Radioactivity

Question 1

State 4 sources of background radiation.

Answer 1

1. Naturally occurring radon gas
2. Nuclear fallout from weapons testing and nuclear accidents.
3. Radioactive rocks and soil.
4. Cosmic rays.

Question 2

State the key features of an N/Z plot.

Answer 2

1. Line of stability is linear up to (20,20)
2. It then curves up to (80,120)
3. The region of alpha decay is only after proton number 60.

Question 3

The decay of unstable nuclei is random. What does this is mean?

Answer 3

1. There is an equal probability of any nucleus decaying.
2. The rate of decay is unaffected by the surrounding conditions.
3. It cannot be known at which time a particular nucleus will decay.

Question 4

What is the decay constant?

Answer 4

The probability of a particular isotope decaying each second.

Question 5

Define half life.

Answer 5

The time taken for half the nuclei of a particular isotope to decay from an initial value. It’s also the time taken for the activity of a particular isotope to half from an initial value.

Question 6

What conclusions about the structure of the atom can be drawn from Rutherford’s gold foil scattering experiment?

Answer 6

1. The positively charged part must occupy a very small volume at the centre.
2. Most of an atom is empty space.
3. Electrons must lie outside of the nucleus.

Question 7

Why can’t alpha particles be used to measure the exact size of the nucleus?

Answer 7

1. The strong force acting between them and the nucleus complicates the results.
2. Scattering is produced by the distribution of protons, not the whole nucleon distribution.
3. Alpha particles are relatively massive, so they cause significant nuclear recoil, which complicates results.

Question 8

What’s electron scattering?

Answer 8

A high energy electron, acting as a de Broglie wave, is diffracted by the nucleus, which allows the nuclear radius and density to be calculated.

Question 9

State 3 advantages of electron scattering over alpha scattering.

Answer 9

1. Electrons don’t feel the strong force, so their scattering pattern is easier to interpret.
2. Electrons give greater resolution, because they get closer to the nucleus.
3. Electrons produce much less recoil, as they are less massive.

Question 10

Define binding energy.

Answer 10

The energy required to separate a nucleus up into its constituent nucleons.

Question 11

What’s a mass defect?

Answer 11

The difference in mass between the mass of a nucleus and its constituent nucleons.

Question 12

If given atomic mass…

Answer 12

Take away electron mass to get the nuclear mass.

Question 13

Define the atomic mass unit.

Answer 13

One twelfth of the mass of an atom of C-12.

Question 14

Energy is released when…

Answer 14

The binding energy per nucleon increases.