Space Dosimetry Research Articles

The importance of time-resolved personal Dosimetry in space: The ISS Crew Active Dosimeter

Monitoring space radiation is of vital importance for risk reduction strategies in human space exploration. Radiation protection programs on Earth and in space rely on personal and area radiation monitoring instruments. Crew worn radiation detectors are crucial for successful crew radiation protection programs since they measure what each crewmember experiences in different shielding configurations within the space habitable volume. The Space Radiation Analysis Group at NASA Johnson Space Center investigated several compact, low power, real-time instruments for personal dosimetry. Following these feasibility studies, the Crew Active Dosimeter (CAD) has been chosen as a replacement for the legacy crew passive radiation detectors. The CAD device, based on direct ion storage technology, was developed by Mirion Dosimetry Services to meet the specified NASA design requirements for the International Space Station (ISS) and Artemis programs. After a successful Technology demonstration on ISS, the CAD has been implemented for ISS Crew operations since 2020. The current paper provides an overview of the CAD development, ISS results and comparison with the ISS Radiation Assessment Detector (RAD) and the Radiation Environment Monitor 2 (REM2) instruments.

Characterization of indigenous OSL phosphors LiCaAlF6:Eu,Y and α-Al2O3:C for space dosimetry

The possibility of using indigenously synthesized Optically Stimulated Luminescence (OSL) phosphors, α-Al2O3:C and LiCaAlF6:Eu,Y is explored for application in space dosimetry. The dosimeters prepared using these phosphors were irradiated in BARC-TIFR Pelletron Accelerator facility with proton beam (8–20 MeV). The OSL properties with proton beam irradiation were compared with beta irradiation corresponding to 90Sr/90Y. No change in the OSL emission was found for both the phosphors when exposed to with low LET 90Sr/90Y beta (0.2 keV/μm) and high LET proton (2 keV/μm, 20 MeV). It was observed that Continuous Wave (CW) OSL signal decays faster with increasing LET of the proton beam for both types of dosimeters α-Al2O3:C and LCAF. The OSL dose response is linear for the high LET proton beam which is similar to the response obtained using low LET beta and gamma irradiation. The variation of OSL efficiency per unit fluence matches reasonably well with the theoretically calculated values of absorbed dose in water.

Morphology and thermoluminescence characteristics of customised Ge-doped optical fibre under Am–Be neutron source as a potential to be used for space radiation detector

In the low Earth orbit (LEO) neutron particles exist from secondary radiations due to interactions of Galactic Cosmic Ray (GCR) or trapped protons in the Earth's inner radiation belt with the Earth's atmosphere or space object materials or the astronaut themselves. Apart from that, high energy neutrons produced during solar activities may survive in the distance travelled to the Earth. For passive dosimetry in space, the presence of neutrons should be considered. In this work, we focused on the capability of Customised Optical Fibres (CusOF) to detect the neutrons produced by 241AmBe neutron source. Also, the morphology of flat fibres (FF) was analysed using scanning electron microscopy (SEM) and Electron Dispersive X-ray (EDX). From the SEM images, ImageJ software was employed to measure the area of the organic shaped core of the FF accurately. From the EDX results, it was found that the effective atomic number of CusOF were in the range of 13.40–15.25, similar to human skeleton. Irradiation of CusOF to 241AmBe neutron source shows that at a distance of 0 cm and 15 cm from the source, CusOF had high coefficient of determination (R2) value of 0.95–0.99, better than that of TLD-100 and TLD-700, 0.86 and 0.92, respectively, at 0 cm. This shows that the CusOF has high potential to be used for neutron radiation detector.

СОВРЕМЕННЫЕ ДОСТИЖЕНИЯ И АКТУАЛЬНЫЕ ЗАДАЧИ КОСМИЧЕСКОЙ РАДИОБИОЛОГИИ

Purpose: Analytical review of space radiobiology current state and promising areas, revision of space radiobiology crucial tasks were the research objectives. Material and methods: Data from a chronic experiment on 700 mature male rats (radiation doses of 10-100 sGr), clinical and physiological data of irradiated pilots-liquidators of the Chernobyl accident consequences (more than 1000 people) and numerous radiation neurophysiological experiments, including with heavy charged particles (HCP) were used methodologically as new experimental patterns. The methods are presented in 3 monographs and 19 journal articles. Results: The main barrier to further human penetration into space is cosmic radiation from various sources: galactic and solar cosmic rays. Complex radiation “cocktails” in space are dangerous, taking into account secondary neutrons and gamma-irradiation. Modeling it on Earth is extremely difficult. The structure of modern space radiobiology includes: radiation situation in near and far space; features of dosimetry in space and the possibility of using various phantoms; multilevel effects of human radiation exposure in space; small doses and the brain; the role of combined effects; elaboration of new approaches for extrapolation on human experimental data obtained on animals; rationing of radiation effects in space, taking into account the numerous non-radiation risks in flight; development of means to increase radioresistance and biomedical protection. New concept of human radiation safety in orbital flights should take into account all the likely immediate and long-term consequences of human radiation exposure in space. It is necessary to verify possible brain disorders from HCP, taking into account combined effect of other flight factors, including the hypomagnetic environment, and to assess the risk of imminent radiation threats, in particular on the Moon or Mars. Modern science is not yet able to predict solar proton events well, knowledge about the spectra of cosmic radiation and methods for calculating doses during the passage of various types of radiation through matter is limited. The new concept of protection can be called “the concept of choosing a lesser amount of evil”. The principle of ALARA is not canceled, but is put on the verge of possible compliance. In the on-board first aid kit, it is necessary to have means that will be a kind of modern “sum of radiobiology” at the time of flight, using the entire arsenal of countermeasures – radioprotectors, radiomitigators, radio-modulators, hibernation, artificial magnetic field, etc. The crew should be selected from the most radio-resistant astronauts (according to geno- and phenotypic criteria). Conclusion: Modern space radiobiology is at a critical stage of finding new ways of development and obtaining breakthrough results.

Monte Carlo simulation of semiconductor-based detector in mixed radiation field in the atmosphere

Calculation of radiation protection quantities in tissue equivalent material from measurements using semiconductor detectors requires correction factors for conversion of the measured values in the semiconductor material to the tissue equivalent material. This approach has been used many times in aircraft and for space dosimetry. In this paper, we present the results of Monte Carlo simulations which reveal the need to take into account both the radiation field and the detector material when performing the conversion of measured values to radiation protection quantities. It is shown that for low Z target material, most of the dose equivalent at aviation altitudes comes from neutrons originating from nuclear reactions, while in high Z targets most of the dose equivalent comes from photons, originating from electromagnetic reactions.

A Comprehensive Review on Rare-Earth Based Thermoluminescence Phosphors for Radiation Dosimetry

When ionizing radiation is incident on an insulating crystal, some of the deposited energy is stored in the lattice at defect sites, colour centres, etc. Upon heating the crystal, this stored energy is released and a fraction of it may be emitted as visible light. This is called ‘Thermoluminescence.’ Within certain limitations, the amount of light emitted is proportional to the radiation dose previously absorbed by the TL material. The application of thermoluminescence (TL) as a methodology for radiation dosimetry of ionizing radiation has been well-established since several decades and has found number of practical applications in various fields, such as personnel and environmental monitoring, retrospective dosimetry, medical dosimetry, space dosimetry, high-dose dosimetry, etc. Especially, alkaline-earth silicates are appropriate compounds as radiation detectors due to their high chemical stability. Doping may either cause the formation of new defect centers or recovering of existing levels within the band-gap for a defective host which changes both the optical and electronic features of the materials. Therefore, it is of great importance by choosing both the dopant as well as the host for thermoluminescence application. It has already been reported that commercially available thermoluminescence phosphor suffers from fading, stability, etc., which justifies the ongoing need to identify factors that can be exploited to make a thermoluminescence phosphor with high efficiency and stability.

Investigation of thermoluminescence and photoluminescence properties of Tb3+, Eu3+, and Dy3+ doped NaYF4 phosphors for dosimetric applications.

Hexagonal phase sodium yttrium fluoride activated with lanthanide ions; Tb3+, Eu3+ and Dy3+ doped NaYF4 phosphors were synthesized using a simplistic hydrothermal method. The photoluminescence studies demonstrated green, red and blue emission lines corresponding to 5D4 → 7FJ (J = 6, 5, 4, 3), 5D0 → 7FJ (J = 1, 2 and 4) and 4F9/2 to 6HJ (J = 15/2 and 13/2) transitions, which are characteristic of Tb3+, Eu3+ and Dy3+ ions, respectively. The as-synthesized samples were subjected to annealing at varying temperatures from 500 °C to 800 °C primarily for the optimization of the thermoluminescence glow curve. Meanwhile, we studied the influence of thermal annealing treatment on the crystal phase, morphological features, and photoluminescence properties of the phosphors. The spherical-like morphology of NaYF4:Tb3+ phosphor changed to micro block-like structures and the hexagonal phase of NaYF4 transforms into a cubic phase at a higher annealing temperature of ∼800 °C. The photoluminescence emission intensity also varied at different annealing temperatures. The systematic study using different dopants and annealing temperatures was carried out to accomplish efficient thermoluminescence (TL) properties. The most suitable TL dosimetric glow peak was attained for NaYF4:0.5%Tb3+ phosphor, which was annealed at a temperature of 800 °C, located at 194 °C. The NaYF4:Tb3+ phosphor exhibited TL response fairly linear in the dose range from 1 kGy to 25 kGy of gamma radiation. The phosphor showed TL response at higher doses, which stipulates that the NaYF4:Tb3+ is reasonably well suitable for high dose measurements and respective applications. The phosphor exhibited negligible fading and good reproducibility features. Trap-level analysis and experimental determination of activation energy were performed using the Tm-Tstop technique and initial rise method (IRM). The trapping parameters of the TL glow curve, such as activation energy (E), order of kinetics (b), and frequency factor (s) were estimated by Chen's glow peak shape (PS) method and glow curve deconvolution (GCD) method. The trapping parameters obtained using the IRM, PS and GCD methods are in good accordance with each other. Henceforth, along with efficient photoluminescence properties, the NaYF4:Tb3+ phosphor exhibited favorable thermoluminescence dosimetric properties. Consequently, this study provides new opportunities for utilizing these phosphors in the area of radiation dosimetry applications such as environmental and food monitoring, space dosimetry etc.

A miniaturized radiation monitor for continuous dosimetry and particle identification in space

A Miniaturized Radiation Monitor (MIRAM) has been developed for the continuous measurement of the radiation field composition and ionizing dose rates in near earth orbits. Compared to currently used radiation monitors, the presented device has an order of magnitude lower weight while being comparable in power consumption and functionality. MIRAM is capable of on-board real-time self-diagnostic. Furthermore, it supports on-board analysis of the measured data to be able to work autonomously. The dose rate is calculated continuously based on the energy deposition in the Timepix3 detector. For the estimation of the particle species composition of the radiation environment, two methods are applied depending on the current flux. At lower fluxes (<104 particles per cm2 per s), a track-by-track analysis based on temporal coincidence is applied. At higher fluxes, a less power and memory consuming method is utilized. This method is using the averaged deposited energy per pixel to estimate the electron and proton content of the radiation field.

A bespoke health risk assessment methodology for the radiation protection of astronauts

An alternative approach that is particularly suitable for the radiation health risk assessment (HRA) of astronauts is presented. The quantity, Radiation Attributed Decrease of Survival (RADS), representing the cumulative decrease in the unknown survival curve at a certain attained age, due to the radiation exposure at an earlier age, forms the basis for this alternative approach. Results are provided for all solid cancer plus leukemia incidence RADS from estimated doses from theoretical radiation exposures accumulated during long-term missions to the Moon or Mars. For example, it is shown that a 1000-day Mars exploration mission with a hypothetical mission effective dose of 1.07 Sv at typical astronaut ages around 40 years old, will result in the probability of surviving free of all types of solid cancer and leukemia until retirement age (65 years) being reduced by 4.2% (95% CI 3.2; 5.3) for males and 5.8% (95% CI 4.8; 7.0) for females. RADS dose–responses are given, for the outcomes for incidence of all solid cancer, leukemia, lung and female breast cancer. Results showing how RADS varies with age at exposure, attained age and other factors are also presented. The advantages of this alternative approach, over currently applied methodologies for the long-term radiation protection of astronauts after mission exposures, are presented with example calculations applicable to European astronaut occupational HRA. Some tentative suggestions for new types of occupational risk limits for space missions are given while acknowledging that the setting of astronaut radiation-related risk limits will ultimately be decided by the Space Agencies. Suggestions are provided for further work which builds on and extends this new HRA approach, e.g., by eventually including non-cancer effects and detailed space dosimetry.

MICRODOSIMETRIC UNDERSTANDING OF DOSE RESPONSE AND RELATIVE EFFICIENCY OF THERMOLUMINESCENCE DETECTORS.

LiF:Mg,Ti detectors show relative efficiency η for heavy charged particles significantly lower than one. It was for a long time not recognised that η varies also for electron energies and, as a consequence for photons. For LiF:Mg,Cu,P detectors measured photon energy response was named ‘anomalous’ because it differed significantly from the ratio of photon absorption coefficients. The decrease of η was explained as a microdosimetric effect due to local saturation of trapping centres around the electron track. For TLD-100 it was noticed by Horowitz that the measured photon energy response disagrees with the ratio of absorption coefficient by about 10%. It was demonstrated that a fraction of the TL signal in LiF:Mg,Ti is generated in the supralinear dose–response range, due to the high local doses generated by photon-induced tracks. Prediction of TL efficiency is particularly important in space dosimetry and in dosimetry of therapeutic beams like protons or carbon ions.

The CERN-EU high-energy Reference Field (CERF) facility: New FLUKA reference values of spectral fluences, present and newly proposed operational quantities

The CERN-EU high-energy Reference Field (CERF) facility provides an almost unique high-energy workplace radiation field for calibrating and testing radiation protection instrumentation employed at high-energy accelerators and for aircraft and space dosimetry. For the available exposure locations, this work provides the particle fluences of the various components of the radiation field, and a new set of reference values for the currently used operational quantities, i.e. ambient dose equivalent, H*(10), and personal dose equivalent Hp(10), as well as for the newly proposed ICRU/ICRP quantities ambient dose, H*, and personal dose, Hp, that may be adopted in the future for radiation protection. Particle spectra and radiological quantities were computed with the latest versions of the FLUKA code and benchmarked against experimental data taken with one of the reference instruments used at the facility.

Recent Advances in Silica Glass Optical Fiber for Dosimetry Applications

In this paper, we review the highly promising silica glass, fabricated as doped and undoped optical fiber for intended use in radiation dosimetry. The dosimetry techniques reviewed here, underpinned by intrinsic and extrinsic defects in silica glass, focus on Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) and Radioluminescence (RL), with occasional references to the much more established Radiation Induced Attenuation (RIA). The other focus in this review is on the various materials that have been reported earlier as dopants and modifiers used in silica glass optical fiber radiation dosimeters. This article also elaborates on recently reported optical fiber structures, namely, cylindrical fibers, photonic crystal fibers and flat fibers, as well as dimensions and shapes used for optimization of dosimeter performance. The various types of optical fiber radiation dosimeters are subsequently reviewed for various applications ranging from medical dosimetry such as in external beam radiotherapy, brachytherapy and diagnostic imaging, as well as in industrial processing and space dosimetry covering a dynamic dose range from μGy to kGy. Investigated dosimetric characteristics include reproducibility, fading, dose response, reciprocity between luminescence yield to dose-rate and energy dependence. The review is completed by a brief discussion on limitations and future developments in optical fiber radiation dosimetry.

Electron Inelastic Mean Free Paths for LiF, CaF2, Al2O3, and Liquid Water from 433 keV down to the Energy Gap.

We report new calculations, which include the influence of the band gap and exciton states, of the electron inelastic mean free path (IMFP) for liquid water, LiF, CaF2, and Al2O3 from the band gap to 433 keV. Among compounds, liquid water is the most studied due to its role in radiobiological research, whereas LiF and CaF2 are the most widely used thermoluminescent dosimeters in environmental monitoring and medical and space dosimetry. Due to its sensitivity, the optically stimulated luminescent dosimeter, Al2O3, has recently begun to be used for personnel monitoring. Previous treatments have modified the integration domain to consider the indistinguishability between the incident electron and the ejected one or the bandgap energy for nonconductors but not to accommodate exciton states within the band gap, and no published IMFP data are available for CaF2. Our calculation was carried out using an electron-beam–solid-state interaction model through the relativistic full Penn algorithm. Integration limits that consider the band gap, the valence band width, and exciton interactions have been used. The results suggest that, at electron energies below 100 eV, the different choices of models for integration limits and the exciton interaction can affect the IMFP by 9–29%. At higher energies, the differences associated with the choice of energy-loss function and other input parameters are around 2.5–7.5%.

A study of the response of depleted type p-MOSFETs to electron dose

The p-MOSFET dosimeter studied in this work has been manufactured at LAAS- CNRS Laboratory in Toulouse France, for applications in personal and space dosimetry. They are proposed for proton, heavy ions and electron and photon dose measurements. The current study investigates the sensitivity of this new type of Metal-Oxide-Semiconductor field effect transistor (MOSFET) to electrons. The sensitivity of the new MOSFET based dosemeters to electrons is linear for wide dose ranges. The influence of the electrons energy on the dosemeters response is also investigated.

Fading of CaSO4 thermoluminescent detectors after exposure to charged particles

Thermoluminescent detectors are often employed in space dosimetry, characteristic with long duration and exposures to mixed radiation fields. Complementing advantages of this dosimeter type are two drawbacks - dependency of response on radiation quality and signal fading in time. This study investigates fading of the thermoluminescent CaSO4:Dy signal after exposure to some charged components of cosmic radiation, 200 MeV protons and 400 MeV/u carbon ions. The results were compared with the fading after exposure to gamma radiation. The loss of the signal was found to be dependent on the radiation quality, with larger long-term fading for the protons and carbon ions comparing to gamma. For carbon ions, the loss of signal after six months was up to 8%, large enough to justify further study of corrections needed for long term measurements of cosmic radiation.

The CERN-EU high-energy Reference Field (CERF) facility: applications and latest developments

The CERF facility at CERN provides an almost unique high-energy workplace reference radiation field for the calibration and test of radiation protection instrumentation employed at high-energy accelerator facilities and for aircraft and space dosimetry. This paper describes the main features of the facility and supplies a non-exhaustive list of recent (as of 2005) applications for which CERF is used. Upgrade work started in 2015 to provide the scientific and industrial communities with a state-of-the-art reference facility is also discussed.

Evaluation of an international doctoral educational program in space life sciences: The Helmholtz Space Life Sciences Research School (SpaceLife) in Germany

Training young researchers in the field of space life sciences is essential to vitalize the future of spaceflight. In 2009, the DLR Institute of Aerospace Medicine established the Helmholtz Space Life Sciences Research School (SpaceLife) in cooperation with several universities, starting with 22 doctoral candidates. SpaceLife offered an intensive three-year training program for early-stage researchers from different fields (biology, biomedicine, biomedical engineering, physics, sports, nutrition, plant and space sciences). The candidates passed a multistep selection procedure with a written application, a self-presentation to a selection committee, and an interview with the prospective supervisors. The selected candidates from Germany as well as from abroad attended a curriculum taught in English. An overview of space life sciences was given in a workshop with introductory lectures on space radiation biology and dosimetry, space physiology, gravitational biology and astrobiology. The yearly Doctoral Students’ Workshops were also interdisciplinary. During the first Doctoral Students’ Workshop, every candidate presented his/her research topic including hypothesis and methods to be applied. The progress report was due after ∼1.5years and a final report after ∼3years. The candidates specialized in their subfield in advanced lectures, Journal Clubs, practical trainings, lab exchanges and elective courses. The students attended at least one transferable skills course per year, starting with a Research Skills Development course in the first year, a presentation and writing skills course in the second year, and a career and leadership course in the third year. The whole program encompassed 303h and was complemented by active conference participation. In this paper, the six years’ experience with this program is summarized in order to guide other institutions in establishment of structured Ph.D. programs in this field. The curriculum including elective courses is documented. The applicants’ statistics revealed that personal contacts and the DLR website were most important the recruitment of doctoral candidates. The evaluation of the application and selection procedure revealed that prediction of thesis success based on master thesis mark or evaluation by the selection committee is difficult. SpaceLife Doctoral Students greatly contributed to the scientific output in terms of peer-reviewed publications of the Institute of Aerospace Medicine with a peak in the fourth year after start of the thesis and they continuously received awards for their scientific work.

Neutron yields and effective doses produced by Galactic Cosmic Ray interactions in shielded environments in space

In order to define the ranges of relevant neutron energies for the purposes of measurement and dosimetry in space, we have performed a series of Monte Carlo transport model calculations that predict the neutron field created by Galactic Cosmic Ray interactions inside a variety of simple shielding configurations. These predictions indicate that a significant fraction of the neutron fluence and neutron effective dose lies in the region above 20 MeV up to several hundred MeV. These results are consistent over thicknesses of shielding that range from very thin (2.7 g/cm2) to thick (54 g/cm2), and over both shielding materials considered (aluminum and water). In addition to these results, we have also investigated whether simplified Galactic Cosmic Ray source terms can yield predictions that are equivalent to simulations run with a full GCR source term. We found that a source using a GCR proton and helium spectrum together with a scaled oxygen spectrum yielded nearly identical results to a full GCR spectrum, and that the scaling factor used for the oxygen spectrum was independent of shielding material and thickness. Good results were also obtained using a GCR proton spectrum together with a scaled helium spectrum, with the helium scaling factor also independent of shielding material and thickness. Using a proton spectrum alone was unable to reproduce the full GCR results.

Cosmic Radiation Detection by Solid State Nuclear Track Detector Technique

Passive Solid State Nuclear Track Detectors (SSNTDs) have been employed successfully during the past two decades in space radiation studies due to their excellent physico-chemical properties. They are useful for charged particle detection in the linear energy transfer (LET) range above the threshold value of ~10 keV μm-1. It was applicable for measurement of cosmic ray primary and secondary particles, including recoil nuclei, projectile and target fragments and secondary neutrons in past projects such as DOSMAP, BRADOS, ALTCRISS, Matroshka or recently in progress as SPD, DOSIS, as well as, in ground based experiment as Icchiban. The continuous development in the understanding of the track formation mechanism and improvement of detection techniques have resulted in the determination of the cosmic ray LET spectrum with less uncertainties and provided improved assessment of the dose burden of astronauts and helped to increase the effectiveness of radiation shielding of spaceships. Space dosimetry by nuclear track methodology stresses the advantages of passive systems for cosmic radiation field studies due to their robustness, compact dimensions, and complete independence from external power supply. SSNTDs cope also with requirement imposed by portable area monitoring or personal dose integrator to assess radiation risk of astronauts during intra or extra-vehicular activity. This review tries to provide a short summary about fundamentals and applications of space radiation studies using SSNTDs.Contents of Paper

Comparative investigations of the relative thermoluminescent efficiency of LiF detectors to protons at different proton therapy facilities

Radiotherapy with proton beam is one of the most modern methods of cancer treatment. The basic dosimetric tools in proton therapy are ionization chambers. However, thermoluminescent detectors (TLDs) are also widely applied, being unrivalled in phantom measurements of spatial dose distribution. The relative thermoluminescent efficiency of LiF detectors for protons, which is important for radiotherapy and space dosimetry, have been studied several times, but the available experimental data concerning this subject are not straightforward. Some researchers show that the efficiency of LiF:Mg, Ti to protons with respect to gamma-rays, may significantly exceed unity (even more than 30%), however, many others show the efficiency close to unity or lower.In relation to this issue a research investigation concerning the efficiency of two commonly used TLDs: LiF:Mg, Ti and LiF:Mg,Cu,P, were started at the Institute of Nuclear Physics (IFJ PAN).The measurements were realized exploiting three separate proton beam accelerators normally used for cancer treatment. Two of them at the IFJ PAN Kraków using the 60 MeV and 230 MeV proton beams and another at the Helmholtz-Zentrum Berlin using the 68 MeV proton beam. The relative TL efficiency was determined for protons with energy ranging from 12 to 218 MeV. The results confirmed general energy dependence of two used TLDs. For LiF:Mg, Ti it was found that efficiency increases with decreasing proton energy and shows a maximum of 1.15 at about 20–25 MeV. For LiF:Mg,Cu,P the relative efficiency decreases systematically with decreasing proton energy and is below unity even for the highest studied proton energy.