1896—Becquerel • Accidently discovered radioactivity • Uranium in a drawer

1903—Marie (and Pierre) Curie• Able to prove rays came from rock• Coined the term “radiation”

1903—Nobel Prize —Becquerel & Curies1911—Nobel Prize —Marie Curie

Radioactivitythe process by which nuclei emit particles and high-energy raysRadiationthe particles and high energy rays emitted during radioactivity

Nuclear Chemistrythe study of radioactivity

• One atom transmutates into a different element• Radioactivity caused by unstable nucleus (DECAY) • LARGE amounts of energy emitted•Temperature and pressure DO NOT affect the rate of reaction

• Multiple atoms/compounds • Types of atoms never change• Chemical bonding caused by unstable valence e- config. • small amounts of energy (comparatively) • Temp and pressure affect the rate of reaction

Complete Atomic Designation

I53

125 –

…gives very precise info about an atomic particle

mass #

atomic #

charge (if any)elementsymbol

Goiter due to lack of iodine

iodine is now added to salt

Nuclear reactions are caused by an unstable nucleus. The nucleus becomes stable through decay. Before we decay, let’s review…

Isotope Protons Neutrons Atomic No. Mass No. Symbol

Uranium-235

92 238

Radium-226

78 53

92 143 92 235 235 U92

Uranium-238 146 92 238 U92

234 Th90

Thorium-234 90 144 90 234

88 138 88 226 226 Ra88

Iodine-131 53 131 131 I53

Now…Let’s decay…

Radioactive Skittles

You have 3 radioactive skittles in front of you:Red: α rad. Orange: β rad. Yellow: rad.One must go in your hand, one must go in your pocket, and the last one must be eaten…

What arrangement will cause you the least harm???

Radiation

Murder with Alpha Decay• In November

2006, former Russian agent Alexander Litvinenko was poisoned with radioactive Polonium at a Sushi Bar in England.

News Video

Radioactive Decay

For nuclear equations, mass (top) and atomic number (bottom) must balance.

alpha () decay:

-particle (i.e., a He nucleus): massive, slow-moving;stopped by paper or clothingCANNOT penetrate skin

23492 U 230

90 Th + 42 He

(atomic number decreases by two)

beta () decay:

-particle (i.e., a fast-moving electron): tiny mass blocked by wood or aluminum foilstops~1 cm into body

23491 Pa 234

92 U + 0–1 e

(atomic number increases by one)

In -decay, the net effect is that a n0 is convertedinto a p+ and an e–. The e– is then released…

10 n 1

1 p + 0–1 e

*NOTE: A neutron is not actually made up of a p+ and an e-, because there are no e- in the nucleus!

gamma radiation ( ):

can penetrate to internal organs

gamma ray:

emitted when nucleonsrearrange into a morestable configuration

gamma radiation often accompanies other nuclear decay

consists of high-energy photons

00 (or just )

23492 U 230

90 Th + 42 He + 0

02

Recap: Types of Radiation

Alpha Beta Gamma

Composition Helium nucleus Electron High energy wave

Symbol 4 He2

-1 e 0 00

Charge 2+ 1- No charge

Mass ~ 4 amu 1/1837 amu

No mass

PenetratingPower

Low Moderate Very High

Transmutation ReactionsThe conversion of an atom from one element to another element

1. Radioactive decay (emission)2. Particles bombarding the nucleus of an atom

Alf-a DecayPo218

84 He2

4 + Pb82

214

Pa231 He2

4 + Ac89

22791

Write a transmutation equation for the alpha decay of francium-208.

Fr208 He2

4 + At85

20487

Write a transmutation equation for the alpha decay of radon-222.

Rn222He2

4 + Po84

21886

Beta EmissionPb210

82 e-1

0 + Bi83

210

Se75 e-1

0 + Br35

7534

Write a transmutation equation for the beta emission of argon-37.

Ar37 e-1

0 + K19

3718

Write a transmutation equation for the beta emission of carbon-14.

C14e-1

0 + N7

146

Stable Isotope

Radioactive materials will continue to decay until they reach a stable material (Usually with an atomic number less than 83.)

There are two forces at work in the nucleus:1. Strong Nuclear Force

– All subatomic particles in very close proximity will attract each other (protons and neutrons)

2. Electromagnetic Repulsions– Particles of similar charges repel each other

Neutrons act as “glue” holding the nucleus together. Therefore, there must be a balance between protons and neutrons. An imbalance causes nuclear instability…

Nuclear Transformations

Band of Stability

Below the belt:Too many p+, not enough n0

Above the belt:Too many n0, not enough p+

Sources of Radiation• 80% from Natural Sources• 20% Man made from x-rays and consumer

products

Half-Life Decay (t1/2)The time required for one-half of the nuclei of a radioisotope sample to decay to products

a. Independent of T, P, and concentration

b. Useful in radioactive dating

Half-lives can be as short as a fraction of a second or billions of years. Different nuclei have different decay patterns, depending on why they are unstable (i.e. too many protons, too many neutrons, )

Carbon-14 emits beta radiation and decays with a half-life of 5730y. Assume you start with a mass of 2.00g of carbon-14.

a. How long is 3 half-lives?b. How many grams will remain at the end of 3 half

lives?c. How many years will it take for only 0.0625g to

remain?

a. t1/2 = 5730y, 3(5730y) = 17190y

b. 2.00g1

1.00g2

0.50g3

0.25g

10.0625g

20.125g

30.25g

40.50g

51.00gc. 2.00g

t1/2 = 5730y, 5(5730y) = 28650y

t½ equation

2.00g1

1.00g2

0.50g3

0.25g

2.00g(1/2)(1/2)(1/2)

mi (1/2)n = mf

If 150.0 g of a radioactive substance undergoes 25 half lives, how many g will remain?

150.0 g (1/2)25 = 4.47 x 10 -6 g

or 2.00(1/2)3 = 0.25 g

mi = initial mass

mf = final mass

n = # of half lives

Detection of Radioactivityphotographic film (film badges):

cheap, “ballpark quantitative”

Geiger counter:ionization of gas producesmeasurable electric current

Nuclear Fission Fission is when a BIG nucleus splits. This requires…neutrons!

Important fissionable nuclei: U-233, U-235, Pu-239

chain reaction: one nuclear reaction leads to one or more others

Anywhere from 1-9 n0 are released!

1

0 n

Uranium consists mainly as U-238 (spent Uranium)

Chain Reaction

critical mass: (contained) the mass of fissionablematerial required to maintain a chain reaction at a constant rate. (Nuclear Reactor)

safe safe criticalmass

(“Run, Forrest, run!”)

supercriticalmass

supercritical mass: (uncontained) the mass above which the chain reaction accelerates

(reactionmaintainedat constant

rate)

Little Boy, later dropped on Hiroshima(“Ah jes’ felt lahk runnING.”)

Nuclear Power (controlled)

Nuclear Fusion (video) When two small nuclei collide and “fuse” together to

form one nucleus. This results in a LARGE amount of energy

This happens at extreme temperatures…like the sun! The search for “cold fusion” is in progress.

Nuclear Fusion

-- also called thermonuclear reactions

-- products are generally NOT radioactive

-- requires high temperatures

(> 40,000,000 K)

-- the tokamak uses magnetic fields to contain and heat the reaction

!!!!