•Dose reduction effect for space radiation by water shielding material was verified.•Absorbed dose and dose equivalent were evaluated with passive dosimeters.•Observed dose reduction rate was found ...to be 37±7% in dose equivalent.•It will effectively reduce the annual dose for space crews and long-term mission.
The dose reduction effects for space radiation by installation of water shielding material (“protective curtain”) of a stack board consisting of the hygienic wipes and towels have been experimentally evaluated in the International Space Station by using passive dosimeters. The averaged water thickness of the protective curtain was 6.3g/cm2. The passive dosimeters consisted of a combination of thermoluminescent detectors (TLDs) and plastic nuclear track detectors (PNTDs). Totally 12 passive dosimeter packages were installed in the Russian Service Module during late 2010. Half of the packages were located at the protective curtain surface and the other half were at the crew cabin wall behind or aside the protective curtain. The mean absorbed dose and dose equivalent rates are measured to be 327μGy/day and 821μSv/day for the unprotected packages and 224μGy/day and 575μSv/day for the protected packages, respectively. The observed dose reduction rate with protective curtain was found to be 37±7% in dose equivalent, which was consistent with the calculation in the spherical water phantom by PHITS. The contributions due to low and high LET particles were found to be comparable in observed dose reduction rate. The protective curtain would be effective shielding material for not only trapped particles (several 10MeV) but also for low energy galactic cosmic rays (several 100MeV/n). The properly utilized protective curtain will effectively reduce the radiation dose for crew living in space station and prolong long-term mission in the future.
We studied the track response of CR-39 plastic nuclear track detectors (PNTD) for low (<6 MeV/n) and high (>100 MeV/n) energy heavy ions using the atomic force microscope (AFM). CR-39 PNTD was ...exposed to several heavy ion beams of different energy at HIMAC (Heavy Ion Medical Accelerator in Chiba). For AFM measurement, the amount of bulk etch was controlled to be ∼2 μm in order to avoid etching away of short range tracks. The response data obtained by AFM for ∼2 μm bulk etch was in good agreement with data obtained by the conventional optical microscope analysis for larger bulk etch. The response data from low energy beams (stopping near the surface) was also consistent with the data from high energy beams (penetrating the detector) as a function of REL (restricted energy loss) with the δ-ray cut off energy of ω0 = 200 eV. We experimentally verified that REL (ω0 = 200 eV) gives a universal function for wide energy range in CR-39 PNTD. This work has been done as part of a basic study in the measurement of secondary short range tracks produced by target fragmentation reactions in proton cancer therapy fields.
► Track response of CR-39 for low and high energy heavy ions was studied. ► Track measurement was carried out with AFM. ► Amount of bulk etch was controlled to be shallowly ∼2 μm ► REL model with the 200 eV δ-ray cut-off energy gives a universal function for wide energy range.
Using data from more than 10 years of observations with the Akeno Giant Air Shower Array (AGASA), we published a result that the energy spectrum of ultra-high energy cosmic rays extends beyond the ...cutoff energy predicted by Greisen Rhys. Rev. Lett. 16 (1966) 748 and Zatsepin and Kuzmin Zh. Eksp. Teor. Fiz. 4 (1966) 114. In this paper, we reevaluate the energy determination method used for AGASA events with respect to the lateral distribution of shower particles, their attenuation with zenith angle, shower front structure, delayed particles observed far from the core and other factors. The currently assigned energies of AGASA events have an accuracy of ±25% in event-reconstruction resolution and ±18% in systematic errors around 10
20 eV. This systematic uncertainty is independent of primary energy above 10
19 eV. Based on the energy spectrum from 10
14.5 eV to a few times 10
20 eV determined at Akeno, there are surely events above 10
20 eV and the energy spectrum extends up to a few times 10
20 eV without a GZK cutoff.
The annual effective doses of aircrew members often exceed the limit of 1 mSv for the public due to the increased level of cosmic radiation at the flight altitudes, and thus, it is recommended to ...monitor them International Commission on Radiation Protection. 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60. Ann. ICRP 21: (1-3), (1991). According to the Monte Carlo simulations Battistoni, G., Ferrari, A., Pelliccioni, M. and Villari, R. Evaluation of the doses to aircrew members taking into consideration the aircraft structures. Adv. Space Res. 36: , 1645-1652 (2005) and Ferrari, A., Pelliccioni, M. and Villari, R. Evaluation of the influence of aircraft shielding on the aircrew exposure through an aircraft mathematical model. Radiat. Prot. Dosim. 108: (2), 91-105 (2004), the ambient dose equivalent rate Ḣ*(10) depends on the location in the aircraft. The aim of this article is to experimentally evaluate Ḣ*(10) on-board selected types of aircraft. The authors found that Ḣ*(10) values are higher in the front and the back of the cabin and lesser in the middle of the cabin. Moreover, total dosimetry characteristics obtained in this way are in a reasonable agreement with other data, in particular with the above-mentioned simulations.
To investigate the long-term biological effect of extreme low dose ionising radiation, we irradiated normal human fibroblasts (HFLIII) with carbon ions (290 MeV u(-1), 70 keV microm(-1)) and ...gamma-rays at 1 mGy (total dose) once at a low dose rate (1 mGy 6-8 h(-1)), and observed the cell growth kinetics up to 5 months by continuous culturing. The growth of carbon-irradiated cells started to slow down considerably sooner than that of non-irradiated cells before reaching senescence. In contrast, cells irradiated with gamma-rays under similar conditions did not show significant deviation from the non-irradiated cells. A DNA double strand break (DSB) marker, gamma-H2AX foci, and a DSB repair marker, phosphorylated DNA-PKcs foci, increased in number when non-irradiated cells reached several passages before senescence. A single low dose/low dose rate carbon ion exposure further raised the numbers of these markers. Furthermore, the numbers of foci for these two markers were significantly reduced after the cells became fully senescent. Our results indicate that high linear energy transfer (LET) radiation (carbon ions) causes different effects than low LET radiation (gamma-rays) even at very low doses and that a single low dose of heavy ion irradiation can affect the stability of the genome many generations after irradiation.
The arrival directions of extremely high energy cosmic rays (EHECR) above 4×10
19 eV, observed by four surface array experiments in the northern hemisphere, are examined for coincidences from similar ...directions in the sky. The total number of cosmic rays is 92. A significant number of double coincidences (doublet) and triple coincidences (triplet) is observed on the supergalactic plane within the experimental angular resolution. The chance probability of such multiplets from a uniform distribution is less than 1% if we consider a restricted region within ±10° of the supergalactic plane. Though there is still a possibility of chance coincidence, the present results on small angle clustering along the supergalactic plane may be important in interpreting EHECR enigma. An independent set of data is required to check our claims.
As a feasibility study, gas chromatography–mass spectrometry (GC–MS) and matrix-assisted laser desorption ionization–mass spectrometry (MALDI–MS) have been applied to analyze etch products of CR-39 ...plastic (one of the most frequently used solid states nuclear track detector) for the understanding of track formation and etching mechanisms by heavy ion irradiation. The etch products of irradiated CR-39 dissolved in sodium hydroxide solution (NaOH) contain radiation-induced fragments. For the GC–MS analysis, we found peaks of diethylene glycol (DEG) and a small but a definitive peak of ethylene glycol (EG) in the etch products from CR-39 irradiated by 60MeVN ion beams. The etch products of unirradiated CR-39 showed a clear peak of DEG, but no other significant peaks were found. DEG is known to be released from the CR-39 molecule as a fragment by alkaline hydrolysis reaction of the polymer. We postulate that EG was formed as a result of the breaking of the ether bond (C–O–C) of the DEG part of the CR-39 polymer by the irradiation. The mass distribution of polyallylalcohol was obtained from the etch products from irradiated and unirradiated CR-39 samples by MALDI–MS analysis. Polyallylalcohol, with the repeating mass interval of m/z=58Da (dalton) between m/z=800 and 3500, was expected to be produced from CR-39 by alkaline hydrolysis. We used IAA as a matrix to assist the ionization of organic analyte in MALDI–MS analysis and found that peaks from IAA covered mass spectrum in the lower m/z region making difficult to identify CR-39 fragment peaks which were also be seen in the same region. The mass spectrometry analysis using GC–MS and MALDI–MS will be powerful tools to investigate the radiation-induced polymeric fragments and helping to understand the track formation mechanism in CR-39 by heavy ions.
The annual effective doses of aircrew members often exceed the limit of 1 mSv for the public due to the increased level of cosmic radiation at the flight altitudes, and thus, it is recommended to ...monitor them. Aircrew dosimetry is usually performed using special computer programs mostly based on results of Monte Carlo simulations. Contemporary, detectors are used mostly for validation of these computer codes, verification of effective dose calculations and for research purposes. One of such detectors is active silicon semiconductor deposited energy spectrometer Liulin. Output quantities of measurement with the Liulin detector are the absorbed dose in silicon D and the ambient dose equivalent H*(10); to determine it, two calibrations are necessary. The purpose of this work was to develop a calibration methodology that can be used to convert signal from the detector to D independently on calibration performed at Heavy Ion Medical Accelerator facility in Chiba, Japan.
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