The MATROSHKA experiments and the related HAMLET project funded by the European Commission aimed to study the dose burden of the crew working on the International Space Station (ISS). During these ...experiments a human phantom equipped with several thousands of radiation detectors was exposed to cosmic rays inside and outside the ISS. Besides the measurements realized in Earth orbit, the HAMLET project included also a ground-based program of calibration and intercomparison of the different detectors applied by the participating groups using high-energy ion beams. The Space Dosimetry Group of the Centre for Energy Research (formerly Atomic Energy Research Institute) participated in these experiments with passive solid state nuclear track detectors (SSNTDs). The paper presents the results of the calibration experiments performed in the years 2008–2011 at the Heavy Ion Medical Accelerator (HIMAC) of the National Institute of Radiological Sciences (NIRS), Chiba, Japan. The data obtained serve as update and improvement for the previous calibration curves which are necessary for the evaluation of the SSNTDs exposed in unknown space radiation fields.
One of the limiting factors of an astronaut’s career is the dose received from space radiation. High energy protons, being the main components of the complex radiation field present on a spacecraft, ...give a significant contribution to the dose. To investigate the behavior of solid state nuclear track detectors (SSNTDs) if they are irradiated by such particles, SSNTD stacks containing carbon blocks were exposed to high energy proton beams (70, 100, 150 and 230 MeV) at the Proteus cyclotron, IFJ PAN -Krakow. The incident protons cannot be detected directly; however, tracks of secondary particles, recoils and fragments of the constituent atoms of the detector material and of the carbon radiator are formed. It was found that as the proton energy increases, the number of tracks induced in the PADC material by secondary particles decreases. From the measured geometrical parameters of the tracks the linear energy transfer (LET) spectrum and the dosimetric quantities were determined, applying appropriate calibration. In the LET spectra the LET range of the most important secondary particles could be identified and their abundance showed differences in the spectra if the detectors were short or long etched. The LET spectra obtained on the SSNTDs irradiated by protons were compared to LET spectra of detectors flown on the International Space Station (ISS): they were quite similar, resulting in a quality factor difference of only 5%. Thermoluminescent detectors (TLDs) were applied in each case to measure the dose from primary protons and other lower LET particles present in space. Comparing and analyzing the results of the TLD and SSNTD measurements, it was obtained that proton induced target fragments contributed to the total absorbed dose in 3.2% and to the dose equivalent in 14.2% in this particular space experiment.
The space radiation can be characterized in several ways: considering its origin, particle type and energy or by registration technique. From the point of view of solid state nuclear track detectors ...(SSNTD) applied for space dosimetry one way of characterization is to distinguish external radiation (primary cosmic ray particles and projectile fragments entering the detector from the surroundings) and internal radiation (secondary particles like target fragments and recoiled ions which are formed mostly by protons and neutrons inside the detector material). The measurable quantities are always the track parameters on the etched surface of the detector sheet, which must be enough to derive the particle fluence, based on reasonable theoretical approach. The “classical” or “conventional” method to obtain the fluence and dose does not distinguish between tracks induced by external or internal particles, and this may introduce systematical errors and generate higher uncertainty, and over- or underestimation of the dose. The latter consequence is demonstrated after the brief description of the classical method. Since the most abundant particles in space are protons, the study deals –as an example- with the determination of the high energy proton induced secondary particle forming events inside the detector, based on experiments.
The career of astronauts is dependent mostly on the lifetime dose received from primary cosmic rays and secondary particles generated within the structuring materials of a space craft. Since the high ...energy protons and He particles have the highest abundance and the secondary neutrons significantly contribute to the dose, the study of the response of solid state nuclear track detectors (SSNTD) to these particles has a great importance. SSNTDs, having been used for dosimetry on the International Space Station (ISS), were exposed to protons at several accelerators (Loma-Linda, BNL, TSL), to He (HIMAC) and to neutrons (iThemba, TSL). The incident particles cause fragmentation of the constituent elements of the SSNTD composed of C
12H
18O
7. The fragments induce latent tracks inside the detector which can be visualized by chemical processes and investigated by optical microscope. The measurable track parameters and appropriate calibration allow to determine the linear energy transfer (LET) spectrum of the fragments and also the absorbed dose in the nearly tissue equivalent detector material. The LET spectra of different exposures are presented and compared. Additionally, a LET spectrum determined from the MATROSHKA space walk simulation outside the International Space Station (ISS) will be compared to some of those obtained from accelerator experiments.
In the framework of “Biology and Physics in Space” project of the European Space Agency (ESA), a returning satellite, Foton-M2, carried an open-to-space sample holder outside of the satellite body, ...called as BIOPAN-5, loaded with exo-biological experiments and dosemeters for
RAdiation
DOsimetry (RADO). One of the RADO experiments (Teflon – TLD) was dedicated to dose distribution measurements of the cosmic radiation by thermo-luminescent (TL) technique. It was found that the maximum surface absorbed dose rate, averaged over the first ∼8
mg/cm
2 thickness, was ∼2
Gy/d and showed a location dependence due the shading effect of the satellite construction elements. The dose rate decreased nearly by 3 orders of magnitude below 500
mg/cm
2.
In the frame of the European Space Agency (ESA) project called “Biology and Physics in Space”, the returning satellite, Foton-M2, carried an open-to-space exposure platform outside of the satellite ...body, called as BIOPAN-5, loaded with exo-biological experiments and facilities for radiation dosimetry (RADO). One of the RADO experiments was dedicated to the detection of the primary galactic cosmic rays (GCR) and secondary neutrons by a track etch detector stack. The daily absorbed dose (
D) and dose equivalent (
H) were calculated from the experimental LET spectra (LET
>
10
keV/μm). Under a shielding of ∼2.8
g/cm
2 the averaged
H was found to be 658
±
8
μSv/d, with a quality factor (
Q) of 6.2
±
1.2. The LET spectra showed a local peak at ∼105
keV/μm suggesting that the majority of tracks were created by trapped protons as it has been predicted by calculations. The low LET dose of the cosmic radiation was determined by 4 TLD stacks, and the total dose was found to be 795
±
14
μSv/d.
The Russian BRADOS experiment onboard the International Space Station (ISS) was aimed at developing methods in radiation dosimetry and radiobiology to improve the reliability of risk estimates for ...the radiation environment in low-Earth orbit. Experimental data from thermoluminescence detectors (TLDs) and solid state nuclear track detectors (SSNTDs) gathered during the BRADOS-1 (24 February–31 October 2001) mission are reviewed and convolved to obtain absorbed dose and dose equivalent from primary and secondary cosmic-ray particles. Absorbed dose rates in the ISS Russian Segment (Zvezda) ranged from
208
±
14
to
275
±
14
μ
Gy
d
-
1
. Dose equivalent rates were determined to range from
438
±
29
to
536
±
32
μ
Sv
d
-
1
, indicating a quality factor between
1.95
±
0.15
and
2.11
±
0.20
. The contribution of densely ionizing particles
(
LET
⩾
10
keV
μ
m
-
1
)
to dose equivalent made up between 54% and 64%.
Radiophotoluminescent (RPL) glass dosimeter type SC-1 has been studied with respect to use it as a photon dosimeter in mixed
neutron
+
gamma
fields. SC-1 is composed of the flat glass element placed ...in a plastic capsule. Energy compensation tin filters to all directions shield the glass card in the capsule. This type of dosimeter was primarily designed for the measurements of photon dose and for use in environmental monitoring around nuclear plants and for accident dosimetry. For a gamma dosimeter to be useful in a mixed
neutron
+
gamma
field it is desirable that the neutron sensitivity is small and accurately known. The response has been characterized for 14.5
MeV neutrons,
238Pu–Be spectra and thermal neutrons. The results show that the plastic holder has an influence to the response. The comparison with TLD-700 shows lower responses for neutrons for all spectra investigated. The relative low neutron sensitivity of RPL dosimeter type SC-1 enables its use for photon dosimetry in the mixed
neutron
+
gamma
fields.
Low dose cell culture irradiation experiments have been carried out at the filtered beam of Budapest Research Reactor for several years. The aim of the present study is to provide along with the ...macroscopically determinable “dose”, more detailed information on the components of the radiation affecting the cells. For this purpose CR-39 detectors with several types of radiator and absorber materials were mounted in different geometrical arrangements on the walls of the cell holder flasks and irradiated under the same conditions as those of the cells. With these detectors individual particles can be investigated using an image analyser and the effect of thermal, intermediate and fast neutrons hitting the cells, the protons induced by neutrons in the wall of the flasks, backscattered by the medium and by the surroundings can be studied. The methods, results of the measurements and dose calculations will be presented.
The aim of the study was to investigate the contribution of secondary neutrons to the total dose inside the International Space Station (ISS). For this purpose solid-state nuclear track detector ...(SSNTD) stacks were used. Each stack consisted of three CR-39 sheets. The first and second sheets were separated by a Ti plate, and the second and third sheets sandwiched a Lexan polycarbonate foil. The neutron and proton responses of each sheet were studied through MC calculations and experimentally, utilising monoenergetic protons. Seven stacks were exposed in 2001 for 249 days at different locations of the Russian segment ‘Zvezda’. The total storage time before and after the exposure onboard was estimated to be seven months. Another eight stacks were exposed at the CERF high-energy neutron field for calibration purposes. The CR-39 detectors were evaluated in four steps: after 2, 6, 12 and 20 h etching in 6 N NaOH at 70°C (VB = 1.34 µm h−1). All the individual tracks were investigated and recorded using an image analyser. The stacks provided the averaged neutron ambient dose equivalent (H*) between 200 keV and 20 MeV, and the values varied from 39 to 73 μSv d−1, depending on the location. The Lexan detectors were used to detect the dose originating from high-charge and high-energy (HZE) particles. These results will be published elsewhere.
