Radioactivity and Particles

What is the top number in a decay equation

Number of nucleons (protons + neutrons)

What is the bottom number in a decay equation

Number of protons

Do electrons count towards the mass number

No - negligible mass

What are isotopes

Atoms with the same number of protons but a different number of neutrons

What are alpha particles

Helium nucleus

What is the top number of an alpha particle

4

What is the bottom number of an alpha particle

2

What is radioactive decay

Spontaneous transformation of an unstable nucleus into a more stable one by release of radiation

Can you predict when radioactive decay will occur?

No - random process

How many protons in an alpha particle

2 protons because it’s helium

Mass number of an alpha particle

mass number 4

What kind of nuclei undergo alpha decay

heavy, unstable ones

What happens to a nucleus after emitting an alpha particle

Changes to a different element - loses 2 protons and 2 neutrons

What is beta decay

Neutron turns into proton and emits beta particle

What is alpha decay

Heavy nucleus emits alpha particle

What is a beta particle

a high-speed electron

What is the top number of a beta particle

0

what is the bottom number of a beta particle

-1 because it’s the overall charge

what happens to a nucleus after beta decay

gains a proton; loses a neutron

what happens to the bottom number after beta decay

+1 because it gained a proton

what happens to the top number after beta decay

stays the same

order the types of radioactive radiation from least to most ionising

gamma, beta, alpha

order the types of radioactive radiation from least to most penetrating

alpha - beta - gamma

what can alpha particles be stopped with

a sheet of paper

what can beta particles be stopped with

a thin sheet of aluminium

what can gamma particles be stopped with

thick piece of lead

what are gamma particles

form of electromagnetic radiation

what happens to the nucleus after gamma decay

literally nothing

how can you define alpha particles, beta particles and gamma rays

ionising radiations emitted from unstable nuclei in a random process

What do you need to investigate penetration powers of different types of radiation

geiger muller tube ; sources of radiation ; paper, aluminium and lead

How would you determine whether a kind of radiation has passed through a material

detect activity using geiger muller tube ; count rate significantly decreases if radiation stopped

what do you use to detect ionising radiations

geiger-muller tube or photographic film

sources of background radiation from earth (4 things)

radon gas from rocks and buildings, food and drink, medical settings, nuclear power/weapons waste

why is carbon-14 more unstable than carbon-12

it has 2 extra neutrons

what unit is used to measure radioactivity

becquerel (Bq)

how do you define 1 becquerel

1 decay per second

if a geiger-muller tube counted 240 in 1 minute, what is the count rate

240 / 60 = 4 decays p/s = 4 becquerels

how can food be a source of background radiation

can contain radioactive isotopes e.g. carbon-14

how are cosmic rays from space a source of background radiation

sun emits a lot of protons which enter the earth’s atmosphere at high speeds, colliding with molecules in the air to produce gamma radiation

what is the largest source of background radiation

radon gas

where is radon gas released from

rocks in the ground; building materials e.g. stone and brick

how is nuclear radiation released from medical settings

x-rays, ct scans, radioactive tracers, radiation therapy all use radiation

how is background radiation accounted for in experiments

take readings with no radioactive source present and then subtract this from readings with the source

name 3 uses of radioactivity

smoke alarms; diagnosis and treatment of cancer; sterilising food and medical equipment

which kind of radioactivity is used in smoke detectors

alpha particles

how does a smoke alarm work

the alpha radiation normally ionises the air within the detector, creating a current. the alpha emitter is blocked when smoke enters. the sensor no longer detects a current and triggers the alarm.

what happens when smoke enters a smoke detector

the alpha particles are absorbed so the current is stopped

what is beta radiation used for

detecting thickness of materials such as paper, cardboard or aluminium foil

why is beta radiation used to measure the thickness of thin materials

it is only partially absorbed

how are gamma rays used in treatment of cancer

gamma rays are directed at cancerous cells and can kill them

why are gamma rays used in radiotherapy, even though they can cause cancer?

they can penetrate the body and reach the tumour

what is a tracer

a radioactive isotope that can be used to track the movement of substances like blood around the body

how are tracers used in medicine

PET scan detects emissions from tracer to diagnose cancer and determine location of tumour

what kind of radiation do tracers give off

gamma rays

what needs to be taken into consideration when picking an isotope to be a tracer

must have long enough half-life to have time to perform the scan; must by short enough that it will not linger in the body and prolong exposure to radiation

why is gamma radiation used to sterilise medical equipment

penetrating enough to irradiate all sides of instruments; can be sterilised without removing packaging

how would you sterilise food/medical equipment?

irradiate with gamma rays

why is food sterilised

kill microorganisms; food lasts longer; reduces risk of food-borne infections

why is alpha radiation used in smoke detectors

beta and gamma would not be absorbed by smoke so the alarm would not be triggered

what is contamination?

the accidental transfer of a radioactive substance onto or into a material

what makes a substance radioactive?

it contains a source of ionising radiation

example of contamination

radiation leak

does contaminating something make it radioactive and why

yes because small amounts of the isotope in contaminated areas will emit radiation

does irradiating something make it radioactive and why

no because the source is not in/on the substance

what is irradiation

the process of exposing a material to ionising radiation

example of irradiation

sterilisation of food or medical equipment

danger of radiation (both irradiation and contamination)

can mutate dna in cells and cause cancer; can damage living cells and tissues

contamination example in human

inhalation of radioactive gas / ingesting contaminated food

how to protect a person from irradiation

shielding e.g. lead-lined clothing

how to protect a person from contamination

airtight suit to prevent radioactive atoms getting on or into the person

why do you need to try distance yourself from radioactive sources in practicals

minimise irradiation; prevent contamination if it gets on/into you

which type of radiation is the most dangerous inside the body and why

alpha - most highly ionising

which type of radiation is the most dangerous outside the body and why

gamma - able to pass through air and skin

why is alpha not dangerous when you are not contaminated by it

it would be absorbed by air before even reaching the skin

how can you manage risk of radiation exposure

handle sources safely and monitor exposure to radiation

safety practices: contamination (5 things)

keep source in lead lined box when not in use; wear gloves and use tongs to move it; keep at as far distance as possible; wash hands; time using should be minimised

minimise risk of irradiation

monitor exposure to radiation with a film badge

what is done with very radioactive waste / long half-life

buried underground in a geologically stable location in strong containers

what is nuclear fusion

Creation of larger nuclei resulting in a loss of mass from smaller nuclei, accompanied by a release of energy

where does fusion occur naturally

inside stars

what nuclear fusion happens in stars

hydrogen nuclei fuse to form a helium nucleus

what are tritium and deuterium

isotopes of hydrogen involved in nuclear fusion

how much energy does fusion release compared to fission

a lot more

what is nuclear fission

the splitting of one large unstable nucleus into two smaller daughter nuclei

what process is used to generate electricity in nuclear power stations

nuclear fission

examples of fissile materials

isotopes of uranium and plutonium

what is spontaneous fission

nucleus undergoes fission without additional energy being put into the nucleus

what is induced fission

the unstable nucleus absorbs a neutron which makes it more unstable so it decays almost immediately

why do isotopes with a long half life need to be induced to undergo fission

they have low activity and release energy very slowly

describe the fission of U-235

collides with and absorbs neutron; splits into two radioactive daughter nuclei and a small number of neutrons; also emits gamma rays

what is the energy source for stars?

nuclear fusion

how is energy released by fission

kinetic energy of the fission products

how can u-235 fission start a chain reaction

neutron emitted from the splitting of nucleus causes further nuclei to split and the neutrons emitted from these cause further fission reactions

what two factors must be controlled in the nuclear reactor

number and energy of free neutrons

purpose of control rods

absorb neutrons

how is the number of neutrons absorbed controlled in a nuclear reactor?

varying the depth of the control rods in the reactor core

what is the purpose of the moderator in the nuclear reactor?

to slow down neutrons by absorbing their kinetic energy in collision

where is the moderator

material which surrounds fuel and control rods inside reactor core

what is shielding for

absorbing hazardous radiation

what is the shielding made out of in a nuclear reactor

steel or concrete