LUNAIRE - LUNAr Ionising Radiation Environment

Experimental and calculated LET distributions in the Cosmos-2044 biosatellite orbit.

Effects of target fragmentation on evaluation of LET spectra from space radiations: Implications for space radiation protection studies

Galactic cosmic rays and solar energetic particles (SEPs) present formidable radiation hazards [e.g., Cucinotta et al., 2010] for human and robotic operations beyond low Earth orbit (LEO). As new plans are conceived for human exploration beyond LEO, these space radiation hazards create critical needs for accurate situational awareness. A new near-real-time tool called PREDICCS (Predictions of Radiation From REleASE, EMMREM, and Data Incorporating the CRaTER, COSTEP, and Other SEP Measurements, http://prediccs.sr.unh.edu) provides the first online system for predicting and forecasting the radiation environment in near-Earth, lunar, and Martian space environments. PREDICCS integrates a host of near-real-time measurements being made by satellites currently in space with numerical models (e.g., EMMREM [Schwadron et al., 2010]) to determine radiation doses and dose equivalents that characterize biological impacts and energetic particle propagation codes that can accurately project radiation levels through the inner solar system and out to Mars. PREDICCS provides updates of the radiation environment on an hourly basis and archives the data weekly, monthly, and yearly to provide a clear historical record of the space radiation environment. The PREDICCS tool provides in-depth data to characterize how hazardous SEP events are throughout the solar cycle, provides detailed information on how often large events that have significant risk associated with them are likely to be observed, and facilitates comparison of the near-Earth and lunar radiation environments to that near Mars. As an example, Table 1 shows the lens doses (in centigrays; 1 centigray = 1 rad) and dose equivalents (in centisieverts; 1 centisievert = 1 rem) for full-sphere radiation exposure from PREDICCS over the last 12 months. The PREDICCS lens dose quantifies the energy per mass deposited in 1 gram per square centimeter of water, which is a proxy for the biological impact to the human eye. Large SEP events on 23 January 2012, on 27 March 2012, and in the summer of 2012 contributed significantly to the hazards of the space environment over this interval. We observe that the dose rate limit of 200 centigrays for the lens dose [Cucinotta et al., 2010] is exceeded for nominal spacecraft shielding. Among the satellite measurements used by PREDICCS are data from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument on NASA's Lunar Reconnaissance Orbiter [Spence et al., 2010]. For the SEP events of 23 January (Figure 1) and 27 March 2012, PREDICCS results are typically within 20%-30% of what CRaTER observed. These highly accurate comparisons have never before been available over such long periods of time. CRaTER not only provides validation that PREDICCS models are accurate but also directly measures the biological impacts of radiation by observing linear energy transfer spectra behind different thicknesses of tissue-equivalent plastic [Spence et al., 2010]. Accurate assessment of the biological impacts of space radiation is vital to fully characterizing the radiation hazards of the space environment. The near-real-time situational awareness provided by PREDICCs will help to enable future human space exploration endeavors, including a return to the Moon and possible missions to Mars. Nathan Schwadron is an associate professor at the University of New Hampshire and the Institute for the Study of Earth, Oceans and Space. His email is n.schwadron@unh.edu.

LET spectrometry of 14 MeV (D–T) neutrons using CR-39 track detectors

Measurement of LET (linear energy transfer) spectra using CR-39 at different depths of water irradiated by 171 MeV protons: A comparison with Monte Carlo simulation

The dosimeter Liulin-MO for measuring the radiation environment on board the ExoMars Trace Gas Orbiter (TGO) is a module in the Fine Resolution Epithermal Neutron Detector (FREND). A number of solar energetic particle (SEP) events were observed in Mars orbit from July 2021 to 2024 during the increasing phase and close to the maximum of the 25th solar cycle activity. The results from the SEPs measurements obtained in 2021-2023 by Liulin-MO have been previously reported. Here we present the Liulin-MO results from the observation of the radiation parameters of the SEP events during January- October 2024. The most powerful SEP event registered up to now in TGO orbit started on 20 May 2024. The maximum dose rate during this SEP event has been 2800 ± 280 µGy h-1 and the maximum particle flux - 383 ± 19 cm-2 s-1. The total event lasted for about 64 hours up to 24 May with a long tail of increased dose rates and fluxes. The total dose from SEPs for the 64 hours of the main phase of the SEP event was 24.7 ± 2.5 mGy. The total dose from SEPs during this event is equal to the dose from the galactic cosmic rays (GCR) received for about 200 days at this phase of solar cycle 25. The total dose from all SEPs during January - September 2024 is 36.6 mGy (in Si), which is approximately equal to the dose received from GCR for the same period. The observations of SEPs in Mars orbit are compared to the observations during the same periods of proton fluxes measured by the GOES satellite in Earth orbit. The results show that some of the SEPs observed in Mars orbit, excluding the biggest SEP events of 20-24 May and 05-07 September, are also seen in the GOES proton fluxes data. SEP events recorded both in Mars and Earth orbits are related to coronal mass ejections (CMEs) observed by the SOHO and STEREO A coronagraphs. The paper shows that responsible for most of the SEP events registered both in the Liulin-MO data and in the GOES proton fluxes data are halo CMEs. The paper also shows that the sources of the three most powerful SEP events in Mars orbit - those of 20 May, 23 July and 05 September - are halo CMEs from the far side of the Sun. Some of these CMEs are associated with major X class far-side flares. Long-term investigations of the GCRs radiation parameters in Mars orbit show that in August 2024 (the last month of our data with no recorded SEP events) the dose rate was 6.5 ± 0.65 µGy h-1 and the particle flux - 1.4 ± 0.07 cm-2 s-1. These values are about 40 % of the corresponding maximal values measured by Liulin-MO during the solar cycle 24 minimum in March 2020. The above results show the importance of long-term measurements (at least during a full solar cycle) of the radiation conditions in Mars vicinity. Such measurements will make it possible to obtain the data necessary for the planning of future manned and robotic missions, as well as for the selection of the best time interval in the solar cycle for a manned flight to the planet.

LET spectrometry for p+nat(Li+C) system at different proton energies using CR-39: Development of autoLET code for automated generation of LET spectra and dose values

Objective. This study aims to assess the composition of scattered particles generated in proton therapy for tumors situated proximal to some titanium (Ti) dental implants. The investigation involves decomposing the mixed field and recording Linear Energy Transfer (LET) spectra to quantify the influence of metallic dental inserts located behind the tumor. Approach. A therapeutic conformal proton beam was used to deliver the treatment plan to an anthropomorphic head phantom with two types of implants inserted in the target volume (made of Ti and plastic, respectively). The scattered radiation resulted during the irradiation was detected by a hybrid semiconductor pixel detector MiniPIX Timepix3 that was placed distal to the Spread-out Bragg peak. Visualization and field decomposition of stray radiation were generated using algorithms trained in particle recognition based on artificial intelligence neural networks (AI NN). Spectral sensitive aspects of the scattered radiation were collected using two angular positions of the detector relative to the beam direction: 0° and 60°. Results. Using AI NN, 3 classes of particles were identified: protons, electrons & photons, and ions & fast neutrons. Placing a Ti implant in the beam’s path resulted in predominantly electrons and photons, contributing 52.2% of the total number of detected particles, whereas for plastic implants, the contribution was 65.4%. Scattered protons comprised 45.5% and 31.9% with and without metal inserts, respectively. The LET spectra were derived for each group of particles identified, with values ranging from 0.01 to 7.5 keV μm−1 for Ti implants/plastic implants. The low-LET component was primarily composed of electrons and photons, while the high-LET component corresponded to protons and ions. Significance. This method, complemented by directional maps, holds the potential for evaluating and validating treatment plans involving stray radiation near organs at risk, offering precise discrimination of the mixed field, and enhancing in this way the LET calculation.

LET spectra behind high-density titanium and stainless steel hip implants irradiated with a therapeutic proton beam

Linear Energy Transfer Measurements and Estimation of Relative Biological Effectiveness in Proton and Helium Ion Beams Using Fluorescent Nuclear Track Detectors

Computation of linear energy transfer of space radiation in biological tissue analog

A novel silicon detector configuration for radiation dose measurements in an environment where solar energetic particles are of most concern is described. The dosimeter would also measure the dose from galactic cosmic rays. In the lunar environment a large range in particle flux and ionization density must be measured and converted to dose equivalent. This could be accomplished with a thick (e.g. 2 mm) silicon detector segmented into cubic volume elements voxels followed by a second, thin monolithic silicon detector. The electronics needed to implement this detector concept include analog signal processors (ASIC) and a field programmable gate array (FPGA) for data accumulation and conversion to linear energy transfer (LET) spectra and to dose-equivalent (Sievert). Currently available commercial ASIC's and FPGA's are suitable for implementing the analog and digital systems.

In preparation for deployment of the Galileo satellite navigation system, Europe has launched a test satellite, Giove-A. One of its objectives is to measure the radiation environment encountered in medium Earth orbit (MEO) which is a new regime for European missions. Giove-A therefore includes two radiation environment monitors: Merlin supplied by QinetiQ and CEDEX supplied by the University of Surrey. Merlin measures electrostatic charging and electron fluxes, total ionising dose, energetic proton fluxes and heavy ion linear energy transfer (LET) spectra. CEDEX monitors energetic proton fluxes, heavy ion linear energy transfer (LET) spectra and ionising dose rates. Giove-A, which was built by SSTL (UK), was successfully launched on 28th December 2005 into a 23,600 km circular, 56 degree inclination orbit. Data received since launch has been analysed and demonstrates that the MEO environment is highly dynamic due to the influence of space weather. Numerous electron belt enhancement events have been observed and the charging effects of these events been characterised. Total ionising dose is also seen to be delivered almost wholly during electron events.

: A specific implementation is presented for calculating the rate of single event upsets in microelectronic devices. The implementation is based on the method of Pickel and Blandford (1980), who combined device test results, the flux distribution of particles in the space environment, and a model for the geometry of the device. The device test data are summarized as an upset cross section expressed as a function of the linear energy transfer (LET). The flux distribution of particles in the environment is described by an integral LET spectrum. The device geometry model is that of a solid rectangular prism. A numerical integration of the LET spectrum and path length distribution in the solid over the upset cross section is performed to obtain the resultant upset rate.

To improve the forecasting capability of impactful solar energetic particle (SEP) events, the relation between coronal mass ejections (CMEs) and SEP events needs to be better understood. Here we present a statistical study of SEP occurrences and timescales with respect to the CME source locations and speeds, considering all 257 fast (v CME ≥ 900 km s−1) and wide (angular width ≥60°) CMEs that occurred between 2006 December and 2017 October. We associate them with SEP events at energies above 10 MeV. Examination of the source region of each CME reveals that CMEs more often accompany a SEP event if they originate from the longitude of E20–W100 relative to the observer. However, an SEP event could still be absent if the CME is <2000 km s−1. For the associated CME–SEP pairs, we compute three timescales for each of the SEP events, namely the timescale of the onset (TO), the rise time (TR), and the duration (TD). They are correlated with the longitude of the CME source region relative to the footpoint of the Parker spiral (ΔΦ) and v CME. The TO tends to be short for 60°. This trend is weaker for TR and TD. The SEP timescales are only weakly correlated with v CME. Positive correlations of both TR and TD with v CME are seen in poorly connected (large ) events. Additionally, TO appears to be negatively correlated with v CME for events with small .