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Purpose: To measure the environmental doses from stray neutrons in the vicinity of a solid slab phantom as a function of beam energy, field size and modulation width, using the proton pencil beam scanning (PBS) technique., Method: Measurements were carried out using two extended range WENDI-II rem-counters and three tissue equivalent proportional counters. Detectors were suitably placed at different distances around the RW3 slab phantom. Beam irradiation parameters were varied to cover the clinical ranges of proton beam energies (100-220MeV), field sizes ((2×2)-(20×20)cm 2 ) and modulation widths (0-15cm)., Results: For pristine proton peak irradiations, large variations of neutron H ∗ (10)/D were observed with changes in beam energy and field size, while these were less dependent on modulation widths. H ∗ (10)/D for pristine proton pencil beams varied between 0.04μSvGy -1 at beam energy 100MeV and a (2×2)cm 2 field at 2.25m distance and 90° angle with respect to the beam axis, and 72.3μSvGy -1 at beam energy 200MeV and a (20×20) cm 2 field at 1m distance along the beam axis., Conclusions: The obtained results will be useful in benchmarking Monte Carlo calculations of proton radiotherapy in PBS mode and in estimating the exposure to stray radiation of the patient. Such estimates may be facilitated by the obtained best-fitted simple analytical formulae relating the stray neutron doses at points of interest with beam irradiation parameters., (Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

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]

Abstract: A fast neutron irradiation field for biological studies was established at the cyclotron facility in the National Institute of Radiological Sciences. Neutron spatial distributions and absorbed dose distributions were measured to characterize the neutron field. By using a simple technique that an aluminum plate activated by neutrons was exposed to the imaging plates, the width of the neutron-irradiated area was measured to be 23.6cm with 2.5mm spatial resolution. The absorbed dose distributions of neutrons and rays were obtained separately by using a tissue-equivalent plastic- and a graphite-walled low-pressure proportional counter. The neutron absorbed dose in a tissue-equivalent plastic was measured to be 144.6 (Gy/C). It was confirmed that this neutron field has only 1.8% contamination of -ray dose and has good quality for neutron irradiation to biological samples. [Copyright &y& Elsevier]

A comparison of two types of dose equivalent meters, a recombination chamber REM-2 and a tissue-equivalent proportional counter (TEPC) Homburg Area Neutron DosImeter (HANDI), were carried out at the CERN-EC high-energy reference field facility, CERF, in October 2001. Here, the mixed high-energy radiation field in commercial flight altitudes can be simulated with dose rates up to 2 orders of magnitude higher. The total absorbed dose and the dose equivalent have been measured at different radiation field intensities. Of particular interest for measuring in the CERF field is the assessment of the low LET-component, i.e. the γ and muon components of the field, which are not taken into account by existing Monte Carlo simulations modeling the radiation field. The new results for the estimation of the low LET-component are compared with previous ones delivered by REM-2 at CERF. The results show good agreement between the REM-2 chamber and the HANDI. [Copyright &y& Elsevier]

A Geant4 model of a tissue-equivalent proportional counter (TEPC) has been developed in which the calculated output spectrum exhibits unparalleled agreement with experiment for monoenergetic neutron fields at several energies below 20 MeV. The model uses the standard release of the Geant4 9.6 p2 code, but with a non-standard neutron cross section file as provided by Mendoza et al., and with the environment variable options recommended by the same authors. This configuration was found to produce significant improvements in the alpha-dominated region of the calculated response. In this paper, these improvements are presented, and the post-processing required to convert deposited energy into the number of ion pairs (which is the quantity actually measured experimentally) is discussed. [ABSTRACT FROM AUTHOR]

Cosmic ray neutrons are produced by the interaction of primary cosmic rays with the air molecules present in the atmosphere. At the ground level, these secondary neutrons are one of the important contributors of natural cosmic ray radiation background dose. With two major peaks around 1 MeV and 100 MeV, the neutron energies can extend up to 10 GeV. At the ground level, considerable presence of thermal neutrons can also be observed due to collisions and moderation of fast neutrons with the soil and other surrounding materials. A study on the evaluation of cosmic ray neutron spectra, and the resulting ambient dose equivalents was carried out at High Altitude Research Laboratory, Gulmarg, India (altitude 2650 m, N34.0484°, E74.3805°) considering the enhanced contribution of cosmic ray background in the region. Extended energy Bonner Sphere Spectrometer (BSS) was used for the continuous measurement of cosmic ray neutrons during the period of October 2018 to June 2019. Neutron spectra and ambient dose equivalents were unfolded from the BSS counts with the Monte Carlo generated response matrix and the FRUIT unfolding code. Along with Bonner sphere spectrometer, Tissue Equivalent Proportional Counter (TEPC) was also used for a limited period for independent measurement of cosmic ray dose equivalents and Linear Energy Transfer (LET) distribution. For comparison, neutron spectra and dose equivalent rates were also calculated using Monte Carlo code FLUKA and EXPACS software program. The ambient dose equivalent rates were found to vary in the range of 24–34 nSv. h−1 during the entire observation period of 9 months. No considerable seasonal variations were observed during the course of the study. Dose equivalent rates, estimated by the TEPC were slightly higher than the neutron dose equivalent rates measured by BSS. Experimentally measured values match reasonably well with theoretically simulated results. • Neutron spectra of cosmic rays. • Ambient dose equivalent H*(10). • Microdosimetric spectra. • Response matrix calculation using Monte Carlo code. • Unfolding of neutron spectra. [ABSTRACT FROM AUTHOR]

Microdosimetric parameters measured by a TEPC have been studied in the mixed radiation fields generated by the two D-T neutron generators developed at BARC and IGCAR facilities of DAE, India. These two generators differ in their sizes and designs. The present study reveals that the radiation fields by these two generators are significantly different. In the case of compact design (IGCAR generator) due to the significant contribution of bremsstrahlung photons in the total radiation field, the frequency and dose mean lineal energy, average quality factors are considerably less (factors of 3 to 6) than the BARC D-T generator. The study also reveals that the photon contribution to the total dose equivalent can be as high as 30% for compact D-T generator. • Measurement of microdosimetric parameters of neutrons produced by D-T generator using TEPC. • Average quality factor of the mixed radiation field of the D-T generator. • Microdosimetric spectra of high energy neutrons. [ABSTRACT FROM AUTHOR]