P7 - Radioactivity

What does a radioactive substance contain?

Unstable nuclei that becomes stable by emitting radiation

What is the main three types of radiation?

Alpha beta and gamma

What is different about radioactive decay?

It is a random event which can't predicted or influence when it happens.

What did Ernest Rutherford do?

He fired alpha radiation particles at an atom. in tur, he discovered that the nucleus of an atom was small but it was where most of an atom's mass was located.

What could the 'plum pudding model' not explain?

It couldn't explain why some a particles were scattered through large angles

Why was Rutherford's nuclear model quickly accepted?

• Agreed with the measurements Geiger and Marsden made in their experiments

• Predicted the existence of the Neutron, which was later discovered.

What is an isotope?

Isotopes of an element are atoms with the same number of protons but different amount of neutrons. This means they have the same atomic numbers but different atomic masses

What is the change in nucleus for alpha and beta particles?

for Alpha, nucleus loses 2 protons and 2 neutrons

for Beta, a neutron in the nucleus turns into a proton

What is the particle emitted for alpha and beta particles?

for alpha, 2 protons and 2 neutrons are emitted as an alpha particle

An electron is created in the nucleus and instantly emitted for a beta particle

what is the equation for beta particles?

What is the equation for alpha radiation?

What are the properties of alpha radiation?

• stopped by paper and has a range of a few centimeters

• Consists of particles, each composed of two protons and two neutrons

• it has the greatest ionising power

What are the properties of beta radiation?

• stopped by a thin sheet of metal

• has a range of one metre in the air

• consists of fast-moving electrons emitted from the nucleus.

• It is less ionising than alpha radiation but more ionising than gamma radiation

What are the properties of gamma radiation

• Gamma is stopped by thick lead and has an unlimited range

• It consists of electromagnetic radiation

What can ionisation do to a cell?

Damage or kill the cell

What is the definition of the half life of a radioactive isotope?

The half life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve.

What is the count rate of a radioactive isotope?

The count rate is the number of counts per second.

What decreases by half every half life?

The number of atoms of a radioactive isotope and the count rate.

The count rate after n half lives =

the initial count rate/2