ion on target were measured with an extended range Bonner sphere spectrometer in the angular range 30–135° with respect to beam direction. Monte Carlo simulations with the FLUKA code were performed to establish a guess spectrum for the unfolding of the experimental data. The results have shown that, lacking Monte Carlo radiation transport codes dealing with ions with masses larger than 1 amu, a reasonable prediction can be carried out by scaling the result of a Monte Carlo calculation for protons by the projectile mass number to the power of 0.85–0.95 for a lead target and 0.88–1.03 for a copper target. [Copyright &y& Elsevier]

Abstract: A multisphere neutron spectrometer was used to determine the features of a 239PuBe neutron source that is used to operate the ESFM-IPN Subcritical Reactor. To determine the source main features it was located a 100cm from the spectrometer which was a 6LiI(Eu) scintillator and 2, 3, 5, 8, 10 and 12 in.-diameter polyethylene spheres. Count rates obtained with the spectrometer were unfolded using the NSDUAZ code and neutron spectrum, total fluence, and ambient dose equivalent were determined. A Monte Carlo calculation was carried out to estimate the spectrum and integral features being less than values obtained experimentally due to the presence of 241Pu in the Pu used to fabricate the source. Actual neutron yield and the mass fraction of 241Pu was estimated. [Copyright &y& Elsevier]

Several experiments have been conducted in the YangYang Underground Laboratory in the Republic of Korea such as the search for dark matter and the search for neutrinoless double beta decay, which require an extremely low background event rate due to the detector system and the environment. In underground experiments, neutrons have been identified as one of the background sources. The neutron flux in the experimental site needs to be determined to design a proper shielding system and for precise background estimation. We measured the neutron spectrum with a Bonner sphere spectrometer, with Helium-3 (3He) proportional counters. The neutron flux at the underground laboratory was so low that the radioactive decays from the radioisotopes contained in the detector created a significant background interference to the neutron measurement. Using Monte Carlo simulations, the intrinsic α background distribution due to the radioactive isotopes in the detector materials, was estimated. The neutron count rate of each Bonner sphere was measured from the pulse height spectrum of the 3He proportional counter, after subtracting the α particle background. The neutron flux and the energy spectrum were determined using the unfolding technique. The total neutron flux measured was (4.46 ± 0.66) × 10−5 cm−2 s−1, and the thermal and fast neutron flux (in the range 1–10 MeV) were (1.44 ± 0.15) × 10−5 cm−2 s−1 and (0.71 ± 0.10) × 10−5 cm−2 s−1, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The characterization of the epithermal beam is performed by different dosimetry techniques that give information on neutron flux as well as neutron and photon doses. One of the possible methods is based on the measurement of thermal neutrons in a moderation environment, which enables the evaluation of neutron flux in a group structure and also neutron dose. The advantage of such a spectrometer consists of the fact that 90% response intervals of the spheres continuously cover the epithermal part of the neutron energy range. The method has been applied to characterize the epithermal neutron beams at several research centers in USA, Finland, the Netherlands and Czech Republic. The comparison of the MIT FCB, HFR HB11, VTT FiR, and LVR-15 beam parameters is presented in this paper. [Copyright &y& Elsevier]

FANT is the acronym of Enhanced Thermal Neutron Source (F uente A mpliada de N eutrones T érmicos , in Spanish). This is a parallelepiped box of high-density polyethylene moderator and an isotopic neutron source. The moderator has a cylindrical irradiation chamber where a rather uniform thermal neutron flux is obtained. The FANT design was previously optimized and the neutron spectra were estimated by Monte Carlo calculations with the MCNP6.1 code. To check the characteristics of the FANT thermal neutron field, measurements have been performed at the reference point inside the irradiation chamber with a Bonner sphere spectrometer holding a small 6LiI(Eu) thermal neutron detector. To unfold the neutron spectrum BUNKIUT with UTA4 response matrix and NSDann Ver 4.0 codes were used. Some issues have been found and recommendations are made about the use of large BSS inside narrow spaces, and about the capacity of NSDann code to unfold these kind of spectra. However, the results confirm that the moderation process in FANT is very effective and allows obtaining useful thermal neutron fluence rates. • FANT is a thermal neutron source based on 241Am/9Be source inside HDPE cavity. • Neutrons from a241Am/9Be source are moderated and scattered in the system. • Designed by Monte Carlo to increase the thermal neutron flux. • Bonner Spheres Spectrometer (BSS) used to determine the neutron spectrum. • BUNKIUT (UTA4) and NSDann Ver 4.0 spectral unfolding codes used. [ABSTRACT FROM AUTHOR]

Accurate nuclear data measurements require a good background control of the experimental environment. At the back-streaming white neutron source (the so-called Back-n White Neutron Source) at China Spallation Neutron Source that is dedicated for nuclear data measurements, comprehensive shielding measures have been employed around the neutron beam line to reduce the neutron and γ backgrounds in the experimental end-stations. The basic background generated by the neutron beam without samples was simulated by the Monte Carlo method and correspondingly measured with a Bonner sphere spectrometer. The results show that the experimental measurements and simulations are generally in good agreement, and the neutron background level meets the requirements of the nuclear data experiments. Moreover, the γ background that was measured by using liquid BC501A and NaI scintillator detectors is mainly from the natural radioactivity of environment, and the beam induced γ background is very weak, whereas the natural γ background can be removed by a coincidence in time with beam bunch or be deducted by background measurement without samples. While the present measurements prove that the neutron/ γ basic background has been well controlled, the experimentalists can devote the effort to solve the background problem caused by the samples. [ABSTRACT FROM AUTHOR]

The response function of a Bonner sphere spectrometer (BSS) plays a crucial role in deriving reliable energy distributions of neutron fluence from the experimental count of each sphere by using unfolding techniques. When using Monte Carlo codes to calculate the responses of a BSS, the factors of Bonner spheres descripted in the codes, e.g., material density and geometrical parameters, will influence the accuracy of the calculated responses. Therefore, experimental evaluation of the calculations using neutron sources is essential for establishing the response matrix. A Monte Carlo code Geant4 was used to calculate the responses of a BSS based on a 3He gas counter. The uncertainties of the calculated responses were analyzed after considering some factors, including the air gap between the gas counter and spherical moderators, the mass density of moderators, and the 3He gas pressure in the counter. Good agreement was found between the calculated responses (within uncertainties) and the experimental results on six ISO recommended monoenergetic neutron sources with energies from 144 keV to 14 MeV. To evaluate the capability of the Geant4 code in establishing the response matrix of a BSS, the calculated responses before and after experimental evaluation were illustrated and compared with the results obtained by using the Monte Carlo code MCNP5 for the BSS response calculation. These comparison results provide primary support of the effectiveness of the Geant4 code in establishing the response matrix of a BSS. • Uncertainties of the calculated responses were analyzed. • Responses in the energy range from 144 keV to 14 MeV were experimentally evaluated. • The comparison of calculated responses between GEANT4 and MCNP5 was carried out to further validate the capability of GENAT4 in establishing the response function of a Bonner sphere spectrometer. [ABSTRACT FROM AUTHOR]