Cosmic Ray Dose Rate Research Articles

Solar Cosmic Ray Dose Rate Assessments During GLE 72 Using MIRA and PANDOCA

AbstractGround level enhancement (GLE) 72, which occurred 10 September 2017, is the most recent of two solar particle‐induced enhancements in ground level measurements of cosmic radiation secondary neutrons in solar cycle 24. GLEs have been unusually rare in this solar cycle. GLEs can significantly increase ionizing radiation dose rates at aviation altitudes for hours to days, leading to concern among crewmembers. Real‐time monitoring and preliminary evaluation of solar proton events, including GLEs, in regard to effective dose rates at aviation altitudes has been ongoing since the U.S. Federal Aviation Administration began operating its Solar Radiation Alert System (SRAS) in 2002. Since then, SRAS has been revised multiple times. In this report, model calculations of dose rates during GLE 72 from Maps of Ionizing Radiation in the Atmosphere (MIRA), the latest SRAS software based on CARI‐7A, are compared with those from the model Professional Aviation Dose Calculator (PANDOCA) developed by the German Aerospace Center (Deutsches Zentrum für Luft‐ und Raumfahrt). At very low cutoff rigidities model calculations agree within 40% and indicate no significant increase in radiation exposures at commercial aviation altitudes. The larger than expected differences at very low cutoff rigidities indicate Geostationary Orbiting Environmental Satellite particle flux data alone that are insufficient to produce consistent solar particle dose estimates.

Segmental interpolating spectra for solar particle events and in situ validation

It is a delicate task to accurately assess the impact of solar particle events (SPEs) on future long-duration human exploration missions. In the past, researchers have used several functional forms to fit satellite data for radiation exposure estimation. In this work we present a segmental power law interpolating algorithm to stream satellite data and get time series of proton spectra, which can be used to derive dosimetric quantities for any short period during which a single SPE or multiple SPEs occur. Directly using the corrected High Energy Proton and Alpha Detector fluxes of GOES, this method interpolates the intensity spectrum of a typical SPE to hundreds of MeV and extrapolates to the GeV level as long as sufficient particles are recorded in the high-energy sensors. The high-energy branch of the May 2012 SPE is consistent with the Band functional fitting, which is calibrated with ground level measurement. Modeling simulations indicate that the input spectrum of an SPE beyond 100 MeV is the major contributor for dose estimation behind the normal shielding thickness of spacecraft. Applying this method to the three SPEs that occurred in 2012 generates results consistent with two sets of in situ measurements, demonstrating that this approach could be a way to perform real-time dose estimation. This work also indicates that the galactic cosmic ray dose rate is important for accurately modeling the temporal profile of radiation exposure during an SPE.

Evaluation of World Population-Weighted Effective Dose due to Cosmic Ray Exposure.

After the release of the Report of the United Nations Scientific Committee of the Effects of Atomic Radiation in 2000 (UNSCEAR2000), it became commonly accepted that the world population-weighted effective dose due to cosmic-ray exposure is 0.38 mSv, with a range from 0.3 to 2 mSv. However, these values were derived from approximate projections of altitude and geographic dependences of the cosmic-ray dose rates as well as the world population. This study hence re-evaluated the population-weighted annual effective doses and their probability densities for the entire world as well as for 230 individual nations, using a sophisticated cosmic-ray flux calculation model in tandem with detailed grid population and elevation databases. The resulting world population-weighted annual effective dose was determined to be 0.32 mSv, which is smaller than the UNSCEAR’s evaluation by 16%, with a range from 0.23 to 0.70 mSv covering 99% of the world population. These values were noted to vary with the solar modulation condition within a range of approximately 15%. All assessed population-weighted annual effective doses as well as their statistical information for each nation are provided in the supplementary files annexed to this report. These data improve our understanding of cosmic-ray radiation exposures to populations globally.

Update on Radiation Dose From Galactic and Solar Protons at the Moon Using the LRO/CRaTER Microdosimeter

The NASA Lunar Reconnaissance Orbiter (LRO) has been exploring the lunar surface and radiation environment since June 2009. In Mazur et al. [2011] we discussed the first 6months of mission data from a microdosimeter that is housed within the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument onboard LRO. The CRaTER microdosimeter is an early version of what is now a commercially available hybrid that accurately measures total ionizing radiation dose in a silicon target (http://www.teledynemicro.com/product/radiationdosimeter). This brief report updates the transition from a deep solar minimum radiation environment to the current weak solar maximum as witnessed with the microdosimeter. The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) microdosimeter is behind about 4.4 g/cm equivalent aluminum, corresponding to the range of ~55MeV protons. Energetic protons are the dominant source of ionizing radiation at the Moon. The measured dose includes contributions from the low-energy part of the galactic cosmic ray proton spectrum and the high-energy portion of typical solar energetic particle events. Figure 1 is the history to date of the total ionizing dose averaged over 12 h intervals. The figure includes the entire Lunar Reconnaissance Orbiter (LRO) orbital history that ranged from ~50 km circular tomore elliptical orbits with aposelene above ~150 km. We did not correct the observed dose rate for the changing amount of solid angle blocked by the Moon in Figure 1 as one would need to do to derive an interplanetary rate. When averaged over 12 h, the variations among the various orbit modes have less than a 5% and 20% effect on the galactic cosmic ray dose rate and peak solar proton dose rate, respectively.

Radiation survey in the International Space Station

The project ALTEA-shield/survey is part of an European Space Agency (ESA) – ILSRA (International Life Science Research Announcement) program and provides a detailed study of the International Space Station (ISS) (USLab and partly Columbus) radiation environment. The experiment spans over 2 years, from September 20, 2010 to September 30, 2012, for a total of about 1.5 years of effective measurements. The ALTEA detector system measures all heavy ions above helium and, to a limited extent, hydrogen and helium (respectively, in 25 Mev–45 MeV and 25 MeV/n–250 MeV/n energy windows) while tracking every individual particle. It measures independently the radiation along the three ISS coordinate axes. The data presented consist of flux, dose, and dose equivalent over the time of investigation, at the different surveyed locations. Data are selected from the different geographic regions (low and high latitudes and South Atlantic Anomaly, SAA). Even with a limited acceptance window for the proton contribution, the flux/dose/dose equivalent results as well as the radiation spectra provide information on how the radiation risks change in the different surveyed sites. The large changes in radiation environment found among the measured sites, due to the different shield/mass distribution, require a detailed Computer-Aided Design (CAD) model to be used together with these measurements for the validation of radiation models in space habitats. Altitude also affects measured radiation, especially in the SAA. In the period of measurements, the altitude (averaged over each minute) ranged from 339 km to 447 km. Measurements show the significant shielding effect of the ISS truss, responsible for a consistent amount of reduction in dose equivalent (and so in radiation quality). Measured Galactic Cosmic Ray (GCR) dose rates at high latitude range from 0.354 ± 0.002 nGy/s to 0.770 ± 0.006 nGy/s while dose equivalent from 1.21 ± 0.04 nSv/s to 6.05 ± 0.09 nSv/s. The radiation variation over the SAA is studied. Even with the reduced proton sensitivity, the high day-by-day variability, as well as the strong altitude dependence is clearly observed. The ability of filtering out this contribution from the data is presented as a tool to construct a radiation data set well mimicking deep space radiation, useful for model validations and improvements.

Nationwide measurements of cosmic-ray dose rates throughout Japan

Cosmic-ray dose rates on the ground were measured throughout Japan. Neutron dose rates were measured as ambient dose equivalent rates (H*(10)) at 240 points using high-sensitivity neutron REM counters. In addition, cosmic rays directly ionising plus photon components were measured with an ionisation chamber. Time variation due to solar modulation during this study was corrected based on the results of sequential measurements. The effects of altitude, geomagnetic latitude, rainfall and snowfall on the neutron dose rate were inferred from the measured results. The mean value of the neutron dose rates (H*(10)) measured at 47 points of prefectural capitals in Japan was 4.0 nSv h(-1). The value corrected for the energy response of the REM counter was 6.4 nSv h(-1), corresponding to 4.8 nSv h(-1) as an effective dose (ISO). The mean value of the cosmic ray directly ionising plus photon components as an effective dose was 31 nSv h(-1).

Isochron dating of sediments using luminescence of K‐feldspar grains

A new method for dating well‐bleached sediments is presented, with results for thirteen samples from China. The method uses an isochron constructed from the measurement of natural radiation doses received by potassium‐feldspar grains in a range of grain sizes using the infrared stimulated luminescence (IRSL) signal. The age of deposition of the sediment is calculated from this isochron and from the internal dose rate to the grains from40K and87Rb in the crystal lattice. This procedure appears to overcome age underestimation due to anomalous fading, a phenomenon that has precluded conventional luminescence dating of K‐feldspars and would be applicable to K‐feldspars for which the natural dose is beyond the linear dose response region. Also, since the isochron IRSL method is reliant on only the internal dose rate, it overcomes problems related to (1) changes in past dose rate due to postdepositional migration of radionuclides, (2) changes in water content as water‐lain sediments dry out, (3) spatial heterogeneity in the gamma dose rate, and (4) uncertainties in the cosmic ray dose rate during the period of sample burial.

Measurements of neutron dose rates with a balloon in Japan

Measurements of cosmic-ray neutron dose rates with a balloon in Sanriku, Japan (geographic location: 39 degrees N, 142 degrees E; corresponding geomagnetic latitude: 30 degrees N) were conducted at an altitude from 0.2 to 25 km on 25-26 August 2004 when solar activity was at an average level. Neutron dose rates given as ambient dose equivalent rates (H(10)) were measured with high-sensitive neutron dose equivalent counters and electronic silicon personal dosimeters (EPDs). The neutron dose rates increased with increasing altitude, but they were saturated around 15-20 km and decreased with increasing altitude beyond 20 km. The neutron ambient dose equivalent rate was 1.5 microSv/h(- 1) at 20 km. Measured values were corrected for the deviation of the energy response of the dose equivalent counter from the fluence-to-ambient dose equivalent conversion coefficient, and the corrected values were very close to the calculated values with EPCARD. On the other hand, neutron measurements by the EPDs gave about 10 times overestimation because of the high sensitivity to cosmic-ray protons.

Sequential Measurements of Cosmic-Ray Neutron Spectrum and Dose Rate at Sea Level in Sendai, Japan

The cosmic-ray neutron energy spectrum and dose rate were measured sequentially for two years from April 2001 up to March 2003 by using three neutron detectors, a 3He-loaded multi-moderator detector (Bonner ball), 12.7 cm diameter by 12.7 cm long NE213 organic liquid scintillator, and high-sensitivity rem (dose equivalent) counter at the Kawauchi campus of Tohoku University in Sendai, Japan of geomagnetic latitude, 29°N, and cutoff rigidity, 10.43 GV. The neutron spectrum has three major peaks, thermal energy peak, evaporation peak around 1 MeV and cascade peak around 100 MeV. The ambient neutron dose equivalent rates measured by the rem counter, and the Bonner ball keep almost constant values of 4.0 and 6.5 (nSv/h), respectively, throughout this time period, after atmospheric pressure correction, and it often decreased about 30% after a large Solar Flare, that is called as the Forbush decrease. The total neutron flux was also obtained by the Bonner ball measurements to be 7.5×10-3 (n cm−2.s−1) in average. The altitude variation of neutron flux and dose was also investigated by comparing the measured results with other results measured at Mt. Fuji area and aboard an airplane, where the cutoff rigidities are similar.

Spacecraft shielding for a Mars mission

The stationary, source-free, one-dimensional solution to the cosmic-ray heliospheric transport equation has been applied to the treatment of cosmic-ray fluxes at solar minimum between the orbits of Earth and Mars. The effective dose rate from these radiations were calculated for cylindrical spacecraft hulls of various compositions both in space and on the surface of Mars. The spatial gradient of the flux between Earth and Mars is quite small so that the cosmic-ray dose-rate can be assumed spatially uniform in the interval between these orbits, between one and one and a half astronomical units. The resulting dose rates for a 2.5-year mission, assuming six months on the surface of Mars, were slightly over one sievert.

New public dose assessment of elevated natural radiation areas of Ramsar (Iran) for epidemiological studies

The potential annual effective doses of the public in Ramsar and its elevated level natural radiation areas (ELNRA) from the external and internal exposures received indoors and outdoors were determined. This paper only reports the potential annual effective doses from the external exposure, the rate of which was measured in 1000 locations outdoors and in 800 locations indoors, 200 in ENLRA and 600 in low level natural radiation areas (LLNRA). An SPP2 Scintillometer, a Reuter-Stokes pressurized ionization chamber and a SAPOS system of an environmental early warning network were used for measuring the exposure rates. The distribution of the absorbed dose rates in air, indoors and outdoors, with their mean values were determined. The absorbed dose rates in the air outdoors range from 0.08 to 20 μGy h −1 with occasional higher values up to 100 μGy h −1 over some hot spots. The isodose and topological exposure rate maps of the region were drawn. The cosmic ray dose rate of 32 nGy h −1 was measured over the Caspian Sea using the pressurized ionization chamber. The absorbed dose rates in the air indoors range from 0.01 to 30 μGy h −1 with occasional higher values up to 105 μGy h −1 on the wall of one room in a house in Talesh Mahalleh. The topological map of the exposure rates over the wall is also reported. As expected, Talesh Mahalleh showed the highest potential effective public doses from terrestrial radiation. The potential annual effective doses of the public in ELNRA range from 0.6 to 131 mSv with a mean value of 6 mSv, and in LLNRA, these range from 0.6 to 1.5 mSv with a mean value of 0.7 mSv. The distributions of percent population in different annual effective dose intervals in Ramsar and its ELNRA were also obtained. The mean potential annual effective doses in ELNRA are about 10 times higher than those in ELNRA, but some individual effective doses are about 200 times higher than the mean of LLNRA. The results are reported and discussed.

Population dose due to natural radiation in Hong Kong.

In densely populated cities such as Hong Kong where people live and work in high-rise buildings that are all built with concrete, the indoor gamma dose rate and indoor radon concentration are not wide ranging. Indoor gamma dose rates (including cosmic rays) follow a normal distribution with an arithmetic mean of 0.22 +/- 0.04 microGy h(-1), whereas indoor radon concentrations follow a log-normal distribution with geometric means of 48 +/- 2 Bq m(-3) and 90 +/- 2 Bq m(-3) for the two main categories of buildings: residential and non-residential. Since different occupations result in different occupancy in different categories of buildings, the annual total dose [indoor and outdoor radon effective dose + indoor and outdoor gamma absorbed dose (including cosmic ray)] to the population in Hong Kong was estimated based on the number of people for each occupation; the occupancy of each occupation; indoor radon concentration distribution and indoor gamma dose rate distribution for each category of buildings; outdoor radon concentration and gamma dose rate; and indoor and outdoor cosmic ray dose rates. The result shows that the annual doses for every occupation follow a log-normal distribution. This is expected since the total dose is dominated by radon effective dose, which has a log-normal distribution. The annual dose to the population of Hong Kong is characterized by a log-normal distribution with a geometric mean of 2.4 mSv and a geometric standard deviation of 1.3 mSv.

Assessment of Cosmic Ray Ionising Component at Ground Level by Means of HPGe Spectrometry

Experimental assessment of the cosmic ray ionising component at ground level has been carried out using a high purity germanium(HPGe) spectrometry system together with a NaI(Tl) scintillation detector. A 14 litre spherical ionisation chamber was used simultaneously in order to distinguish between the dose rate from gamma rays below 3 MeV and that from the cosmic ray ionising component detected in the higher energy region. Various cosmic ray dose rates and corresponding count rates were made available by utilising the shielding effect of a multi-storied building, including measurements at an outdoor flat and a mountain top. As a result Y = 30.25 X G + 1.42 and Y = 19.83 X N + 1.32 were derived, where Y is dose rate due to cosmic ray ionisation in nGy h -1 , and X G and X N are the corresponding count rates in cps measured by the HPGe and NaI(Tl) spectrometers, respectively, in the region of 3 to 100 MeV.

３′′φ球形ＮａＩ（Ｔｌ）シンチレーション検出器を用いた屋内宇宙線線量率の簡便測定法

Two kinds of major techniques are usually applied to measurement of the ionizing component of the cosmic ray dose rate. One is a “precise method” by which the cosmic ray dose rate is obtained from the difference between the reading of an ionization chamber and that of a gamma ray detector such as a NaI(T1) scintillation detector. The former detects both gamma ray and cosmic ray, and the latter only gamma rays. The other is the “simplified method” by which the cosmic ray dose rate is obtained from the count rate above 3MeV of the gamma ray detector based on the assumption that the cosmic ray dose rate is proportional to the count rate. It is reasonable to apply the simplified method in the open air near the ground since the cosmic ray spectrum does not change much. However, attenuation of low energy component by building materials must be considered when the simplified method is applied to indoor measurement because the cosmic ray spectrum may be changed.From a series of measurements by the precise method with a spherical air equivalent ionization chamber of 14 liters and a 3″ diameter spherical NaI(T1) scintillation detector under several environmental coditions, proportionality was found between the cosmic ray dose rate and the count rate above 3MeV. The proportional constant was evaluated to be 20±1.4nGy/h/cps. Also, no apparent difference in the proportional constants was found between indoor and outdoor. It is concluded that the simplified method can be applied to indoor measurement as well as outdoor measurement of the cosmic ray dose rate.

The natural thermoluminescence of meteorites: III. lunar and basaltic meteorites

Natural thermoluminescence (TL) data have been obtained for the lunar meteorite MacAlpine Hills 88104/5 and for 65 eucrites, howardites, diogenites, and mesosiderites in order to investigate their recent thermal and radiation histories. All these meteorites have low levels of natural TL compared to chondrites, which is primarily because they display “anomalous fading” (i.e., fading by non-classical mechanisms). However, some have especially low natural TL (<5 krad at 250°C in the glow curve) which cannot be attributed to anomalous fading or thermal fading over especially large terrestrial ages, and which must reflect heating within the last 10 5–10 6 y. In some cases, this heating may have been associated with shock (e.g., LEW85303) or regolith processes (Kapoeta), but in most cases (Bununu, Lowicz, the diogenites ALHA77256, ALHA84001, EET79002, and maybe others) solar heating at perihelia <0.8 AU may be responsible for the low TL values. The fraction of basaltic meteorites thought to have had small perihelia (about 20%) is comparable to the fraction of chondrites with low natural TL and to the fraction of observed falls and fireballs with small perihelia. This may imply ejection from the asteroid belt via similar mechanisms. Assuming plausible values for cosmic ray dose rate, and that the natural TL of MAC88104/5 was totally drained by ejection from the moon, the parameters for TL decay determined in the present study suggest that the Moon-Earth transit times for MAC88104 and MAC88105 were 2,000 and 1,800 y, respectively, compared with 19,000 and 2,500 y for Y791197 and ALHA81005, respectively. Although they are clearly not paired, the possibility that MAC88104/5 and ALHA81005 were ejected from the moon by the same event should be considered, since diverse rock types are found in close proximity on the lunar surface. The natural TL data confirm most previous published pairings among basaltic meteorites and suggest others.

生活環境中におけるγ線および宇宙線線量率分布とその特徴

A series of environmental radiation surveys was carried out from the viewpoint of characterizing the natural radiation dose rate distribution in the living environment, including natural and artificial ones. Through the analysis of the data obtained at numbers of places, several aspects of the radiation field in living environments were clarified. That is, the gamma ray dose rate varies due to the following three dominant causes: 1) the radionuclide concentration of surrounding materials acting as gamma ray sources, 2) the spatial distribution of surrounding materials, and 3) the geometrical and shielding conditions between the natural gamma ray sources and the measured point; whereas, the cosmic ray dose rate varies due to the thickness of upper shielding materials. It was also suggested that the gamma ray dose rate generally shows an upward tendency, and the cosmic ray dose rate a downward one in artificial environment. This kind of knowledge is expected to serve as fundamental information for accurate and realistic evaluation of the collective dose in the living environment.

居住環境における放射線場の特性 （ＩＩ） 東京都内電車路線でのγ線および宇宙線の線量率分布

A series of environmental radiation survey was carried out on train lines within Tokyo metropolitan area to clarify the characteristics of radiation field in living environment. Eleven JR, 18 private and 10 subway lines were surveyed, which cover 97% of whole train lines in Tokyo district in terms of annual number of passengers.The characteristics of environmental radiation field on train lines were discussed. The mean absorbed dose rate in air due to γ-rays on the subway lines was higher than those on the JR and private lines. It is due to the difference in the radioactivity concentration and the distribution of surrounding materials as the γ-ray sources.On the other hand, the mean dose rate due to cosmic-rays on the subway lines was lower than those on the JR and private lines. It is due to the shielding effect of the upper materials such as soil or building materials of tunnels.The mean dose rates for the JR, private and subway lines were calculated using these obtained data. Though the ratio of mean dose rate of γ-rays to that of cosmic-rays for the subway lines was different from those for the JR and private lines, the sum of γ- and cosmicray dose rates for the JR, private and subway lines were comparable, 40-50nGy/h for any of them.These data will be useful for a precise and realistic evaluation of collective dose, considering the life style of the public and the variation characteristics of environmental radiation.

居住環境における放射線場の特性 （１） 東京都内におけるγ線および宇宙線線量率分布とその特徴

A series of environmental radiation survey was carried out in Tokyo, a typical artificial environment, to clarify the characteristics of radiation field in living environment. Portable instruments were used to perform the measurement moving within the objective area. Considering the actual dose condition to environmental radiation, measurement courses were established to involve walking or on-a-train section to reflect the realistic life style.It was observed that the level of γ-ray dose rate varies from place to place due to the difference in the radioactivity concentration of surrounding materials, source geometry and shielding geometry, and that the level of cosmic-ray dose rate diminutes due to the thickness of upper shieldings such as building materials. The causes of these variations and its degree were also discussed based on the obtained data.These results will be used for precise and realistic dose evaluation taking the characteristics of environmental radiation into account.

Space radiations: natural and man-made.

Throughout the history of man, his advancement has been colored by his environment. No advance, technological or otherwise, has been possible unless man himself has been able either to adapt to or control his surroundings. The past fifteen years have seen tremendous strides in the application of nuclear energy from destruction to construction. The primary limitation to continued advance lies in the radiation environment of this energy source and its possible untoward effects on the health of man. Man is on the threshold of another scientific adventure—the entry into space. Here again the question of the environmental limits to progress has arisen. In this new area of effort, radiation appears to be of primary concern. Since radiation exists as one of the hostile perimeters of space, and since nuclear energy with its concomitant radiation may be necessary for significant advance in space conquest, it appears only reasonable to review our knowledge of the field. Physical and Biological Concepts of Naturally Occurring Space Radiations Cosmic Rays: The presence of cosmic rays has been known for many years. The majority of the measurements which have contributed to our knowledge have been made within the atmosphere and up to its top. The physical nature of cosmic rays is reasonably familiar. The primary cosmicray beam apparently originates in interstellar space and it will, therefore, be with us in any travels, whether in this galaxy or others. The primary component is found to consist of 79 per cent protons, 20 per cent alpha particles (He nuclei), 0.78 per cent carbon, oxygen, and nitrogen nuclei, and 0.22 per cent nuclei of atomic number greater than 10. The kinetic energies of these particles are found to vary from one to several billion electron volts (Bev) per nucleon. Thus, an iron nucleus with an atomic number of 56 and an energy of 10 Bev per nucleon would have a total energy of 560 Bev. When the primary cosmic ray interacts with an interposed material, such as the “skin” of a spaceship or our atmosphere, secondaries are produced. These depend upon the interposed material but would generally consist of particles of lower atomic number than the primary—electrons, mesons, gamma rays, and neutrons. The cosmic-ray intensity varies with respect to the observer's relation to the earth's geomagnetic field and with respect to solar flare incidence. Over long periods, however, at any particular position with respect to the magnetic field the average intensity is fairly constant. Thus, it is reasonable to estimate the average cosmicray dose rate. In “free” space (away from the shielding effect of the earth), the cosmic-ray dose rate approximates 25 mrads per day. The presence of a spaceship “skin” and other materials might tend to increase this ionization figure by a factor of as much as 4. It is apparent that rates of this order are entirely acceptable if the biological effects are not enhanced by the particles themselves.