Radioisotope: an unstable isotope that spontaneously changes its nuclear structure and releases energy in the form of radiation.

Isotopes

StableRadioisotopes

Unstable

An unstable atom with a nucleus that can spontaneously disintegrate is said to be radioactive.

Abundant

Stable Isotopes

β+decay

β- decay

Radioactive Isotopes

These are just a few examples, there are more stable and unstable isotopes for tin!

AbundantAll isotopes of Uranium are

radioactive. None are stable.

...

IsotopesStable

Radioisotopes

Unstable

How long does it take for a radioactive atom to disintegrate? How do we find out?

Half-life: the average length of time it takes radioactive material to decay to half of its original mass

The half life of Cobalt-60 is 5.27 years. Does that mean that it takes 5.27 years for an isotope atom to decay?

Examplehalf life of Cobalt-60 is 5.27 years

It takes 5.27 years for the sample to decay to half of it’s original mass

100 g 50 g81 g 69 g

50 g counting only the blue Cobalt-60 atoms

Example continuedWhat if we wait another 5.27 years?

50 g

It takes 5.27 years for the sample to decay to half of it’s original mass

25 g32 g

Trying it outCarbon-15 has a half-life of 2.5 s.

If the sample is 100g, how much carbon-15 will be remaining after 10s?

Time (s) Mass of carbon-15 (g)

0 100

2.5 50

5 25

7.5 12.5

10 6.25

ApplicationsWhich elements are used for determining the

age of:

- a living thing that has died

- the moon or the earth

Explanation together.

Nuclear Fission

Same amount of energy in one reaction as about 7 million times as great as the energy released when the same mass of dynamite explodes.

Heavy water: water that contains a high level of deuterium

Nuclear CANDU ReactorOur focus in this course: the transformations

of energy.

Photo source: http://www.nucleartourist.com/type/candu.htm

Nuclear fission produces neutrons and thermal energy.Heavy water moderates neutrons and absorbs thermal

energy.Thermal energy is transferred to the steam generator.Heavy water cools and flows back.Normal water absorbs thermal energy and vaporizes into

steam. Steam pressure builds and transforms thermal energy into

mechanical energy causing the turbine to turn.The electrical generator converts the mechanical energy into

electrical energy.

Nuclear FusionNuclear fusion: a nuclear reaction in which

the nuclei of two atoms fuse together to form a larger nucleus.

Proton-proton chain

CNO chain

Photo source: http://en.wikipedia.org

Nuclear FusionNuclear fusion produces significantly more

energy per mass of fuel than fission reactions.The only man-made fusion device to achieve

ignition to date is the hydrogen bomb.Nuclear fusion occurring in stars.