Spectra of linear energy transfer and other dosimetry characteristics as measured in C290 MeV/n MONO and SOBP ion beams at HIMAC-BIO (NIRS, Japan) with different detectors.

Active mobile dosimetry unit (Liulin), passive plastic nuclear track detectors (PNTD) and thermoluminescent detectors (TLD) were exposed in a C290 MeV/n beam at HIMAC-BIO (NIRS, Japan). Two different types of beam configuration were used--monoenergetic beam (MONO) and spread-out Bragg peak (SOBP); the detectors were placed at several depths from the entrance up to the depths behind the Bragg peak. Relative response of TLDs in beams has been studied as a function of the depth, and it was re-proved that it can depend on the linear energy transfer (LET). Liulin measures energy deposition in Si; the spectra of energy deposited in Si can be transformed to the spectra of lineal energy or LET. PNTDs are able to determine the LET of registered particles directly. The limitation of both methods is in the range in which they can determine the LET-Liulin is able to measure perpendicularly incident charged particles up to ∼35 keV/µm (in water), PNTD can measure from ∼7 to 400 keV/µm, independently of the registration angle. The results from both methods are compared and combined for both beams' configuration, and a good agreement is observed.

Monitoring on board spacecraft by means of passive detectors.

To estimate the radiation risk of astronauts during space missions, it is necessary to measure dose characteristics in various compartments of the spacecraft; this knowledge can be further used for estimating the health hazard in planned missions. This contribution presents results obtained during several missions on board the International Space Station (ISS) during 2005-09. A combination of thermoluminescent and plastic nuclear track detectors was used to measure the absorbed dose and dose equivalent. These passive detectors have several advantages, especially small dimensions, which enabled their placement at various locations in different compartments inside the ISS or inside the phantom. Variation of dosimetric quantities with the phase of the solar cycle and the position inside the ISS is discussed.

Spectrometry of linear energy transfer with track-etched detectors in carbon ion beams, MONO and SOBP.

Five various materials employed as track-etched detectors (TEDs) were exposed in beams of carbon ions with energy 290 MeV. u(-1) in the HIMAC-BIO facility in Japan. The exposures were performed behind various types of polymethyl methacrylate shielding. The beam had two possible set-ups--monoenergetic set-up and modulated spread-out Bragg peak set-up. All used TEDs are polyallyl diglycol carbonates (PADCs): Page from Mouldings (Pershore) Ltd, Tastrak from Track Analysis Systems Ltd, both from the UK; USF4 from American Technical Plastics from the USA and two products of Japan Fukuvi Chemical Industry Co., Ltd--TD1 and Baryotrak. Spectra of linear energy transfer and depth-dose distributions were obtained. Besides, differences among PADCs are discussed.

Liulin-type spectrometry-dosimetry instruments.

The main purpose of Liulin-type spectrometry-dosimetry instruments (LSDIs) is cosmic radiation monitoring at the workplaces. An LSDI functionally is a low mass, low power consumption or battery-operated dosemeter. LSDIs were calibrated in a wide range of radiation fields, including radiation sources, proton and heavy-ion accelerators and CERN-EC high-energy reference field. Since 2000, LSDIs have been used in the scientific programmes of four manned space flights on the American Laboratory and ESA Columbus modules and on the Russian segment of the International Space Station, one Moon spacecraft and three spacecraft around the Earth, one rocket, two balloons and many aircraft flights. In addition to relative low price, LSDIs have proved their ability to qualify the radiation field on the ground and on the above-mentioned carriers.

Use of energy deposition spectrometer Liulin for individual monitoring of aircrew.

Silicon energy deposition spectrometer Liulin was primarily developed for cosmic radiation monitoring onboard spacecrafts. Nowadays, Liulin type detectors are also used to characterise radiation field on board aircraft, at alpine observatories and behind the shielding of heavy ion accelerators. In this work, experiments and calibrations performed in these radiation fields are presented and the method developed for calculation of ambient dose equivalent H*(10) on board aircraft is described. Since 2001, a simple method employing the energy deposition spectra had been used to determine H*(10) on board aircraft but, in 2004, it became clear that the resulting values were strongly biased at locations close to Earth's equator. An improved method for the determination of H*(10) on board aircraft using the Liulin detector was developed. It took into account the composition of the radiation field via the ratio of absorbed doses D(low) and D(neut) reflecting the contributions from low-LET particles and neutrons, respectively. It resulted in much better agreement with the EPCARD computer code for all aircraft locations; relative differences were within 11 % for low-LET and 20 % for neutron components of H*(10).

Characterization of the radiation environment by Liulin-type spectrometers.

Liulin-type spectrometers can characterise the type of predominant particles and their energy in the radiation environment. The results from calibrations and space and aircraft experiments revealed that the most informative is by the shape of the deposited energy spectrum. Spectra generated by galactic cosmic rays (GCR) protons and their secondaries look like straight lines in the coordinates deposited energy/deposited per channel dose rate. The position of the maximum of the deposited energy spectra depends on the incident energy of the incoming protons. Spectra generated by relativistic electrons in the outer radiation belt have a maximum in the first channels. For higher energy depositions, these spectra are similar to the GCR spectra. All types of spectra have a knee close to 6.3 MeV of deposited energy, which corresponds to the stopping energy of protons in the detector.

Routine individual monitoring of aircraft crew exposure; Czech experience and results 1998-2008.

Individual monitoring of aircrew of airline operators registered in the Czech Republic has been performed since 1998. In this work, annual effective doses and annual collective effective doses of aircrew from occupational exposure in the period from 1998 to 2008 are presented, methods used for their evaluation and verification are described, and general trends observed in the data are discussed. Annual effective doses were calculated using the computer code CARI from flight schedules provided by airline operators and typical flight profiles. The method was verified via a comparison with (i) measurements using different types of detectors and (ii) calculations using the CARI and EPCARD codes with actual flight data. It was found that average annual effective doses in the period from 1998 to 2008 were in the range from 1.2 to 2.0 mSv and followed the trend of the solar cycle. Annual collective effective doses increased from 1.4 manSv in 1998 to 4.1 manSv in 2008 as the number of aircrew increased from 857 to 2158 during this period. Combined relative uncertainties (coverage factor ) of reported individual and collective effective doses were ∼ 25 %, which is well within the range given by the factor of 1.5. More work is needed to achieve a higher accuracy of this estimate.

Overview of on-board measurements during solar storm periods.

Radiation exposure of aircraft crew caused by cosmic radiation is regulated in Europe by the European Community Council Directive 96/29/EURATOM and implemented into law in almost every country of the European Union. While the galactic cosmic radiation (GCR) leads on average to an exposure of about 3 mSv per year, solar cosmic radiation can lead to 1 mSv per one subsonic flight during solar storm periods. Compared to GCR, solar cosmic radiation shows a much softer proton spectrum but with a larger contribution of several orders of magnitude. This is the reason for the large radiation exposure in high northern and southern geographic latitudes during solar particle events. Here an overview of active radiation in-flight measurements undertaken during solar storms is given. In particular, tissue-equivalent proportional counter on-board measurements are shown and the radiation quality during solar storm periods with that for GCR is compared.

Validation of modelling the radiation exposure due to solar particle events at aircraft altitudes.

Dose assessment procedures for cosmic radiation exposure of aircraft crew have been introduced in most European countries in accordance with the corresponding European directive and national regulations. However, the radiation exposure due to solar particle events is still a matter of scientific research. Here we describe the European research project CONRAD, WP6, Subgroup-B, about the current status of available solar storm measurements and existing models for dose estimation at flight altitudes during solar particle events leading to ground level enhancement (GLE). Three models for the numerical dose estimation during GLEs are discussed. Some of the models agree with limited experimental data reasonably well. Analysis of GLEs during geomagnetically disturbed conditions is still complex and time consuming. Currently available solar particle event models can disagree with each other by an order of magnitude. Further research and verification by on-board measurements is still needed.

Determinations of H(10) and its dose components onboard aircraft.

Aircrew is in general receiving a higher average annual dose than other occupationally exposed personnel, and about half of the effective dose is deposited by high-LET neutron secondaries. A recent investigation of the cancer incidence following the atomic bombs at Hiroshima and Nagasaki has put forward the possibility that the relative biological efficiency for neutrons could be underestimated. If so, the effective dose to aircrew from this component would increase and the estimation of this component will become even more important. Different ambient dose equivalent measurement techniques and calculation methods have recently been compared on a dedicated flight. The experimental results are compared with calculations made with the codes EPCARD 3.2 and an updated version of FLUKA and different galactic proton spectra. The aircraft circulated within the target areas at two constant altitudes with a flight route variation of only about 1 degrees in longitude and latitude to reduce the influence from variations in atmospheric and geomagnetic shielding. The instrumentation consisted of tissue-equivalent proportional counters (TEPC) and a silicon diode spectrometer. Measurements were performed for 2 h to reduce the statistical uncertainties in the results. The TEPCs were evaluated either according to single-event analysis techniques or the variance-covariance method. Besides the total ambient dose equivalent, the instruments can be evaluated to reveal the low- and high-LET components. The EPCARD and FLUKA simulations can determine the contribution from each type of particle directly. The ratio between the calculated and the measured average value of the ambient dose equivalent rate was 1.00 +/- 0.08 with all instruments included for EPCARD and 0.97 +/- 0.07 when FLUKA was used. The measured high-LET component and the calculated neutron component are not quite identical, but should be similar. The agreement was always within 20%. The high-LET component contributed with about 57% at N57 E8 and 48% at N42 E12.

Contribution of secondary particles to the dose in 12C radiotherapy and other heavy ion beams.

The results of experimental studies performed in a radiotherapy (12)C ion beam with a nominal energy of 500 MeV/amu and in (16)O and (56)Fe ion beams with a nominal energy of 1 GeV/amu have been described. Linear energy transfer (LET) spectra have been established by means of an LET spectrometer based on a chemically etched track detector, and the measured results were also compared with theoretical calculations obtained using the program Stopping and Range of Ions in Matter (SRIM). It was observed that with increasing depth in a beam, the LET spectra are shifted towards higher values of LET; one can also observe an important widening of the spectra along the range, as well as an increasing amount of nuclear reaction products and/or of fragments in the spectra. The relative contribution of these secondary particles to the total absorbed dose was assessed.

The problems associated with the monitoring of complex workplace radiation fields at European high-energy accelerators and thermonuclear fusion facilities.

The European Commission is funding within its Sixth Framework Programme a three-year project (2005-2007) called CONRAD, COordinated Network for RAdiation Dosimetry. The organisational framework for this project is provided by the European Radiation Dosimetry Group EURADOS. One task within the CONRAD project, Work Package 6 (WP6), was to provide a report outlining research needs and research activities within Europe to develop new and improved methods and techniques for the characterisation of complex radiation fields at workplaces around high-energy accelerators, but also at the next generation of thermonuclear fusion facilities. The paper provides an overview of the report, which will be available as CERN Yellow Report.

On the neutron contribution to the exposure level onboard space vehicles.

The neutron contribution to the spacecraft crew exposure could represent an important part of the total dose equivalent value. The determination of this contribution represents a rather complex and difficult task, both through experimental and theoretical estimation. This paper will present an attempt to determine the neutron contribution onboard the International Space Station and Foton capsule using the data measured by means of a Si-diode based energy deposition spectrometer. As such a spectrometer, the MDU-Liulin equipment, developed in one of our laboratories was used. The equipment allows the data accumulated during the passage in or out of the South Atlantic Anomaly (SAA). In this paper, only the data obtained out of the SAA were analysed, assuming that the neutron spectra are similar to those onboard aircraft and/or at the CERF high-energy radiation field. The excess of deposited energy in the region above 1 MeV, when comparing with the aircraft field, was expected to represent the primary high-energy charged particles. Total dosimetry characteristics obtained in this way are in reasonable agreement with other data, neutron contribution representing approximately 40% of the total dose equivalent for the flight duration outside of the SAA.

Microdosimetry distributions for 40-200 MeV protons.

Theoretical calculations have been performed to obtain microdosimetrical characteristics for protons in energy range from 40 to 200 MeV. This energy range is a representative of proton energies in tissue during radiation therapy and it also represents a large portion of the proton fluency in the South Atlantic Anomaly. Distributions of deposited energy calculated using Monte Carlo track structure code TRIOL and own-made programs were compared with experimental data obtained using spherical tissue-equivalent proportional counter. A good agreement between calculated and experimentally obtained microdosimetry spectra has been found.

Radiation dosimetry for microbial experiments in the International Space Station using different etched track and luminescent detectors.

The laboratory of Microbiology at SCK.CEN, in collaboration with different universities, participates in several ESA programmes with bacterial experiments that are carried out in the International Space Station (ISS). The main objective of these programmes is to study the effects of space flight conditions such as microgravity and cosmic radiation on the general behaviour of model bacteria. To measure the radiation doses received by the bacteria, different detectors accompanied the microbiological experiments. The results obtained during two space flight missions are discussed. This dosimetry experiment was a collaboration between different institutes so that the doses could be estimated by different techniques. For measurement of the high linear energy transfer (LET) doses (>10 keV microm(-1)), two types of etched track detectors were used. The low LET part of the spectrum was measured by three types of thermoluminescent detectors ((7)LiF:Mg,Ti; (7)LiF:Mg,Cu,P; Al(2)O(3):C) and by the optically stimulated luminescence technique using Al(2)O(3):C detectors.

The comparison of calculated and experimental microdosimetric distributions for carbon ions.

The aim of this work is to present microdosimetric characteristics of 400 MeV amu(-1) and 500 MeV amu(-1) carbon ions obtained by theoretical calculations and to analyse them with respect to experimental data obtained by tissue-equivalent proportional counter in a scope of project ICCHIBAN and by etched track detector CR 39 Page irradiated by LHE nuclotron at JINR, Dubna, Russia. Track structures provided by Monte Carlo code TRIOL are used as an input data for calculations of energy distributions. The calculations of frequency f(y) and dose d(y) distributions are performed using own developed programs.

Biological weighted effective dose in 205 MeV clinical proton beam.

The contribution of high linear energy transfer (L) charged particles to dosimetric and microdosimetric characteristics in a clinical proton beam was experimentally studied using an ionization chamber and track etched detectors. The particles mentioned are produced by proton nuclear interactions; at the Bragg peak region slowed down protons also contribute in the L region above several keV microm(-1). Due to these particles the biological weighted effective dose (BWED) of the beam changes with depth. The spectra of particles with L above 7 keV microm(-1) were established by means of track etched detectors, which permitted us to determine their contribution to dosimetric and microdosimetric characteristics of clinical proton beams. The studies were realized in the clinical proton beam of the JINR Dubna Phasotron, with a primary energy of 205 MeV. The relative contribution to the absorbed dose of the particles with L above 7 keV microm(-1) increases from several per cent at the beam entrance to several tens of per cent at the Bragg peak region. The relative biological weighted efficiency (RBWE) for radiotherapy has been calculated using a biological weighting function. It increases with depth from 1.02 at the beam entrance to about 1.25 at the Bragg peak region.

Some recent measurements onboard spacecraft with passive detector.

Several passive detectors were used to estimate dosimetry and microdosimetry characteristics of radiation field onboard spacecraft, namely: thermoluminescent detectors (TLDs), mainly to appreciate the contribution of radiation with low-linear energy transfer (LET); Si diode, to try to establish the contribution of fast neutrons; an LET spectrometer based on the chemically etched polyallyldiglycolcarbonate etched track detectors (PADC-TEDs). Detectors have been exposed onboard MIR and International Space Station (ISS) since 1997, they were also used during the MESSAGE 2 biological experiment, October 2003. The results are presented, analysed and discussed. Particular attention is devoted to the possibility of estimating neutron contribution based on data obtained with PADC-TED spectrometer of LET.

Aircrew dosimetry by means of experimental measurements and calculations: results obtained during the year 2003.

The results of measurements performed during the year 2003 onboard aircraft, mostly during regular commercial flights of the Czech Airlines (CSA) are presented. The studies were performed during more than 30 individual flights, several dosemeters and equipments were used for both neutron and non-neutron components of the onboard radiation field. CSA colleagues submitted us for all flights with navigation data necessary for the calculation of onboard aircraft crew exposure with transport codes EPCARD and CARI. Direct readings of experimental equipments were corrected on the base of the calibration in CERN high-energy radiation fields. A reasonable agreement of measured and calculated data was observed. During one of the flights, a very deep Forbush decrease occurred. The experimental results confronted with calculation permitted to obtain new view on the influence of such events on aircraft crew exposure.

An international dosimetry exchange for boron neutron capture therapy. Part I: Absorbed dose measurements.

An international collaboration was organized to undertake a dosimetry exchange to enable the future combination of clinical data from different centers conducting neutron capture therapy trials. As a first step (Part I) the dosimetry group from the Americas, represented by MIT, visited the clinical centers at Studsvik (Sweden), VTT Espoo (Finland), and the Nuclear Research Institute (NRI) at Rez (Czech Republic). A combined VTT/NRI group reciprocated with a visit to MIT. Each participant performed a series of dosimetry measurements under equivalent irradiation conditions using methods appropriate to their clinical protocols. This entailed in-air measurements and dose versus depth measurements in a large water phantom. Thermal neutron flux as well as fast neutron and photon absorbed dose rates were measured. Satisfactory agreement in determining absorbed dose within the experimental uncertainties was obtained between the different groups although the measurement uncertainties are large, ranging between 3% and 30% depending upon the dose component and the depth of measurement. To improve the precision in the specification of absorbed dose amongst the participants, the individually measured dose components were normalized to the results from a single method. Assuming a boron concentration of 15 microg g(-1) that is typical of concentrations realized clinically with the boron delivery compound boronophenylalanine-fructose, systematic discrepancies in the specification of the total biologically weighted dose of up to 10% were apparent between the different groups. The results from these measurements will be used in future to normalize treatment plan calculations between the different clinical dosimetry protocols as Part II of this study.