ASEN 5016 Lecture 16: Space Radiation

 OBJECTIVES

1.      Describe basic categories of space radiation

2.      Summarize biological effects of exposure

3.      Describe countermeasure philosophies

4.      Discuss current research

1. Radiation

  • Electromagnetic (EM)

Characterized by l and C, high flux, low energy

- waves or streams of massless particles traveling in a wave-like fashion and each carrying energy (photons)

Decay at 1/x2 from the source

Primary source is the sun (solar wind)

Radio, light, X-rays, IR, extreme UV

Gamma (g) rays are most abundant and originate outside the solar system

  • Particulate

Characterized by mass and n 2, low in flux, high energy

HZE particles (cosmic sources) à High Mass and Energy (Z = atomic number, E = energy)

SEPs – Solar Energetic Particles, also SPEs Solar Particle Events

GCRs – Galactic Cosmic Radiation (neutrons, protons & nuclei)

            http://helios.gsfc.nasa.gov/gcr.html

 

Electrons, protons, neutrons and nuclei

Ranges from helium to uranium, with peak in abundance of iron

a - helium nuclei (solar and galactic)
b - electrons (sun and van Allen belts)

ionizing radiation – dislodged electron, capable of producing charged atoms (ions) as passes through matter

UV is non-ionizing

·        Trapped Belt Radiation

Van Allen Belts (inner 1-3x Earth Radii, outer 4.5-10x)

- Verified by Explorer I (31 Jan 58)

SAA – cusp in VA Belts

-         ~90% of exposure in LEO occurs in the SAA region

·        Solar Flares

-         EM waves reach Earth in ~8.5 min

-         Magnetic cloud (particulates) reaches Earth 2-3 days later

-         Solar Max moderates GCRs but increases SEPs

Auroras, as seen from space

Units, lots of units…

RAD = Radiation Absorbed Dose (amount of energy absorbed in the body by radiation)

RBE – Relative Biological Effectiveness (varies dependent on type of radiation)

Roentgen – basic unit for measuring amount of radiation exposure

REM (Roentgen Equivalent, Man - measure of biological effect)

REM = [dose, RAD] x RBE = ~1.3 RAD

SI: Sievert (Sv) = 100 REM

1 RAD = absorption of 100 ergs/gm = 0.01 Gray (Gy) or 10 mGy (SI)

1 Gy = absorption of 1 J/kg

mGy = 0.1 RAD

2. Biological Effects

http://www.nsbri.org/Radiation/HumanAffects.html

 

Two general categories:  somatic (exposed individual) and genetic (hereditary effects)

Different types of radiation produce different amounts of damage

HZE and low energy protons > electrons and high energy protons

Higher rate of energy loss per length of track à Linear Energy Transfer (LET)

Tissue effects = thermal, chemical, cellular and genetic

Sensitivity proportional to complexity e.g. eyes > skin > bone

 

Symptoms: nausea, vomiting, illness, death

~RADs required for inactivation/death

·        Molecules                   107

·        Viruses                        105

·        Bacteria                      104-106

·        Mammalian cells          100-104

·        Mammals                    320-540

LD50 for humans = 320-540 RAD

Sickness can occur at 25-30 RAD

Ave exposure in the US: ~40 mREM / year (soil, rocks, wood, etc.)

East coast ~20 mREM / year

Rocky Mtn area ~90 mREM / year

Cosmic Rays: add ~40 mREM / year (~160 mREM high in the Rocky Mtns)

Food and water: add ~ 20-50 mREM / year

NY to Paris flight: add ~4 mREM

à ~ 100 mREM / year compared to  ~65 – 195 mREM / typical shuttle flight

Activity / Dose
Smoking a pack of cigarettes / 2.5 mrem
Chest X-ray / 10 - 20 mrem

EPA Home on Radiation

Biological effects are cumulative

Effects are acute (early) or chronic (late)

    • tissue damage
    • loss of fertility
    • lens opacification
    • cancer induction
    • heritable effects

Sunburn à melanoma

Carcinogenic effects are of great concern

Proliferating cells of renewing tissue & organs are most sensitive - bone marrow, lymph, intestine and reproductive organs

Younger people and women are more susceptible to radiation damage in general

            - Youth have longer for potential damage to develop

- Women have additional radiation sensitive organs (breasts and ovaries) and a longer expected life span than men

3. Countermeasures

·        Distance from local source (decays at 1/x2)

·        Timing of exposure (when radiation is least intense) e.g. no scheduled EVAs over SAA

·        Shielding (but secondary effects…) evaluation of effectiveness is complex and depends on actual composition of the impacting radiation

·        Pharmaceutical treatment

Shielding stops or alters the trajectory of high energy particles before the reach humans

Hydrogen-based materials are best

Protection against non-ionizing radiation is relatively simple, but ionizing sources create secondary and tertiary particles, some of which produce gamma rays

Low (equatorial) orbits are considerably less hazardous than polar orbits

Current Recommendation is to keep exposure “ALARA” – As Low As Reasonably Achievable

Can Humans go to Mars?

It is anticipated that future biological research will:

·        determine ways to improve the ability of the body to repair damaged cells or to rid itself of those cells that are too damaged to be repaired

·        help to understand why some individuals are more susceptible than others

·        develop better tools for early diagnosis of changes that may lead to cancer so that they can be treated sooner when chances of success are greatest

4. Research Highlights

 

A little dated, but useful information on ISS research…

http://www.nsbri.org/Radiation/ISS-EXP.html

 

International Workshop on Space Radiation Research

http://www.dsls.usra.edu/meetings/radiation2004/

 

Materials for Shielding (towards bottom of article)

 

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