Fig 1.
Three key areas that must be developed together to ultimately provide the GCR simulator at NSRL.
Development focused on establishing irradiation requirements and balancing facility capabilities and limitations, including constraints imposed by animal and cellular model systems. GCR, galactic cosmic radiation; NSRL, NASA Space Radiation Laboratory.
Fig 2.
Relative contribution to fluence (squares), dose (diamonds), and dose equivalent (circles) of different elements in the free-space GCR environment during solar minimum conditions (June 1976) as described by the Badhwar–O'Neill 2010 GCR model [14] (Adapted from Durante and Cucinotta [3]).
Plot data available in S1 Data. GCR, galactic cosmic radiation.
Fig 3.
GCR particle spectra at solar minimum conditions (June 1976) denoted by solid lines and solar maximum conditions (June 2001) denoted by dashed lines in (A) free space and (B) behind 20 g/cm2 of aluminum to female BFOs as described by the Badhwar–O’Neill 2010 GCR model [14], HZETRN transport code [13,16,17], and human phantoms [15,18,19]. Plot data available in S1 Data. BFO, blood-forming organ; GCR, galactic cosmic radiation; HZETRN, High Charge and Energy Transport.
Table 1.
Summary of exploration mission exposures.
Fig 4.
Vehicle shielding is combined with shielding afforded by a crew member’s body surrounding critical organs to determine the primary and secondary radiation environment at points within the crew member.
(A) Human phantoms are used to calculate the body’s self-shielding of critical organs. (B) Shield thickness provided by the vehicle are depicted as green intersecting rays in a crew exploration vehicle (similar to Orion).
Fig 5.
Three basic strategies for beam selection.
(A) Beam selection is representative of the external, free-space GCR spectrum and is approximated by discrete ion and energy beams delivered onto a shielding and tissue equivalent material placed within the beam line, in front of the biological target. (B) Beam selection is representative of the shielded tissue spectrum found in space (e.g., average tissue flux behind vehicle shielding) and is approximated by discrete ion and energy beams delivered directly onto the biological target. (C) Beam selection is representative of energies less than free space with thinner amounts of vehicle shielding and variable thicknesses of tissue equivalent materials to represent the differences in body self-shielding between the physical sizes of species. GCR, galactic cosmic radiation.
Table 2.
Average tracks per cell nucleus per year, dose (mGy/year), and percent contribution of particles to dose for reference field during 1-year solar minimum and normalized to 500 mGy.
Fig 6.
Reference field spectra in the female BFOs behind 20 g/cm2 of aluminum shielding during solar minimum conditions.
(A) Neutron, hydrogen, and helium energy spectra. (B) The corresponding differential LET spectra with and without contributions from hydrogen and helium. Based on calculations from Slaba and colleagues, 2016 [8]. Plot data available in S1 Data. BFO, blood forming organ; LET, lineal energy transfer.
Fig 7.
Illustration of beam selection strategy for GCR simulator.
The total LET spectrum (light blue) and the HZE spectrum (dark blue) are shown separately. The green bars are representative of the number of single-ion beam experiments performed at NSRL as a function of LET (scaled for plot clarity). The black line is representative of ICRP-60 quality factor weighting [11] to estimate biological damage (scaled for plot clarity). Plot data available in S1 Data. GCR, galactic cosmic radiation; HZE, high charge and high energy ions; ICRP, International Commission on Radiological Protection; LET, linear energy transfer; NSRL, NASA Space Radiation Laboratory.
Fig 8.
Representation of the reference field using discrete monoenergetic beams.
The hydrogen and helium energy spectra are considered directly (A), whereas HZE ions are represented within the LET spectrum (B). Solid blue lines are the reference spectra from Fig 6. The bin widths for 1 GeV/n protons and helium particles are at lower fluences and not shown on the figure; however, these data are included in supplementary data file. All plot data available in S1 Data. HZE, high charge and high energy ions; LET, linear energy transfer.
Table 3.
“NSRL GCR Simulation” beam definition normalized to 500 mGy.
Fig 9.
Mouse and rat voxel models used to evaluate dose distributions in tissues from exposure to GCR simulation.
Digimouse (A) has been scaled by a factor of 3.15 to obtain and estimate of a rat’s body self-shielding, referred to here as “digirat” (B). Transport of full GCR simulation field provides homogeneous dose distribution within voxel mouse model (A) and scaled rat model (B). GCR, galactic cosmic radiation.
Table 4.
Calculated Digimouse tissue and skeleton doses after pseudoisotropic (6 direction) irradiation with GCR simulator beams.
Table 5.
Calculated “digirat” tissue and skeleton doses after nonisotropic (2-direction) irradiation with GCR simulator beams.
Fig 10.
Cumulative dose as a function of LET comparing simulated environments within phantoms to the reference field and GCR simulation beam exposure.
Plot data available in S1 Data. GCR, galactic cosmic radiation; LET, linear energy transfer.
Table 6.
Simplified 5-ion mixed field normalized to 500 mGy.
Fig 11.
Facility layout of NSRL at BNL.
(A) Tools to reliably control system hardware settings, from ion production by the LIS through booster injection, acceleration, extraction, and delivery to the NSRL target room were developed to sequentially deliver the GCR simulator ion-energy beam combinations. (B) Position of imaging chamber behind target (top, left-hand side), cut-off chamber (top, right-hand side) near beam entrance to target room, and photo of large-area degrader (binary filter) system (bottom) in NSRL beam line to maintain control and uniformity of 60 × 60 cm2 beam. BNL, Brookhaven National Laboratory; EBIS, Electron Beam Ion Source; GCR, galactic cosmic radiation; LINAC, Linear Accelerator; LIS, laser ion source; NSRL, NASA Space Radiation Laboratory.
Fig 12.
Housing array for mouse (A) and rat (B) irradiations in the 60 × 60 cm2 beam. Exposure boxes, made of approximately 2-mm thick polyethylene, stack together and are held in an array using a fabricated frame strucure. (C) Ventilation lids for air circulation are provided. The nonventilated sides of the lids are painted red to serve as a quick visual cue that the lids are in the correct orientation for air flow.
Fig 13.
Modified incubator for use in beamline (A) with a holder that can accommodate up to 15 T75 flasks in a 3 × 5 array or 44 T25 flasks (B).
Fig 14.
Computer screen shot measuring GCR simulator doses per particle for the 20.8 mGy cycle.
GCR, galactic cosmic radiation.