Measured Neutron Energy Spectra Research Articles

Feasibility study on epithermal neutron field for cyclotron-based boron neutron capture therapy.

To realize the accelerator-based boron neutron capture therapy (BNCT) at the Cyclotron and Radioisotope Center of Tohoku University, the feasibility of a cyclotron-based BNCT was evaluated. This study focuses on optimizing the epithermal neutron field with an energy spectrum and intensity suitable for BNCT for various combinations of neutron-producing reactions and moderator materials. Neutrons emitted at 90 degrees from a thick (stopping-length) Ta target, bombarded by 50 MeV protons of 300 microA beam current, were selected as a neutron source, based on the measurement of angular distributions and neutron energy spectra. As assembly composed of iron, AlF3/Al/6LiF, and lead was chosen as moderators, based on the simulation trials using the MCNPX code. The depth dose distributions in a cylindrical phantom, calculated with the MCNPX code, showed that, within 1 h of therapeutic time, the best moderator assembly, which is 30-cm-thick iron, 39-cm-thick AlF3/Al/6LiF, and 1-cm-thick lead, provides an epithermal neutron flux of 0.7 x 10(9) [n cm(-2) s(-1)]. This results in a tumor dose of 20.9 Gy-eq at a depth of 8 cm in the phantom, which is 6.4 Gy-eq higher than that of the Brookhaven Medical Research Reactor at the equivalent condition of maximum normal tissue tolerance. The beam power of the cyclotron is 15 kW, which is much lower than other accelerator-based BNCT proposals.

Measurement of neutron energy spectra from 15 to 150 MeV using stacked liquid scintillators

A multiple liquid scintillator system for measuring the energy spectrum of a neutron beam in the range 15–150 MeV is described. Two or more slabs of NE213 scintillator (13×13×7 cm 3) are stacked behind one-another and only events in which a neutron interacts in the upstream scintillator are analysed. The system is designed to minimise the escape of forward recoil protons from the detecting media. Test measurements and Monte Carlo simulations of the detector response to quasi-monoenergetic neutron beams of energies 62.5 and 97.5 MeV are presented.

Measurement and analysis of leakage neutron energy spectra around the Kinki University Reactor, UTR-KINKI

The highly sensitive cylindrical multi-moderator type neutron spectrometer was constructed for measurement of low level environmental neutrons. This neutron spectrometer was applied for the determination of leakage neutron energy spectra around the Kinki University Reactor. The analysis of the leakage neutron energy spectra was performed by MCNP Monte Carlo code. From the obtained results, the agreement between the MCNP predictions and the experimentally determined values is fairly good, which indicates the MCNP model is correctly simulating the UTR-KINKI.

Fusion neutron energy spectra measured by time-of-flight spectrometers

Evaluation of measured neutron energy spectra provides information on the central ion velocity distribution; e.g. ion temperature and fast ions induced by NBI- or ICR-heating and on impurity content in fusion grade plasmas. Two self-contained high-energy resolution time-of-flight neutron spectrometers have been used at the JET- and JT-60U tokamaks during DD-operation. In the spectrometers, each neutron undergoes (n, p) elastic scattering in two sets of hydrogen based scintillators. Elapsed time between the two scatter events is measured and the energy of the neutron is evaluated. Interpretation of acquired data together with results obtained from other diagnostics yields information on central plasma parameters. Deduced ion temperatures, fast ion fractional contributions during auxiliary NBI- and ICR-heating and impurity content is presented. In general, good agreement is obtained between neutron data and data from other diagnostics.

Russian measurements of neutron energy spectra on the Mir orbital station

Results of the experiments on neutron energy spectra measurements within broad energy range from 5×10 −7 to 2×10 2 MeV aboard the Mir orbital station and equivalent neutron dose estimation are presented. Four measurement techniques were used during the experiments. The shape of spectra and their absolute values are in good agreement. According to those experiments, an equivalent neutron dose depends upon effective shielding thickness and spacecraft mass. The neutron dose mentioned is comparable with that of ionizing radiation. Neutron flux levels measured aboard the Mir station have shown that a neutron spectrometer involving broad energy range will be used within the radiation monitoring systems in manned space flights.

Prediction and measurement of neutron energy spectrum in a material test research reactor

The objective of this work is to calculate and measure the neutron energy spectrum in the Pakistan Research Reactor-1 (PARR-1), which is a typical Material Test Reactor (MTR) fueled with low enriched uranium. The method of multiple foil activation was used with the adjustment code MSITER, a modified version of the code STAY'SL, to obtain the experimentally measured spectrum. The calculated spectrum, which was used as pre-information in the adjustment procedure, was obtained through modeling the core and its surroundings in three-dimensions and the use of the transport code WIMS-D/4 and the diffusion code CITATION. A comparison between the calculated and measured spectra shows that the ratio of measured to calculated flux density in the thermal region ( E ⩽0.5 eV) is 0.998. This ratio is 1.02 for resonance (1/ E) region (0.5 eV < E ⩽ 0.5 MeV) and 0.932 for the fast region ( E > 0.5 MeV). This result is compared with other published results that report an agreement within 10 to 30% between the calculated and measured spectra.

Results from Monte Carlo simulations of the neutron transport for the new 2.45 MeV neutron time-of-flight spectrometer for the JT-60U tokamak

A 2.45 MeV neutron time-of-flight spectrometer is under design and construction for the measurements of neutron energy spectra from the JT-60U Tokamak. This paper describes the results from the Monte Carlo code, McTOF, which was written for the simulations of the response functions of the spectrometer. The spectrometer consists of two fast plastic scintillators (50 and 1800 cm 2; thickness, 2 cm) located on a constant time-of-flight sphere. By introducing a second time-of-flight sphere, it was found that if the first scattering scintillator was tilted an angle of 70° (utilizing the properties of the second sphere), the resolution of the instrument improved by more than 30%. For a given standard set-up of the spectrometer, the resolution was obtained as 105 keV (4.3%) with an efficiency of 2.8×10 −2 cm 2. This means that for high JT-60U neutron yields (∼10 16 n/s), five to 10 neutron spectra can be measured per plasma pulse. The simulated response functions showed a Gaussian distribution. The parameters of the Gaussian could then be expressed as third-degree polynomials in the source neutron energy interval 1.6–3.6 MeV. This implies that, to extract the measured neutron spectrum, a quick procedure for the folding of a guessed source neutron energy spectrum and an analytical value of the response function can be made.

Spectral measurements of neutrons, protons, deuterons and tritons produced by 100 MeV/nucleon He bombardment

We measured angular and energy distributions of neutrons, protons, deuterons and tritons produced by 100 MeV/nucleon He ions stopping in thick carbon, aluminum, copper and lead targets using the HIMAC (Heavy Ion Medical Accelerator in Chiba) of NIRS (National Institute of Radiological Sciences), Japan by using the time-of-flight method coupled with the Δ E– E counter system. The Δ E counter of the NE102A plastic scintillator was used to discriminate charged particles from noncharged particles and to measure charged particle energy spectra. The E counter of the NE213 liquid scintillator was used to measure neutron energy spectra. The experimental spectra were compared with the calculation using the LCS code and the calculated spectra are generally in rather good agreement with the measured spectra of these four secondary particles.

New Methods for Measurement of Neutron Energy Spectrum with CR-39 Nuclear Track Detectors

The techniques for measurement of neutron energy spectrum with CR-39 detectors have been recently developed, which are based on measurements of the mixed restricted energy loss (REL) (i.e., part of energy loss where energy carried by δ-ray electrons is less than the ω0-ceiling on the energy of delta rays) distribution of the recoil nuclei of C and O inside CR-39 induced by fast neutrons. One of the methods for obtaining the neutron energy spectrum from the REL distribution of the recoil nuclei of C and O inside CR-39 is to determine the true ratio of C/O in each channel of REL distribution, which can be carried out using the computer program written by us. The other method is similar to the Monte Carlo simulations, which can be done by obtaining a calculated REL distribution of the recoil nuclei of C and O through the angular distributions of the scattering neutrons in the center of the mass system under an assumed neutron energy spectrum. For the sake of checking the correctness and the accuracy of these methods, measurements of monoenergetic neutrons (En=13.3 MeV) have been carried out by these methods. The feasibility of measuring the neutron energy spectrum with CR-39 with these techniques has been shown.

Measurements and Calculations of Neutron Energy Spectra Behind Polyethylene Shields Bombarded by 40- and 65-MeV Quasi-Monoenergetic Neutron Sources

Measurements of neutron energy spectra behind 30.5-, 61.0-, 122.0-, 183.0-cm-thick polyethylene shields bombarded by 40- and 65-MeV quasi-monoenergetic neutrons are performed at the 90-MeV AVF cyclotron of the TIARA (Takasaki Ion Accelerator for Advanced Radiation Application) at JAERI (Japan Atomic Energy Research Institute). Source neutrons are produced at 3.6- and 5.2-mm-thick7 Li targets bombarded by 43- and 68-MeV protons, respectively. A BC501A organic liquid scintillator and multi-moderator spectrometer with a 3He counter (Bonner ball) are used for spectrometry of transmitted neutrons and their energy spectra are obtained with the unfolding technique. The energy spectra from a few MeV up to a peak energy are obtained by the BC501A scintillator measurement and those below a few MeV down to thermal energy are obtained by the Bonner ball measurement. The measurements are performed on the neutron beam axis and at off-center positions, and attenuation profiles of neutron fluxes along the beam axis are obtained. The MORSE Monte Carlo calculations are performed with the DLC119/HIL086 multi-group cross section library for comparison with the measured data. The calculation generally gives a little overestimated fluxes, and a few % longer attenuation lengths of peak flux and dose equivalent.

Neutron Dose Equivalent Rates Calculated from Measured Neutron Angular and Energy Distributions in Working Environments

The estimation of non-isotropic neutron dose equivalent quantities in multidirectional fields is complicated. The estimation must be based on the neutron fluence rate as a function of both energy and angle. There are several well developed techniques for measuring neutron energy spectra. However, the directional characteristics have not usually been investigated in detail. The personal dose equivalent inside the PWR stations studied varies by a factor of 4 between AP and ISO irradiation geometries, but only by a factor of 2 between different locations for AP irradiation. This indicates the importance of knowing the directional distribution, in order to interrelate personal dose equivalent, effective dose equivalent (effective dose) and ambient dose equivalent, and to interpret dosemeter and instrument readings. A purpose built phantom has been constructed and used for the separation of the neutron fluence into 18 incident directions. Measurements with the phantom have been made at workplaces at Ringhals Nuclear Power Plant. The phantom consists of a 19 cm diameter boron doped paraffin sphere. Boron was added to decrease the transmission of neutrons through the sphere and to decrease the photon contribution from (n;gamma) reactions inside the phantom to the measurement of dose equivalent from incident photons. The phantom has proved to be capable of separating the incident neutrons into 18 directions and effective in reducing (n;gamma) reactions. Measured neutron angular distributions with coarse energy information were used with previously measured neutron spectra, to make better estimates of the neutron personal dose equivalent rates at these workplaces in Swedish nuclear facilities. The values of personal dose equivalent calculated with separation into 18 incident directions are slightly lower than those calculated for 2 or 3 directional distributions (AP, ISO and/or ROT). Results of calculations of neutron personal dose equivalent using the new (ICRP Publication 60) Q(L) function and new stopping powers, are also given, with and without resolution into 18 incident directions.

Measurement of Neutron Energy Spectrum below 10 keV in an Iron Shield Bombarded by Deuterium-Tritium Neutrons and Benchmark Test of Evaluated Nuclear Data from 14 MeV to 1 eV

Neutron spectra below 10 keV in an iron shield assembly bombarded by deuterium-tritium neutrons are measured with accuracy between 5 to 13% by adopting the slowing-down time method. The measurement supplemented previous spectrum measurements for higher energies so that the neutron spectrum in the whole energy range from 14 MeV down to 0.3 eV is now available. Benchmark tests of iron data in JENDL-3.1, JENDL-3.2, JENDL fusion file, and FENDL/E-1.0 were carried out in the whole energy range with experimental uncertainty at ∼10% by utilizing the present and previous experiments. As a result, it was found that cross-section data in the newer versions of JENDL were improved in terms of agreement with the experiment. Calculation with JENDL fusion file and FENDL/E-1.0 could predict neutron fluxes in the whole energy range within 20 and 15%, respectively. Possible over- and underestimations for nonelastic and elastic cross sections, respectively, at 14 MeV in all JENDLs were pointed out. It was confirmed that low-energy neutron fluxes were very sensitive to Q values for discrete inelastic cross sections of natural iron and 57Fe(n,n’1,) reaction, which were not adequately treated in JENDL-3.1.

Measurements and Calculations of Neutron Energy Spectra Behind Polyethylene Shields Bombarded by 40- and 65-MeV Quasi-Monoenergetic Neutron Sources.

Measurements of neutron energy spectra behind 30.5-, 61.0-, 122.0-, 183.0-cm-thick polyethylene shields bombarded by 40- and 65-MeV quasi-monoenergetic neutrons are performed at the 90-MeV AVF cyclotron of the TIARA (Takasaki Ion Accelerator for Advanced Radiation Application) at JAERI (Japan Atomic Energy Research Institute). Source neutrons are produced at 3.6- and 5.2-mm-thick7 Li targets bombarded by 43- and 68-MeV protons, respectively. A BC501A organic liquid scintillator and multi-moderator spectrometer with a 3He counter (Bonner ball) are used for spectrometry of transmitted neutrons and their energy spectra are obtained with the unfolding technique. The energy spectra from a few MeV up to a peak energy are obtained by the BC501A scintillator measurement and those below a few MeV down to thermal energy are obtained by the Bonner ball measurement. The measurements are performed on the neutron beam axis and at off-center positions, and attenuation profiles of neutron fluxes along the beam axis are o...

Spallation neutron spectra measurements Part I: Time-of-flight technique

We present an experimental method based on a time-of-flight technique between the tagged incident particles and a thick liquid NE213 scintillator to measure neutron energy spectra from 3 to 400 MeV at the Saturne synchrotron of Saclay. Efficiency measurements are made using a pulsed neutron source from the Tandem Van de Graaff of Bruyères-le-Châtel at low energies and a quasi-monoenergetic neutron beam at Saturne up to 50 MeV.

Measurements of fast and intermediate neutron energy spectra on MIR space station in the second half of 1991

This paper describes the neutron energy spectra measured inside and outside the Mir space station. The measurements were made during the second half of 1991 with nuclear emulsions and a neutron and recoil proton spectrometer, whose output data was telemetry-transmitted. In the fast-neutron ( E n > 1.0 MeV) range, the measurements were carried out using the method of recoil protons in a stack of nuclear photoemulsions (NPE) and in an organic scintillator. To determine spectra of intermediate-energy resonance neutrons (1.0 MeV ≥ E n ≥ 10 −2 MeV), an attempt was made to use the NPE method by adding lithium salts. The measurements are characterized by long-term (133 days) exposures of passive detectors and by sizeable effective shielding thicknesses of the inside detector estimated to be ∼40 g cm −2. The experimental results are compared with each other and with the data published elsewhere. The neutron spectra measured are used to calculate the equivalent dose rates inside and outside the Mir station in various neutron energy ranges. The equivalent neutron dose estimated by measuring the spectra in the (1–10 MeV) range only (as done in earlier works) is observed to entail substantial underestimating of the true neutron dose. Comparison is made of the calculated neutron doses with similar calculations of ionizing-radiation doses for shielding thickness of ∼ 40 g cm −2. It is emphasized that the study should be continued.

High resolution measurements of neutron energy spectra from Am[sbnd]Be and Am[sbnd]B neutron sources

A 3He sandwich spectrometer incorporating two semiconductor detectors and a proportional counter region has been designed and constructed to perform high resolution measurements of neutron energy spectra in the energy range 100 keV to 15 MeV. The efficiency of the spectrometer was determined experimentally, using a 252Cf spontaneous fission source, in the low-scatter facility of the National Physical Laboratory. The Monte Carlo technique was also used to determine the efficiency and these calculated values were used to extrapolate the measured efficiency to higher energies. The neutron energy spectra from two different sized AmBe neutron sources and an AmB neutron source were measured. Although these spectra have been measured previously, the present work represents an improvement in the energy resolution and extends the energy range. Average values for dose equivalent quantities for neutrons from these sources are also presented. The spectral data is available from the authors, as a printed table or on a computer diskette, on request.

Measurements of fusion neutron energy spectra at JET by means of time-of-flight techniques

High fluxes of neutrons are emitted from the JET tokamak when deuterium plasmas are raised to high temperatures with neutral beam injection and ion cyclotron resonance heating. The energy distribution of these neutrons carries valuable information concerning the velocity distributions of the reacting ions. A double scattering time-of-flight spectrometer is used for measuring the neutron energy distribution. This spectrometer provides an efficiency of 5 × 10 −2 cm 2, an energy resolution of 4.6% (FWHM) and is cascade of a maximum count-rate of ≈ 2 × 10 4c/s. An overview of results obtained at the JET tokamak is provided. The methods of analysis used to obtain information on ion temperatures, fractional contributions of the different neutron source reactions, high energy tail formation and on reactions with impurity ions are described. The use of a time-of-flight counter to measure the ratio of neutron fluences from deuterium-tritium and deuterium-deuterium reactions during the first deuterium-tritium experiment is also described.

９９０．ＰｕＯ２‐ＵＯ２混合燃料および含鉛アクリル遮蔽体透過後の中性子スペクトル測定

９９０．ＰｕＯ２‐ＵＯ２混合燃料および含鉛アクリル遮蔽体透過後の中性子スペクトル測定

The JET neutron time-of-flight spectrometer

Abstract An instrument for measuring neutron energy spectra over the interval 1 to 20 MeV has been developed and tested. It is based on time-of-flight measurements in between correlated events in two spatially separated sets of plastic scintillators. This instrument has been installed at the Joint European Tours (JET). We describe here the required operating conditions, performance tests and results of three years of operation during which neutron energy spectra in the 2–3 MeV range from D(d, n)3He reactions in JET were studied. Some technical details are given and the results from Monte Carlo and analytical model calculations of the spectrometer energy resolution and response function are presented. The efficiency of the system is ≈ 1 × 10−2 cm2 counted at the position of the first detector. Together with the geometry conditions at JET this yields 6 × 102 counts per 1015 neutrons emitted. The energy resolution is in the interval from 125 to 133 keV (FWHM) depending on conditions and is known to an accuracy of ±5 keV. Correction for the inevitable random background is dealt with in detail and a reduction procedure valid for fast variations in neutron count-rates is provided. Plasma ion temperatures deduced from the neutron spectra agree within statistical limits with the results from other diagnostic techniques in use at JET. Stable behaviour up to useful count-rates of 3 × 103 counts/s have been obtained, making possible the study of neutron spectra on the short time-scales typical of fusion plasmas.

The application of the bubble detector to the measurement of intense neutron fluences and energy spectra

A novel type of bubble detector is developed which can measure neutron fluences on the order of 10/sup 11/ n/cm/sup 2/ (or a few grays). These detectors use superheated droplets which are much smaller than those in conventional bubble detectors. Preliminary studies involving several types of these microdroplet detectors having different neutron energy thresholds have been performed. The goal is to develop a set of such detectors which can be used as a simple neutron spectrometer needed in connection with TREE applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>