P2 - Atoms & Radiation

Question 0

What are the masses and charges of protons, neutrons and electrons?

Answer 0

Protons have a mass of 1 and a charge of +1

Neutrons have a mass of 1 and no charge (0)

Electrons have a mass of 1/2000 and a charge of -1

Question 1

Describe how the theory of atoms developed over time

Answer 1

Dalton thought that each element was made of a different type of atom and that atoms couldn’t be broken up

100 years later, Thomson discovered that electrons could be removed from atoms and suggested that atoms were spheres of positive charge with tiny negative electrons stuck in them (plum pudding theory)

10 years later, Rutherford and Marsden fired a beam of alpha particles at thin gold foil and expected that the positively charged alpha particles would be deflected by the electrons in the plum pudding model

However, most of the particles went straight through but a few came straight back at them

From this, they suggested the atomic model we use today

Question 2

What are isotopes?

Answer 2

Isotopes are variants of atoms that have the same number of protons and electrons but a different number of neutrons

Question 3

What do isotopes tend to do?

Answer 3

They are usually radioactive which means that they decay into other elements and give out radiation

Question 4

What is interesting about radioactivity?

Answer 4

It is completely random when radiation is emitted and it isn’t affected by any physical conditions like temperature etc.

Question 5

Describe the relative proportions of background radiation

Answer 5

51% radon gas

14% rocks and building materials

12% food

12% medical X-rays

10% cosmic rays

1% nuclear industry

Question 6

What does it mean if something is ionising and what affects this?

Answer 6

It is a measure of how much they can bash into atoms and knock electrons off them creating ions

Particles are more ionising if they are larger because they are more likely to hit atoms and ionise them

Question 7

What does it mean if something has high penetrating power and what affects this?

Answer 7

It can penetrate further through materials

Smaller particles penetrate further because they don’t hit as many atoms etc.

Question 8

What are the 3 types of radiation?

Answer 8

Alpha particles

Beta particles

Gamma radiation

Question 9

What is an alpha particle?

Answer 9

2 protons and 2 neutrons which is the same as a helium nucleus

+2 charge

Question 10

What are the properties of alpha radiation?

Answer 10

Relatively large and heavy and slow moving

Low penetration power and high ionising ability

Question 11

What are beta particles?

Answer 11

Simply an electron with virtually no mass and a -1 charge

Question 12

What are the properties of beta radiation?

Answer 12

Quite fast and quite small so they penetrate and ionise moderately

Question 13

What happens when beta particles are emitted?

Answer 13

A neutron turns into a proton in the nucleus

Question 14

What are gamma rays?

Answer 14

They are high frequency electromagnetic waves that have no charge or mass

Question 15

What are the properties of gamma radiation?

Answer 15

Weakly ionising and a high penetration power

Question 16

How do you do calculations for alpha decay?

Answer 16

Example:

238 234 4
U –> Th + He
92 90 2

Question 17

How do you do calculations for beta decay?

Answer 17

Example:

14 14 0
C –> N + e
6 7 -1

Question 18

How do you do calculations for gamma radiation?

Answer 18

Nothing changes because gamma rays have no mass or charge

Question 19

How are the 3 types of radiation deflected by electric and magnetic fields?

Answer 19

Alpha and beta particles are deflected in opposite directions because alpha is positive and beta is negative

Gamma doesn’t have a charge so the fields don’t affect it

Question 20

What are the 5 locations / occupations that give a larger radiation dose?

Answer 20

Underground rocks can cause higher levels at the surface especially if they release radon gas which gets trapped in houses

Nuclear industry workers need to wear protective clothing and face masks to stop them touching or inhaling radioactive material

Radiographers in hospitals wear lead aprons and stand behind lead screens

At high altitudes, you are at higher risk of cancer because of cosmic rays (problem for pilots)

Miners have an increased risk because of the rocks underground that are all around them

Question 21

How does the number of decays per second change as a radioactive sample gets older?

Answer 21

It decreases

Question 22

Why do we use half-life to measure how quickly the activity drops?

Answer 22

Because the activity never actually reaches zero

Question 23

What is half-life?

Answer 23

The average time is takes for the number of nuclei in a radioactive sample to halve

Question 24

What is the activity of a radioactive sample measured in?

Answer 24

Bequerels

Counts per minute

Etc.

Question 25

How do you calculate the half-life of a sample in the exam?

Answer 25

Example:

The activity of a sample has gone from 640 to 80 cpm in 2 hours. Calculate the half life

Initial - 640

After one - 320

After two - 160

After three - 80

So 2 hours is 3 half-lives meaning that a half-life is 40 minutes

Question 26

How do you calculate the half-life of a sample from an activity / time graph?

Answer 26

Look at the initial activity

Half it

Go across from the “half activity” until you touch the curve

Then go down and the time that you get to is the half-life

Question 27

What are the 4 main uses of radiation?

Answer 27

Smoke detectors

Tracers in medicine

Radiotherapy

Sterilisation of food and medical instruments

Question 28

How do smoke detectors use radiation?

Answer 28

A weak source of alpha radiation is placed in the detector close to 2 electrodes

The source causes ionisation which causes a current between the electrodes

If smoke absorbs the radiation, the current stops and the alarm sounds

Question 29

How is radiation used for tracers in medicine?

Answer 29

Some isotopes can be injected into the body and their progress can be monitored by an external detector

The injected sample must be beta or gamma so that the radiation passes out of the body and the half-life should be short so that the patient isn’t exposed to radiation for too long

Question 30

How does radiotherapy work?

Answer 30

Gamma rays kill at living cells so they can be used to kill cancerous cells

The rays have to be directed carefully and at just the right dosage to kill the cancer without damaging the normal cells too much

Question 31

How is sterilisation of food and medical equipment done with radiation?

Answer 31

Gamma rays can be used to kill microbes on food and medical instruments

Question 32

What is the advantage of using gamma rays to sterilise medical equipment?

Answer 32

The high temperatures of boiling are not needed

Question 33

Describe how radiation causes cancer

Answer 33

All types of radiation enter living cells and ionises or destroys them

This causes mutated cells to divide uncontrollably and cause cancer

Question 34

Which are the most dangerous types of radiation that cause cancer?

Answer 34

Beta and gamma are the most dangerous outside the body because they are the most likely to penetrate the body

Alpha is the most dangerous inside the body because the radiation doesn’t penetrate out of the body

Question 35

What are the 5 safety measures to do with radioactivity?

Answer 35

Use radioactive sources for a short time as possible to keep exposure time down

Use tongs (never allow skin contact with a source)

Hold source at arm’s length to keep down the amount of radiation that hits you

Keep source pointing away from you and avoid looking directly at it

For larger operations, use lead aprons, screens etc. as a protective measure because it stops all types of radiation although a lot is needed to stop gamma