Measurement Of Neutron Spectra Research Articles

Development of a Bonner sphere spectrometer with emphasis on decreasing the contribution of scattering by using a new designed shadow cone

In this study, the Bonner sphere spectrometer (BSS) used for measurement of neutron spectra based a BF3 long counter. The most important problem for this system was a high count of scattered neutrons. This spectrometer was established by designed a new shadow cone with a smaller length and improved attenuation coefficient. Because of shortening the length of the shadow cone, distance of source and center of the sphere was decreased. Furthermore, external part of the thermal detector was covered with a suitable layer to reduce the contribution count of scattering neutrons. Experimental results show that BSS system with BF3 long cylindrical counter, applying the proper developments, can be used in neutron fluence spectrometry.

Design and performance analysis of a compact magnetic proton recoil spectrometer for DT neutrons

A magnetic proton recoil (MPR) spectrometer is a novel instrument with superior performance, including high energy resolution, high count rate and good signal-to-noise ratio (SNR) for measurements of neutron spectra from inertial confinement fusion (ICF) experiments and high power Tokomaks. In this work, the design of a compact MPR spectrometer (cMPR) was evaluated for deuteron-tritium (DT) neutron spectroscopy. The characteristics of the spectrometer were analyzed using 2-D beam transport simulations, 3-D particle transport calculations and Monte-Carlo simulations. Based on the theoretical results, an instrument design that satisfies special experimental requirements is proposed. The energy resolution and efficiency of the spectrometer are also evaluated. The results indicate that the proposed cMPR spectrometer would achieve a detection efficiency and energy resolution of approximately 10−8 and 4%, respectively, for DT neutrons.

Shielding Experiments at High Energy Accelerators of Fermilab (III): Neutron Spectrum Measurements in Intense Pulsed Neutron Fields of The 120-GeV Proton Facility Using A Current Bonner Sphere Technique

High Energy Accelerator Research Organization, 1-1, Oho, Tsukuba, Ibaraki 305-0801, Japan Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195, Japan Kyushu University, 744, Motooka, Nishi-ku, Fukuoka 819-0395, Japan Fermilab, Batavia, IL 60510-5011, USA Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8578, Japan Shimizu Corporation, 4-17, Etchujima, 3-chome, Koto-ku, Tokyo 135-8530, Japan

Neutron Flux Measurements in ITER-TBM Simulating Assemblies by means of Multi-Foil Activation Method

We measured neutron spectra in beryllium and an ITER-TBM simulating assemblies by means of a Multi-Foil Activation Method (MFAM) at the FNS facility of JAEA to confirm applicability of MFAM. An unfolding code, NEUPAC, was used to determine neutron flux spectra. Initial guessed neutron spectra were calculated with the Monte Carlo code MCNP4C and a nuclear data library FENDL-2.1. JENDL Dosimetry File 99 was adopted as response data for reaction rates. We deduced neutron flux spectra in the simulated assemblies with the MFAM. From the experiments, it was found out that MFAM gave appropriate results, which indicated that MFAM was a prospect to the application of neutron spectrum measurement in ITER-TBM. However, it was also pointed out that some improvements for measurement of slow neutron below 10 eV were necessary.

Neutron Spectra Measurements at JAEA MOX Fuel Facility

Neutron Spectra Measurements at JAEA MOX Fuel Facility

New technical solution for using the time-of-flight technique to measure neutron spectra

New technical solution is proposed for using the time-of-flight technique to measure neutron spectra on VITA-facility. During 200 ns the energy of protons increases from 1.865 up to 1.915 MeV by supplying the square pulse of 50 kV on the neutron-generating target, which is isolated from facility body. During these 200 ns the generation of neutrons is performed. The spectrum can be obtained measuring the time of flight by a remote neutron detector.

有機液体シンチレータを用いた150 MeV 陽子入射におけるタングステンターゲットからの中性子スペクトル測定

有機液体シンチレータを用いた150 MeV 陽子入射におけるタングステンターゲットからの中性子スペクトル測定

Characteristics of the magnetic analysis system for a compact MPR-type spectrometer

The magnetic proton recoil (MPR) spectrometer is a novel diagnostic instrument with high performance for measurements of neutron spectra in inertial confinement fusion (ICF) experiments and high power fusion devices. A compact MPR-type spectrometer dedicated to the research of pulsed deuterium-tritium (DT) neutron spectroscopy of special experimental conditions is currently under design. Analyses of the main parameters and performance of the magnetic analysis system through 3-D particle transport calculations and MonteCarlo simulations and calibration of the system performance as a test using CR-39 solid track detector and α particle from 239Pu and 226Ra radioactive sources are presented in this paper. The results indicate that the magnetic analysis system will achieve a detection efficiency level of 10−5 −10−4 at an energy resolution of 1.5%–2.1%, and fulfills the design goals of the spectrometer.

CTOF measurements and Monte Carlo analyses of neutron spectra for the backward direction from a lead target irradiated with 200–1000 MeV protons

A calorimetric-time-of-flight technique was used for real-time, high-precision measurement of neutron spectra at an angle of 175 o from the initial proton beam direction, which hits a face plane of a cylindrical lead target of 20 cm in diameter and 25 cm thick. A comparison was performed between the neutron spectra predicted by the MARS, RTS&T, MCNP6, and the MCNPX 2.6.0 transport codes and that measured for 200, 400, 600, 800, and 1000 MeV protons. Neutron spectra were measured within the energy range from 0.7 to 250 MeV almost continuously. The transport codes tested here describe with different success the measured spectra, depending on the energy of the detected neutrons and on the incident proton energy, but all the models agree reasonably well with our data.

Measurement of neutron spectra and neutron doses at the Munich FRM II therapy beam with Bonner spheres

Abstract The neutron field at the FRM II neutron therapy was characterised by means of a Bonner sphere spectrometer. Inside the therapy room and the adjacent radiography room, gold foils were used in the center of the moderating polyethylene (PE) spheres of the spectrometer, to detect the moderated neutrons. The measured neutron spectra are dominated – as expected – by neutrons with an energy of about 1 MeV. The spectra were in quantitative agreement with those calculated by means of the MCNP code, by Breitkreutz and co-workers. Outside the therapy room, 3 He proportional counters were used to detect the neutrons moderated by the PE spheres of the spectrometer. Here, the spectra were much softer and included thermal neutrons as major component. Based on these neutron spectra, the neutron ambient dose equivalent rate H ˙ ∗ ( 10 ) was calculated. The resulting H ˙ ∗ ( 10 ) values were between 0.92 and 1.68 μSv/h, depending on the position outside the shielding. These values were in close agreement to the one measured by means of the AMIRA tissue-equivalent proportional counter. It is concluded that the neutron spectra at the neutron therapy facility at the new FRM II research reactor at Garching, Germany, are now well characterised.

Neutron dose distribution from 12C induced reactions on Ti and Ag using proton recoil scintillator

Abstract We measured the double differential neutron yield at 0°, 30°, 60° and 90° from 12 C 5+ induced reactions on thick targets of Ti and Ag at 12 MeV/amu at the Cyclotron at National Institute of Radiological Sciences, Inage, Japan, with 5″ × 5″ proton recoil scintillation detectors BC-501. The measured neutron spectra were unfolded using pulse height unfolding algorithm and energy and angular distribution obtained. Energy distribution of neutron ambient dose equivalent, H*(10) and absorbed dose, D at different angles was determined from double differential neutron spectra using ICRP recommended fluence to dose conversion coefficients.

Neutron spectra measurements in the south Atlantic anomaly region

Abstract In this work we present the results of measurements of the cosmic-ray neutron induced flux and spectra from the ground level up to the altitude of 2400 m, in the region between 22° S and 45° W, which is under the influence of the South Atlantic Anomaly (SAA). The measurements of neutron spectra induced by cosmic rays were carried out using a Bonner multi-sphere neutron spectrometer with a scintillation crystal of 6 LiI(Eu) and the data obtained by a modified Hanson and McKibben long-counter directed to the zenith were used to normalize the spectra.

The simulated workplace field with a high-energy neutron component produced by irradiating a Fe-target with 200 MeV/u 12C-ions

Abstract Recent developments in accelerator physics have led to new challenges for radiation protection dosimetry. Doses have to be determined for workplace fields which are characterized by high-energy radiation, a dominant contribution from neutrons, high intensities and pulsed time structure This may present problems for active measuring devices. As is well known, the ambient dose equivalent is often underestimated by area monitors operating in high-energy neutron fields behind shielding. Therefore, it is desirable to calibrate survey monitors in a characterized neutron field with the type of spectral fluence distribution that is expected behind shielding, i.e. where the main dose from neutrons arises from two peaks with mean energies of about 1 MeV and 100 MeV, respectively. Such a neutron fluence distribution is produced by the irradiation of a Fe-target with 200 MeV/u 12C-ions. Measurements with the extended range Bonner sphere spectrometer NEMUS of PTB were performed at two positions inside the experimental area Cave A of the heavy-ion synchrotron SIS at GSI. The measured neutron spectra show different fluence contributions for the two peaks at the two positions. The results were compared to Monte Carlo Simulations with MCNPX and FLUKA.

Measurement with Bonner spheres spectrometer in pulsed neutron fields

Paper presents results of measurements of neutron spectra with Bonner spheres spectrometer around radiotherapeutic linac producing undesirable photoneutrons and around plasma focus device PF-1000 in which neutrons are generated in 2 H + 2 H → n + 3 He reaction. In the Bonner spheres an active detector, proportional counter filled with 3 He, was replaced by passive one to avoid overloading of the active detector during very short period of neutrons generation. For the measurements around linac track detectors with 10 B radiator were used and around plasma focus device pairs of TLDs ( 6 LiF and 7 LiF).

Dosimetry and spectrometry at accelerator based neutron source for boron neutron capture therapy

Abstract An innovative accelerator-based neutron source for boron neutron capture therapy has started operation at the Budker Institute of Nuclear Physics, Novosibirsk. This facility is based on a compact vacuum insulation tandem accelerator designed to produce proton current up to 10 mA. Epithermal neutrons are proposed to be generated by 1.915 MeV protons bombarding a lithium target using 7 Li( p , n ) 7 Be threshold reaction. In the article, techniques to detect neutron and gamma-rays at the facility are described. Gamma radiation is measured with NaI and BGO gamma-spectrometers. The total yield of neutrons is determined by measuring the 477 keV γ-quanta from beryllium decay. For the rough analysis of the generated neutron spectrum we used bubble detectors. As the epithermal neutrons are of interest for neutron capture therapy the NaI detector is used as activation detector. We plan to use a time-of-flight technique for neutron spectra measurement. To realize this technique a new solution of short time neutron generation is proposed.

Measurements of leakage neutron spectra from a high-energy accumulation ring using Extended Range Bonner Sphere Spectrometers

Abstract Within the INFN–UAB cooperation, an experimental neutron spectrometry exercise was organized in DAΦNE, the high-energy Φ-meson producing accelerator (Φ-factory) of the INFN–Frascati National Laboratories. Particularly, the workplace neutron fields produced by a 510 MeV positron beam accumulated in the DAΦNE ring were characterized. As suitable instruments, the INFN and UAB Extended Range Bonner Sphere Spectrometers (ERBSS) were employed. These systems rely on different central detectors and have different sets of extended-range spheres. The experimental data were unfolded with the FRUIT unfolding code, especially designed for workplace measurements in absence of detailed pre-information on the neutron field. This analysis allowed studying the high-energy (>10 MeV) component of the neutron fields and assessing the performance of the two different ERBSS in this energy domain. Besides the discussion on ERBSS, this paper presents experimental data that may be used in radiation protection of high-energy positron beams.

Design and experimental validation of a Bonner Sphere Spectrometer based on Dysprosium activation foils

Abstract The increasing demand of rapid and reliable experimental techniques for the dosimetric characterization of high-intensity neutron fields, as those produced by radiotherapy and radioisotope installations, is the main reason for this study. In the past years INFN implemented a Bonner Sphere System, equipped with TLDs or gold activation foils, which was successfully employed for neutron spectra measurements around medical LINACs. The INFN–ENEA collaboration extended this methodology to Dysprosium activation foils. Taking advantage of the high activation cross section (2700 barn at 0.025 eV), the photon insensitivity and the reasonably short half live (2.334 h), the Dy-based BSS (Dy-BSS) is highly suited for operational measurements, where short irradiations and short measurement times are desirable. This work presents the response matrix of the Dy-BSS, calculated with MCNPX, and the results of its experimental validation, performed with reference neutron fields at the ENEA-Bologna labs. In addition, the newly developed Dy-BSS and the traditional gold foil-based BSS are compared, underlying the advantages of the new system.

Testing Bonner sphere spectrometers in the JRC-IRMM mono-energetic neutron beams

Within the framework of the Euratom Transnational Access programme, a specific sub-programme, called NUDAME (neutron data measurements at IRMM), was dedicated to support neutron measurement experiments at the accelerator-based facilities of the JRC-IRMM Geel, Belgium. In this context, the INFN-LNF and UAB groups undertook two separate experiments at the 7 MV Van de Graaff facility, aimed at testing their Bonner sphere spectrometers (BSS) with mono-energetic neutron beams. Both research groups routinely employ the BSS in neutron spectra measurements for radiation protection dosimetry purposes, where accurate knowledge of the BSS response is a mandatory condition for correct dose evaluations. This paper presents the results obtained by both groups, focusing on: (1) the comparison between the value of neutron fluence provided as reference data and that obtained by applying the FRUIT unfolding code to the measured BSS data and (2) the experimental validation of the response matrices of the BSSs, previously derived with Monte Carlo simulations.

Re-characterization of irradiation facilities for k0-NAA at RPI after conversion to LEU fuel and re-arrangement of core configuration

The 1 MW pool-type Portuguese research reactor (RPI) was converted from using highly enriched uranium (HEU) to using low enriched uranium (LEU) fuel in September 2007. Although the new LEU core has the same number of fuel assemblies as the first HEU core, it has three assemblies less than the last HEU core and also has a different arrangement of the beryllium reflectors. Therefore, the primary irradiation positions that are used with the k 0-based neutron activation analysis ( k 0-NAA) at the RPI were redefined and characterized. The neutron spectrum parameters of the deviation of the epithermal neutron spectrum distribution from the 1/ E shape ( α), the thermal to epithermal neutron flux ratio ( f), the thermal to fast neutron flux ratio ( f F) and the neutron temperature ( T n) were determined by using a combination of Au, Lu, Ni and Zr monitors. The experimental results of the neutron spectrum parameters obtained in this study are compared to the results were obtained prior to the refuel conversion in the applicable irradiation positions. The synthetic multi-element standard SMELS was used to verify the accuracy of k 0-NAA applied to practical samples using the newly measured neutron spectrum parameters.

Accelerator Experiments on Source Term and Radiation Shielding Performed by Japan Atomic Energy Agency

Three accelerator experiments on source term and radiation shielding performed by the staffs of Japan Atomic Energy Agency (JAEA) to validate the accuracy of the radiation behavior simulation code PHITS (Particle and Heavy Ion Transport code System) are reviewed. In the measurement of neutron spectra from a thin beryllium target bombarded with ˜10-MeV protons, measured peak energies and values of the cross section were the same as those in the Evaluated Nuclear Data File ENDF/B-VII. In the measurements of forward-direction neutron spectra from thick targets bombarded with 140-, 250-, and 350-MeV protons, the calculated spectra from an iron target by the PHITS code agreed well with the measured spectra. In the measurement of neutron spectra from a tungsten target bombarded with ˜400-MeV protons, the shape of neutron spectra and its intensity are compared with that in Los Alamos Neutron Science Center/Weapons Neutron Research.