radioactivity

Question 1

what is a becquerel

Answer 1

an activity of one nucleus decaying per second, to measure radioactivity

Question 2

atomic number

Answer 2

number of protons in a nucleus

Question 3

mass number

Answer 3

number of protons and neutrons in a nucleus

Question 4

isotope

Answer 4

an element with the same number of protons but different number of neutrons

Question 5

what are the three types of radiation?

Answer 5

alpha, beta, gamma

Question 6

what are alpha, beta and gamma?

Answer 6

ionising radiation emitted from an unstable nuclei

Question 7

alpha

Answer 7

Helium nucleus (no electrons)
charge of 2+
easily stopped by paper, only travel a few cm
very ionising

Question 7

beta

Answer 7

an electron, almost no mass
charge of -1
medium penetration and ionisation, stopped by a sheet of aluminium
formed when there are too many neutrons, so one turns into a proton and an electron; the proton remains in the nucleus, whilst the electron is ejected energetically.

Question 8

gamma

Answer 8

waves of electromagnetic radiation
no mass/charge
often emitted after beta or alpha
high penetration and low ionisation, stopped by lead

Question 9

describe an experiment to test the penetration power of different radiation

Answer 9

Detect using a Geiger Müller Tube.
Try the three different materials in order, paper then aluminium then lead.
Count rate will significantly decrease if radiation is stopped.

Question 10

alpha radiation effect on nucleus

Answer 10

2 protons and 2 neutrons are lost.
mass number decreases by 4
atomic number decreases by 2

Question 11

beta radiation affect on nucleus

Answer 11

1 neutron converted to an electron and proton
mass number unchanged
atomic number increases by one

Question 12

gamma radiation effect on nucleus

Answer 12

Energy is lost from an atom in the form of an electromagnetic wave
Mass number is unchanged
Atomic number is unchanged

Question 13

neutron radiation effect on nucleus (?)

Answer 13

if there are too many neutrons, one is emitted
mass number decreases by one
atomic number is unchanged

Question 14

how do you measure radiation?

Answer 14

a geiger muller tube detects ionising radiations

Question 15

sources of background radiation

Answer 15

radon in air
food and drink
rocks
cosmic rays
medical equipment

Question 16

what happens to the activity of a radioactive source

Answer 16

it decreases over time

Question 17

what is half life?

Answer 17

either: overall rate of decay of all the isotopes in the sample
or: time taken for the number of radioactive nuclei in a sample to halve (better)
varies with the isotope

Question 18

use of radiation

Answer 18

Smoke detectors (alarms)
Monitoring the thickness of materials
Medical procedures including diagnosis and treatment of cancer
Sterilising food (irradiating food)
Sterilising medical equipment
Determining the age of ancient artefacts

Question 19

how does a smoke detector work?

Answer 19

alpha particles are used within the detector.
they normally ionise the air inside the detector, creating a current.
the alpha particles are blocked when the smoke enters and absorbs the alpha particles, stopping the current
the alarm is triggered by a microchip when it sense no more alpha radiation.

Question 20

how do we measure the thickness of materials using radiation?

Answer 20

beta radiation is usually partially absorbed by materials such as aluminium and paper, but not fully.
the amount of beta particles penetrating the material can be measured by a radiation detector, allowing us to monitor the thickness and keep it consistent.
if the material is thicker, more particles are absorbed, and the count rate decreases (vice versa).
if alpha was used, almost all particles would be absorbed. if gamma was used, almost all radiation would penetrate.

Question 21

how can we use radiation to diagnose cancer?

Answer 21

a tracer is a radioactive isotope that can be used top detect the movement of substances, like blood, around the body.
a PET scan can detect emissions from the tracer to diagnose cancer and determine the location of a tumour.

Question 22

how can we use radiation to treat cancer?

Answer 22

with radiotherapy.
although radiation causes cancer, ionising radiation can kill living cells so is very effective at treating cancer. bacteria and cancer cells are more susceptible to radiation than other cells.
beam of gamma rays are directed at the tumour (because they can penetrate the body and reach the cancer). the beams are moved around to minimise concentrated exposure.

Question 23

how can we use radiation to sterilise food and medical equipment?

Answer 23

gamma radiation is used because it is the most penetrating, so can reach al sides of the instrument, inside the packaging.
Food can be irradiated in order to kill any microorganisms that are present on it
This makes the food last longer and reduces the risk of food-borne infections

Question 24

irradiation

Answer 24

the process of exposing a material to ionising radiation

Question 25

contamination

Answer 25

The accidental transfer of a radioactive substance onto or into a material. this means the material becomes radioactive.

Question 26

dangers of radiation

Answer 26

causes mutations in living organisms radiation damages skin cells and tissue, especially if ingested. alpha is the most ionising so most harmful if ingested. gamma is the most penetrative so most harmful form outside.

Question 27

how to minimise the risks of radiation

Answer 27

minismise contamination: - keep radioactive sources in a shielded container (eg lead linen) - wear gloves and use tongs - wear protective clothing - limit the time minimise irradiation: - measure dosage and exposure

Question 28

nuclear waste

Answer 28

alpha: nuclear waste stored in plastic or metal beta: nuclear waste stored in metal or concrete silos gamma: nuclear waste stored in thick concrete or lead-linen silos can emit radiation for many years can be stored underground, big environmental consequences

Question 29

what types of reactions release nuclear energy?

Answer 29

radioactive decay, fission and fusion

Question 30

process of fission

Answer 30

use uranium-235 a neutron is absorbed by the nucleus, mailing it unstable. this causes the uranium-235 top split apart into 2 daughter nuclei and 3 neutrons. involves sudden release of heat and radiation. this releases kinetic energy, which is transferred to thermal energy store to produce steam and turn a turbine.

Question 31

chain reaction

Answer 31

when the number of neutrons isn't controlled, so the fission continues unregulated.

Question 32

control rods

Answer 32

control rods, usually boron, absorb most of the neutrons to keep the fission reactions under control and prevent an explosion/ limit the rate of fusion.

Question 33

moderator

Answer 33

moderator, usually water, slows down the emitted neutron so it can be absorbed by the nucleus.

Question 34

shielding

Answer 34

the high energy neutrons and gamma rays are highly penetrating, so shielding (usually thick concrete) is used to absorb the radiation.

Question 35

fusion vs fission

Answer 35

fission splits a nucleus apart, fusion fuses two light nuclei together.

Question 36

fusion

Answer 36

the creation of a larger nuclei from two separate, smaller, lighter nuclei. the larger nuclei has a smaller mass than both lighter nuclei, so some of the mass is converted to energy. source of energy for stars.

Question 37

conditions for nuclear fusion

Answer 37

really high pressures and temperatures. because the positively charged nuclei need to get very close to fuse, so need to move very fast to overcome the strong forces of electro-static repulsion. makes this expensive.