radiation
CHM 102/Sinex
radiation
ionize electrons
break bonds
Source: http://www.arpansa.gov.au/basics/ion_nonion.htm
…and now ionizing radiation
Which form of radiation is the most penetrating?
Which form of radiation is the
most biological damaging?
Penetrating Power of Radiation
a
b
g
paper
0.5 cm lead
10 cm lead
Relative penetration power
a:b:g
1:100:10,000
…and now a pop quiz
Most penetrating form of radiation?
a
b
g
wrong
wrong
correct
Easiest form of radiation to shield from?
a
b
g
correct
wrong
wrong
Radiation Damage
g-ray
What happens
when the water
molecule is
struck by the
gamma ray?
H
water molecule
.
.
2 OH  H2O2
.
OH (hydroxyl radical)
 All forms of nuclear radiation are considered ionizing
radiation. There energy is large enough to ionize
electrons from a molecule.
H2O  H2O+ + e Ar  Ar+ + e- This formation of ion pairs is the
basis of the Geiger Counter.
 In some cases even bonds are broken. The products
.
formed can be extremely reactive, such as the OH
radical!
 See how water and radiation can interact or the
radiolysis of water – click here
Radiation Damage
Radiation
WR
alpha
20
fast neutron
10
slow neutron
5
beta
1
gamma rays
1
Source: http://www.euronuclear.org/info/encyclopedia/d/dose.htm
Increasing biological damage
Radiation weighting factor, WR or relative
damage that can be caused in a biological
system.
Why does an alpha particle have a high WR or
cause a large amount of biological damage?
answer
Although alpha particles travel only
short distances, they are massive and
cause major damage in their path.
Alpha particles are much more dangerous
when inhaled or ingested compared to
external exposure. Why?
answer
Clothes and dead skin cells provide shielding
externally, while internally alpha particles
have direct contact with cells.
Radiation detection
Geiger-Mueller tube
High voltage 800-1200 v
cathode Ar (g)
anode +
Ion pair formation: Ar  Ar+ + e-
Current flows due to production of ion pairs.
thin window
of mica
incoming
radiation
a, b , or g
Radiation Protection
U source
detector
Activity (cpm)
600
500
400
How does the radiation level vary if
200
the detector is moved away?
300
100
0
0
1
2
3
4
5
6
Distance (m)
start
Radiation Protection
U source
detector
Activity (cpm)
600
500
400
300
200
100
0
0
1
2
3
Distance (m)
4
5
6
Radiation Protection
U source
detector
Activity (cpm)
600
500
400
300
200
100
0
0
1
2
3
Distance (m)
4
5
6
Radiation Protection
U source
detector
Activity (cpm)
600
500
400
300
200
100
0
0
1
2
3
Distance (m)
4
5
6
Radiation Protection
U source
detector
Activity (cpm)
600
500
400
300
200
100
0
0
1
2
3
Distance (m)
4
5
6
Derive the mathematical relationship
between activity and distance.
Distance,
m
1.0
2.0
3.0
4.0
5.0
answer
500
A 2
d
Activity,
cpm
500.0
125.0
55.6
31.3
20.0
This is known as the inverse square law.
The intensity of the radiation drops as
the square of the distance.
Radiation protections involves:
• Shielding
• Distance
• Time of exposure
So use these three factors to address the next slide.
lead-lined walls
Rank the laboratory workers
in terms of their safety
2
4
1
How could person 1
improve there hazardous
situation?
Limit time of exposure!
3
highly radioactive g-source
safest: _____
2
> _____
4
> _____
3
> _____
1
Large-scale Nuclear Reactions
Natural uranium: 0.7%
235U,
99.3% 238U
Nuclear reactors: 3 - 4% 235U enriched
235U as fuel in US commercial electric power
production – controlled fission
different kinetics!
Nuclear weapons: 90% 235U enriched
atomic bomb: uncontrolled fission 235U 239Pu (Pu
produced in spent fuel of nuclear reactors)
H-bomb: fission-fusion - larger scale energy
release
How do you separate isotopes, same chemistry?
Isotope separation
Calutron: production-scale mass spectrometer to
separated uranium metal ions (235 U for Hiroshima
bomb)
gaseous diffusion: Graham’s Law used UF6 (s)  UF6
(g) at 56oC to separate 235UF6 from 238UF6
gas centrifuge: spin mixture of 235UF6 and
heavier gas to outside, lighter in center
238UF
6
http://en.wikipedia.org/wiki/Enriched_uranium
Where are most nuclear reactors located?
World map of nuclear reactors
http://www.insc.anl.gov/pwrmaps/map/world_map.php
Oklo: Natural Nuclear Reactors
1.7 – 1.8 billion year old rock
Level of 235U was ~3% at that time
TODAY Many isotopes common
in spent nuclear reactor
fuel occur in rock
 235U is depleted to as
low as 0.44% (most 0.7%)
 239Pu was naturally
produced at Oklo
http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml
Nuclear weapons
Explosive power: 1 megaton = 106 tons of TNT
Largest H-bomb tested:
50 Mtons
Tsar Bomba (Russia)
Atomic bombs used in wartime
– Hiroshima:
60 kg 235U
90,000 deaths
– Nagasaki:
~6.4 kg 239Pu
70,000 deaths
13 kilotons
21 kilotons
http://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki
Fallout (airborne radionuclides) from
weapons testing and reactor accidents
• Atmospheric testing of nuclear weapons
–
90Sr
in milk
• Nuclear reactor accidents
– Three Mile Island: 1979, radioactive gases
released (Kr)
– Chernobyl: 1986, radioactive nuclear fuel
dispersed by chemical explosion, radiation
measured globally!
Natural background radiation
What is the largest source of to the
average person?
What is the largest source of
background radiation to a person
that smokes?
Sources of Background Radiation
Source: http://web.princeton.edu/sites/ehs/osradtraining/backgroundradiation/background.htm
Estimate your background radiation exposure – click here
If you smoke
Radioactive sources in your house
Smoke detector 241Am
Gas mantles for camping lanterns 232Th
Constant glowing watch dials 3H or
147Pm while older vintage watches (pre1970’s) 226Ra
Vintage orange plates Fiesta Ware and
some older Cloisonné Jewelry 238U
based ceramic glaze
http://hps.org/documents/consumerproducts.pdf
Applications of Isotopes
radioisotopes
Nuclear medicine for diagnosis and treatment
99m
131 I,
Tc, t1/2 = 6 hours, workhorse in nuclear medicine
t1/2 = 8 days, is used to diagnose and treat thyroid disorders
Food irradiation to control pathogenic and spoilage
bacteria
60
Co and 137 Cs
Modern irradiation is mostly done with x-rays.
Dating objects
Can determine N/No ratio using mass spectroscopy and calculate tage
Consider using tritium, 3H, with a half-life of 12.32 yrs
Present day rain water – 32 pCi/L water = No
A 12 year old bottle of wine – 16 pCi/L
A 25 year old bottle of scotch - 8 pCi/L
14C
with a t1/2 = 5730 yr is used in archeology
Parent/Daughter used in Earth Sciences for rocks an meteorites
235U/207Pb
0.704 by
40K/40Ar
1.25 by
238U/206Pb
4.47 by
87Sr/87Rb
48.8 by
stable isotopes
Reaction mechanisms in chemistry
The oxygen in the acetic acid is 16O, while the ethanol contains 18O.
Which molecules does the OH group get removed from? The two paths
below illustrate the possible reactions.
O
H3C
C
O
O
H3C
H3C
+
C
OH
+
H
OH
CH3
CH2
OH
CH2
The
18O
is all found in the ester.
O
Which OH group is removed?
16
O
H3C
18
O
C
O
CH2
+
H
CH3
Mass spectroscopy is used to determine distribution of isotopes.
answer
OH