NASA SP-413 Space Settlements - Saint Ann's School

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NASA SP-413 — SPACE SETTLEMENTS — A Design Study
X rays
Gamma rays
TABLE 2-2 — IONIZING RADIATIONS IN SPACE
Name Charge (Z) RBE Location
0
1
0
1
Electrons
1.0 MeV
0.1 MeV
Protons
100 MeV
1.5 MeV
0.1 MeV
Neutrons
0.05 eV (thermal)
.0001 MeV
.005 MeV
.02 MeV
.5 MeV
1.0 MeV
10.0 MeV
Alpha particle
5.0 MeV
1.0 MeV
Heavy primaries
1
1
1
1
1
0
0
0
0
0
0
0
2
2
*3
1
1.08
1-2
8.5
10
2.8
2.2
2.4
5
10.2
10.5
6.4
15
20
(see text)
Radiation belts, solar radiation and
in the secondaries made by nuclear
reactions, and by stopping electrons
Radiation belts
Cosmic rays, inner radiation belts,
solar cosmic rays
Produced by nuclear interactions;
found near the planets and the Sun
and other matter
Cosmic rays
Cosmic rays
Figure 2-8 plots the ionizing power of protons in silicon
dioxide as a function of proton energy. Since the units of
ionizing power are in units of mass traversed, the same
values are reasonably accurate for all matter with a low
charge number (Z), for example, human tissue. This basic
curve holds for any ion species when the vertical axis is
multiplied by the ion’s charge number squared (Z 2 ).
Essentially the result is that the ionizing power increases as
the particle energy decreases, so as to cause the more slowly
moving particles to be the most damaging. In the extreme
relativistic energy region the damage effects are basically
constant — at a level which is termed the ionization
minimum. At the lowest velocities the charged particles are
finally neutralized by picking up electrons.
Figure 2-8 — Ionizing power of protons in Si0 2 vs. energy.
represent the same amount of biological danger. (For X-rays
1 rem results from the exposure of 1 roentgen.) The RBEs of
most of the common kinds of radiation are given in the
table.
The damaging power of heavy charged particles with charge
numbers equal to or greater than 3 is most conveniently
described in terms of their ionizing power. This measures
how many chemical bonds per unit of body mass are broken
and thereby gives a rough measure of the tissue damage
sustained.
REFERENCES
1. La Grange, J. L.: Oeuvres, vol. 6, pp. 262-292, Sewer
and Darbaux, Paris, 1873, “Essai Sur Le Probleme bese
Trois Corps” (L’Academie Royale de Sciences de Paris,
vol. 9, 1772).
2. Szebehely, V. G.: Theory of Orbits, the Restricted
Problems of Three Bodies, Academic Press, New York,
1967, and Analytical and Numerical Methods of
Celestial Mechanics, American Elsevier Publ. Co., N.Y.,
1967, pp. 227, 229.
3. Katz, J. L: Numerical Orbits Near the Triangular Lunar
Libration Points, Icarus, vol. 25, June 1975, pp. 336-359.
4. Kamel, A. A.: Perturbation Theory Based on Lie
Transforms and Its Application to the Stability of Motion
near Sun-Perturbed Earth-Moon Triangular Libration
Points, NASA CR-1622, 1970.
Chapter 2 — Physical Properties Of Space