Download - radiation CHM 102/Sinex radiation
radiation
CHM 102/Sinex
radiation
ionize electrons break bonds
Source: http://www.arpansa.gov.au/basics/ion_nonion.htm
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
1:100:10,000
Most penetrating form of radiation?
Easiest form of radiation to shield from?
wrong wrong
wrong wrongcorrect
correct
…and now a pop quiz
OH. (hydroxyl radical)
H.
Radiation Damage
water molecule
-ray
2 OH. H2O2
What happens when the water molecule is struck by the gamma ray?
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 weighting factor, WR or relative damage that can be caused in
a biological system.
Radiation WR
alpha 20
fast neutron 10
slow neutron 5
beta 1
gamma rays 1 Incr
easi
ng b
iolo
gic
al dam
age
Source: http://www.euronuclear.org/info/encyclopedia/d/dose.htm
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.
answer
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
Ar (g)
incomingradiationor
Ion pair formation: Ar Ar+ + e-
Geiger-Mueller tube
High voltage 800-1200 v thin window of mica
anode +
cathode -
Current flows due to production of ion pairs.
Radiation Protection
0
100
200
300
400
500
600
0 1 2 3 4 5 6
Distance (m)
Act
ivit
y (c
pm)
U source detector
start
How does the radiation level vary if the detector is moved away?
Radiation Protection
0
100
200
300
400
500
600
0 1 2 3 4 5 6
Distance (m)
Act
ivit
y (c
pm)
U source detector
Radiation Protection
0
100
200
300
400
500
600
0 1 2 3 4 5 6
Distance (m)
Act
ivit
y (c
pm)
U source detector
Radiation Protection
0
100
200
300
400
500
600
0 1 2 3 4 5 6
Distance (m)
Act
ivit
y (c
pm)
U source detector
Radiation Protection
0
100
200
300
400
500
600
0 1 2 3 4 5 6
Distance (m)
Act
ivit
y (c
pm)
U source detector
Distance, m
Activity, cpm
1.0 500.0
2.0 125.0
3.0 55.6
4.0 31.3
5.0 20.0
Derive the mathematical relationship between activity and
distance.
2d500
A This is known as the inverse square law.The intensity of the radiation drops as the square of the distance.
answer
Radiation protections involves:
• Shielding• Distance• Time of exposure
So use these three factors to address the next slide.
1
2
3
4
highly radioactive -source
Rank the laboratory workersin terms of their safety
safest: _____ > _____ > _____ > _____
lead-lined walls
2 4 3 1
How could person 1 improve there hazardous situation?
Limit time of exposure!
Large-scale Nuclear Reactions
Natural uranium: 0.7% 235U, 99.3% 238U
Nuclear reactors: 3 - 4% 235U enriched235U as fuel in US commercial electric power production – controlled fission
Nuclear weapons: 90% 235U enrichedatomic 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?
different kinetics!
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 238UF6 heavier gas to outside, lighter in center
http://en.wikipedia.org/wiki/Enriched_uranium
World map of nuclear reactors
http://www.insc.anl.gov/pwrmaps/map/world_map.php
Where are most nuclear reactors located?
http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml
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
Nuclear weapons
Explosive power: 1 megaton = 106 tons of TNT
Largest H-bomb tested: Tsar Bomba (Russia) 50 Mtons
Atomic bombs used in wartime– Hiroshima: 60 kg 235U 13 kilotons
90,000 deaths – Nagasaki: ~6.4 kg 239Pu 21 kilotons
70,000 deaths
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!
What is the largest source of to the average person?
What is the largest source of background radiation to a person that smokes?
Natural background radiation
Sources of Background Radiation
Estimate your background radiation exposure – click here
Source: http://web.princeton.edu/sites/ehs/osradtraining/backgroundradiation/background.htm
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 (pre-1970’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
Nuclear medicine for diagnosis and treatment
Food irradiation to control pathogenic and spoilage bacteria
99m Tc, t1/2 = 6 hours, workhorse in nuclear medicine
131 I, t1/2 = 8 days, is used to diagnose and treat thyroid disorders
60 Co and 137 Cs
radioisotopes
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 by40K/40Ar 1.25 by238U/206Pb 4.47 by87Sr/87Rb 48.8 by
CH3 C
OH
OCH3 CH2
OH
CH3 C
O CH2
CH3
O
H OH
CH3 C
O CH2
CH3
O
H OH
+
+
+Which OH group is removed?
16O 18O
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.
The 18O is all found in the ester.
answer
stable isotopes
Mass spectroscopy is used to determine distribution of isotopes.