NUCLEAR CHEMISTRY

NUCLEAR CHEMISTRY

nuclear chemistry/physics:processes that occur in the NUCLEUS—these arenot chemical reactions!

Objectives

• What is radiation? Understand the meaning of terminology related to radioactivity.

• Know the three main types of nuclear radiation.

• Be able to write correct nuclear equations.

Radioactivity

• 1896: Henri Becquerel discovers that uranium affects photographic film.

• Marie Curie calls it radioactivity: the process of materials emitting “rays”

• radiation: the rays/particles given off by a radioactive source

• radioisotope: unstable isotope that emits radiation

Three Types of Radiation

• a: Alpha (helium nucleus emitted)

Total charge (subscript) and mass (superscript) must be conserved.

• b: Beta (electrons emitted as no → p+ + e-)

• g: Gamma (high energy EM radiation)

92238

90234

24U Th H e

614

714

10C N e

12

13

24

01H H He n

Radiation Problems

83212

24B i H e ?

? 612

10C e

? 60145

24Nd He

Objectives

• Why do atoms decay? Understand the concept of nuclear stability.

• Be able to determine the type of radioactive decay based on various circumstances.

• Be able to determine the products of various transmutation reactions.

Nuclear Stability

• Protons repel, but the nuclear strong force holds p+ and no together.

• A stable p+ / no ratio is needed.

• Elements “decay” to make a stable ratio. 1:1

1:1.5

Transmutations

• transmutation: an atom is converted into a different atom (a different element)

• occurs through radioactive decay

*positron: positive electron (antimatter)*neutrino (v): may be massless

88226

86222

24Ra R n H e alpha

712

612

10N C e v beta

512

612

10B C e v beta

(nucleus is too heavy)

(too many neutrons)

(too many protons)

Decay Series

Transmutations

• bombardment: particles collides with the nucleus to cause transmutations (like bowling!)

714

24

817

11N He O H

The discovery of the p+ and the no were achieved using bombardment.

49

24

612

01B e H e C n

Rutherford

Objectives

• How long does it take for a nucleus to decay? Understand the concept of half-life.

• Simulate the radioactive decay of an imaginary radioisotope and determine the half-life of the isotope.

• Be able to make simple half-life calculations.

Half-Life

• half-life (T1/2): the time it takes for one-half of the nuclei of a radioisotope to decay to products

• 64 nuclei → 32 → 16 → 8 → 4 → 2 → 1

• If T1/2 = 200 years, it takes six half-lives (1200 years) to decay from 64 to 1.

Measuring Nuclear Decay

• Fermium has a half-life of 100.5 days. How much of a 5.2 mg sample of fermium will remain after 365 days?

N N eOt

0 6931 2

./T

Objectives

• What is nuclear energy? Understand the processes of nuclear fission.

• Be able to discuss how various technologies employ nuclear fission.

• Be familiar with the process of nuclear fusion.

Nuclear Fission

• fission: the splitting of a large nucleus

• products have less mass than reactants

• mass is converted into energy (E=mc2)

92235

01

3691

56142

013U n Kr B a n energy

Nuclear Fission Power

• Nuclear power plants use controlled nuclear fission to release energy slowly.

• Heat creates steam that generates electricity.

Fission Reactor Core

Three-Mile Island

Chernobyl

The Fission A-Bomb

• The WWII bombs used uncontrolled nuclear fission.

• Material must have a critical mass to explode.

• Test bomb/Nagasaki: implosion of Pu-239

• Hiroshima: gun-type with U-235

Nuclear Fusion• nuclear fusion: small

nuclei combine and release much more energy than fission reactions.

• occurs in the sun and nuclear weapons

4 211

24

10H He e v

Thermonuclear Weapons• Modern “nukes” use fission to start a fusion reaction.• 100 times more powerful than the A-bomb (1.2

megatons vs. 15 kilotons of TNT).