# Presentation: 529551

## What are the Forms of Hazardous Radiation?

- Stanley B. Curtis
- Fred Hutchinson Cancer Research Center, ret.
- & Dept. of Environmental Health
- University of Washington
- Seattle, WA

## Slide 2

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

## Three Main Radiation Environments

- Trapped Radiation Belts
- Not an important factor, but for Apollo missions, this contribution was appreciable.
- Galactic Cosmic Rays (GCR)
- Dose equivalent rate varies from 2 to 3 over the solar cycle depending on available shielding; it is highest at solar minimum.  Risk from the highly ionizing component (HZE’s) is still under intense study and presently carries the greatest uncertainty.
- Large Solar Particle Events (SPE)
- Potentially the largest contributor if missions occur during the active portion of the solar period and if enough shielding is not available in a timely manner.

## Trapped Radiation Belts

- Important during outgoing and returning spacecraft traversal of the magnetosphere.
- For the Apollo program, this environment was not inconsequential.
- Dynamic maps of the trapped belts are important for dose prediction purposes.

## Galactic Cosmic Rays (GCR)

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

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

** ****for a 40-year old male**
**Solar Minimum**

| 

Mission | 
Shielding 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 – 10.8 |

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

- Cucinotta, et al., 2004

## Solar Particle Events (SPE’s)

- Variable in time, intensity and composition throughout the solar active period.
- Giant SPE’s could be extremely hazardous if adequate shielding is not available.
- 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**

| 

Mission | 

Shielding thickness

(g/cm2 Al) | 

Absorbed 
dose

(Gy) | 

Effective dose

(Sv) | Probability of radiation-induced death
( %) | 

95% confidence limits |
| --- | --- | --- | --- | --- | --- |
| 90-day lunar mission
Solar max
1972 SPE | 

5 | 

0.45 | 

0.69 | 

2.7 | 

0.95 – 7.6 |
| 90-day lunar mission
Solar max
1972 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 Career Limits for Low-Earth Orbit  (in Sv)

| 
Age at exposure
(y) | 

25 | 

35 | 

45 | 

55 |
| --- | --- | --- | --- | --- |
| 
Females | 
0.4 | 
0.6 | 
0.9 | 
1.7 |
| 
Males | 
0.7 | 
1.0 | 
1.5 | 
3.0 |

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

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

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

## Health Effects

- No radiation-associated health effects reported during Apollo
- Astronauts did see streaks and flashes of light during missions
- Predicted in 1952 by C. A. Tobias
- Frequency of flashes was consistent with fluences from HZE particles (high energy GCR with z>2) through the retina

## Increased probability of cataracts

- In a preliminary study in a population of 295 astronauts, increased risk and earlier appearance of cataracts were found for those receiving an equivalent dose greater than 8 mSv (average 45 mSv) than for those receiving a lower dose (average 3.6 mSv).  It was suggested that this increased risk is due to the highly ionizing component of the GCR.
-      Cucinotta et al., Radiat. Res. *156*, 460–466 (2001)

## Present Activity in the Radiation Health Community

- A vigorous experimental program is underway at  the NASA Space Radiation Laboratory at Brookhaven using high energy beams of heavy ions throughout the periodic table.
- An NCRP Committee on Information Needed to Make Radiation Protection Recommendations for Travel Beyond Low-Earth Orbit is nearing the completion stage.
- An NCRP Committee on Radiation Safety in NASA Lunar Missions is formulating recommendations on acceptable risks on lunar missions.

## Collaboration with the Solar and Space Physics Community

- Prediction of the occurrence (i.e., advanced warning), time course, magnitude, composition and spectral shape of SPE’s, particularly those with hard energy spectra
- More knowledge of the atmosphere and surface characteristics of Mars
- Development of dynamic maps of the proton and electron belts around the earth
- Development of better dosimetry (i.e., charge and dE/dx or velocity) for onboard and individual determination of dose and equivalent and/or effective dose

##   
   Concluding remark
   We have come a long way since the early days of the Van Allen belts to understand the radiation environments important in planning exploratory missions.  I hope this conference will contribute to this tradition and together we can provide the information necessary to help make exploratory missions as safe as possible for the space travelers of the future.

- _  _
-    _Concluding remark_
-    We have come a long way since the early days of the Van Allen belts to understand the radiation environments important in planning exploratory missions.  I hope this conference will contribute to this tradition and together we can provide the information necessary to help make exploratory missions as safe as possible for the space travelers of the future.

## Thank you