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.