Overview of the Liulin type instruments for space radiation measurement and their scientific results

The neutron dose equivalent rate measurements by R3DR/R2 spectrometers on the international space station

The data from two Bulgarian-German instruments with the basic name "Radiation Risk Radiometer-Dosimeter" (R3D) are discussed. The R3DR instrument worked inside the ESA EXPOSE-R facility (2009-2010), while R3DR2 worked inside the ESA EXPOSE-R2 facility (2014-2016). Both were outside the Russian Zvezda module on the International Space Station (ISS). The data from both instruments were used for calculation of the neutron dose equivalent rate. Similar data, obtained by the Russian "BTNNEUTRON" instrument on the ISS are used to benchmark the R3DR/R2 neutron dose equivalent rate. The analisys reveals that the "BTNNEUTRON" and R3DR/R2 values are comparable both in the equatorial and in the South Atlantic Anomaly (SAA) regions. The R3DR/R2 values are smaller than the "BTNNEUTRON" values in the high latitude regions. The comparison with the Monte Carlo simulations of the secondary galactic cosmic rays (GCR) neutron ambient dose equivalent rates (El-Jaby and Richardson, 2015, 2016) also shows a good coincidence with the R3DR/R2 spectrometer data obtained in the equatorial and high latitude regions.

Results of long-term radiation environment monitoring by the Russian RMS system on board Zvezda module of the ISS

The Radiation monitoring system (RMS) continuously operated in various configurations since the launch of the Zvezda module of the International Space Station (ISS). The RMS consisted of 7 units, namely: the R-16 dosimeter, 4 DB-8 dosimeters, utility and data collection units. The obtained data covers a time of 22 years. This paper analyses the radiation environment variations on board the "Zvezda" module. Variations of the onboard daily dose rate associated with changes of ISS altitude and 11-year cycle galactic cosmic rays' variations are analyzed and discussed. It is shown that the observed increase in the daily dose from 0.20 - 0.25 to 0.35 - 0.50 mGy/day is mostly due to the increase of ISS orbit altitude, resulting in a substantial increase of the dose contribution from the South Atlantic Anomaly (SAA) Region. Dose rate variations in the SAA as well as latitude and longitude dose rate distributions are discussed in detail. Analysis confirms that the well-known westward drift effect of the SAA is clearly visible from radiation dose measurements on the ISS.

Calibration and simulation of a silicon dosemeter for ambient dose equivalent in low-earth orbit space

A particle dosemeter (PD) is a payload of NEXTSat-2 in the low-earth orbit (LEO). The absorbed dose in LEO needs to be converted into the ambient dose equivalent (H*(10)). Due to a mixed field in LEO, the calibration factors (klow and khigh) should be determined for the low-and high-linear energy transfers (LET) (below and above 1.5 keV/μm), respectively. The PD was irradiated with a 137Cs source at the Korea Radiation Solution facility to obtain H*(10) and absorbed doses. However due to the lack of sources for the high-LET calibration, H*(10) and an absorbed dose were calculated by simulating PD for the high-energy neutron field at CERN-EU high-energy Reference Field. The measured klow of PD had a difference of 5.1% and 9.5% from the calculated value of PD and the measured value of Liulin detectors, respectively. However, a difference in khigh between PD and Liulin was explained by the contribution of non-neutron components to Liulin in the measurements.

SPACEDOS: AN OPEN-SOURCE PIN DIODE DOSEMETER FOR APPLICATIONS IN SPACE

A new Open-Source dosemeter, SPACEDOS, has been developed for measurements of cosmic radiation on board spacecraft and small satellites. Its main advantages are that it is small and lightweight with low power consumption. It can be adjusted for specific applications, e.g. used in pressurized cabins of spacecraft or in vacuum environments in CubeSats or larger satellites. The open-source design enables better portability and reproduction of the results than other similar detectors. The detector has already successfully performed measurements on board the International Space Station. The obtained results are discussed and compared with those measured with thermoluminescent detectors located in the same position as SPACEDOS.

CALIBRATION OF SILICON DETECTORS LIULIN AND AIRDOS USING COSMIC RAYS AND TIMEPIX FOR USE AT FLIGHT ALTITUDES

Silicon detectors such as Liulin and AIRDOS are used for cosmic radiation measurements onboard aircraft. These measurements can be used for the verification of computer programs assessing aircraft crew radiation exposure. Recently performed intercomparison flights showed large variances of absorbed doses among individual detectors and significant differences between results of silicon detectors and computer programs. In order to explain for these differences, we have developed energy calibration method that can be performed on short flights. The method is based on cross-calibration of Liulin and AIRDOS deposited energy spectra with deposited energy spectra measured by Timepix which has superior detection properties in terms of energy resolution and the detection threshold. Moreover, the portion of dose which is omitted due to low sensitivity for low-energy deposits was calculated. The resulting absorbed dose rates at two intercomparison flights show significantly improved variation of results and better agreement with modelled absorbed dose rates.

Solar modulation of the GCR flux and dose rate, observed in space between 1991 and 2019

The paper presents the solar modulation of the long-term galactic cosmic rays (GCR) flux and dose rates variations, observed during 14 space experiments by 10 Bulgarian build Liulin-type spectrometers (LTS) (Dachev et al., 2015a). They worked in near Earth space and in the interplanetary radiation environment between January 1991 and January 2019. Data were collected by LTS in the low Earth orbit (LEO) in the L range between 4 and 6.2 or outside the magnetosphere. The major advantage of the data sets are that they are obtained by the electronically identical LTS. The Liulin measurements of about monthly averaged flux and dose rate data are compared with the monthly values of the modulation parameter, reconstructed from the ground based cosmic ray data (Usoskin et al., 2017). A good correlation between the two data sets is observed. The most important achievement of the paper is that for the first time a proof of the solar modulation of the long-term variations of the monthly averaged dose rates is obtained. These long-term experimentally obtained dose rate data could be used for modeling of the GCR space radiation risks to humans in the near Earth radiation environment. Parallel to the long-term dose rate varitions, the monthly averaged flux variations are also presented.

Design, Implementation, and Operation of a Small Satellite Mission to Explore the Space Weather Effects in LEO

Ten-Koh is a 23.5 kg, low-cost satellite developed to conduct space environment effects research in low-Earth orbit (LEO). Ten-Koh was developed primarily by students of the Kyushu Institute of Technology (Kyutech) and launched on 29 October 2018 on-board HII-A rocket F40, as a piggyback payload of JAXA’s Greenhouse gas Observing Satellite (GOSAT-2). The satellite carries a double Langmuir probe, CMOS-based particle detectors and a Liulin spectrometer as main payloads. This paper reviews the design of the mission, specifies the exact hardware used, and outlines the implementation and operation phases of the project. This work is intended as a reference that other aspiring satellite developers may use to increase their chances of success. Such a reference is expected to be particularly useful to other university teams, which will likely face the same challenges as the Ten-Koh team at Kyutech. Various on-orbit failures of the satellite are also discussed here in order to help avoid them in future small spacecraft. Applicability of small satellites to conduct space-weather research is also illustrated on the Ten-Koh example, which carried out simultaneous measurements with JAXA’s ARASE satellite.

Analytical Representations for Characterizing the Global Aviation Radiation Environment Based on Model and Measurement Databases

The Nowcast of Atmospheric Ionizing Radiation for Aviation Safety climatological model and the Automated Radiation Measurements for Aerospace Safety (ARMAS) statistical database are presented as polynomial fit equations. Using equations based on altitude, L shell, and geomagnetic conditions an effective dose rate for any location from a galactic cosmic ray (GCR) environment can be calculated. A subset of the ARMAS database is represented by a second polynomial fit equation for the GCR plus probable relativistic energetic particle (REP; Van Allen belt REP) effective dose rates within a narrow band of L shells with altitudinal and geomagnetic dependency. Solar energetic particle events are not considered in this study since our databases do not contain these events. This work supports a suggestion that there may be a REP contribution having an effect at aviation altitudes. The ARMAS database is rich in Western Hemisphere observations for L shells between 1.5 and 5; there have been many cases of enhanced radiation events possibly related to effects from radiation belt particles. Our work identifies that the combined effects of an enhanced radiation environment in this L shell range are typically 15% higher than the GCR background. We also identify applications for the equations representing the Nowcast of Atmospheric Ionizing Radiation for Aviation Safety and ARMAS databases. They include (i) effective dose rate climatology in comparison with measured weather variability and (ii) climatological and statistical weather nowcasting and forecasting. These databases may especially help predict the radiation environment for regional air traffic management, for airport overflight operations, and for air carrier route operations of individual aircraft.

Overview of the Radiation Dosimetry Experiment (RaD-X) flight mission

The NASA Radiation Dosimetry Experiment (RaD-X) stratospheric balloon flight mission addresses the need to reduce the uncertainty in predicting human exposure to cosmic radiation in the aircraft environment. Measurements were taken that characterize the dosimetric properties of cosmic ray primaries, the ultimate source of aviation radiation exposure, and the cosmic ray secondary radiations that are produced and transported to aviation altitudes. In addition, radiation detectors were flown to assess their potential application to long-term, continuous monitoring of the aircraft radiation environment. RaD-X was successfully launched from Fort Sumner, New Mexico (34.5°N, 104.2°W), on 25 September 2015. Over 18 h of science data were obtained from a total of four different type dosimeters at altitudes above 20 km. The RaD-X flight mission was supported by laboratory radiation exposure testing of the balloon flight dosimeters and also by coordinated radiation measurements taken on ER-2 and commercial aircraft. This paper provides the science background and motivation for the RaD-X flight mission, a brief description of the balloon flight profile and the supporting aircraft flights, and a summary of the articles included in the RaD-X special collection and their contributions to the science goals of the RaD-X mission.

High dose rates obtained outside ISS in June 2015 during SEP event

The R3DR2 instrument performed measurements in the European Space Agency (ESA) EXPOSE-R2 platform outside the Russian "Zvezda" module of the International Space Station (ISS) in the period 24 October 2014-11 January 2016. It is the Liulin-type deposited energy spectrometer (DES) (Dachev et al., 2015a). Took place in November 2014, this was the first attempt to monitor a small solar energetic particle (SEP) event outside ISS using the Liulin-type DES (Dachev et al., 2015d). In this study, we describe the dosimetric characteristics of the largest SEP event, observed on 22 June 2015 with the R3DR2 instrument outside ISS. The main finding of this study is that SEP protons with a minimum energy of approximately 7MeV at the surface of the R3DR2 detector produced high dose rates, reaching >5000µGyh(-1), while the inner radiation belt maximum dose was at the level of 2200µGyh(-1). If a virtual external vehicle activity (EVA) was performed in the same period of the SEP maximum on 22 June 2015, the doses obtained in the skin of cosmonauts/astronauts can reach 2.84mGy after 6.5h, which is similar to the average absorbed dose inside ISS for 15days (Reitz et al., 2005). A comparison with other extreme events measured with Liulin-type instruments shows that SEPs similar to that observed on 22 June 2015 could be one of the most dangerous events for the cosmonauts/astronauts involved in EVA.

Radiation Measurements Performed with Active Detectors Relevant for Human Space Exploration

A reliable radiation risk assessment in space is a mandatory step for the development of countermeasures and long-duration mission planning in human spaceflight. Research in radiobiology provides information about possible risks linked to radiation. In addition, for a meaningful risk evaluation, the radiation exposure has to be assessed to a sufficient level of accuracy. Consequently, both the radiation models predicting the risks and the measurements used to validate such models must have an equivalent precision. Corresponding measurements can be performed both with passive and active devices. The former is easier to handle, cheaper, lighter, and smaller but they measure neither the time dependence of the radiation environment nor some of the details useful for a comprehensive radiation risk assessment. Active detectors provide most of these details and have been extensively used in the International Space Station. To easily access such an amount of data, a single point access is becoming essential. This review presents an ongoing work on the development of a tool that allows obtaining information about all relevant measurements performed with active detectors providing reliable inputs for radiation model validation.