P4 - Atomic Structure And Radiation

Question 1

Define radioactive decay

Question 2

Define activity

Answer 2

Activity is the rate at which a source of unstable nuclei decays

Question 3

What is activity measured in?

Answer 3

Activity is measured in becquerel (Bq)

Question 4

Define count-rate

Answer 4

Count-rate is the number of decays recorded each second by a detector such as a Geiger-Muller tube

Question 5

What types of nuclear radiation may be emitted?

Answer 5

An alpha particle
A beta particle
A gamma ray
A neutron

Question 6

What is an alpha particle composed of?

Answer 6

Two neutrons and two protons; same as a helium nucleus

Question 7

What does a beta particle consist of?

Answer 7

A high speed electron ejected from the nucleus as a neutron turns into a proton

Question 8

An unstable nucleus becomes more stable by…

Answer 8

Emitting an alpha or beta particle, or a gamma ray

Question 9

What is a gamma ray composed of?

Answer 9

Electromagnetic radiation from the nucleus

Question 10

Students should be able to apply their knowledge to the uses of radiation and evaluate the best sources for given situations

Question 11

Explain why the emission of a gamma ray is different to an alpha and beta particle

Answer 11

Gamma ray is uncharged and has no mass
So its emission does not change the number of protons or neutrons in a nucleus
So the mass and the charge of the nucleus are unchanged

Question 12

Compare the changes in the nucleus and particles emitted in alpha and beta decay

Answer 12

In alpha decay, the nucleus loses 2 protons and 2 neutrons, whereas in beta decay, a neutron in the nucleus changes into a proton

In alpha decay, 2 protons and 2 neutrons are emitted as an alpha particle, whereas in beta decay, an electron is created in the nucleus and instantly emitted

Question 13

Alpha decay causes ____ the mass and charge of the nucleus to ____

Answer 13

Both
Decrease

Question 14

Beta decay does not cause the mass of the nucleus to ___ but does cause the charge of the nucleus to ___

Answer 14

Change
Increase

Question 15

Describe, in quantitative terms, what happens when an unstable nucleus emits an alpha and beta particle

Answer 15

Alpha: atomic number decreases by 2 and mass number decreases by 4
Beta: atomic number increases by 1 and mass number is unchanged (because a neutron changes into a proton)

Question 16

Describe a method for to determine background radiation and specific radiation emitted by a radioactive source

Answer 16

Measure the count rate without the radioactive source present. This is the background count rate

Measure the count rate with the source in place

Subtract both of these measurements to get the count rate from the source alone

Question 17

Describe a method to test the range that each type of radiation travels in air

Answer 17

Move the Geiger tube away from the source in a sealed container
When the tube is far enough away from the source so that it’s no longer detecting any radiation, the count rate from the source will fall to 0

Question 18

Describe a method to test the absorption of each type of radiation

Answer 18

Place different materials between a Geiger tube and a radioactive source in a sealed container

Add more layers of material until the count rate from the source is 0. This is when the radiation from the source has been stopped by the absorber material

Question 19

Compare the penetrating power, range in air and ionising power of each radiation source

Answer 19

Alpha particles has a range of 5cm, beta particles have a range of 1m and gamma rays have unlimited range in air because they spread out without being absorbed

Alpha particles are absorbed by a thin sheet of paper, beta by an aluminium or lead sheet and gamma by thick lead sheet or concrete

Alpha particles have the greatest ionising power and gamma rays have the weakest

Question 20

Define radioactive contamination

Answer 20

Contamination is the unwanted presence of materials containing radioactive atoms on other materials . The hazard is due to the decay of the contaminating atoms and this depends on the type of radiation emitted (higher ionisation emissions are more hazardous)

Question 21

Define irradiation (compare with radioactive contamination)

Answer 21

Irradiation is the process of exposing an object to nuclear, ionising radiation such as x-rays or gamma rays. The irritated object does not become radioactive

Question 22

Compare the hazards associated with contamination and irritation

Question 23

Describe the process of ionisation

Answer 23

The radiation from a radioactive substance can knock electrons out of atoms. The atoms become charged because they lose electrons.

Question 24

Suggest suitable precautions that should be taken to protect against any hazard that the radioactive source used in the process of irradiation may present

Answer 24

Keeping as far away as possible from the source of radiation by using special handling tools with long handles

Spending little time in high risk areas

Shielding themselves by staying behind thick concrete barriers or using thick lead plates

Question 25

Why is peer review important?

Answer 25

It is important that the findings of studies into the effects of radiation on humans are published and shared with other scientists so that they can be checked by peer review

Question 26

Why is ionisation damaging?

Question 27

What is the half life of a radioactive isotope?

Answer 27

Time it takes for the number of nuclei of the isotope to halve

OR

Time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level

Question 28

Students should be able to explain the concept of half life and how it is related to the random nature of radioactive decay

Question 29

What is the formula to calculate the net decline, expressed as a ratio, in a radioactive emission after a given number of half lives?

Answer 29

The count rate after n half-lives = initial count rate / 2^n

Question 30

A Geiger counter clicks even without a radioactive source near it. Suggest why this is

Answer 30

Background radiation

Question 31

Define background radiation

Answer 31

The constant low-level ionising radiation present in the environment.

The level and radiation dose may be affected by occupation and location

Question 32

Where does background radiation come from?

Answer 32

Natural sources such as rocks and cosmic rays in space due to radon gas
Man-made sources such as the fallout from nuclear weapons testing and nuclear accidents

Question 33

What is radiation dose measured in?

Answer 33

Sieverts (Sv)

Question 34

1 sievert = ?

Answer 34

1 Sv = 1000 mSv

Question 35

Isotopes with the shortest half-lives have the most _______ _______, so they emit a lot of radiation in a ____ time

Answer 35

Unstable nuclei
Short

Question 36

What does the effect of radiation on living cells depend on?

Answer 36

Type and amount of radiation received (dose)
Whether the source is inside or outside the body
How long the cells are exposed to the radiation

Smaller doses pose less risk, but the risk is never 0 due to background radiation

Question 37

As the activity of a radioactive source _____, the rate it gives out radiation decreases. This means hazards decrease with time according to the half-lives of their isotopes

Answer 37

Decreases

Question 38

Compare the use of alpha radiation inside and outside of the body

Answer 38

Inside: dangerous as affects all surrounding tissue. High ionisation can damage cells and cause mutations in DNA. They also can stay in the body for a long time, irradiating cells and increasing cancer development

Outside: some danger as they are absorbed by skin and this can cause localised radiation burns and damage retinal cells. However, they have low penetrating power. Still, they can be inhaled and the effects are described above.

Question 39

Why is gamma and beta radiation not commonly used inside and outside of the body?

Answer 39

Very dangerous in both cases because:

• High penetration power and range, so they can penetrate tissues and organs, however with less ionising intensity compared to alpha radiation

Question 40

What are nuclear radiations used for in medicine?

Answer 40

Exploration of internal organs
Control or destruction of unwanted tissue

Question 41

How are radioactive tracers used in medicine?

Why is radioactive iodine used to test if a patient’s kidney is blocked?

Answer 41

Traces the flow of a substance through the organ. It contains a radioactive isotope that emits gamma radiation as it can be detected outside the system

Half life of 8 days, so it lasts enough for the test to be done. It can be detected outside of the body and it decays into a stable product

Question 42

How are gamma cameras used in medicine?

Why is a gamma emitter used only?

Answer 42

Used to take images of internal body organs. Before an image is taken, a patient is injected with a solution that contains a gamma-emitting radioactive isotope. The solution is then absorbed by the organ and nearby gamma cameras detects the radiation emitted

It must have a half life long enough to give a useful image, but short enough to decay into a stable product after the image is taken

Question 43

How is gamma radiation in a narrow beam used?

Answer 43

Used to destroy cancerous tumours. Gamma is used because it can penetrate deeper into the body

Question 44

How are radioactive implants used in medicine?

Answer 44

Destroy cancer cells in some tumours. Permanent implants use isotopes with half lives long enough to irradiate the tumour over a given time, but short enough so that most of the unstable nuclei will decay soon afterwards