What are the Forms of What are the Forms of Hazardous Radiation?Hazardous Radiation?

Stanley B. CurtisStanley B. CurtisFred Hutchinson Cancer Research Center, ret.Fred Hutchinson Cancer Research Center, ret.

& Dept. of Environmental Health& Dept. of Environmental HealthUniversity of WashingtonUniversity of Washington

Seattle, WASeattle, WA

Van Allen, Ludwig, Ray and Mc llwain, Prelim. Report Satellites 1958 Alpha and 1958 Gamma, IGY Bull., NAS, 1958

Three Main Radiation Three Main Radiation EnvironmentsEnvironments

Trapped Radiation BeltsTrapped Radiation Belts Not an important factor, but for Apollo missions, this Not an important factor, but for Apollo missions, this

contribution was appreciable.contribution was appreciable.

Galactic Cosmic Rays (GCR)Galactic Cosmic Rays (GCR) Dose equivalent rate varies from 2 to 3 over the solar Dose equivalent rate varies from 2 to 3 over the solar

cycle depending on available shielding; it is highest at cycle depending on available shielding; it is highest at solar minimum. Risk from the highly ionizing component solar minimum. Risk from the highly ionizing component (HZE’s) is still under intense study and presently carries (HZE’s) is still under intense study and presently carries the greatest uncertainty.the greatest uncertainty.

Large Solar Particle Events (SPE)Large Solar Particle Events (SPE) Potentially the largest contributor if missions occur during Potentially the largest contributor if missions occur during

the active portion of the solar period and if enough the active portion of the solar period and if enough shielding is not available in a timely manner.shielding is not available in a timely manner.

Trapped Radiation BeltsTrapped Radiation Belts

Important during outgoing and returning Important during outgoing and returning spacecraft traversal of the spacecraft traversal of the magnetosphere.magnetosphere.

For the Apollo program, this environment For the Apollo program, this environment was not inconsequential. was not inconsequential.

Dynamic maps of the trapped belts are Dynamic maps of the trapped belts are important for dose prediction purposes. important for dose prediction purposes.

Galactic Cosmic Rays (GCR)Galactic Cosmic Rays (GCR) Dose equivalents, that is, doses Dose equivalents, that is, doses

taking into account that highly taking into account that highly ionizing radiation is more effective ionizing radiation is more effective than sparsely ionizing radiation, are than sparsely ionizing radiation, are in the range of 0.3 Sv/y (solar max.) in the range of 0.3 Sv/y (solar max.) up to 1 Sv/y (solar min.) for thin up to 1 Sv/y (solar min.) for thin shielding and 0.6 Sv/y for thick shielding and 0.6 Sv/y for thick shieldingshielding

Risk Estimates of Cancer Mortality for Exploratory Missions for a 40-year old male

Solar Minimum

MissionShielding thickness(g/cm2 Al)

Absorbed dose(Gy)

Effective dose(Sv)

Probability of radiation-induced death( %)

95% confidence

limits

90-day lunar mission,

solar minimum

5 0.03 0.084 0.34 0.10 - 1.2

90-day lunar mission,

solar minimum

20 0.03 0.071 0.28 0.09-0.95

1000-day Martian

mission, 600 days on surface

5 0.42 1.07 4.2 1.3 – 13.6

1000-day Martian

mission, 600 days on surface

20 0.41 0.96 3.4 1.1 – 10.8From Cucinotta, Kim and Ren, Managing Lunar and Mars Mission Radiation Risks

Part I: Cancer Risks, Uncertainties, and Shielding Effectiveness, NASA/TP-2005-213164

Probability distribution functions (PDF's) for risk of exposure induced death (REID) Probability distribution functions (PDF's) for risk of exposure induced death (REID) to 40-y males on 600-day Mars mission behind 20 g/cm2 shields of aluminum, to 40-y males on 600-day Mars mission behind 20 g/cm2 shields of aluminum, polyethylene or liquid hydrogen. polyethylene or liquid hydrogen. Effective doses, and point estimates and 95% CI for REID are shown in box.Effective doses, and point estimates and 95% CI for REID are shown in box.

Cucinotta, et al., 2004

Solar Particle Events (SPE’s)Solar Particle Events (SPE’s)

Variable in time, intensity and composition Variable in time, intensity and composition throughout the solar active period.throughout the solar active period.

Giant SPE’s could be extremely hazardous Giant SPE’s could be extremely hazardous if adequate shielding is not available.if adequate shielding is not available.

Improved prediction methods are critical.Improved prediction methods are critical.

Risk Estimates of Cancer Mortality for Exploratory Missions for a 40-year old male

Solar Maximum including the 1972 SPE

MissionShielding thickness

(g/cm2 Al)

Absorbed dose

(Gy)

Effective dose

(Sv)

Probability of

radiation-induced death( %)

95% confidence limits

90-day lunar mission

Solar max1972 SPE

5 0.45 0.69 2.7 0.95 – 7.6

90-day lunar mission

Solar max1972 SPE

20 0.04 0.09 0.36 0.12 – 1.2

1000-day Martian

mission, 600 days on surface

5 0.66 1.24 4.8 1.6 – 14.2

1000-day Martian

mission, 600 days on surface

20 0.25 0.60 2.4 0.76 – 7.8

From Cucinotta, Kim and Ren, Managing Lunar and Mars Mission Radiation Risks

Part I: Cancer Risks, Uncertainties, and Shielding Effectiveness, NASA/TP-2005-213164

NCRP Effective Dose 10-Year NCRP Effective Dose 10-Year Career Limits for Low-Earth Career Limits for Low-Earth

Orbit (in Sv)Orbit (in Sv)

Age at Age at exposurexposur

ee

(y)(y)

2525 3535 4545 5555

FemaleFemaless

0.40.4 0.60.6 0.90.9 1.71.7

MalesMales 0.70.7 1.01.0 1.51.5 3.03.0

These limits are expressly for low-earth These limits are expressly for low-earth orbits and are not intended to be applied orbits and are not intended to be applied to exploratory missions. to exploratory missions.

An NCRP committee has been tasked to An NCRP committee has been tasked to determine what acceptable limits might determine what acceptable limits might be for exploratory lunar missions.be for exploratory lunar missions.

Health EffectsHealth Effects

No radiation-associated health effects No radiation-associated health effects reported during Apolloreported during Apollo

Astronauts did see streaks and flashes Astronauts did see streaks and flashes of light during missionsof light during missions

Predicted in 1952 by C. A. TobiasPredicted in 1952 by C. A. Tobias Frequency of flashes was consistent Frequency of flashes was consistent

with fluences from HZE particles (high with fluences from HZE particles (high energy GCR with z>2) through the energy GCR with z>2) through the retinaretina

Increased probability of Increased probability of cataractscataracts

In a preliminary study in a population of 295 In a preliminary study in a population of 295 astronauts, increased risk and earlier astronauts, increased risk and earlier appearance of cataracts were found for appearance of cataracts were found for those receiving an equivalent dose greater those receiving an equivalent dose greater than 8 mSv (average 45 mSv) than for those than 8 mSv (average 45 mSv) than for those receiving a lower dose (average 3.6 mSv). receiving a lower dose (average 3.6 mSv). It was suggested that this increased risk is It was suggested that this increased risk is due to the highly ionizing component of the due to the highly ionizing component of the GCR.GCR.

Cucinotta et al., Radiat. Res. Cucinotta et al., Radiat. Res. 156156, 460–466 (2001), 460–466 (2001)

Present Activity in the Present Activity in the Radiation Health CommunityRadiation Health Community

A vigorous experimental program is underway A vigorous experimental program is underway at the NASA Space Radiation Laboratory at at the NASA Space Radiation Laboratory at Brookhaven using high energy beams of heavy Brookhaven using high energy beams of heavy ions throughout the periodic table.ions throughout the periodic table.

An NCRP Committee on Information Needed to An NCRP Committee on Information Needed to Make Radiation Protection Recommendations Make Radiation Protection Recommendations for Travel Beyond Low-Earth Orbit is nearing for Travel Beyond Low-Earth Orbit is nearing the completion stage.the completion stage.

An NCRP Committee on Radiation Safety in An NCRP Committee on Radiation Safety in NASA Lunar Missions is formulating NASA Lunar Missions is formulating recommendations on acceptable risks on lunar recommendations on acceptable risks on lunar missions.missions.

Collaboration with the Solar Collaboration with the Solar and Space Physics Communityand Space Physics Community

Prediction of the occurrence (i.e., advanced Prediction of the occurrence (i.e., advanced warning), time course, magnitude, composition and warning), time course, magnitude, composition and spectral shape of SPE’s, particularly those with hard spectral shape of SPE’s, particularly those with hard energy spectraenergy spectra

More knowledge of the atmosphere and surface More knowledge of the atmosphere and surface characteristics of Marscharacteristics of Mars

Development of dynamic maps of the proton and Development of dynamic maps of the proton and electron belts around the earthelectron belts around the earth

Development of better dosimetry (i.e., charge and Development of better dosimetry (i.e., charge and dE/dx or velocity) for onboard and individual dE/dx or velocity) for onboard and individual determination of dose and equivalent and/or determination of dose and equivalent and/or effective doseeffective dose

Concluding remarkConcluding remark We have come a long way since the early We have come a long way since the early

days of the Van Allen belts to understand the days of the Van Allen belts to understand the radiation environments important in planning radiation environments important in planning exploratory missions. I hope this conference exploratory missions. I hope this conference will contribute to this tradition and together will contribute to this tradition and together we can provide the information necessary to we can provide the information necessary to help make exploratory missions as safe as help make exploratory missions as safe as possible for the space travelers of the future.possible for the space travelers of the future.

Thank youThank you