Safety1) Radiation Effects to Humans
Important Factor to the Health of Humans --Dose Equivalent = The biological effect on
specific organs from all radiation
expressed on a common scale
Dose equivalent = Absorbed Dose (D) x
Quality Factor (Q)
Absorbed Dose =The Energy imparted to matter
by ionizing radiation per unit mass of irradiated
material at the point of interest
Units => Gray (Gy)
=> Rad (ergs/g)
1 Gy = 1 joule/kg=10,000 ergs/g
= 100 Rad
1 Rad = 0.01 Gy = 10 mGy=100 ergs/g
Note : 1 Roentgen (R) is defined as the amount of
radiation ( X ray or gammas) that creates
2.58 x 10 -4 coulomb /kg of air
1 R ( 0.1-3 MeV) ≈ 0.87 rad in air
≈ 0.98 rad in soft tissue
Radiation Effects to Humans
Dose Equivalence = Absorbed Dose • Quality Factor
Absorbed Dose (AD)
" Energy Imparted to Matter
by Ionizing Radiation per
Unit Mass of Irradiated
Material."
Quality Factor (QF)
"Relates the Absorbed Dose
to the Biological Effects and
is Dependent on the Linear
Energy Transfer (LET) of
Ionizing Radiation."
QF
Rad = 100 ergs/gram
Gray = 100 Rads
LET in H 2O (keV/µ)
1
2
5
10
20
Rem = Rad • QF
(SI Units) Sievert = Gray • QF
<3.5
7
23
53
175
Acute Radiation Effects From Whole Body Exposure to Gamma Radiation
--->10,000
8
600
7
200
5
75
3
2
1
0
50
25
90% Chance of Radiation Sickness, Moderate WBC Depression
10% Chance of Temporary Hair Loss
100
4
Lethal to Most People in 3-30 Days
50% Chance of Death-30 Days
400
6
Lethal in 1 d
10% Chance of Nausea
Reduction in WBC Count-Return to Normal After Few Weeks
Subtle WBC Reductions-Hard to Detect
200
400
600
Exposure-Rem
800
1000
1200
Average Annual Radiation Dose to Average U. S. Citizen
X-ray (medical)
Nuclear
Medicine
Radon
Consumer
Products
Cosmic Rays
Terrestrial
Radiation
Internal
Isotopes
0.35 Rem/y
Radiation Environment in Space
• Geomagnetically Trapped Particles
-Inner Zone (<2.8 Earth radii), Protons & Electrons
-Outer Zone (2.8-12 Earth radii), Electrons & Protons
-Intensities Vary Slowly from Solar Activity, Magnetic Storms,
& Solar Cycles
• Galactic Cosmic Rays (GCR)
-87% Protons, 12% He Ions, 1% HZE (high Z & energy ions)
-HZE is a Major GCR Dose Contributor
-Intensities Vary with Solar Wind, Magnetic Field, & Solar Cycles
• Solar Particle Events (SPE)
-Sporadic Large Solar Emissions of Protons, He, & Heavier Ions
-Wide Variations in Intensity & Duration
-Ave. Time from Detection to Arrival ≈ 15 h (range of 0.25-60 h)
The Recommended Career Dose Limits for Space Activities Depend on Gender and
Age
500
After: NCRP Report # 98, 1989
Dose Equivalent-Rem
400
Male
300
Career Whole Body Limits
Female
200
100
Annual
Short Term BFO Limits-All Ages
30 Days
0
20
25
30
35
40
Age
45
50
55
60
The Anticipated Background Radiation Doses During Space Missions Are Reasonable
Except For Mars Missions
300
Note-Spacecraft Shield of 2 g/cm2 Al Shield, -
Career Limit-35 y male/45 y female
Dose Equivalent-Rem
250
200
150
Career limit-25 y male/32 y female
Surface
100
Flight
Annual guideline dose
50
30 day guideline dose
0
LEO, 90 day flight
-57°/450 km
Lunar-4 day flight, 86 day
surface
Mars- 2 y flight, 1 y
surface