Linear Energy Transfer Spectra Research Articles

Track etch and thermo luminescent detectors response to high energy charged particles

Charged particles can be registered in a track etch detector (TED) when the linear energy transfer (LET) of a particle is higher than a threshold. Relative response of thermo luminescent detectors (TLDs) generally decreases with increasing LET of radiation depositing in them energy. The exposure of both these detectors in high energy charged particle beams permits to improve knowledge concerning the possibility of theirs use. Two types of poly allyldiglycolcarbonate (PADC) TED and two different TLDs have been exposed since several past years to high energy charged particles with energies up to 1 GeV/amu, and LET up to 600 keV / μ m in water. Some unknown (“blind”) exposures were also realised. Basic results like LET spectra, relative response of TLDs as the function of LET, etc., are presented. Particular attention is devoted to the results of evaluation of both detectors after blind exposures, theirs analysis and discussion.

DOsimetry of BIological EXperiments in SPace (DOBIES) with luminescence (OSL and TL) and track etch detectors

The objective of the “DOsimetry of BIological EXperiments in SPace” (DOBIES) project is to develop a standard dosimetric method as a combination of different techniques to estimate absorbed dose, dose equivalent, and linear energy transfer (LET) spectrum in biological samples in space experiments. The detectors investigated in the project include various types of thermoluminescence detectors (TLDs), such as LiF:Mg,Ti, LiF:Mg,Cu,P, CaSO 4 :Dy, as well as Al 2 O 3 :C used as TLD and optically stimulated luminescence detectors (OSLDs), and track-etch detectors (TED). This paper describes the DOBIES project and reports preliminary results obtained during the BASE-A experiment carried out at the International Space Station (ISS) in September, 2006. The results are compared to data from previous space exposures carried out by the members of the DOBIES project.

Model for Cumulative Solar Heavy Ion Energy and Linear Energy Transfer Spectra

A probabilistic model of cumulative solar heavy ion energy and LET spectra is developed for spacecraft design applications. Spectra are given as a function of confidence level, mission time period during solar maximum and shielding thickness. It is shown that long-term solar heavy ion fluxes exceed galactic cosmic ray fluxes during solar maximum for shielding levels of interest. Cumulative solar heavy ion fluences should therefore be accounted for in single event effects rate calculations and in the planning of space missions.

Dependence of thermoluminescent detectors relative response on the linear energy transfer; some examples of use

The relative response (RR) of the most thermoluminescent detectors (TLDs) decreases with increasing linear energy transfer (LET) of particles depositing energy in a TLD. Three TLDs have been mostly studied: Al–P glasses, Al 2 O 3 : C , and CaSO 4 : Dy . They have been exposed, since several years, to high energy charged particles with energies up to 1 GeV/amu, and LET up to 600 keV / μ m in water. The RR of TLDs as a function of LET is presented. In two cases, the sets of obtained data permitted us to regress them and obtain general LET dependences of RRs for Al–P glasses and Al 2 O 3 : C and for their ratios. These functions, in combination with LET spectra established by means of track etch based LET spectrometer were also used to appreciate their ability to establish total dosimetric characteristics in some high-energy radiation beams and fields, also those usable for hadron therapy.

LET calibration for CR-39 detectors in different oxygen environments

High LET (linear energy transfer) radiation is the main contributor to the radiation field in low Earth orbit (LEO) in terms of dose equivalent. CR-39 plastic nuclear track detectors (PNTDs) can measure the LET spectrum and charge spectrum for the complicated radiation field in space. Previous research indicated that the sensitivity of CR-39 is different for CR-39 PNTDs working in different oxygen environments. LET calibration for CR-39 detectors in different oxygen environments is needed. Almost all the previous LET calibration work was carried out for CR-39 detectors in good-oxygen condition, LET calibration work for CR-39 in poor-oxygen condition has not been conducted until our work. Systematic LET calibrations were carried out by JSC-SRAG (Space Radiation Analysis Group) for CR-39 detectors working in different oxygen environments and abundant results of LET calibrations were obtained. This paper introduces the method for CR-39 LET calibration, presents and discusses the calibration results and some applications.

Radiation measured for ISS-Expedition 12 with different dosimeters

Radiation in low Earth orbit (LEO) is mainly from Galactic Cosmic Rays (GCR), solar energetic particles and particles in South Atlantic Anomaly (SAA). These particles’ radiation impact to astronauts depends strongly on the particles’ linear energy transfer (LET) and is dominated by high LET radiation. It is important to investigate the LET spectrum for the radiation field and the influence of radiation on astronauts. At present, the best active dosimeters used for all LET are the tissue equivalent proportional counter (TEPC) and silicon detectors; the best passive dosimeters are thermoluminescence dosimeters (TLDs) or optically stimulated luminescence dosimeters (OSLDs) for low LET and CR-39 plastic nuclear track detectors (PNTDs) for high LET. TEPC, CR-39 PNTDs, TLDs and OSLDs were used to investigate the radiation for space mission Expedition 12 (ISS-11S) in LEO. LET spectra and radiation quantities (fluence, absorbed dose, dose equivalent and quality factor) were measured for the mission with these different dosimeters. This paper introduces the operation principles for these dosimeters, describes the method to combine the results measured by CR-39 PNTDs and TLDs/OSLDs, presents the experimental LET spectra and the radiation quantities.

Effect of inhomogeneous activity distributions and airway geometry on cellular doses in radon lung dosimetry

The human tracheobronchial system has a very complex structure including cylindrical airway ducts connected by airway bifurcation units. The deposition of the inhaled aerosols within the airways exhibits a very inhomogeneous pattern. The formation of deposition hot spots near the carinal ridge has been confirmed by experimental and computational fluid and particle dynamics (CFPD) methods. In spite of these observations, current radon lung dosimetry models apply infinitely long cylinders as models of the airway system and assume uniform deposition of the inhaled radon progenies along the airway walls. The aim of this study is to investigate the effect of airway geometry and non-uniform activity distributions within bronchial bifurcations on cellular dose distributions. In order to answer these questions, the nuclear doses of the bronchial epithelium were calculated in three different irradiation situations. (1) First, CFPD methods were applied to calculate the distribution of the deposited alpha-emitting nuclides in a numerically constructed idealised airway bifurcation. (2) Second, the deposited radionuclides were randomly distributed along the surface of the above-mentioned geometry. (3) Finally, calculations were made in cylindrical geometries corresponding to the parent and daughter branches of the bifurcation geometry assuming random nuclide activity distribution. In all three models, the same 218Po and 214Po surface activities per tissue volumes were assumed. Two conclusions can be drawn from this analysis: (i) average nuclear doses are very similar in all three cases (minor differences can be attributed to differences in the linear energy transfer (LET) spectra) and (ii) dose distributions are significantly different in all three cases, with the highest doses at the carinal ridge in case 3.

SU‐GG‐AUD‐07: Development of a Novel Detector for Measuring Proton Energy Spectra

Purpose: The purpose of this study was to design an instrument for measuring proton energy spectra, and present energy deposition results that compare calibration runs with two state of the art Monte Carlo codes, HETC‐HEDS, and GEANT. Method and Materials: The proton energy spectrum analyzer developed in this study is based on a telescope called the Cosmic Ray telescope of the Effects of radiation (CRaTER), originally designed to achieve characterization of the global lunar radiation environment and its biological impacts. It employs a stack of silicon detectors and tissue‐equivalent plastic (TEP) to establish the linear energy transfer (LET) spectra of cosmic radiation relevant for human and electronic parts considerations. Measured and calculated spectra were obtained using dE/dX= (E0−Ef)/L, where E0 and Ef are the energies of the particles as measured by the silicon detectors at either end of each TEP section and L is the length of the material. Results: Results show a very good agreement between experimental and computer models. A comparison of the peak position shows that HETC‐HEDS simulation of the instrument in a clinical proton beam yield a peak at channel 50. In comparison, the peak channel was 55 with Geant and 57 from the MGH data. The reason for the discrepancy is that the HETC‐HEDS analysis was performed for energies down to 0.2 MeV, while the analyses with GEANT and the MGH data included around 20 more energy channels. Conclusion: An LET energy spectrum was designed and computational testing for proton therapy. Comparisons between calibration runs and two simulation runs using GEANT and HETC‐HEDS show promising results in being able to use the instrument for proton therapy calibration purposes. Future investigations will include analyses for different geometrical configurations, as well as investigating the detector's response to other charged particles.

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.

Neutron detection on the Foton-M2 satellite by a track etch detector stack

In the frame of a European Space Agency (ESA) project called 'Biology and Physics in Space', a returning satellite, Foton-M2, was orbiting a container, the BIOPAN-5, loaded with biological experiments and facilities for radiation dosimetry (RADO) in the open space. One of the RADO experiments was dedicated to the detection of the primary cosmic rays and secondary neutrons by a track etch detector stack. The system was calibrated at high-energy particle accelerators and neutron generators. The developed detectors were investigated by an image analyser, and from the track parameters the linear energy transfer spectra and the absorbed dose were determined (26 microGy/d). Also, the neutron flux was estimated below 5 MeV and found to be 2.4 cm(-2) s(-1) directly from the space. The construction of the stack allowed to investigate the neutrons also from the direction of the carrying satellite, where the flux was found somewhat higher.

Radiation measured with TEPC and CR-39 PNTDs in low earth orbit

The radiation impact to astronauts depends strongly on the particles’ linear energy transfer (LET) and is dominated by high LET radiation. It is important to investigate the LET spectrum for the radiation field in low Earth orbit (LEO) and the influence of radiation on astronauts. The best active dosimeter used for all LET is the tissue equivalent proportional counter (TEPC); the best passive dosimeter used for high LET is CR-39 plastic nuclear track dosimeters (PNTDs). TEPC and CR-39 PNTDs were used to investigate the radiation in LEO. LET spectra and radiation quantities were obtained for STS-112 and STS-114 missions with TEPC and CR-39 PNTDs. This paper introduces the operation principles for the two types of dosimeters, presents radiation results measured and compares the results obtained with different dosimeters.

Simultaneous observation of the radiation environment inside and outside the ISS

The low-Earth orbit (LEO) radiation environment has been directly observed by the Intra-Vehicular (IV) and Extra-Vehicular (EV) Charged Particle Directional Spectrometers (CPDS) aboard the International Space Station (ISS). The EV instrument is mounted on the S0 truss of the ISS and consists of three separate silicon detector telescopes which are oriented in different directions. The IV instrument is a single silicon detector telescope located inside the US Laboratory module of the ISS. We report on the current state of the data analysis for these instruments, which includes the proton stopping particle spectrum, relative carbon, nitrogen, and oxygen ion (CNO) abundances, and linear energy transfer (LET) spectra.

Status and calibration results of Liulin-5 charged particle telescope designed for radiation measurements in a human phantom onboard the International Space Station

This is a report on the status of the particle telescope Liulin-5 developed for investigation of the radiation environment dynamics within the Russian spherical tissue-equivalent phantom on the International Space Station (ISS). Liulin-5 experiment will be a part of the international project MATROSHKA-R on ISS and is planned to start in 2007. Its aim is a long-term investigation of the depth–dose distribution in the phantom, mounted in the Russian Segment of ISS. The instrument is capable of simultaneously measuring energy deposition spectra, linear energy transfer (LET) spectra, flux and dose rates for electrons, protons and heavy charged particles at different depths of the phantom’s radial channel. Dose equivalent rate will be calculated from the absorbed dose rate multiplied by quality factor Q(LET). We present the inter-calibration results of the Liulin-5 instrument exposure to heavy ions, at the National Institute of Radiological Sciences (NIRS), Chiba, Japan that was done as part of the ICHIBAN project. The inter-comparison with the radiation dosimeters and spectrometers resulted in definition of the sensitive volumes of the instrument’s silicon detectors as well as estimations of the LET range of the Liulin-5 instrument.

Doses and LET spectra in the beam of 12C with energy 500 MeV amu−1

This paper describes the results of experimental studies performed at the Joint Institute for Nuclear Research (JINR) in a (12)C ion beam with the primary nominal energy 500 MeV amu(-1). Data measured by means of a diamond detector and a spectrometer of linear energy transfer (LET) based on chemically etched track detectors are presented, analysed and discussed. LET spectra are also calculated by program SRIM.

Incorporation of microdosimetric concepts into a biologically-based model of radiation carcinogenesis

The generalised state-vector model of radiation carcinogenesis (SVM) simulates radiation induced biological effects by expressing the transition rates between the various initiation and promotion stages in terms of dose rate for low and high linear energy transfer (LET) particles. In the present work, the SVM has been reformulated to incorporate single track characteristics of particles with varying LET. Transition rates of the initiation phase were expressed as functions of LET by describing the complexity and clustering of DNA double strand breaks (DSBs) and its effect on repair kinetics, while the promotion phase was reformulated based on a multi-target single-hit hypothesis. Such an approach allows the consideration of hit frequencies and the variability of the specific energy and LET spectra of radon progeny alpha particles in bronchial target cells for different exposure conditions.

Dosimetry and microdosimetry using LET spectrometer based on the track-etch detector: radiotherapy bremsstrahlung beam, onboard aircraft radiation field

The spectrometer of linear energy transfer (LET) based on the chemically etched polyallyldiglycolcarbonate (PADC) track-etch detector was developed several years ago in our institute. LET spectra are estimated through track parameters determination carried out by an automatic optical image analyzer LUCIA G. This LET spectrometer enables determining LET of particles approximately from 10 to 700 keV/µm. From the LET spectra, dose characteristics can be calculated. This contribution presents the use of this spectrometer in some applications – studies in 18 MV radiotherapy bremsstrahlung beam and investigation onboard a commercial aircraft during more than 6 months long exposure. The LET spectra obtained in both experiments represent mainly the contribution of secondary or tertiary particles created through the nuclear reactions of photons (bremsstrahlung beam) or neutrons and neutron-like reacting particles (onboard aircraft) in the detector itself or in the surroundings material. The dose due to the photoparticles represents about 3 × 10-4 of the photon dose; for the dose equivalent this value is about 2 × 10-3 Sv/Gy. Regarding the onboard aircraft exposure, the results obtained using LET spectrometer were compared with those achieved with other methods and a reasonable agreement were stated.

Past and future application of solid-state detectors in manned spaceflight

The radiation exposure in space missions can be reduced by careful mission planning and appropriate measures, such as provision of a radiation shelter, but it cannot be eliminated. The reason for that is the high penetration capability of the radiation components owing to their high energies. Radiation is therefore an acknowledged primary concern for manned spaceflight and is a potentially limiting factor for long-term orbital and interplanetary missions. The radiation environment is a complex mixture of charged particles of solar and galactic origin and of the radiation belts, as well as of secondary particles produced in interactions of the galactic cosmic particles with the nuclei of atmosphere of the earth. The complexity even increases by placing a spacecraft into this environment owing to the interaction of the radiation components with the shielding material. Therefore it is a challenge to provide for appropriate measurements in this radiation field, coping with the limited resources on experiment power and mass. Solid-state dosemeters were already chosen for measurements in the first manned flights. Thermoluminescence dosemeters (TLDs) and plastic nuclear track detectors (PNTD) especially found a preferred application because they are light-weighted, need no power supply and they are tissue-equivalent. Most of the data available until 1996 were gathered by using these passive detectors; this especially holds for heavy ion particle spectra. The systems, supplemented by converter foils or fission detectors and bubble detectors, provide information on dose, particle flux-, energy- and linear energy transfer spectra of the ionising radiation and neutron fluxes and doses. From 1989, silicon detectors were used for dose and flux measurements and later on for particle spectrometry. Silicon detectors were demonstrated as a powerful tool for the description of space radiation environment. Optical simulated luminescence (OSL) detectors have now been introduced as a new system in space research. Both, OSL and superheated drop detectors are candidates for personal dosimetry systems. The article will summarise past results, and results of measurements performed recently on the ISS, and conclude with future aspects.

Detection of primary and secondary cosmic ray particles aboard the ISS using SSNTD stacks

To study the radiation environment inside the International Space Station, solid state nuclear track detector stacks were used. Within the BRADOS experiments, Phase 1, seven stacks were exposed at different locations of the Russian segment 'Zvezda' for 248 days in 2001. It was supposed that the radiation field inside the ISS was composed from primary cosmic ray particles penetrating the wall of the ISS and secondaries, mainly neutrons induced by primaries in the wall and other structural materials surrounding the detectors. Based on the calibration made by utilising the high energy neutron reference field CERF at CERN (Geneva, Switzerland), the tracks induced by neutrons were separated from those induced by primary particles. Thus, the stacks, on one hand, provided the secondary neutron ambient dose equivalent. On the other hand, from the analysis of the rest of the tracks, the linear energy transfer spectra were computed and the flux and the dose of the primary particles were determined as shown in this paper.

Modelling the effect of non-uniform radon progeny activities on transformation frequencies in human bronchial airways

The effects of radiological and morphological source heterogeneities in straight and Y-shaped bronchial airways on hit frequencies and microdosimetric quantities in epithelial cells have been investigated previously. The goal of the present study is to relate these physical quantities to transformation frequencies in sensitive target cells and to radon-induced lung cancer risk. Based on an effect-specific track length model, computed linear energy transfer (LET) spectra were converted to corresponding transformation frequencies for different activity distributions and source-target configurations. Average transformation probabilities were considerably enhanced for radon progeny accumulations and target cells at the carinal ridge, relative to uniform activity distributions and target cells located along the curved and straight airway portions at the same exposure level. Although uncorrelated transformation probabilities produce a linear dose-effect relationship, correlated transformations first increase depending on the LET, but then decrease significantly when exceeding a defined number of hits or cumulative exposure level.

Spectra of linear energy transfer along the range of 500 MeV carbon ions beam

The contribution describes the results of experimental studies performed at the Joint Institute for Nuclear Research (JINR) with 12C ion beam of primary energy 500 MeV/amu. Depth dose distributions of linear energy transfer ( L) spectra and the dosimetry characteristics deduced from them have been established by means of an L-spectrometer based on chemically etched track detectors (TED), chemically polyallyldiglycolcarbonate. Experimentally established average L-values increase from about 10 keV/μm at the beam entrance to about 100 keV/μm in the region of the Bragg peak. At the same time, important widening of L-spectra is observed along the range. Depth dose distributions deduced from the L-spectrometer data are compared with those measured by means of diamond detector. A reasonable correlation of results is found.