Which form of radiation is the most penetrating?
Which form of radiation is the
most biological damaging?
…and now ionizing radiation
paper 0.5 cm lead 10 cm lead
Penetrating Power of Radiation
Relative penetration power
Most penetrating form of radiation?
Easiest form of radiation to shield from?
α β γ
α β γ
…and now a pop quiz
when the water
struck by the
All forms of nuclear radiation are considered ionizing
radiation. There energy is large enough to ionize
electrons from a molecule.
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
See how water and radiation can interact or the
radiolysis of water – click here
Radiation weighting factor, WR or relative
damage that can be caused in a biological
fast neutron 10
slow neutron 5
gamma rays 1
Why does an alpha particle have a high WR or
cause a large amount of biological damage?
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.
α, β , or γ
Ion pair formation: Ar Ar+
High voltage 800-1200 v thin window
Current flows due to production of ion pairs.
0 1 2 3 4 5 6
U source detector
How does the radiation level vary if
the detector is moved away?
Derive the mathematical relationship
between activity and distance.
This is known as the inverse square law.
The intensity of the radiation drops as
the square of the distance.
Radiation protections involves:
• Time of exposure
So use these three factors to address the next slide.
highly radioactive γ-source
Rank the laboratory workers
in terms of their safety
safest: _____ > _____ > _____ > _____
2 4 3 1
How could person 1
improve there hazardous
Limit time of exposure!
Large-scale Nuclear Reactions
Natural uranium: 0.7% 235
U, 99.3% 238
Nuclear reactors: 3 - 4% 235
U as fuel in US commercial electric power
production – controlled fission
Nuclear weapons: 90% 235
atomic bomb: uncontrolled fission 235
produced in spent fuel of nuclear reactors)
H-bomb: fission-fusion - larger scale energy
How do you separate isotopes, same chemistry?
Calutron: production-scale mass spectrometer to
separated uranium metal ions (235
U for Hiroshima
gaseous diffusion: Graham’s Law used UF6 (s) UF6
(g) at 56o
C to separate 235
UF6 from 238
gas centrifuge: spin mixture of 235
UF6 and 238
gas to outside, lighter in center
World map of nuclear reactors
Where are most nuclear reactors located?
Oklo: Natural Nuclear Reactors
1.7 – 1.8 billion year old rock
Level of 235
U was ~3% at that time
Many isotopes common
in spent nuclear reactor
fuel occur in rock
U is depleted to as
low as 0.44% (most 0.7%)
Pu was naturally
produced at Oklo
Explosive power: 1 megaton = 106
tons of TNT
Largest H-bomb tested: Tsar Bomba (Russia)
Atomic bombs used in wartime
– Hiroshima: 60 kg 235
U 13 kilotons
– Nagasaki: ~6.4 kg 239
Pu 21 kilotons
Fallout (airborne radionuclides) from
weapons testing and reactor accidents
• Atmospheric testing of nuclear weapons
Sr in milk
• Nuclear reactor accidents
– Three Mile Island: 1979, radioactive gases
– Chernobyl: 1986, radioactive nuclear fuel
dispersed by chemical explosion, radiation
What is the largest source of to the
What is the largest source of
background radiation to a person
Natural background radiation
Sources of Background Radiation
Estimate your background radiation exposure – click here
If you smoke
Radioactive sources in your house
Smoke detector 241
Gas mantles for camping lanterns 232
Constant glowing watch dials 3
H or 147
while older vintage watches (pre-1970’s)
Vintage orange plates Fiesta Ware and
some older Cloisonné Jewelry 238
Applications of Isotopes
Nuclear medicine for diagnosis and treatment
Food irradiation to control pathogenic and spoilage
Tc, t1/2 = 6 hours, workhorse in nuclear medicine
I, t1/2 = 8 days, is used to diagnose and treat thyroid disorders
Co and 137
Modern irradiation is mostly done with x-rays.
Can determine N/No ratio using mass spectroscopy and calculate tage
Consider using tritium, 3
H, 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
C with a t1/2 = 5730 yr is used in archeology
Parent/Daughter used in Earth Sciences for rocks an meteorites
Pb 0.704 by
Ar 1.25 by
Pb 4.47 by
Rb 48.8 by
Which OH group is removed?
Reaction mechanisms in chemistry
The oxygen in the acetic acid is 16
O, while the ethanol contains 18
Which molecules does the OH group get removed from? The two paths
below illustrate the possible reactions.
O is all found in the ester.
Mass spectroscopy is used to determine distribution of isotopes.