Moon Village Meeting

Issues on radiological protection
in deep space missions
深宇宙ミッションにおける宇宙放射線防護の課題

in 10 min

保田浩志 (広島大)Hiroshi Yasuda (Hiroshima Univ.)
1

Deep space exploration (DSE)

深宇宙ミッション

https://www.inverse.com/article/33217-mars-moon-phobos-baseMission to the moon

月へのミッション

https://www.nasa.gov/specials/apollo50th/back.html

Mars mission - it’s long..

火星ミッション―これは長い..

ReturnSun

EarthOutboundMarsFig. A typical route of Mars Mission planned by NASA.

Solar particle event (SPE)

太陽粒子現象 (SPE)Energetic particles (mainly protons)
are generated by a huge explosion(flare) on the Sun’s surface.

Predicted dose from SPE
SPEによる予測線量
100
Dose [GyEq]

1010.1
0.01
0.001
Aluminum thickness [g/cm2]
Fig. Predicted doses of selected organs as functions of the thicknessof aluminum shielding for the hypothetical largest SPE (comparableto the Carrington event) with RBE=1.5 [Townsend et al., 2006].

確定的影響のしきい値

Threshold doses of selected deterministic effects
表. 主な確定的影響とそのしきい線量および潜伏期 [ICRP, 2007等].
組織／臓器症状

しきい線量

潜伏期

骨髄造血機能障害～0.5 Gy

3～7日

一時的不妊（男性）～0.15 Gy

3～9週永久不妊（男性）

3～6 Gy～3週

一時的不妊（女性）～1.5 Gy～1週

永久不妊（女性）

2～7 Gy

～1週

一時的脱毛

3 Gy

2～3週

皮膚紅斑

2～6 Gy1～4週

皮膚熱傷

5～10 Gy

2～3週

精巣

卵巣

皮膚腸

中枢神経

下痢、下血死亡（100％）
痙攣、麻痺等死亡（100％）

6～20 Gy

20 Gy~

数日
1～2週
直後
数日以内

Organ dose limits for LEO astronauts (NASA)

低軌道宇宙飛行士のための組織線量限度 (NASA)

Table. Recommended RBE-weighted dose limits regarding thedeterministic effects for LEO astronauts [NCRP, 2000].

PeriodRBE-weighted dose limit [GyEq]
Bone marrow

Lens of the eyeSkinCareer-

4.0

6.0

1 year0.50

2.0

3.030 days

0.25

1.0

1.5

* These limits are applied to all ages. The career effective-dose limits forstochastic effects are given separately.

Effects of space radiation exposures on the reproductive
potentials of astronauts have not yet been considered...

Is SPE predictable? – Not yet.

SPEを予測できるか? – まだできないFig. Image of an astronaut hurrying to return to the moon base.

Exposure to SPE is hard to avert
SPEによる被ばくを回避するのは難しい

0.384 million km(1.3 sec by light)
Moon
149.6 million kmEarthSun

Table Estimates of the time for averting the exposure.

EnergyVelocity [km s-1]

Time [min]1 GeV

2.63 105

10100 MeV

1.28 1052010 MeV

0.43 10558

Male reproductive organ – Testis –男性の生殖器 ―精巣―

Table. The RBE values of neutrons and selected heavy ions forspermatogorium killing in mice [Wang and Yasuda, 2020].

Energy orsource

RBE value

Carbon400-670 MeV/u<3Alpen et al. (1981)

Oxygen400-670 MeV/u<3Alpen et al. (1981)

Neon

400-670 MeV/u<3Alpen et al. (1981)

Argon

400-670 MeV/u<3Alpen et al. (1981)

Neutron

1 MeV

5.7

Gasinska et al. (1985)

Neutron

5.5 MeV

4.6

Gasinska (1985)

Particle

Courtesy of Dr. Bing Wang (QST)

ReferenceFemale reproductive organ – Ovary –女性の生殖器 ―卵巣―Table. The RBE values of neutrons and selected heavy ionsfor oocyte killing in mice [Wang and Yasuda, 2020].

Energy orsourceRBE value

Carbon80 MeV/u

1.3－1.5

Zhang et al. (2006)

Neon

450 MeV/u0.4－0.6

ICRP (1989)

Silicon

670 MeV/u

0.4－3.0

ICRP (1989)

Argon

570 MeV/u

0.4－2.2ICRP (1989)

Neutron0.43 MeV

1.7

Straume et al. (1987)

Neutronfrom 252Cf

1.6 – 3.5

Satow et al. (1989)

Particle

Courtesy of Dr. Bing Wang (QST)

ReferenceLifestyle on the moon or Mars

月や火星での生活様式

Fig. Illustration of a possible lunar base in near future.

Lifestyle on the moon or Mars

月や火星での生活様式

Fig. Illustration of a possible lunar base in near future.

Lifestyle on the moon or Mars

月や火星での生活様式

π πnπnγpe

νμpe

νπnnμν

Fig. Illustration of a possible lunar base in near future.

Summaryまとめ One of the most serious concerns in futureinterplanetary missions is potential exposures toSPE particles that would threaten the lives ofastronauts.
 To avoid a high-dose exposure during the long
mission, the reliability and precision of the space
weather forecast system regarding the SPE
occurrence will be desirably improved.
 In parallel, intensive studies on the biologicaleffects of high-LET particles (protons, heavy ions,neutrons and pions) are needed for protecting
the health of astronauts.

ムーンヴィレッジ勉強会 (オンライン, 2021年6月24日)“深宇宙ミッションにおける宇宙放射線防護の課題”
保田浩志 (広島大)Thank you for your attention.