1.3 Risk Factors for Radiation Exposure
Exposure Levels at which Health Effects Appear in Healthy Adults _____________________________________________________
Effects Acute dose (Gy)
_____________________________________________________
Blood count changes 0.50 Vomiting (threshold) 1.00 Mortality (threshold) 1.50 LD50/60 (minimal supportive care) 3.2-3.6 LD50/60 (supportive medical treatment) 4.8-5.4 LD50/60 (autologous bone marrow or stem cell transplant) >5.4
_____________________________________________________
Source: NCRP Report 98 "Guidance on Radiation Received in Space Activities", NCRP, Bethesda(MD) (1989).
Biological Effects of Radiation
Energy Loss of Radiation
As higher the energy of the
radiation, as deeper penetration into the surface of the material!
The energy loss depends on E and charge z of radiation particle.
Bragg-Curve: radiation with
certain energy E reaches a certain range R where most of the
radiation particles are stopped!
R dE
dE dx
m
z f E
E
=
∫
0 ∝ 2 ⋅ ( )dE
dx ∝ z2 ⋅ f E( )
Monte Carlo simulation
of electron scattering
Depth Profiling with Radiation
Radiation can be used for depth profiling!
charge z and mass m of radiation determines depth resolution ∆R
electrons alphas
R
0.5 1.0
Rel. Intensity
depth
∆Rα
∆Re
Interaction between radiation and matter takes place over depth range of penetration Ö signature
Origin of Radiation
Natural Radioactivity:
• long-lived radioactivity has originated in Supernova explosions prior to solar system;
• or is being produced by Cosmic Ray bombardment of earth atmosphere.
Man-made Radioactivity:
• Accelerator based experiments
• Reactor based experiments
Man-Made Radioactivity
Exposure to Natural and Man-Made Radioactivity
Tobacco contains α-emitter
210Po with T1/2=138.4 days.
Through absorption in
bronchial system smoking adds 280 mrem/year to the annual dose of US population
Sources of Natural and Radioactivity
Spectrum of CR
Cosmic Rays origin from:
• solar flares;
• distant supernovae;
Cosmic Ray Bombardment
Low energy CR
High energy CR
Cosmic Rays in High Altitude
Earth is relatively protected from cosmic rays through atmosphere shield; typical exposure is H=3.2 µrem/h. Mountain climbers and
airline crews and passengers are exposed to higher doses of radiation.
Dose doubles every 1500 m in height. At 10 km height dose is about 100 times sea-level dose H=0.32mrem/h.
Example: Total dose H:
• after 10h of flight:
H=3.2 mrem,
• for round trip:
H=6.4 mrem
• Frequent flyer with about 10 transatlantic flights/year H=64 mrem/year.
Compare to natural dose (100 mrem/y) !
Drastic Effects!
Wife’s ring with ground level dose!
Husband’s ring with transatlantic high altitude dose
Au γ-activity
Ö 8 times
more dose
14 C Enrichment in Environment
14C is produced by interaction of cosmic rays with 14N in the
atmosphere. Fall out of 14C and implementation into bio-material by photosynthesis. Decay counting may start after bio-material is dead.
Evolution of Carbon Content in our Atmosphere
Steady increase through industrial activities and exhaust causes change In atmospheric carbon
14C content!
14 C/ 12 C Ratio in Atmosphere
Based on ice-and tree-ring calibrations it was determined that 14C/12C ratio is
not constant with time, correction necessary!
Average ratio:14C/12C=1.3·10-12
Carbon dating example
[ ]
[ ]
The piece of carbon has a mass of M 25 g. This translates into the number of carbon 12 atoms:
=
= ⋅ =
= ⋅
⋅
C N( C N nuclei mole
A g mole M . [nuclei mole]
g mole g
12 A
6 022 1023
12 25
) [ ]
[ ] 1 mole of material has a mass of A [g]!
e.g. 1 mole 12C ≡ 12 g; 1 mole 56Fe ≡ 56 g;
1 mole 197Au ≡ 197g; 1 mole of 208Pb ≡ 208 g 1 mole AlO3 ≡ 27 g + 3·16 g = 75 g
You find in the ruins of a lost city - in a cold forgotten fireplace - a 25g piece of
charcoal. How much carbon is in there?
Some Reminder?
1 mole of any kind of material contains NA= 6.022·1023 particles (Avogadro’s number)
N(12C) = 1.25 ·1024 atoms
14 C-Dating, how old is the piece of charcoal?
[ ] [ ] [ ]
[ ]
λ
λ
λ λ
= =
⋅ ⋅ = ⋅
= ⋅
⇒ = ⋅ ⋅ ⋅ = ⋅
= ⋅ =
= ⋅ ⇒ = =
⋅
− −
−
− ⋅
− −
ln .
. .
) . [ ];
) . . . [ ]
) min]
( )
ln ( ) ln
. ;
2 0 693
5730 315 10 384 10
125 10
125 10 13 10 163 10
370
370 250 384 10
1 2 7
12 1
12 24
14 12 14 24 12 12
0
14
0
0
12 1
T y s y s
N( C atoms
C C N( C atoms
A N( C [decays
A t A e t
A A t
s t
t
number of C atoms in wood:
if has been constant
initial activity:
12
= 3250[ ]y
You analyze some weak activity of A(t)=dN/dt=250 decays/min, this gives you the clue for determining its age.
The atmospheric ratio is:
14 12
13 10 12
C
C = . ⋅ −
Sources of Natural Terrestrial Material
Natural alpha decay chains from long-lived heavy radioisotopes
• Uranium Series: 238U Ö 206Pb +8α
• Actinium Series: 235U Ö 207Pb +7α
• Thorium Series: 232Th Ö 208Pb +6α
• Neptunium Series: 241Pu Ö 209Pb +8α
There are several long-lived α-emitters in the chain: 234U
230Th, 226Ra!
Natural Radioactivity in the US
Long lived 40 K Radioactivity
40K
40Ar 40Ca
β+ β-
γ
40K has a half-life of T1/2=1.28·109 years its natural abundance is 0.0118 %
Potassium-Argon dating method
40Ar
40K
Internal γ Glowing
On average, 0.27% of the mass of the human body is potassium K of which 0.021% is radioactive 40K with a half-life of T1/2=1.25·109 [y].
Each decay releases an average of Eavg= 0.5 MeV β- and γ-radiation, which is mostly absorbed by the body
but a small fraction escapes the body.
Calculate, how many radioactive
40K atoms are in your body system!
Some Mass and Number Considerations
[ ] [ ]
[ ]
[
particles]
N kg
m N
g particles m
N
N particles
g m m
m
atoms K
g
m .
m .
m
m .
m m
K K body
body K
K body
K body
body K K
body K
body
20 15
7 23
7
23 40
7 40
10 83 . 6 :
body 80
for
gramm.
in mass
body the
need you
, calculate
to
/ 10
54 . 8
40
10 67 . 5 10
023 . 10 6
67 . 5
10 023 . 6 of
40
10 67 5 00021
0 :
body in the
K e
radioactiv of
mass
0027 0
: body in the
K potassium of
mass
: body the
of mass
40 40
40
40 40
40
⋅
=
⋅
=
⋅ =
⋅
⋅
≡ ⋅
⋅
⋅
=
⋅
≡
⋅
⋅
=
⋅
=
∗
⋅
=
∗
∗
−
−
−
Example: 40 K
Calculate the absorbed body dose over an average human lifetime of t = 70 y for this source of internal exposure.
[ ]
∗ = = ⋅ ⋅
∗ = ⋅ = ⋅
= ⋅
⋅ ⋅ ⋅ ⋅ ⋅
= ⋅ = ⋅ = ⋅
= ⋅
−
− −
−
Dose D E
m t A K E
m
Activity A K N T N
D y g m MeV
m
D MeV kg J kg Gy
with eV J
absorbed body
avg body
K K
body
body
: ( )
: ( ) ln
[ ] ln
( . [ ] ) . [ ]
. . [ / ] . [ ]
: [ ] . [ ]
40
40
1 2
15 1
10 2 2
19
40
2
4070 2
4 88 10 0 5
9 47 10 15 10 15 10
1 1602 10
λ
1.25 10 [y]
9 8.54[ ] [ ] [ ]
[ ] eV [ ] J
with
Gy kg
J kg
MeV D
19
2 2
11
10 602
. 1 1
:
10 63
. 2 /
10 63
. 2 /
10 66
. 1
−
−
−
⋅
=
⋅
=
⋅
=
⋅
=
Why do we die?
Lifetime dose from K is:
since and radiation has a weighting factor of the equivalent lifetime dose is:
40
D Gy
Q
H D Sv
= ⋅
− ≈
= ⋅ = ⋅
−
−
15 10
1
1 15 10
2
2
. [ ]
. [ ]
β γ
2.6·10
-22.6·10
-2The risk for radiation induced fatal cancer is 5·10-2 [Sv-1], Ö the overall risk for 40K radiation self-induced cancer is 0.13%.
40K-activity is powerful tool in archaeology and anthropology
