Nuclear Equations

In nuclear equations, we balance

nucleons (protons and neutrons). The

atomic number (number of protons) and

the mass number (number of nucleons)

are conserved during the reaction.

Nuclear Equations

Alpha Decay

Nuclear Equations

Beta Decay

Nuclear Equations

Beta Decay

Nuclear Equations

Positron Emission: A positron is a particle

equal in mass to an electron but with opposite

charge.

Nuclear Equations

Electron Capture: A nucleus absorbs an

electron from the inner shell.

Nuclear Equations

EXAMPLE 4.1 Balancing Nuclear Equations

Write balanced nuclear equations for each of the

following processes. In each case, indicate what new

element is formed.

a. Plutonium-239 emits an alpha particle when it

decays.

b. Protactinium-234 undergoes beta decay.

c. Carbon-11 emits a positron when it decays.

d. Carbon-11 undergoes electron capture.

Write balanced nuclear equations for each of the

following processes. In each case, indicate what new

element is formed.

a. Radium-226 decays by alpha emission.

b. Sodium-24 undergoes beta decay.

c. Gold-188 decays by positron emission.

d. Argon-37 undergoes electron capture.

Exercise 4.1

EXAMPLE 4.1 Balancing Nuclear Equations continued

In the upper atmosphere, a nitrogen-14 nucleus absorbs

a neutron. A carbon-14 nucleus and another particle are

formed. What is the other particle?

EXAMPLE 4.2

5

More Nuclear Equations

Half-Life

Half-life of a radioactive sample is the

time required for ½ of the material to

undergo radioactive decay.

Half-Life

Half-Life

Fraction Remaining = 1/2n

Half-life

T1/2 = 0.693/ k(decay constant)

If you know how much you started with and

how much you ended with, then you can

determine the number of half-lives.

If you also know the start and end time, you

can divide the time by the number of half-

lives to give you the T1/2.

Half-life

To determine starting amounts or ending

amounts:

ln(Nt/No) = -kt

Nt is the number of radioactive nuclei at your

ending

No is the number of radioactive nuclei at the

start

K is the decay constant

Radioisotopic Dating

Radioisotopic Dating

Carbon-14 Dating: The half-life of

carbon-14 is 5730 years. Carbon-14 is

formed in the upper atmosphere by the

bombardment of ordinary nitrogen atoms

by neutrons from cosmic rays.

Radioisotopic Dating

Tritium Dating: Tritium is a radioactive

isotope of hydrogen. It has a half-life of

12.26 years and can be used for dating

objects up to 100 years old.

Nuclear Chain Reaction

Fission of one

nucleus produces

neutrons that can

cause the fission of

other nuclei, thus

setting off a chain

reaction.

Manhattan Project

The Manhattan Project was launched by

President Roosevelt in 1939. It consisted

of 4 separate research teams attempting

to:

a. Sustain the nuclear fission reaction.

b. Enrich uranium.

c. Make fissionable plutonium-239.

d. Construct a fission atomic bomb.

Manhattan Project

Replicas of “Little Boy”

(dropped on Hiroshima)

and “Fat Man”

(dropped on Nagasaki).

Manhattan Project

Mushroom cloud over

Nagasaki from the

detonation of “Fat

Man,” August 9, 1945.

Radioactive Fallout

Many radioactive isotopes are produced in a nuclear

bomb blast. Some are particularly harmful to humans.

Among these are strontium-90 and iodine-131.

Strontium-90: Half-life = 28.5 years, chemically similar to

calcium. Obtained from dairy and vegetable products

and accumulates in bone.

Iodine-131: Half-life = 8 days. Concentrates in the thyroid

glands.

Nuclear Power Plants

Civilian nuclear power plants use less

enriched uranium (2.5-3.5% uranium-235

rather than 90% for weapons-grade).

The nuclear chain reaction is controlled

for the slow release of heat energy. The

heat is used to make steam, which turns a

turbine to produce electricity.

The Nuclear Age