Intro to Nuclear Chemistry

How does a nuclear reactor work?

How does a small mass contained in this bomb cause……

• Nuclear Bomb of 1945 known as “fat man”

…this huge nuclear explosion?

Is there radon in your basement?

Notation

Nucleons

• Protons and Neutrons

• The nucleons are bound together by the strong force.

Isotopes

• Atoms of a given element with: same #protons

but different # neutrons

H H H

http://education.jlab.org/glossary/isotope.html

Isotopes of Carbon

• Isotopes of certain unstable elements that spontaneously emit particles and energy from the nucleus.

• Henri Beckerel 1896 accidentally observed radioactivity of uranium salts that were fogging photographic film.

• His associates were Marie and Pierre Curie.

Radioactive Isotopes

Marie Curie: born 1867, in Poland as Maria Sklodowska

• Lived in France• 1898 discovered the

elements polonium and radium.

Marie Curie a Pioneer of Radioactivity

• Winner of 1903 Nobel Prize for Physics with Henri Becquerel and her husband, Pierre Curie.

• Winner of the sole 1911 Nobel Prize for Chemistry.

3 Main Types of Radioactive Decay

• Alpha

• Beta

• Gamma

Emission of alpha particles :

• helium nuclei • two protons and two neutrons • charge +2e  • can travel a few inches through air• can be stopped by a sheet of

paper, clothing.

Alpha Decay

Alpha Decay

Uranium Thorium

Alpha Decay

Beta Decay

• Beta particles : electrons ejected from the nucleus when neutrons decay

( n -> p+ +- ) • Beta particles have the same charge and

mass as "normal" electrons.

Beta Decay

• Beta particles : electrons ejected from the nucleus when neutrons decay

n -> p+ +-

• Beta particles have the same charge and

mass as "normal" electrons.

• Can be stopped by aluminum foil or a block of wood.

Beta Decay

Beta Decay

Thorium Protactinium

• Gamma radiation electromagnetic energy that is released. 

• Gamma rays are electromagnetic waves.• They have no mass.• Gamma radiation has no charge.

– Most Penetrating, can be stopped by 1m thick concrete or a several cm thick sheet of lead.

Gamma Decay

Examples of Radioactive DecayAlpha Decay

Po Pb + He

Beta Decay p n + en p + e

C N + eGamma Decay

Ni Ni + (excited nucleus)

Which is more penetrating? Why?

Part II

•Nuclear Stability •Half-Life

Nuclear Stability

• Depends on the neutron to proton ratio.

Band of Stability

Number of Neutrons, (N)

Number of Protons (Z)

What happens to an unstable nucleus?

• They will undergo decay

• The type of decay depends on the reason for the instability

What type of decay will happen if the nucleus contains too many

neutrons?

• Beta Decay

Example:C N + e

In N-14 the ratio of neutrons to protons is 1:1

14

7 -1

014

6

• Nuclei with atomic number > 83 are radioactive

Radioactive Half-Life (t1/2 ):

• The time for half of the radioactive nuclei in a given sample to undergo decay.

Common Radioactive Isotopes

Isotope Half-Life Radiation Emitted

Carbon-14 5,730 years

Radon-222 3.8 days

Uranium-235 7.0 x 108 years

Uranium-238 4.46 x 109 years

Radioactive Half-Life

• After one half life there is 1/2 of original sample left.

• After two half-lives, there will be 1/2 of the 1/2 = 1/4 the original sample.

Graph of Amount of Remaining Nuclei vs Time

A=Aoe-t

A

Example

You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years.

• How many grams are left after one half-life? Answer:50 g

• How many grams are left after two half-lives?

Problem

A sample of 3x107 Radon atoms are trappedin a basement that is sealed. The half-life ofRadon is 3.83 days. How many radon atoms are left after 31 days?

answer:1.2x105 atoms