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Proceedings ArticleDOI

Performance Tests of Survey Instruments used in Radiation Fields Around High-Energy Accelerators

16 May 2005-pp 1595-1597
TL;DR: In this paper, measurements were carried out in a high-energy reference field at CERN to investigate the responses of the different detectors to a mixed radiation field under controlled conditions, and the results will contribute to a global quality assurance system for CERN's radiation protection instrumentation.
Abstract: Measurements of ambient dose equivalent in stray radiation fields behind the shielding of high-energy accelerators are a challenging task. Several radiation components (photons, neutrons, charged particles), spanning a wide range of energies, contribute to the total dose equivalent. Usually for measurements of the total dose equivalent, a set of radiation detectors consisting of ionisation chambers and so-called REM counters is employed. Ionisation chambers are sensitive to all radiation components, whereas REM counters are used to determine separately the neutron component. In this study measurements were carried out in a high-energy reference field at CERN to investigate the responses of the different detectors to a mixed radiation field under controlled conditions. In addition, the field and the corresponding ambient dose equivalents were simulated with FLUKA Monte Carlo calculations. The outcome of these studies determines the choice of radiation detectors for LHC and serves as a basis for a future certification of these instruments. In addition, the results will contribute to a global quality assurance system for CERN’s radiation protection instrumentation.

Summary (1 min read)

INTRODUCTION

  • Radiation dosimetry in mixed stray radiation fields behind the shielding of high-energy accelerators is a demanding task because of the complexity of the radiation field.
  • In routine-measurements, the total dose equivalent is measured by a set of radiation detectors including ionisation chambers and REM counters.
  • In addition, the experimental results were compared to Monte Carlo simulations.

RADIATION FIELD

  • The CERN-EU High Energy Reference Field (CERF).
  • Facility provides a well-known mixed high-energy radiation field for the investigation and calibration of various instruments.
  • It resembles very well the stray radiation fields behind thick lateral shielding at a highenergy hadron accelerator.
  • The particle fluences and spectra are well known from simulations with the April 2004 release of the MC program FLUKA [3, 4] at these reference positions.

STUDIES WITH IONISATION CHAMBERS

  • At CERF, comprehensive studies were performed to quantify the response of ionisation chambers of type IG5 manufactured by Centronic to mixed radiation fields.
  • Moreover, the relative contribution from each particle type to the total charge per primary particle is shown separately.
  • The major contribution to the expected ambient dose equivalent outside the shielding originates from neutrons as neutrons have the highest radiation weighting factor.
  • Experimentally, the Monte Carlo results were verified for the argon- and hydrogen-filled chamber and are reported in [6].

STUDIES WITH REM COUNTERS

  • REM (Roentgen Equivalent Man) counters are used to measure the ambient dose equivalent due to neutrons over a wide range of neutron energies.
  • With exception of the WENDI-2 which is specified to measure neutrons up to several GeV all detectors belong to the category of conventional neutron dose rate monitors which usually cover neutron energies up to 20 MeV.
  • In addition, measurements were carried out with a different type of detector, the HANDI-TEPC (tissue equivalent proportional counter), which is able to measure microdosimetric spectra.
  • This device is usually taken as reference device at CERF because of its proven reliability for measuring the total dose equivalent in radiation fields with a dominant dose equivalent component due to high-energy particles [7].
  • In Figure 3 the measurement results together with the simulation are plotted exemplarily for the reference position CT6/10.

CONCLUSION

  • With the objective to equip the LHC with state of the art radiation detectors and CERN with a general quality assurance system for its radiation protection instrumentation, measurement campaigns were performed in the high-energy reference CERF-field.
  • Ionisation chambers measuring the total dose equivalent as well as REM counters measuring neutron dose equivalents were intercompared.
  • In addition, the experimental results were compared to FLUKA Monte Carlo simulations.
  • Field calibration factors for REM counters could be derived for measurements in unknown high-energy radiation fields behind the shielding around a high-energy accelerator.

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PERFORMANCE TESTS OF SURVEY INSTRUMENTS USED IN
RADIATION FIELDS AROUND HIGH-ENERGY ACCELERATORS
S. Mayer
#
, D. Forkel-Wirth, M. Fuerstner, H.G. Menzel, S. Roesler, C. Theis, and H.Vincke,
CERN, Geneva, Switzerland
Abstract
Measurements of ambient dose equivalent in stray
radiation fields behind the shielding of high-energy
accelerators are a challenging task. Several radiation
components (photons, neutrons, charged particles),
spanning a wide range of energies, contribute to the total
dose equivalent. Usually for measurements of the total
dose equivalent, a set of radiation detectors consisting of
ionisation chambers and so-called REM counters is
employed. Ionisation chambers are sensitive to all
radiation components, whereas REM counters are used to
determine separately the neutron component. In this study
measurements were carried out in a high-energy reference
field at CERN to investigate the responses of the different
detectors to a mixed radiation field under controlled
conditions. In addition, the field and the corresponding
ambient dose equivalents were simulated with FLUKA
Monte Carlo calculations. The outcome of these studies
determines the choice of radiation detectors for LHC and
serves as a basis for a future certification of these
instruments. In addition, the results will contribute to a
global quality assurance system for CERN’s radiation
protection instrumentation.
INTRODUCTION
Radiation dosimetry in mixed stray radiation fields
behind the shielding of high-energy accelerators is a
demanding task because of the complexity of the
radiation field. These fields are dominated by photons and
neutrons spanning an energy range from fractions of eV
to several GeV. Although in most cases neutrons
represent the major constituent of the ambient dose
equivalent, the other components of the mixed field such
as gamma radiation and charged particles have to be
assessed correctly as well. The total dose equivalent
strongly depends on the field composition with respect to
particle types and particle energies.
In routine-measurements, the total dose equivalent is
measured by a set of radiation detectors including
ionisation chambers and REM counters. Ionisation
chambers are sensitive to all radiation components,
whereas REM counters are designed to respond mainly to
neutrons. Provided that the response of the detectors to
the various particle types and energies is known, the total
dose equivalent can be correctly assessed by using
appropriate corrections and calibration factors. To deepen
the knowledge on the detector response, measurements
were carried out in a high-energy reference field at
Figure 1: Fluence spectra (normalized by beam particle) for various particle types at CERF
(Reference position CT6-10) [5].
___________________________________________
#
Sabine.Mayer@cern.ch
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-09 1.E-08 1.E-07 1.E-
d
)
/ d ln(E) (cm
-2
GeV
-1
)
kaons
pion+
pion-
neutrons
protons
photons
06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01
Energy (GeV)
Proceedings of 2005 Particle Accelerator Conference, Knoxville, Tennessee
1595 0-7803-8859-3/05/$20.00
c
2005 IEEE

CERN. This facilitiy allows to study the response of the
different detectors to mixed high-energy radiation fields
under well controlled conditions. In addition, the
experimental results were compared to Monte Carlo
simulations.
RADIATION FIELD
The CERN-EU High Energy Reference Field (CERF)
Facility provides a well-known mixed high-energy
radiation field for the investigation and calibration of
various instruments. It resembles very well the stray
radiation fields behind thick lateral shielding at a high-
energy hadron accelerator. The reference field is created
by a positively charged mixed hadron beam (61% pions,
35% protons, 4% kaons) with a momentum of 120 GeV/c
directed to a copper target, which is located either below
an 80 cm concrete or a 40 cm iron shield [1]. The beam
intensity is monitored by a Precision Ionisation Chamber
(PIC). One PIC count corresponds to (2.2 ± 0.1) × 10
4
particles impinging on the target [2]. The secondary
particles produced in the copper target traverse the
shielding above of the beamline where several, well
defined reference exposure positions are available. The
particle fluences and spectra are well known from
simulations with the April 2004 release of the MC
program FLUKA [3, 4] at these reference positions. In
Figure 1 [5] the fluence spectra for different particle types
simulated for the reference position CT6-10 (concrete
shield) are given as an example.
STUDIES WITH IONISATION
CHAMBERS
At CERF, comprehensive studies were performed to
quantify the response of ionisation chambers of type IG5
manufactured by Centronic to mixed radiation fields. The
responses of the chambers with a volume of 5.2 litres and
a filling-pressure of 20 bar were simulated using three
different gas-fillings: hydrogen, argon and nitrogen. In
Figure 2 the calculated responses for each gas-filling, are
presented for the reference position CT6/10 in terms of
created electrical charge per primary particle. Moreover,
the relative contribution from each particle type to the
total charge per primary particle is shown separately.
The simulations show that in the CERF reference field,
the response of the argon- or nitrogen-filled chamber is
approximately five times higher than for the hydrogen
chamber. This indicates that in a CERF-like field the
argon- or nitrogen-filled chamber would be the preferred
instrument regarding response. However, the major
contribution to the expected ambient dose equivalent
outside the shielding originates from neutrons as neutrons
have the highest radiation weighting factor. Therefore, it
is of great importance to know the response of the
detectors to neutrons to be able to choose the one which
measures the corresponding dose contribution best. In
Figure 2, one can see that regarding the contribution from
each particle type to the total calculated electrical charge
the hydrogen chamber is the most sensitive one for
neutrons. Being aware of the different responses to the
particle types a qualified choice for future use of the
chambers can be made.
0% 20% 40% 60% 80% 100%
Nitrogen
Argon
Hydrogen
gas filling
contribution from each particle type to total charge
neutrons
protons
pions+
pions-
photons
36%
20%
35%54
59% 17%
22
20%
30% 24% 6 5 35%
response per
primary particle
2.9 x 10
-18
C
1.7 x 10
-17
C
1.4 x 10
-17
C
Figure 2: Relative contribution from each particle type to
the total created charge (per primary particle) for a mixed
radiation field encountered at the reference position
CT6/10 at CERF.
Experimentally, the Monte Carlo results were verified
for the argon- and hydrogen-filled chamber and are
reported in [6]. The experimental investigation of the
nitrogen-filled chamber is foreseen for the near future.
The use of nitrogen-filled chambers instead of argon-
filled chambers could be of advantage as they can be even
used under recombination.
STUDIES WITH REM COUNTERS
REM (Roentgen Equivalent Man) counters are used to
measure the ambient dose equivalent due to neutrons over
a wide range of neutron energies. They generally rely on
capture reactions for neutrons, e.g.
10
B(n, Į)
7
Li or
3
He(n, p)
3
H, in an inner detector which is surrounded by a
polyethylene moderator. The instruments investigated in
this study were the Thermo WENDI-2, the Thermo
Biorem, the EG&G Berthold LB6411, the Studsvik
2202D and the Centronic REM Ionisation Chamber
(RIC). With exception of the WENDI-2 which is
specified to measure neutrons up to several GeV all
detectors belong to the category of conventional neutron
dose rate monitors which usually cover neutron energies
up to 20 MeV.
Measurements were performed with the instruments for
different beam intensities at various reference positions
behind the concrete shielding. In addition, measurements
were carried out with a different type of detector, the
HANDI-TEPC (tissue equivalent proportional counter),
which is able to measure microdosimetric spectra. This
device is usually taken as reference device at CERF
because of its proven reliability for measuring the total
(neutron) dose equivalent in radiation fields with a
dominant dose equivalent component due to high-energy
particles [7]. In Figure 3 the measurement results together
with the simulation are plotted exemplarily for the
reference position CT6/10.
Proceedings of 2005 Particle Accelerator Conference, Knoxville, Tennessee
0-7803-8859-3/05/$20.00
c
2005 IEEE 1596

The study at the CERF facility (Figure 3) showed that
the simulation results agree with the measurement results
of the HANDI-TEPC and the WENDI-2 within the
respective uncertainties [8]. As expected, the
conventional types of REM counters, which were
designed for neutron energies up to 20 MeV and which
are calibrated in radiation fields of reference sources,
underestimate the neutron dose equivalent by a factor of
two. As a result of these studies a field calibration factor
for each detector can now be deduced. This field
calibration factor provides a better estimate of the neutron
dose equivalent in a presumably similar, but unknown
high-energy field around an accelerator, than a calibration
factor determined in a radiation field of a standard
reference neutron source like
252
Cf of Am-Be. In addition,
the experimental results provide an input for setting
standards for ambient dose equivalent measurements in
mixed high-energy radiation fields. Existing standards for
portable neutron dose equivalent ratemeters cover only an
energy range up to 16 MeV.
0 1000 2000 3000 4000 5000
0
50
100
150
200
250
300
350
400
CT6/10
Neutron dose equivalent per hour (µSv/h)
Beam intensity per spill (PIC counts)
Simulation
HANDI-TEPC
Berthold
Studsvik
RIC
WENDI-2
BIOREM
Figure 3: Neutron dose equivalent measured with various
types of REM counters and the HANDI-TEPC behind
concrete shielding at CERF [8]. For comparison results of
Monte Carlo simulations are shown.
CONCLUSION
With the objective to equip the LHC with state of the
art radiation detectors and CERN with a general quality
assurance system for its radiation protection
instrumentation, measurement campaigns were performed
in the high-energy reference CERF-field. Various
detectors were studied, including those that are presently
in use, as well as potential candidates for future use
around the LHC. Ionisation chambers measuring the total
dose equivalent as well as REM counters measuring
neutron dose equivalents were intercompared. In addition,
the experimental results were compared to FLUKA
Monte Carlo simulations.
The results of these studies confirmed that the adequate
detectors had been chosen for the LHC (ionisation
chambers and WENDI-2). Field calibration factors for
REM counters could be derived for measurements in
unknown high-energy radiation fields behind the
shielding around a high-energy accelerator. Simple
calibration of these detectors in the field of reference
sources tends to underestimate the actual dose equivalent,
since a typical source spectrum covers only neutron
energies up to 11 MeV. Furthermore, the studies form a
solid basis for quality assurance and possible future
certification of the instruments in high-energy radiation
fields.
REFERENCES
[1] A. Mitaroff and M. Silari, “The CERN-EU high-
energy reference field (CERF) facility for dosimetry
at commercial flight altitudes and in space”, Radiat.
Prot. Dosim., 102 (2002), p.7-22.
[2] H. Vincke, H., S. Mayer, I. Efthymiopoulos, A.
Fabich, D. Forkel-Wirth, M.J. Müller, C. Theis,
“Accurate PIC calibration by the use of a coincidence
of two scintillators”, Technical Note, CERN-SC-
2004-90-RP-TN, (2004).
[3] A. Fassò, A.Ferrari and P.R. Sala, “Electron-photon
transport in FLUKA: status”, Proc.: Monte Carlo
2000 Conference, Lisbon, Springer-Verlag Berlin,
(2001), p.159-164 .
[4] A. Fassò, A. Ferrari, J. Ranft and P. R. Sala,
“FLUKA: Status and prospective for hadronic
applications”, Proc.: Monte Carlo 2000 Conference,
Lisbon, Springer-Verlag Berlin, (2001), p.955-960.
[5] C. Theis, “Characterization of ionization chambers in
a mixed radiation field and investigation of their
application as accessible area monitor for the LHC”,
Diploma thesis, CERN/TU-Graz, (2005).
[6] C. Theis, D. Forkel-Wirth, D. Perrin, R. Roesler and
H. Vincke, “Characterization of ionization chambers
to a mixed radiation field and investigation study of
their suitability as radiation monitors for the LHC”,
Proc. ICRS10 (May 2004).
[7] U.J Schrewe, W.G. Alberts, A.V. Alvera, A. Ferrari,
T. Otto and M. Silari, “Calibration problems,
calibration procedures and reference fields for
dosimetry at flight altitudes “. Radiat. Prot. Dosim.
86 (4), (1999), p.289-295.
[8] S. Mayer, D. Forkel-Wirth, M. Fuerstner, H.G.
Menzel, M. J. Mueller, D. Perrin, C. Theis and H.
Vincke, “Response of neutron detectors to high-
energy mixed radiation fields“. Proc. IM2005,
Vienna (April 2005).
Proceedings of 2005 Particle Accelerator Conference, Knoxville, Tennessee
1597 0-7803-8859-3/05/$20.00
c
2005 IEEE
Citations
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Journal ArticleDOI
TL;DR: Neutron spectrometry around the target volume showed two main components at the thermal and fast energy ranges and revealed the large dependence of the energy distribution of neutrons, and consequently of out-of-field doses, on the primary beam direction (directional emission of intranuclear cascade neutrons) and energy.
Abstract: Purpose: To characterize stray radiation around the target volume in scanning proton therapy and study the performance of active neutron monitors. Methods: Working Group 9 of the European Radiation Dosimetry Group (EURADOS WG9—Radiation protection in medicine) carried out a large measurement campaign at the Trento Centro di Protonterapia (Trento, Italy) in order to determine the neutron spectra near the patient using two extended-range Bonner sphere spectrometry (BSS) systems. In addition, the work focused on acknowledging the performance of different commercial active dosimetry systems when measuring neutron ambient dose equivalents, H ∗(10), at several positions inside (8 positions) and outside (3 positions) the treatment room. Detectors included three TEPCs—tissue equivalent proportional counters (Hawk type from Far West Technology, Inc.) and six rem-counters (WENDI-II, LB 6411, RadEye™ NL, a regular and an extended-range NM2B). Meanwhile, the photon component of stray radiation was deduced from the low-lineal energy transfer part of TEPC spectra or measured using a Thermo Scientific™ FH-40G survey meter. Experiments involved a water tank phantom (60 × 30 × 30 cm3) representing the patient that was uniformly irradiated using a 3 mm spot diameter proton pencil beam with 10 cm modulation width, 19.95 cm distal beam range, and 10 × 10 cm2 field size. Results: Neutron spectrometry around the target volume showed two main components at the thermal and fast energy ranges. The study also revealed the large dependence of the energy distribution of neutrons, and consequently of out-of-field doses, on the primary beam direction (directional emission of intranuclear cascade neutrons) and energy (spectral composition of secondary neutrons). In addition, neutron mapping within the facility was conducted and showed the highest H ∗(10) value of ∼51 μSv Gy−1; this was measured at 1.15 m along the beam axis. H ∗(10) values significantly decreased with distance and angular position with respect to beam axis falling below 2 nSv Gy−1 at the entrance of the maze, at the door outside the room and below detection limit in the gantry control room, and at an adjacent room (<0.1 nSv Gy−1). Finally, the agreement on H ∗(10) values between all detectors showed a direct dependence on neutron spectra at the measurement position. While conventional rem-counters (LB 6411, RadEye™ NL, NM2-458) underestimated the H ∗(10) by up to a factor of 4, Hawk TEPCs and the WENDI-II range-extended detector were found to have good performance (within 20%) even at the highest neutron fluence and energy range. Meanwhile, secondary photon dose equivalents were found to be up to five times lower than neutrons; remaining nonetheless of concern to the patient. Conclusions: Extended-range BSS, TEPCs, and the WENDI-II enable accurate measurements of stray neutrons while other rem-counters are not appropriate considering the high-energy range of neutrons involved in proton therapy.

52 citations

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TL;DR: The study demonstrated the need for improved measurement tools, especially at the high neutron energy range, and more accurate physical models and cross sections within the Monte Carlo code to correctly assess secondary neutron doses in proton therapy applications.
Abstract: Monte Carlo calculations are increasingly used to assess stray radiation dose to healthy organs of proton therapy patients and estimate the risk of secondary cancer. Among the secondary particles, neutrons are of primary concern due to their high relative biological effectiveness. The validation of Monte Carlo simulations for out-of-field neutron doses remains however a major challenge to the community. Therefore this work focused on developing a global experimental approach to test the reliability of the MCNPX models of two proton therapy installations operating at 75 and 178 MeV for ocular and intracranial tumor treatments, respectively. The method consists of comparing Monte Carlo calculations against experimental measurements of: (a) neutron spectrometry inside the treatment room, (b) neutron ambient dose equivalent at several points within the treatment room, (c) secondary organ-specific neutron doses inside the Rando-Alderson anthropomorphic phantom. Results have proven that Monte Carlo models correctly reproduce secondary neutrons within the two proton therapy treatment rooms. Sensitive differences between experimental measurements and simulations were nonetheless observed especially with the highest beam energy. The study demonstrated the need for improved measurement tools, especially at the high neutron energy range, and more accurate physical models and cross sections within the Monte Carlo code to correctly assess secondary neutron doses in proton therapy applications.

34 citations

Journal ArticleDOI
Gabriele Zorloni1
28 Mar 2022
TL;DR: In this article , the authors compared the reliability of different rem-counters in the Mevion S250i Hyperscan system in the presence of high-energy neutrons and found that only the LUPIN allowed for a correct assessment of H*(10) within a 20% uncertainty.
Abstract: Objective Proton therapy is gaining popularity because of the improved dose delivery over conventional radiation therapy. The secondary dose to healthy tissues is dominated by secondary neutrons. Commercial rem-counters are valuable instruments for the on-line assessment of neutron ambient dose equivalent (H*(10)). In general, however, a priori knowledge of the type of facility and of the radiation field is required for the proper choice of any survey meter. The novel Mevion S250i Hyperscan synchrocyclotron mounts the accelerator directly on the gantry. It provides a scanned 227 MeV proton beam, delivered in pulses with a pulse width of 10 µs at 750 Hz frequency, which is afterwards degraded in energy by a range shifter modulator system. This environment is particularly challenging for commercial rem-counters; therefore, we tested the reliability of some of the most widespread rem-counters to understand their limits in the Mevion S250i stray neutron field. Approach This work, promoted by the European Radiation Dosimetry Group (EURADOS), describes a rem-counter intercomparison at the Maastro Proton Therapy centre in the Netherlands, which houses the novel Mevion S250i Hyperscan system. Several rem-counters were employed in the intercomparison (LUPIN, LINUS, WENDI-II, LB6411, NM2B-458, NM2B-495Pb), which included simulation of a patient treatment protocol employing a water tank phantom. The outcomes of the experiment were compared with models and data from the literature. Main results We found that only the LUPIN allowed for a correct assessment of H*(10) within a 20% uncertainty. All other rem-counters underestimated the reference H*(10) by factors from 2 to more than 10, depending on the detector model and on the neutron dose per pulse. In pulsed fields, the neutron dose per pulse is a fundamental parameter, while the average neutron dose rate is a secondary quantity. An average 150-200 µSv/GyRBE neutron H*(10) at various positions around the phantom and at distances between 186 cm and 300 cm from it was measured per unit therapeutic dose delivered to the target. Significance Our results are partially in line with results obtained at similar Mevion facilities employing passive energy modulation. Comparisons with facilities employing active energy modulation confirmed that the neutron H*(10) can increase up to more than a factor of 10 when passive energy modulation is employed. The challenging environment of the Mevion stray neutron field requires the use of specific rem-counters sensitive to high-energy neutrons (up to a few hundred MeV) and specifically designed to withstand pulsed neutron fields.

2 citations

References
More filters
Journal ArticleDOI
Angela Mitaroff1, M. Silari
TL;DR: The facility is described, reports on the latest neutron spectral measurements, gives an overview of the most important experiments performed by the various collaborating institutions over recent years and briefly addresses the possible application of the facility to measurements related to the space programme.
Abstract: A reference facility for the calibration and inter-comparison of active and passive detectors in broad neutron fields has been available at CERN since 1992. A positively charged hadron beam (a mixture of protons and pions) with momentum of usually 120 GeV/c hits a copper target, 50 cm thick and 7 cm in diameter. The secondary particles produced in the interaction traverse a shield, at 90° with respect to the direction of the incoming beam, made of either 80 to 160 cm of concrete or 40 cm of iron. Behind the iron shield, the resulting neutron spectrum has a maximum at about 1 MeV, with an additional high-energy component. Behind the 80 cm concrete shield, the neutron spectrum has a second pronounced maximum at about 70 MeV and resembles the high-energy component of the radiation field created by cosmic rays at commercial flight altitudes. This paper describes the facility, reports on the latest neutron spectral measurements, gives an overview of the most important experiments performed by the various collaborating institutions over the past years, addresses the possible application of the facility to measurements related to the space programme and discusses the latest calculations performed in view of its development for such use.

243 citations

Book ChapterDOI
TL;DR: The present version of the FLUKA code can handle with similar or better accuracy also muons, low energy neutrons and electromagnetic effects as discussed by the authors, and most important of all it can simulate the transport of all these radiation components and their reciprocal interactions at the same time.

218 citations

Book ChapterDOI
01 Jan 2001
TL;DR: The standalone FLUKA code as mentioned in this paper is capable of handling transport and interactions of hadronic and electromagnetic particles in any material over a wide energy range, from thermal neutrons to cosmic rays.
Abstract: The standalone FLUKA code [1] is capable of handling transport and interactions of hadronic and electromagnetic particles in any material over a wide energy range, from thermal neutrons to cosmic rays. It is intrinsecally an analogue code, but can be run in biased mode for a variety of deep penetration applications.

160 citations

Journal ArticleDOI
C. Theis1, D. Forkel-Wirth1, Daniel Perrin1, Stefan Roesler1, H. Vincke1 
TL;DR: It is demonstrated that ionisation chambers of type IG5 (Centronic Ltd) can be characterised sufficiently enough to serve their function as radiation monitors for the LHC.
Abstract: Monitoring of the radiation environment is one of the key tasks in operating a high-energy accelerator such as the Large Hadron Collider (LHC). The radiation fields consist of neutrons, charged hadrons as well as photons and electrons with energy spectra extending from those of thermal neutrons up to several hundreds of GeV. The requirements for measuring the dose equivalent in such a field are different from standard uses and it is thus necessary to investigate the response of monitoring devices thoroughly before the implementation of a monitoring system can be conducted. For the LHC, it is currently foreseen to install argon- and hydrogen-filled high-pressure ionisation chambers as radiation monitors of mixed fields. So far their response to these fields was poorly understood and, therefore, further investigation was necessary to prove that they can serve their function well enough. In this study, ionisation chambers of type IG5 (Centronic Ltd) were characterised by simulating their response functions by means of detailed FLUKA calculations as well as by calibration measurements for photons and neutrons at fixed energies. The latter results were used to obtain a better understanding and validation of the FLUKA simulations. Tests were also conducted at the CERF facility at CERN in order to compare the results with simulations of the response in a mixed radiation field. It is demonstrated that these detectors can be characterised sufficiently enough to serve their function as radiation monitors for the LHC.

23 citations

Journal ArticleDOI
TL;DR: In this paper, the response of various portable detectors sensitive to neutrons was studied at CERN's High-Energy Reference Field Facility (CERF), and the experimentally determined neutron dose equivalent results were compared with Monte Carlo (MC) simulations.
Abstract: Radiation protection around CERN's high-energy accelerators represents a major challenge due to the presence of complex, mixed radiation fields. Behind thick shielding neutrons dominate and their energy ranges from fractions of eV to about 1 GeV. In this work the response of various portable detectors sensitive to neutrons was studied at CERN's High-Energy Reference Field Facility (CERF). The measurements were carried out with conventional rem counters, which usually cover neutron energies up to 20 MeV, the Thermo WENDI-2, which is specified to measure neutrons up to several GeV, and a tissue-equivalent proportional counter. The experimentally determined neutron dose equivalent results were compared with Monte Carlo (MC) simulations. Based on these studies field calibration factors can be determined, which result in a more reliable estimate of H*(10) in an unknown, but presumably similar high-energy field around an accelerator than a calibration factor determined in a radiation field of a reference neutron source.

19 citations

Frequently Asked Questions (1)
Q1. What have the authors contributed in "Performance tests of survey instruments used in radiation fields around high-energy accelerators" ?

In this study measurements were carried out in a high-energy reference field at CERN to investigate the responses of the different detectors to a mixed radiation field under controlled conditions. Although in most cases neutrons represent the major constituent of the ambient dose equivalent, the other components of the mixed field such as gamma radiation and charged particles have to be assessed correctly as well. The total dose equivalent strongly depends on the field composition with respect to particle types and particle energies. Provided that the response of the detectors to the various particle types and energies is known, the total dose equivalent can be correctly assessed by using appropriate corrections and calibration factors. To deepen the knowledge on the detector response, measurements were carried out in a high-energy reference field at Figure 1: Fluence spectra ( normalized by beam particle ) for various particle types at CERF ( Reference position CT6-10 ) [ 5 ].