Unit 2 Notes – Radioactivity Part II

Mr Nelson

Transuranium elements & Radioactivity

Transuranium elements are just elements #93-11? (anything after Uranium!)

All elements after Bismuth (Z = 83) are radioactive

Half Life

½ life: the time for ½ of a sample of nuclei to decay For U-238, it is 4.5 billion years Pa-234 has a ½ life of 1.2 minutes!!

Carbon Dating (Radioactive Dating)

Based on the radioactivity of carbon-14, which decays through -particle production.

eNC 01

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Carbon-14 is continuously made in the atmosphere when neutrons from space hit the nitrogen in the air.

HCnN 11

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10

147

More on carbon dating:

Living things always have the same amount of C-14 because they take it in through the air.

As soon as a living thing dies it stops taking in carbon from the atmosphere. The C-14 decays. The ½ life of C-14 is 5730 years. If a piece of wood has ½ the C as a living tree, it is

5730 years old. What are some of the problems with this method?

Detecting Radiation

High energy particles from radioactive decay make ions when they travel through matter. The fast particles “knock” electrons off the atoms

they hit.

A geiger counter can detect these ions through the flow of electricity

A geiger counter

Effects of Radiation

Different particles penetrate in different ways energy mass How easily they make ions Chemical properties

These things make radiation more or less harmful

Inverse Square Law

Intensity =

Conclusions About Radiation

Binding Energy & Mass Defect

Binding Energy – energy that holds nucleus together

Mass defect – the ‘missing mass’ when the mass of nucleons are added together.

Example: page 14 of HW Packet

E = mc2

Einstein’s idea

E = energy m = mass in kilograms c = speed of light 3x108 m/s

Fission and Fusion

Combining two light nuclei to make a heavier nucleus is called fusion

Splitting a heavy nucleus to form two nuclei with smaller masses is called fission.

Fission

Releases a lot of energy!

Can cause chain rxns

Chain Rxns

At least one neutron must go on to split another nucleus

Nuclear Reactors

Controlling Nuclear Reactors

Boron and Cadmium are used as neutron absorbers to slow down or stop the reaction.

Nuclear Bomb

The same type of chain reaction is used in a nuclear bomb, but it is not controlled.

Nuclear Fusion

Produces more energy than fission! Takes very high temperatures to get protons

close enough to “stick” to each other

energyeHeHHe

energyHHeHeHe

energyHeHH

energyeHHH

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42

11

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Fusion & Tokamak Reactor

Fusion would be a superior method of generating power. the products of the

reaction are not radioactive.

The bad news is that in order to achieve fusion, the material must be in the plasma state at several million degrees.