P4

Question 1

What is the meaning of radioactive activity?

Answer 1

The number of unstable atoms that decay per second in a radioactive source

Question 2

What is alpha radiation?

Answer 2

Alpha particles (two protons and two neutrons) emitted by unstable nuclei. It’s the most ionising but least penetrating

Question 3

What can be used to stop alpha radiation?

Answer 3

A thin piece of paper

Question 4

What is the atomic number?

Answer 4

The number of protons in an atom (sometimes called the proton number)

Question 5

What is beta radiation?

Answer 5

A fast moving electrons emitted from unstable nuclei. It’s neither the most penetrating nor most ionising ray, and can be stopped by a sheet of aluminium

Question 6

What is the count rate and how is it measured?

Answer 6

The Geiger-Muller Tube. It’s the number of counts per second

Question 7

What is gamma radiation?

Answer 7

It’s an electromagnetic wave emitted from unstable nuclei in radioactive substances. It’s the most penetrating radiation and can be stopped by a thick wall of lead

Question 8

What is the half life of a substance?

Answer 8

The average time taken for the number of nuclei of the isotope (or the mass of the isotope) in a sample to halve

Question 9

What is ionisation?

Answer 9

Any process in which atoms become charged

Question 10

What does it mean for a substance to be irradiated?

Answer 10

Exposed to radiation but it doesn’t become radioactive

Question 11

What is the mass number of an atom?

Answer 11

The number of protons and neutrons

Question 12

What is a moderator?

Answer 12

The substance in a nucleus reactor that slows down fission neutrons

Question 13

What is nuclear fission?

Answer 13

Th process in which certain nuclei (U-235 and Pl-239) split into two fragments, releasing energy and two or three neutrons as a result

Question 14

What is a nuclear fission reactor?

Answer 14

Reactors that release energy steadily due to the fission of a suitable isotope, such as Uranium-235

Question 15

What is nuclear fusion?

Answer 15

The process where small nuclei are forced together to fuse and form a larger nucleus

Question 16

What is a reactor core?

Answer 16

The thick steel vessel used to contain fuel rods, control rods and the moderator in a nuclear fission reactor

Question 17

What is radioactive contamination?

Answer 17

The unwanted presence of materials containing radioactive atoms on other materials

Question 18

What s the use of alpha radiation?

Answer 18

Smoke detectors- they send alpha particles across a gap which ionises the air so there’s a current across the gap. Smoke absorbs the current so the alarm is triggered when there isn’t a current

Question 19

What are the uses of beta radiation?

Answer 19

Thickness monitoring- if the sheet doesn’t detect particles, it can tell you the right thickness of something
Leak detection- a radioactive tracer is added. If there is a leak, the count rate will increase

Question 20

What are the uses of gamma radiation?

Answer 20

Irradiating food- cobalt-60 is a gamma emitter that is used to sterilises food because it kills the bacteria on it

Question 21

What does it mean for something to be ionising?

Answer 21

It’s got an ability to create ions

Question 22

What does it mean for something to be penetrating?

Answer 22

The ability for radiation to pass through substances

Question 23

What are fuel rods made out of and why?

Answer 23

Made up of 2-3% of U-235. This ensures that there isn’t too many chain reactions

Question 24

What is a chain reaction?

Answer 24

The process of neutrons emitted from fission reactions being absorbed by larger, more unstable nuclei which results in more fission

Question 25

What is background radiation?

Answer 25

Radiation that is found in small quantities all around us and originates from natural sources such as rocks and cosmic rays, as well as from man-made sources such as nuclear weapons testing and accidents.

Question 26

What are nuclear explosions?

Answer 26

Uncontrolled chain reactions, meaning large amounts of energy are produced in short periods of time

Question 27

What is spontaneous fission?

Answer 27

The occurrence of nuclear fission without a neutron. It’s very rare

Question 28

What are moderators and constant in a nuclear reactor?

Answer 28

Water or graphite- it slows down the neutrons for a successful fission reaction because it must be moving at the right pace for fission to occur

Question 29

What do control rods do?

Answer 29

They absorb neutrons and are made of boron or cadmium. They can also be moved up and down- if lifted up, it speeds up the reaction due to less neutrons being absorbed and vice versa (lowered down to slow down reactions due to more neutrons being absorbed)

Question 30

What are the uses of nuclear radiation in medicine?

Answer 30

Medical tracers and radiotherapy

Question 31

Why is it important that the tracers and isotopes used in medicine have short half lives?

Answer 31

Tracers- so they only emit radiation for a short period and can stop being harmful
Isotopes- so they don’t emit radiation for too long

Question 32

Why is it important that the tracers and isotopes used in medicine have short half lives?

Answer 32

Tracers- so they only emit radiation for a short period and can stop being harmful
Isotopes- so they don’t emit radiation for too long

Question 33

Can radioactive decay be predicted?

Answer 33

No, it’s a completely random process