Nuclear Instruments and Methods in Physics Research, Nov 1, 2022
The need for a relativistic approach when calculating proton recoil telescope efficiencies
Nuclear Instruments and Methods, Aug 1, 1980
Abstract The importance is pointed out of employing the full relativistic centre-of-mass to labor... more Abstract The importance is pointed out of employing the full relativistic centre-of-mass to laboratory transformation when ENDF/B cross section values are used to calculate proton recoil telescope efficiencies.
Determination of the He3 number density for the proportional counter used in the NPL Bonner sphere system
At the National Physical Laboratory, the standard instruments for measuring the neutron fluence o... more At the National Physical Laboratory, the standard instruments for measuring the neutron fluence of accelerator based neutron fields are long counters. This work follows on from an earlier project to derive improved knowledge of the response functions of the instruments using Monte Carlo calculations and measurements. In the present work new values for the effective centre as a function of energy have been calculated and validated experimentally. The efficiency values from the earlier work have been revisited in the light of new measurements and calculations. A sensitivity analysis has been performed to investigate the uncertainties in the calculated values. A final set of effective centre and efficiencies has been produced with realistic uncertainties for both the De Pangher and McTaggart type long counters.
Nuclear Instruments and Methods in Physics Research, Dec 1, 2007
The discrimination of neutron and gray events in an organic scintillator with the pulse gradient ... more The discrimination of neutron and gray events in an organic scintillator with the pulse gradient analysis (PGA) method is verified against that achieved via the digital measurement of time of flight (TOF). Events arising from the 7 Liðp; nÞ 7 Be reaction have been detected with an LS-301 organic liquid scintillator and recorded with a fast digital sampling oscilloscope. Both qualitative (via the crossreferencing of scatter diagrams) and quantitative (via the neutron/g-ray ratio) comparisons are reported. Discrimination afforded by the PGA method is observed to be consistent with that achieved by digital TOF.
Characterisation of a gold foil-based Bonner sphere set and measurements of neutron spectra at a medical accelerator
Nuclear Instruments and Methods in Physics Research, 2002
The characteristics of a Bonner sphere set with gold foils as the thermal neutron sensor are desc... more The characteristics of a Bonner sphere set with gold foils as the thermal neutron sensor are described. To illustrate the application of this neutron spectrometer in a pulsed field with an intense photon component, the results of measurements at a hospital electron accelerator are presented.
Corrigendum to Revision of the 252Cf and D2O moderated 252Cf reference neutron fields for use in radiation protection dosimetry. Radiat. Phys. Chem. Vol.184, (July 2021), 109433
Calibration and Monte Carlo modelling of the NPL long counters at 22.8 keV
An extensive programme was successfully carried out during the 1995 to 1998 NMS programme to re-c... more An extensive programme was successfully carried out during the 1995 to 1998 NMS programme to re-calibrate and model by Monte Carlo simulations the characteristics of two NPL long counters that are routinely used to standardise neutron fluences [Ta98, Ta00] for neutron energies above 500 keV. The present work is a continuation of it in that the counters responses and effective centres have been measured and simulated for a neutron energy of 22.8 keV using an antimony-beryllium (124SbBe) photon-neutron source. The neutron source emission rate was measured using the manganese sulphate bath technique. The efficiency and effective centres of both counters have been measured in a low scatter facility at NPL and calculations have been performed using MCNP4C.
Experimental Determination of the Response of Four Bonner Sphere sets to Monoenergetic Neutrons
Radiation Protection Dosimetry, Jun 1, 1988
In a joint PTB/NPL/GSF experimental programme the responses of four sets of Bonner Spheres were d... more In a joint PTB/NPL/GSF experimental programme the responses of four sets of Bonner Spheres were determined experimentally using monoenergetic neutrons in the range from 8 keV to 2.5 MeV. The measurements showed effects which can be understood qualitatively, but there are discrepancies with calculated values. It is questionable if these discrepancies can be explained by differences in the polyethylene density and detector characteristics employed in this experiment and those assumed in the calculations.
Experimental comparison of 241Am-Be Neutron fluence energy distributions
Radiation Protection Dosimetry, May 13, 2007
(241)Am-Be(alpha,n) neutron sources provide one of the most commonly used neutron fields for rout... more (241)Am-Be(alpha,n) neutron sources provide one of the most commonly used neutron fields for routine calibration of neutron sensitive devices. The neutron energy distribution of the IRSN standard (241)Am-Be source was measured in the energy region above 1.65 MeV using a BC501A proton-recoil liquid scintillator. The experimental data were compared to the ISO-recommended neutron energy distribution for an (241)Am-Be source. Some differences in shape were observed, with large variations mainly within the energy interval 3-6 MeV and around 8 MeV. Within the framework of a collaboration between three national metrological institutes (PTB, Germany; NPL, UK and LNE-IRSN, France), the neutron energy distributions of (241)Am-Be sources at each laboratory have been compared. The IRSN-BC501A proton-recoil scintillator was used to measure all the sources. The results show different energy distributions a priori influenced by the origin of the source, i.e. the manufacturing process. The maximum deviation observed for the integral dose equivalent, in the measured BC501A energy range, is within the 4% uncertainty recommended by ISO standard 8529-2 to allow for variations of the neutron spectrum among different (241)Am-Be sources. However, knowledge of the energy distribution of an (241)Am-Be source provides a way to reduce the uncertainty in the dose equivalent rate delivered by such a source.
A directional neutron spectrometer named NCT-WES (Neutron Capture Therapy Wide Energy Spectromete... more A directional neutron spectrometer named NCT-WES (Neutron Capture Therapy Wide Energy Spectrometer) was developed for quality assurance of the therapeutic neutron beam in Neutron Capture Therapy (NCT). NCT-WES operates as a "parallelized" Bonner spheres spectrometer, embedding six semiconductor-based thermal neutron detectors in a collimated cylindrical moderator. With the objective of validating the simulation model used to derive its response matrix, irradiations in reference monoenergetic fields were performed at National Physical Laboratory (UK). As the energy distributions of neutron beams in NCT extend from keV to a few MeV, monoenergetic fields in this domain were chosen, namely 71.5 keV, 144.2 keV, 565.1 keV, 841.9 keV and 1200.4 keV. The results of the experiment confirm the correctness of the NCT-WES simulation model, within an overall uncertainty lower than ± 2%.
The European Radiation Dosimetry e.V. is a non-profit organization promoting research and develop... more The European Radiation Dosimetry e.V. is a non-profit organization promoting research and development and European cooperation in the field of the dosimetry of ionizing radiation. It is registered in the Register of Associations (Amtsgericht Braunschweig, registry number VR 200387) and certified to be of non-profit character (Finanzamt Braunschweig-Altewiekring, notification from 2008-03-03). Liability Disclaimer No liability will be undertaken for completeness, editorial or technical mistakes, omissions as well as for correctness of the contents.
<title>Developments in neutron spectrometry for radiation protection</title>
Proceedings of SPIE, Mar 3, 1995
Following a brief review of neutron spectrometers used for measurements around nuclear installati... more Following a brief review of neutron spectrometers used for measurements around nuclear installations, and of the results obtained to date with these devices, the reasons for performing spectrometry measurements are outlined. The implications of measured spectral shapes for neutron dosimetry are then discussed.
Neutron scatter characteristics of the low-scatter facility of the Chadwick Building, NPL
The aim of this work was to provide information which could be used to improve the efficiency and... more The aim of this work was to provide information which could be used to improve the efficiency and cost effectiveness with which regular calibrations and checks of area survey instruments and personal dosemeters are carried out. To this end the variation in functional scatter component with distance from the neutron source has been determined using calculations, spectrometry and by reviewing the results of calibrations carried out since 1989, together with studies performed at NPL in 1982 and 1988. Scatter fraction relationships have been produced for 241Am-Be and 252 Cf sources, in terms of neutron fluence, ambient dose equivalent and instrument responses.
Measurement of the fast neutron component in the beam of the NPL Thermal Neutron Column using a Bonner sphere spectrometer
Following a recent refurbishment of the NPL Thermal Neutron Facility I the spectrum of the epithe... more Following a recent refurbishment of the NPL Thermal Neutron Facility I the spectrum of the epithermal and fast neutron component of the beam produced by the thermal column of this facility was measured over the energy range from thermal to 20 MeV using a Bonner sphere spectrometry system. The effect of the presence of epithermal and fast neutrons on the measured response of commonly-used thermal neutron dosemeters was calculated.
A high resolution neutron spectrometry system for the 50 to 1500 keV energy region
The response of neutron personal dosemeters as a function of neutron energy and angle of incidenc... more The response of neutron personal dosemeters as a function of neutron energy and angle of incidence is typically measured by mounting the dosemeters on a slab phantom and exposing them to neutrons from an accelerator-based or radionuclide source. The phantom is placed close to the source (75 cm) so that the effect of scattered neutrons is negligible. It is usual to mount several dosemeters on the phantom together. Because the source is close, the source distance and the neutron incidence angle vary significantly over the phantom face, and each dosemeter may receive a different dose equivalent. This is particularly important when the phantom is angled away from normal incidence. With accelerator-produced neutrons, the neutron energy and fluence vary with emission angle relative to the charged particle beam that produces the neutrons, contributing further to differences in dose equivalent, particularly when the phantom is located at other than the straight-ahead position (08 8 8 8 8 to the beam). Corrections for these effects are quantified and discussed in this article.
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