Angle dependence of response characteristics of neutron survey instruments

Roberts, Neil; Bartlett, D. T.; Hager, Luke; Jones, L. N.; Molinos, Cesar; Tanner, R.J.; Taylor, G C; Thomas, David J.

doi:10.1093/rpd/nch130

Cited by 11 publications

(6 citation statements)

References 1 publication

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“…The same spherical moderator has been used with CR39 dosimeters and a 3 He proportional counter as a dual-detector extended-range rem counter (conventional, i.e. for non-pulsed fields) by Agosteo et al [18]. The only difference is the electrostatic shield that contains the detector and the polyethylene plug.…”

Section: Moderatormentioning

confidence: 99%

LUPIN, a new instrument for pulsed neutron fields

Caresana

Ferrarini

Manessi

et al. 2013

Nuclear Instruments and Methods in Physics Research Section A:

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HeNeutron detection Pulsed field Linac Proportional counter Logarithmic amplifier a b s t r a c t A number of studies focused in the last decades on the development of survey meters to be used in pulsed radiation fields. This is a topic attracting widespread interest for applications such as radiation protection and beam diagnostics in accelerators. This paper describes a new instrument specifically conceived for applications in pulsed neutron fields (PNF). The detector, called LUPIN, is a rem counter type instrument consisting of a 3 He proportional counter placed inside a spherical moderator. It works in current mode with a front-end electronics consisting of a current-voltage logarithmic amplifier, whose output signal is acquired with an ADC and processed on a PC. This alternative signal processing allows the instrument to be used in PNF without being affected by saturation effects. Moreover, it has a measurement capability ranging over many orders of burst intensity. Despite the fact that it works in current mode, it can measure a single neutron interaction. The LUPIN was first calibrated in CERN's calibration laboratory with a PuBe source. Measurements were carried out under various experimental conditions at the Helmholtz-Zentrum in Berlin, in the stray field at various locations of the CERN Proton Synchrotron complex and around a radiotherapy linear accelerator at the S. Raffaele hospital in Milan. The detector can withstand single bursts with values of Hn(10) up to 16 nSv/burst without showing any saturation effect. It efficiently works in pulsed stray fields, where a conventional rem-counter underestimates by a factor of 2. It is also able to reject the very intense and pulsed photon contribution that often accompanies the neutron field with good reliability.

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Section: Moderatormentioning

confidence: 99%

LUPIN, a new instrument for pulsed neutron fields

Caresana

Ferrarini

Manessi

et al. 2013

Nuclear Instruments and Methods in Physics Research Section A:

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“…This fact explains part of the complexity of ambient dosimetry and of the limits of such instrumentation. Other known limitations associated to these instruments come from the angular dependence of their response (Roberts et al 2004, Tanner et al 2006 296 MeV of 35%. Similarly, the Wendi II detector was found in this work to respond within ±30% in neutron fields with strong high or low energy contributions (P9 and P6 points).…”

Section: Discussionmentioning

confidence: 99%

“…The neutron reference dose was acquired with the Studsvik detector, placed in between the two moderators. Because the Studsvik does not have spherical symmetry, its response presents large angle dependency, more than 30% at 180°w ith respect to the reference direction (Roberts et al 2004). Since the angular dependence is lower with the angle about the detector central axis (within 10%), the instrument was placed in vertical position (figure 3(b)).…”

Section: Quantification Of the Impact Of The Use Of Standard Calibrat...mentioning

confidence: 99%

Study of the responses and calibration procedures of neutron and gamma area and environmental detectors for use in proton therapy

et al. 2019

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Ambient dose equivalent measurements with radiation protection instruments are associated to large uncertainties, mostly due to the energy dependence of the instrument response and to the dissimilarity between the spectra of the standard calibration source and the workplace field. The purpose of this work is to evaluate its impact on the performance of area and environmental detectors in the proton therapy environment, and to provide practical solutions whenever needed and possible. The study was carried out at the Centre Antoine Lacassagne (CAL) proton therapy site, and included a number of commercially available area detectors and a home-made environmental thermoluminescent dosimeter based on a polyethylene moderator loaded with TLD600H/TLD700H pairs. Monte Carlo simulations were performed with MCNP to calculate, first, missing or partially lacking instrument responses, covering the range of energies involved in proton therapy. Second, neutron and gamma spectra were computed at selected positions in and outside the CAL proton therapy bunkers. Appropriate correction factors were then derived for each detector, workplace location and calibration radionuclide source, which amounts to up to 1.9 and 1.5 for neutron and photon area detectors, respectively, and suggest that common ambient dose equivalent instruments might not meet IEC requirements. The TLD environmental system was calibrated in situ and appropriate correction factors were applied to account for the cosmic spectra. Measurements performed with this system from 2014 to 2017 around the installation were consistent with reference natural background dose data and with pre-operational levels registered at the site before the construction of the building in 1988, showing thus no contribution from the site clinical activities. An in situ verification procedure for the radiation protection instruments was also implemented in 2016 at the low energy treatment room using the QA beam reference conditions. The method presents main methodological, practical and economic advantages over external verifications.

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“…Instruments with other geometries or equipped with important electronics (such as a photomultiplier, preamplifier near the detector, integrated electronics for displaying, etc) have, however, fluence or ambient-doseequivalent responses that vary with the neutron direction. This has been studied in detail for survey meters by [10,13,14], revealing response variations up to 50% as shown in figure 4.…”

Section: Angular Response Functionmentioning

confidence: 99%

“…The dosimeter is placed at the centre of the front face of the phantom and this assembly is rotated to several angles with respect to the neutron beam direction. This study has to [14]. For the spherical detectors, the angle 0 • is the reference direction, that is, irradiation from the end opposite the electronics.…”

Section: Angular Response Functionmentioning

confidence: 99%

Calibration of neutron-sensitive devices

Gressier¹,

Taylor²

2011

Metrologia

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The calibration of a neutron-sensitive device can range from a simple calibration factor at a single energy or energy distribution to a full response characterization over the entire energy range to which the device is sensitive. As the responses of neutron-sensitive devices and the fluence-to-dose-equivalent conversion coefficients can vary with neutron energy and incident angle, both simulation and experiments in standard neutron fields are required. Although several ISO standards present calibration principles in general and detailed discussion on many specific areas, there are certain omissions and limitations that this paper intends to highlight, along with some new recommendations derived from the recent literature, mainly focused on the effective centre, corrections for geometry and neutron scattering, as well as the problem of calibrating in terms of personal dose equivalent.

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Angle dependence of response characteristics of neutron survey instruments

Cited by 11 publications

References 1 publication

LUPIN, a new instrument for pulsed neutron fields

LUPIN, a new instrument for pulsed neutron fields

Study of the responses and calibration procedures of neutron and gamma area and environmental detectors for use in proton therapy

Calibration of neutron-sensitive devices

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