Analysis of the radiation hazard observed by RAD on the surface of Mars during the September 2017 solar particle event

May combine two claims.

The approximately 10% difference between B and E dose rates is expected from the different detector responses to energetic charged particles, with a small additional neutron contribution to the E dose rate.

“The ~ 10% difference in dose rates is expected based on the different responses of the detectors to energetic charged particles.; there is also a small contribution to the E dose rate from high-energy neutrons (E > 6 MeV), on the order of a few percent of the total during solar quiet time (Köhler et al., 2014).”

• cites Köhler et al., 2014 sourcePartly supported

  Section 2.1 says neutrons can deposit energy in detector E, and section 5 reports that 8–740 MeV neutrons account for 7% of the total Martian surface dose rate. The paper does not establish that neutrons above 6 MeV contribute a few percent specifically to E’s dose rate during solar-quiet time, or explain an approximately 10% difference between B and E dose rates by their responses to energetic charged particles. (LLM, conf=0.84)

  Experimental — accuracy not yet measured

May combine two claims.

Mars was not magnetically connected to the acceleration site until a later phase; had the active region been better connected to Mars, the dose rate increases would likely have been much larger.

“Mars was not magnetically connected to the acceleration site until a later phase (Guo et al., 2018); had the active region been better connected to Mars, the dose rate increases would likely have been much larger.”

• cites Guo et al., 2018 sourcePartly supported

  Section 5 reports that particles arrived at Mars later than at Earth, but says it is unclear whether their onset resulted from cross-field diffusion, a later magnetic connection, or both. The Summary and Conclusion repeats those alternatives, so the cited paper does not establish later magnetic connection as fact. The dose-rate counterfactual follows the citation and is not attributed to this source. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

May combine two claims.

Dose rates fell gradually until about 05:00 UTC on September 13, at which point they fell steeply.

“Dose rates then fell gradually until about 05:00 UTC September 13, at which point they fell steeply”

May combine two claims.

The neutral particle count rate increased by less than a factor of 2 relative to solar quiet time and appeared delayed by several hours relative to the arrival of charged particles.

“The increase in flux relative to solar quiet time is less than a factor of 2. The increase of the neutral count rate appears to have been delayed by several hours relative to the arrival of charged particles.”

May combine two claims.

The stopping flux increased by about a factor of 5 compared to quiet time, but after excluding the electron contribution, the flux of stopping protons increased by about a factor of 30 compared to quiet time.

“The stopping flux increased by about a factor of 5 compared to quiet time, but more detailed analysis that excludes the electron contribution shows that the flux of stopping protons increased by about a factor of 30 compared to quiet time.”

May combine two claims.

Despite the significant dose rate increase during the event, the peak dose equivalent rate in the B detector was only about 50% greater than the galactic cosmic ray dose equivalent rates before and after the event, and the average dose equivalent rate during the event was nearly identical to galactic cosmic ray dates before.

“Despite the significant dose rate increase during the event, the peak dose equivalent rate in the B detector - which can be considered to be something like a skin exposure - was only about 50% greater than the GCR dose equivalent rates before and after the event, and the average dose equivalent rate during the event was nearly identical to GCR dates before.”

May combine two claims.

The event as seen on Mars was unambiguously underway by about 21:00 UTC on September 10, and dose rates doubled within about 7 hours.

“The event as seen on Mars was unambiguously underway by about 21:00 UTC on 10 September, and dose rates doubled within about 7 hours.”

May combine two claims.

Galactic cosmic ray rates then recovered gradually, and by mid-October had returned to the levels seen before the event.

“GCR rates then recovered gradually, and by mid-October had returned to the levels seen before the event.”

May combine two claims.

The B detector dose rate averaged over 8 and 9 September was 244 μGy/day in water after conversion from silicon, and the E detector dose rate averaged 268 μGy/day in plastic for the same days.

“The B dose rate averaged over 8 and 9 September was 244  Gy/day in water (after conversion from silicon), and the E dose rate averaged 268  Gy/day in plastic for the same days.”

May combine two claims.

Following the steep fall associated with the arrival of the interplanetary coronal mass ejection shock front at Mars, no evidence of solar particles was observed, and galactic cosmic ray rates dropped to a highly significant level 15-20% below pre-event rates.

“Following the steep fall, associated with the arrival of the shock front of the interplanetary coronal mass ejection (ICME) at Mars, no evidence of solar particles was observed, and GCR rates dropped to a (highly significant) level 15-20% below the rates prior to the event.”

May combine two claims.

Integrating B and E dose rates from the start of the event until the shock front arrived at Mars, the solar particle event contributed 544 μGy of dose in water as measured by B and 369 μGy as measured by E, above galactic cosmic ray levels.

“Integrating the B and E dose rates for the period from the start of the event until the arrival of the shock front at Mars, we find that the SPE contributed 544  Gy of dose in water as measured by the B detector, and 369  Gy of dose as measured by E. These are the estimated doses above GCR that are attributable to the SPE.”

May combine two claims.

The effective <Q> for the 30-day period including the event is 2.15, slightly less than the galactic cosmic ray <Q>, due to dilution by the predominantly low-LET particles in the solar particle event.

“Note that the effective <Q> for the 30-day period including the event is 2.15, slightly less than the GCR <Q> due to dilution by the predominantly low-LET particles in the SPE.”

• AssumptionRests on an assumption: The galactic cosmic ray background during the solar particle event can be represented by measurements taken before the event because there was no galactic cosmic ray suppression during the event.

May combine two claims.

The average radiation quality factor <Q> during the most intense portion of the solar particle event was 1.17, compared to 2.3 for galactic cosmic ray-only periods before and after the event.

“For the most intense portion of the SPE, <Q> was 1.17, compared to values of 2.3 found for GCR-only periods before and after the event.”

• AssumptionRests on an assumption: The galactic cosmic ray background during the solar particle event can be represented by measurements taken before the event because there was no galactic cosmic ray suppression during the event.

May combine two claims.

The count rate of neutral particles in the E detector, dominantly low-energy neutrons, rose by a factor of about 2 during the event, while counts of penetrating and stopping particles rose by factors of 3 and 5, respectively.

“The count rate of neutral particles in the E detector, dominantly low-energy neutrons, rose by a factor of about 2 during the event, while the counts of penetrating (Eproton > 113 MeV) and stopping particles rose by factors of 3 and 5, respectively.”

May combine two claims.

Folding the LET spectrum of vertical-going particles with the ICRP60 quality factor yields an average quality factor <Q> of 1.17 during the peak of the event, compared to values of about 2.3 for galactic cosmic ray-only spectra before and after the event.

“Folding the LET spectrum of vertical-going particles with the ICRP60 quality factor yields an average quality factor <Q> of 1.17 during the peak of the event, compared to values of about 2.3 found for GCR-only spectra before and after the event.”

• AssumptionRests on an assumption: The galactic cosmic ray background during the solar particle event can be represented by measurements taken before the event because there was no galactic cosmic ray suppression during the event.

May combine two claims.

Galactic cosmic rays include high-energy heavy ions whose biological effects per unit dose can be very large for some biological endpoints compared to more common radiation types such as gamma rays or x-rays.

“This is because the GCRs include high-energy heavy-ions, the biological effects of which may are known to be - for some biological endpoints - very large per unit dose compared to more common radiation types such as  -rays or x-rays (Blakely and Kronenberg, 1998).”

• cites Blakely and Kronenberg, 1998 sourceNot checked — no full text of the source

May combine two claims.

The event had a hard spectrum, a conclusion supported by spectral analysis presented elsewhere in the same issue and by a ground-level enhancement seen at Earth.

“It is also clear that the event had a hard spectrum, a conclusion further supported by the spectral analysis presented elsewhere in this issue and by the fact that a ground-level enhancement (GLE) was also seen at Earth starting at about 16:15 UTC September 10.”

Classified as probably not a substantial claim.

The biological damage caused by radiation does not depend simply on physical dose, which is the energy deposited per unit mass.

“It has long been known that the biological damage caused by radiation does not depend simply on physical dose, which is the energy deposited per unit mass (Rossi, 1964).”

• cites Rossi, 1964 sourceNot checked — no full text of the source

May combine two claims.

There was no indication of galactic cosmic ray suppression during the event, so data taken before the event were used to estimate the galactic cosmic ray spectrum during the event.

“Although GCR dose rates dropped by 15-20% immediately after the end of the event at Mars, there is no indication of GCR suppression during the event; we therefore use data taken prior to the onset of the event to estimate the GCR spectrum during the event.”

• AssumptionRests on an assumption: The galactic cosmic ray background during the solar particle event can be represented by measurements taken before the event because there was no galactic cosmic ray suppression during the event.

Classified as probably not a substantial claim.

The ICRP 60 quality factor Q(L) is 1.0 for LET values below 10 keV/μm.

“The ICRP 60 report defines Q(LET), or Q(L), as a piece-wise function with a value of 1.0 for LETs below 10 keV/  m, the range populated by the large majority of the observed SEPs.”

• cites ICRP, 1991Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

At the mean Martian elevation, the vertical column depth of atmosphere is 16 g/cm2.

“At the mean Martian elevation, the vertical column depth of atmosphere is 16 g cm -2”

May combine two claims.

During the event, the B detector dose rate exceeded the E detector dose rate because E is shielded by surrounding detectors and low-energy solar particles that deposit energy in B stop before reaching E.

“During the event, the dose rate in the B detector exceeded that in E because E is shielded by the surrounding detectors, and low-energy solar particles that deposit energy in B stop before they reach E.”

May combine two claims.

The atmospheric shielding above RAD during the event was 23 g/cm2, which is greater than at higher elevations on Mars.

“Also, the atmospheric shielding above RAD - 23 g cm -2 during the event - is greater than at higher elevations on Mars.”

May combine two claims.

The galactic cosmic ray <Q> of 2.3 is less than the previously reported value of 3.0 from early in the mission, primarily because of seasonal variations in the atmospheric column depth.

“The GCR <Q> of 2.3 is less than our previously-reported value of 3.0 from early in the mission (Hassler et al., 2014), owing primarily to seasonal variations in the atmospheric column depth.”

• cites Hassler et al., 2014 sourceNot checked — no full text of the source

• AssumptionRests on an assumption: The galactic cosmic ray background during the solar particle event can be represented by measurements taken before the event because there was no galactic cosmic ray suppression during the event.

May combine two claims.

The flux of penetrating particles started increasing before the stopping flux did, reflecting the earlier arrival times of more energetic ions.

“The flux of penetrating particles started increasing before the stopping flux did, reflecting the earlier arrival times of more energetic ions.”

May combine two claims.

Mars was not magnetically connected to the active region on the sun at the time of the 10 September flare; a well-connected event with the same hard spectrum would certainly produce much larger dose rates on the Martian surface and would likely produce a stronger Forbush decrease following the solar particle event.

“Mars was not magnetically connected to the active region on the sun at the time of the 10 September flare; a well-connected event with the same hard spectrum would certainly produce much larger dose rates on the Martian surface and would likely produce a stronger FD following the SPE.”

Probably not a substantial claim: may not pass S4 (based).

It is not possible to generalize from one medium-size event to other solar particle event scenarios.

“However, it is not possible to generalize from one medium-size event to other SPE scenarios.”

May combine two claims.

For purposes of calculating dose equivalent, the decrease in <Q> tends to offset the increase in dose rates, so that the dose equivalent rate was only slightly greater than during the preceding solar quiet time in the B detector and was actually slightly below the quiet-time rate in the E detector.

“For purposes of calculating dose equivalent, the decrease in <Q> tends to offset the increase in dose rates, so that the dose equivalent rate was only slightly greater than during the preceding solar quiet time in the B detector and was actually slightly below the quiet-time rate in the E detector.”

May combine two claims.

NCRP has defined 30-day exposure limits for astronauts, the smallest of which is 250 mGy-Eq for the heart and blood-forming organs.

“NCRP has also defined 30-day exposure limits for astronauts (NCRP, 1989). Multiplying the SPE doses quoted above (544  Gy in B and 369  Gy in the more-shielded E detector) by the proton RBE of 1.5 yields exposures far below even the smallest of the 30-day exposure limits, which is 250 mGy-Eq for the heart and blood-forming organs.”

• cites NCRP, 1989Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.