Nuclear ChemistryUnit 4

Radiation

In this part of the unit, we will focus on the nucleus! It’s very small (10-13 cm)

It’s very dense (1.6 ×14 g/cm3)

A lot of energy holds it together!(millions of times more than involved in chemical

reactions!)

Many nuclei are RADIOACTIVE!

They spontaneously decompose or DECAY (break apart) forming a different nucleus & producing

one or more particles

3 Main Types of Decay Particles

Alpha (α) particles Slow moving

nucleus of a helium atom.

Not very dangerous, can be stopped by▪ Skin▪ A piece of paper

3 Main Types of Decay Particles

Beta ( β) Particles Faster moving

electrons Are harmful Can be stopped by

wood or metal sheets

3 Main Types of Decay Particles Gamma (γ)

Particles High-energy

photon of light Very dangerous Partially stopped by

6 inches of lead or 6 feet of concrete

Half-Life (t1/2)

Time it takes for half of a radioactive material to decay away.

Example: You have 100.g of Ra-221. It’s half-life is

30 seconds.▪ What does that mean?

▪ How much Ra-221 would be left after 90 seconds?

More Half-Life Problems

The half-life of I-131 is 8.02 days. How much I-131 is left after 32.08 days? You originally have 600.g.

The half-life of Pu-239 is 24,360 years. Starting with 1000.g, how much would be left after 146,160 years?

Would it ever completely decay away?

Half-Life Equation

t1/2 = mass of material 2# of half-lives

Let’s try it!

Fission

Process of splitting a heavy nucleus into two more stable nuclei with smaller mass numbers

Releases a lot of energy

Fission

Chain reaction When you have a

lot of a radioactive substance and the fission of one nucleus gives off particles that hit other nuclei that give off more particles that hit more nuclei. . .

Fission

Critical Mass The mass of

material required to produce a chain reaction.

Fusion

Process of combining two light nuclei to form a heavier, more stable nucleus.

Produces a lot more energy than fission!