Radioactive Substances

Question 1

What do radioactive substance emit?

Answer 1

They emit radiation from the nuclei of their atoms all the time. These nuclear radiations can be very useful but may also be very dangerous

Question 2

What does the use of radioactive substances depend on?

Answer 2

It depends on their penetrating power and half-life

Question 3

What is the basic structure of an atom?

Answer 3

a small central nucleus composed of protons and neutrons surrounded by electrons

Question 4

What is the mass and charge of a proton?

Answer 4

mass = 1
charge = +

Question 5

What is the mass and charge of a neutron?

Answer 5

mass = 1
charge = neutral

Question 6

What is the mass and charge of an electron?

Answer 6

mass = very small (0)
charge =  -

Question 7

Why does an atom not have an overall electric charge?

Answer 7

Because the number of electrons is equal to the number of protons in the nucleus

Question 8

What are ions?

Answer 8

When atoms gain or lose electron to from a charged particles

Question 9

Describe the atoms of an element?

Answer 9

They always have the same number of protons, but have different numbers of neutrons for each isotope

Question 10

What is the atomic number?

Answer 10

The total number of protons in an atom

Question 11

What is the mass number?

Answer 11

It is the total number of protons and neutrons in an atom

Question 12

What are radioactive substances?

Answer 12

Some substances give out radiation from the nuclei of their atoms all the times, whatever is done to them.

Question 13

What are some origins of background radiation?

Answer 13

Rocks (graphite)
the ground
the fallout from nuclear weapons test
nuclear accidents

Question 14

Describe the structure of an alpha particle

Answer 14

neutrons = 2
protons = 2
(same as helium)

Question 15

Describe the structure of a beta particle

Answer 15

It has an electron from the nucleus

It is a fast moving electron

Question 16

What is a gamma particle

Answer 16

it is an electromagnetic radiation

Question 17

When an unstable nucleus decays, there are three ways that it can do so.What may it give out?

Answer 17

an alpha particle
a beta particle
a gamma ray

Question 18

Radon decays into polonium when it emits an alpha particle. Here is the equation:
219              215
    Rn ------>       Po     +    
86                  84
Finish of the equation

Answer 18

4
H
2

Question 19

Carbon-14 is a radioactive isotope of carbon.  Here is the equation for the beta decay of carbon-14 into nitrogen.
14                    14
  C  ---------->      N   +
6                      7
Finish the euqation

Answer 19

0 -
e
-1

Question 20

Alpha radiation:

Answer 20

Alpha particles are relatively slow and heavy.
They have a low penetrating power - you can stop them with just a sheet of paper.
Because they have a large charge, alpha particles ionise other atoms strongly.

Question 21

Beta radiation:

Answer 21

They are fast, and light.
Beta particles have a medium penetrating power - they are stopped by a sheet of aluminium or plastics such as perspex.
Beta particles ionise atoms that they pass, but not as strongly as alpha particles do.

Question 22

Gamma radiation:

Answer 22

Gamma rays are waves, not particles.
This means that they have no mass and no charge.
Gamma rays have a high penetrating power - it takes a thick sheet of metal such as lead, or concrete to reduce them significantly.
Gamma rays do not directly ionise other atoms, although they may cause atoms to emit other particles which will then cause ionisation.
We don’t find pure gamma sources - gamma rays are emitted alongside alpha or beta particles. Strictly speaking, gamma emission isn’t ‘radioactive decay’ because it doesn’t change the state of the nucleus, it just carries away some energy.

Question 23

What can both alpha and beta radiations do which gamma radiation cannot?

Answer 23

They are deflected by both electric and magnetic fields. Alph particles deflected less than beta particles and in the opposite direction

Question 24

What are the uses of nuclear radiations?

Answer 24

smoke detectors
sterilising
cancer treatment
Radioactive tracers

Question 25

How do smoke detectors work?

Answer 25

Smoke alarms contain a weak source made of Americium-241.
Alpha particles are emitted from here, which ionise the air, so that the air conducts electricity and a small current flows.
If smoke enters the alarm, this absorbs the a particles, the current reduces, and the alarm sounds.
Am-241 has a half-life of 460 years.

Question 26

How does sterilising work?

Answer 26

Even after it has been packaged, gamma rays can be used to kill bacteria, mould and insects in food. This process prolongs the shelf-life of the food, but sometimes changes the taste.
Gamma rays are also used to sterilise hospital equipment, especially plastic syringes that would be damaged if heated.

Question 27

How does cancer treatment work?

Answer 27

Because Gamma rays can kill living cells, they are used to kill cancer cells without having to resort to difficult surgery. This is called “Radiotherapy”, and works because cancer cells can’t repair themselves when damaged by gamma rays, as healthy cells can.
It’s vital to get the dose correct - too much and you’ll damage too many healthy cells, too little and you won’t stop the cancer from spreading in time.

Question 28

How do radioactive tracers work?

Answer 28

The most common tracer is called Technetium-99 and is very safe because it only emits gamma rays and doesn’t cause much ionisation.
Radioisotopes can be used for medical purposes, such as checking for a blocked kidney.
To do this a small amount of Iodine-123 is injected into the patient, after 5 minutes 2 Geiger counters are placed over the kidneys.
Also radioisotopes are used in industry, to detect leaking pipes. To do this, a small amount is injected into the pipe. It is then detected with a GM counter above ground.

Question 29

What are the problems with using nuclear radiation?

Answer 29

are all ionising radiations which can damage living cells.
Some cancers are easier to treat with radiotherapy than others - it’s not too difficult to aim gamma rays at a breast tumour, but for lung cancer it’s much harder to avoid damaging healthy cells. Also, lungs are more easily damaged by gamma rays, therefore other treatments may be used.

Question 30

What happens in ionisation?

Answer 30

Ionising radiation can break molecules into smaller fragments. These charged particles are called ions. Ions can then take part in other chemical reactions in the living cells. As a result, ionising radiation damages substances and materials, including those in the cells of living things. The ions themselves can take part in chemical reactions, spreading the damage. This may result in the living cells dying or becoming cancerous. Radiation can also affect DNA, causing mutations.

Question 31

Give example of radiations which cause ionisation

Answer 31

Ultraviolet radiation, which is found in sunlight
X-rays, which are used in medical imaging machines
Gamma rays, which are produced by some radioactive material

Question 32

What is the half-life of a radioactive isotope?

Answer 32

It is the average time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate from a sample containing the isotope to fall to half its initial level