P7 Radioactivity

Question 1

What are the two types of radiation discovered by Ernest Rutherford?

Answer 1

Alpha radiation which was stopped by paper and beta radiation which went through paper.

Question 2

Why are some atoms radioactive and what does that cause?

Answer 2

It is because they have an unstable nucleus which becomes more stable by emitting alpha, beta or gamma radiation this is called decaying which is a random event that happens on its own.

Question 3

What did Rutherford’s results about alpha particles show?

Answer 3

They show most of the alpha particles passed straight through the metal foil, the number of deflections decreased as the angle increased and a very small number were deflected more than 90 degrees.

Question 4

What did the gold foil experiment tell him about the atom?

Answer 4

The nucleus is much smaller than the atom as most alpha particles passed through without deflection and where most of the mass of the atom is located.

Question 5

What is the plum pudding model?

Answer 5

Scientists knew that atoms contained electrons so they thought of the plum pudding model but Rutherford’s discovery disclosed that theory.

Question 6

What was Bohr’s model of the atom?

Answer 6

H said the electrons in an atom orbit the nucleus at specific distances and specific energy values or energy levels. This showed they can move to another orbit by absorbing electromagnetic radiation to move closer to the nucleus.

Question 7

What is the atomic number?

Answer 7

The amount of protons in the atom.

Question 8

What is the mass number?

Answer 8

The number of protons and neutrons in an atom.

Question 9

What is an isotope?

Answer 9

Atoms of the same element with different numbers of neutrons.

Question 10

What is radioactive decay?

Answer 10

An unstable nucleus becoming more stable by emitting an alpha or beta particle or by emitting a gamma ray.

Question 11

What happens when an unstable nucleus emits an alpha particle?

Answer 11

The atomic number goes down by 2 and the mass number goes down by 4. The mass and the charge of the nucleus are both reduced.

Question 12

What happens when an unstable nucleus emits a beta particle?

Answer 12

The atomic number of the nucleus goes up by 1 and its mass number is unchanged. The charge of the nucleus is increased and the mass of the nucleus is unchanged.

Question 13

What happens when an unstable nucleus emits a gamma ray?

Answer 13

It is uncharged and has no mass so it doesn’t change the number of protons and neutrons in a nucleus, so the mass and the charge of the nucleus are both unchanged.

Question 14

Why are neutrons emitted?

Answer 14

As a result of alpha particles colliding with unstable nuclei in the substance which causes the unstable nuclei to become more unstable and emit a neutron.

Question 15

What is emitted by an alpha particle?

Answer 15

2 protons and 2 neutrons

Question 16

What is emitted by a beta particle?

Answer 16

An electron is creased in the nucleus and immediately emitted.

Question 17

How do you measure count rate?

Answer 17

You need to measure the count rate without the radioactive source present which is the background radiation and then you measure the count rate with the source in place and subtract the background count rate from this giving you the count rate from the source alone.

Question 18

How far can an alpha particle travel in air and what stops it?

Answer 18

5cm in air and a thin sheet of paper.

Question 19

How far can a beta particle travel in air and what stops it?

Answer 19

About 1m and an aluminium sheet.

Question 20

How far can a gamma ray travel in air and what stops it?

Answer 20

Travels forever without being absorbed and a thick lead sheet.

Question 21

What are the dangers to reactivity?

Answer 21

It can knock electrons out of atoms, becoming charged because they lose electrons(ionisation). They can also contaminate other materials they come into contact with.

Question 22

How can workers reduce their exposure to ionising radiation?

Answer 22

Keeping as far as possible from the source of radiation, spending as little time as possible in risky areas and shielding yourself behind concrete barriers.

Question 23

How can alpha and beta particles be used?

Answer 23

Through the alpha particles being stopped by the smoke in a smoke alarm and the beta particles doing thickness monitoring in paper production where if it does not go through you make it thinner.

Question 24

What is the activity of radioactive source?

Answer 24

The number of unstable atoms in the source that decay per second. The unit for this is the Becquerel which is one decay per second

Question 25

What is a half life?

Answer 25

The average time it takes fort he number of nuclei of the isotope in a sample to halve and for the count rate in an isotope in a sample to fall to half its initial values.

Question 26

How are radioactive isotopes used in medicine?

Answer 26

Through medical imaging, treatment of cancer and as tracers to monitor organs.

Question 27

What determines how useful a radioactive isotope is?

Answer 27

The half life and the type of radiation it give out.

Question 28

What is nuclear fission?

Answer 28

A nucleus of an atom of a fissionable substance being struck by a neutron causing the nucleus to split into two smaller fragment nuclei of roughly equal size and releasing around 3 neutrons, meaning it is a chain reaction.

Question 29

What is a nuclear reactor like?

Answer 29

There is a chamber with uranium fuel rods spaced out in the core. The fission neutrons are slowed down by collisions with the water atoms so the neutrons don’t cause further fission. There are control rods to absorb surplus neutrons keeping the chain reaction under control. The water is heated and pumped through the core then it foes through the sealed pipes to and from a heat exchanger outside the core.

Question 30

What is nuclear fusion?

Answer 30

Two small nuclei release energy when they are fused together to form a single larger nucleus. Some of the mass is converted to energy which is transferred as nuclear radiation from the large nucleus that’s formed.

Question 31

What is background radiation?

Answer 31

The radiation caused by radon gas that seeps through the ground from radioactive substances in rocks deep underground.

Question 32

What is nuclear waste?

Answer 32

Used fuel rods are very hot and radioactive so they need to be in tanks of water for up to a year to cool them. The radioactive elements are removed and the waste can be stored in secure conditions for many years.

Question 33

What are some of the features new reactors could have?

Answer 33

A standard design to reduce costs and construction, a longer operating life, more safety features and much less effect on the environment.