| 1. |
- Kodaira, S., et al.
(author)
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On the use of CR-39 PNTD with AFM analysis in measuring proton-induced target fragmentation particles
- 2015
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In: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 349, s. 163-168
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Journal article (peer-reviewed)abstract
- In addition to energy loss by ionization process, protons of energy >similar to 50 MeV, such as those used in proton radiotherapy, can undergo nuclear interactions with nuclei of Z > 1, resulting in the production, of short range (<20 gm), high-LET (linear energy transfer) target fragment particles. One of the few methods to detect these short-range particles is by means of CR-39 plastic nuclear track detector (PNTD) analyzed with an atomic force microscope (AFM). However, due to the LET-dependent angular sensitivity of CR-39 PNTD, multiple detectors exposed at a range of incident angles to the primary proton beam, must be analyzed in order to accurately determine the LET spectrum, absorbed dose and dose equivalent. The LET spectrum of 160 MeV proton-induced secondary particles was experimentally measured with CR-39 PNTDs, which were exposed at six different incident angles to take into account the intrinsic sensitivity of the critical angle for track registration. The irradiated detectors were chemically processed to remove a 1 gm thick volume of CR-39 PNTD. The measured LET range of short range tracks was from 15 key/mu m up to 1.5 MeV/mu m. The absorbed dose contribution (D-s/D-p) from secondary particles to primary proton dose was similar to 1%, while the dose equivalent contribution (H-s/D-p) was found to be similar to 20%. Analysis of CR-39 PNTD by AFM yielded similar to 60% higher value for absorbed dose compared to standard optical microscopy analysis.
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| 2. |
- Pachnerova Brabcová, Katerina, 1978, et al.
(author)
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CONTRIBUTION OF INDIRECT EFFECTS TO CLUSTERED DAMAGE IN DNA IRRADIATED WITH PROTONS
- 2015
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In: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 166:1-4, s. 44-48
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Journal article (peer-reviewed)abstract
- Protons are the dominant particles both in galactic cosmic rays and in solar particle events and, furthermore, proton irradiation becomes increasingly used in tumour treatment. It is believed that complex DNA damage is the determining factor for the consequent cellular response to radiation. DNA plasmid pBR322 was irradiated at U120-M cyclotron with 30 MeV protons and treated with two Escherichia coli base excision repair enzymes. The yields of SSBs and DSBs were analysed using agarose gel electrophoresis. DNA has been irradiated in the presence of hydroxyl radical scavenger (coumarin-3-carboxylic acid) in order to distinguish between direct and indirect damage of the biological target. Pure scavenger solution was used as a probe for measurement of induced OH center dot radical yields. Experimental OH center dot radical yield kinetics was compared with predictions computed by two theoretical models-RADAMOL and Geant4-DNA. Both approaches use Geant4-DNA for description of physical stages of radiation action, and then each of them applies a distinct model for description of the pre-chemical and chemical stage.
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| 3. |
- Puchalska, Monika, 1977, et al.
(author)
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PHITS simulations of absorbed dose out-of-field and neutron energy spectra for ELEKTA SL25 medical linear accelerator
- 2015
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In: Physics in Medicine and Biology. - 0031-9155 .- 1361-6560. ; 60:12, s. N261-N270
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Journal article (peer-reviewed)abstract
- Monte Carlo (MC) based calculation methods for modeling photon and particle transport, have several potential applications in radiotherapy. An essential requirement for successful radiation therapy is that the discrepancies between dose distributions calculated at the treatment planning stage and those delivered to the patient are minimized. It is also essential to minimize the dose to radiosensitive and critical organs. With MC technique, the dose distributions from both the primary and scattered photons can be calculated. The out-of-field radiation doses are of particular concern when high energy photons are used, since then neutrons are produced both in the accelerator head and inside the patients. Using MC technique, the created photons and particles can be followed and the transport and energy deposition in all the tissues of the patient can be estimated. This is of great importance during pediatric treatments when minimizing the risk for normal healthy tissue, e.g. secondary cancer. The purpose of this work was to evaluate 3D general purpose PHITS MC code efficiency as an alternative approach for photon beam specification. In this study, we developed a model of an ELEKTA SL25 accelerator and used the transport code PHITS for calculating the total absorbed dose and the neutron energy spectra infield and outside the treatment field. This model was validated against measurements performed with bubble detector spectrometers and Boner sphere for 18 MV linacs, including both photons and neutrons. The average absolute difference between the calculated and measured absorbed dose for the out-of-field region was around 11%. Taking into account a simplification for simulated geometry, which does not include any potential scattering materials around, the obtained result is very satisfactorily. A good agreement between the simulated and measured neutron energy spectra was observed while comparing to data found in the literature.
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| 4. |
- Sato, T., et al.
(author)
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Overview of particle and heavy ion transport code system PHITS
- 2015
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In: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 82, s. 110-115
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Journal article (peer-reviewed)abstract
- A general purpose Monte Carlo Particle and Heavy Ion Transport code System, PHITS, is being developed through the collaboration of several institutes in Japan and Europe. The Japan Atomic Energy Agency is responsible for managing the entire project. PHITS can deal with the transport of nearly all particles, including neutrons, protons, heavy ions, photons, and electrons, over wide energy ranges using various nuclear reaction models and data libraries. It is written in Fortran language and can be executed on almost all computers. All components of PHITS such as its source, executable and data-library files are assembled in one package and then distributed to many countries via the Research Organization for Information Science and Technology, the Data Bank of the Organization for Economic Co-operation and Development's Nuclear Energy Agency, and the Radiation Safety Information Computational Center. More than 1500 researchers have been registered as PHITS users, and they apply the code to various research and development fields such as nuclear technology, accelerator design, medical physics, and cosmic-ray research. This paper briefly summarizes the physics models implemented in PHITS, and introduces some important functions useful for specific applications, such as an event generator mode and beam transport functions. (C) 2014 Elsevier Ltd. All rights reserved.
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| 5. |
- Sihver, Lembit, 1962, et al.
(author)
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Improvements and developments of physics models in PHITS for space applications
- 2015
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In: IEEE Aerospace Conference Proceedings. - 1095-323X. - 9781479953806 ; 2015-June
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Conference paper (peer-reviewed)abstract
- Precise predictions of the radiation environment inside space vehicles, and inside the human body, are essential when planning for long term deep space missions. Since these predictions include complex geometries, as well as the contributions from many different types of radiation, including neutrons, 3-D Monte Carlo codes with precise physics models are needed. In this paper, we present improvements and developments of some physics models used in the general purpose 3-D Monte Carlo code PHITS [1]. The total reaction cross section (σR) and the decay lifetime of a projectile particle are the first essential quantities in MC calculations, since these determine the mean free path of the transported particles and the probability function according to which a projectile particle will collide within a certain distance in the matter depends on the σR. This will also scale the calculated partial fragmentation cross sections. In this paper we present comparisons of calculated and measured σR using the Kurotama Hybrid σR, model [2] which is incorporated into PHITS. The prediction of the fragmentation reactions of relativistic heavy ions is also essential for ensuring radiation safety of astronauts. The default model for nuclear-nuclear reactions is JQMD in PHITS. However, JQMD cannot accurately enough describe the nucleon and d, t, 3He and 4He induced reactions. Therefore the Intra-Nuclear Cascade of Liège (INCL) [3] has been selected as the default model for these reactions. Moreover, it has been realized that the production of light fragments is underestimated by conventional simulation codes based on a combination of intranuclear cascade and statistical decay models. This is because this combination cannot reproduce the high multiplicity events that are responsible for the production of light fragments. To better reproduce high multiplicity events, we have simulated fragmentation cross sections using a combination of JQMD/INCL, statistical multi-fragmentation model (SMM) [4,5] and the generalized evaporation model (GEM). Examples of these simulations will be presented. A new approach to describe neutron spectra of deuteron-induced reactions in the Monte Carlo simulations has also been developed by combining the INCL and the Distorted Wave Born Approximation (DWBA) calculation [6]. We have incorporated this combined method into PHITS and applied it to estimate (d,xn) spectra on light targets at incident energies ranging from 10 to 40 MeV. In this paper, we will show that the double differential cross sections obtained by INCL and DWBA successfully reproduced broad peaks and discrete peaks, respectively.
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| 6. |
- Sihver, Lembit, 1962, et al.
(author)
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Radiation Environment at Aviation Altitudes and in Space
- 2015
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In: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 164:4, s. 477-483
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Journal article (peer-reviewed)abstract
- On the Earth, protection from cosmic radiation is provided by the magnetosphere and the atmosphere, but the radiation exposure increases with increasing altitude. Aircrew and especially space crew members are therefore exposed to an increased level of ionising radiation. Dosimetry onboard aircraft and spacecraft is however complicated by the presence of neutrons and high linear energy transfer particles. Film and thermoluminescent dosimeters, routinely used for ground-based personnel, do not reliably cover the range of particle types and energies found in cosmic radiation. Further, the radiation field onboard aircraft and spacecraft is not constant; its intensity and composition change mainly with altitude, geomagnetic position and solar activity (marginally also with the aircraft/spacecraft type, number of people aboard, amount of fuel etc.). The European Union Council directive 96/29/Euroatom of 1996 specifies that aircrews that could receive dose of >1 mSv y(-1) must be evaluated. The dose evaluation is routinely performed by computer programs, e.g. CARI-6, EPCARD, SIEVERT, PCAire, JISCARD and AVIDOS. Such calculations should however be carefully verified and validated. Measurements of the radiation field in aircraft are thus of a great importance. A promising option is the long-term deployment of active detectors, e.g. silicon spectrometer Liulin, TEPC Hawk and pixel detector Timepix. Outside the Earth's protective atmosphere and magnetosphere, the environment is much harsher than at aviation altitudes. In addition to the exposure to high energetic ionising cosmic radiation, there are microgravity, lack of atmosphere, psychological and psychosocial components etc. The milieu is therefore very unfriendly for any living organism. In case of solar flares, exposures of spacecraft crews may even be lethal. In this paper, long-term measurements of the radiation environment onboard Czech aircraft performed with the Liulin since 2001, as well as measurements and simulations of dose rates on and outside the International Space Station were presented. The measured and simulated results are discussed in the context of health impact.
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| 7. |
- Sihver, Lembit, 1962, et al.
(author)
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Radiation environment onboard spacecraft at LEO and in deep space
- 2016
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In: IEEE Aerospace Conference Proceedings. - 1095-323X. - 9781467376761 ; 2016-June, s. Art. no 7500765-
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Conference paper (peer-reviewed)abstract
- It is well known that outside the Earth's protective atmosphere and magnetosphere, the environment is very harsh and unfriendly for any living organism, due to the micro gravity, lack of oxygen and protection from high energetic ionizing cosmic radiation, as well as from powerful solar energetic particles (SEPs). The space radiation exposure leads to increased health risks, including tumor lethality, circulatory diseases and damages on the central nervous systems. In case of SEP events, exposures of spacecraft crews may be lethal. Space radiation hazards are therefore recognized as a key concern for human space flight. For long-term interplanetary missions, they constitute a limiting factor since current protection limits might be approached or even exceeded. Better risk assessment requires knowledge of the radiation quality, as well as equivalent doses in critical radiosensitive organs, and different risk coefficient for different radiation caused illnesses and diseases must be developed. The use of human phantoms, simulating an astronaut's body, provides detailed information of the depth-dose distributions, and radiation quality, inside the human body. In this paper we will therefore review the major phantom experiments performed at Low Earth Orbits (LEO) [1]. However, the radiation environment in deep space is different from LEO. Based on fundamental physics principles, it is clear that hydrogen rich, light and neutron deficient materials have the best shielding properties against Galactic Cosmic Rays (GCR) [2,3]. It has also been shown [4,5] that water shielding material can reduce the dose from Trapped Particles (TP), the low energetic part of GCR, and from low energetic SEP events. However, the total dose from GCR, for moderate shielding thicknesses, is actually increasing when increasing the shielding thickness due to the buildup of secondary fragments, protons and neutrons [5]. Examples of promising shielding materials are polyethylene and hydrogen rich carbon composite materials. Nevertheless, not even these shielding materials have been proven to significantly reduce the radiation health risks compared to e.g. aluminum shielding due to the high energetic GCR particles, the created fragments, and the large radiobiological uncertainties in the GCR risk projection [6,7]. A better understanding of the radiobiological effects of GCR are therefore needed, as well as better cancer risk models, and models for estimating the risks for circulatory diseases and damages on the central nervous systems. To reduce the health risks, a combination of passive and active shielding might be a realistic option for long term interplanetary missions, in combination with means to minimizing the time in deep space and to perform the missions during solar maximum to minimize the flux of GCR. Suitable radioprotectors, e.g. agents that act directly to protect cellular component and oppose the action of radiation induced free radicals, and reactive oxygen species, as well as radiomitigators, e.g. agents that accelerate post-radiation recovery and prevent complications, could also be developed. There might also be a need to accept an increased risk for carcinogenesis than what is stated by current dose limits.
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