Radioactivity

Particle Theory

Model that helps explain the properties of solids, liquids and gases

What did Dalton discover?

Atoms are small solid spheres

How did Dalton discover atoms shape?

Gas experiments

atomic model of Dalton

Strength of the Dalton model

Simple

Weakness of Dalton's Model

Doesn't show the relative size of particles

What did Thomson discover?

electrons and that they are negatively charged and hardly any mass

How did Thomson discover the Electron?

Electricity gun

Thomson's Model

Plum pudding model

Strength of plum pudding model

Shows electrons

Disadvantage of plum pudding model

Doesn't show neutrons

What did Rutherford discover?

Atom has a small positively charged solid nucleus in the centre

Rutherford model of the atom

How did Rutherford discover the nucleus?

Gold foil experiment

How did the gold foil experiment work?

alphaparticles were shot through very thin gold foil with a detector around the foil. Almost all of the particles went straight through the foil, very few were deflected and an even fewer were bounced straight back.

Why did most particles get transmitted in the gold leaf experiment?

Most of the atom is empty space

Why did some particles get deflected in the gold leaf experiment?

The post it I've nucleus deflects the alpha particles

Why did very few particles get reflected in the gold leaf experiment?

The nucleus is very small and very hard, dense

Strength of the Rutherford model?

Shows positive nucleus

What did Chadwick discover?

neutron

How did Chadwick discover the neutron?

Weighed the atom

Where is all of the mass of an atom?

nucleus

Nucleons

protons and neutrons

atomic number

the number of protons in the nucleus of an atom

mass number

the sum of the number of neutrons and protons in an atomic nucleus

How are atoms neutral?

same number of protons and electrons

What is an isotope?

Atoms of the same element that have different numbers of neutrons

electromagnetic radiation

When we provide electrons with energy, they absorb the energy and electrons can jump to higher energy levels (electron orbits/shells). After short time, electrons return back to their original shell releasing energy as electromagnetic radiation that we see as colours.

Ionisation

If we give too much energy - electrons escape all together, making the atom a charged particle (ion)

emission spectrum

Each colour emitted from electromagnetic radiation is a different wavelength of light.

background radiation

Low level of radiation to which we are exposed to every day from environment and space

Sources of background radiation

Radon gas, cosmic rays, rocks, building materials, medical x-rays, food, nuclear industry

what is randon gas?

Radioactive gas that has no smell, colour or taste. Produced from the radioactive decay of uranium

How to measure radiation

Dorsimeter, or Geiger-Muller tube

Dorsimeter

Used to be photographic films that would get darker the more radiation it absorbed

Geiger-Müller counter

instruments that detect radiation by counting electric pulses carried by gas ionised by radiation

Decay

When a nucleus emits a particle or a wave.

Why can you not predict when an atom decays?

The process is random

What are the types of radiation

alpha, beta, gamma

alpha particle

a type of nuclear radiation consisting of two protons and two neutrons

beta particle

a high-speed electron with a 1- charge that is emitted during radioactive decay

gamma rays

high-energy electromagnetic waves emitted from a nucleus as it decays. They have no charge

Beta minus decay

The process of a neutron inside a nucleus turning into a proton, and emitting a beta-minus particle (an electron)

Beta plus decay

The process of a proton inside a nucleus turning into a neutron, and emitting a beta-plus particle (a positron)

Ionising radiation

radiation that provides enough energy for an atom to lose an electron and become an ion

radioactive

emits ionising radiation

What is a property of alpha radiation related to ionising power?

High ionising power due to high mass and charge.

What is a property of alpha radiation related to penetrating power?

Low penetrating power with a range of a few cm in air.

What can block alpha radiation?

Skin or a sheet of paper.

What is the ionising power of beta radiation?

Medium ionising power

What is the penetrating power of beta radiation?

Medium penetrating power, with a range of a few meters in air

What material can block beta radiation?

3mm thick aluminium

What is the ionising power of gamma radiation?

Low ionising power

What is the penetrating power of gamma radiation?

High penetrating power

What is the range of gamma radiation in air?

A few kilometers

What material can block gamma radiation?

Many centimetres of lead

nuclear equation

a type of equation that shows the atomic number and mass number of the particles involved

half-life

time taken for half a nuclei to decay

Radioactivity

how many nuclei decai per second

What is radioactivity measured in?

Bequerels (Bq)

How is radiation used in killing microorganisms?

Gamma rays transfer energy to bacteria, killing them and sterilising food. Making it safer to eat and meaning it can be stored for longer without going off

How is radiation used in radioactive detecting?

A gamma source added to water is used to detect leaks in water pipes underground. Where there is a leak, water flows into the surrounding earth, and a Geiger muller tube following the path will detect higher levels of radiation where there is a leak

How is radiation used in smoke alarms?

Americium is used in smoke alarms and it is an alpha emitter.

o This is stopped by a few centimetres of air (as it is weakly penetrating)

o The alpha particles ionise air particles and makes them charged therefore making a current

o If smoke enters the air around the alarm, the current drops in the circuit

▪ Causing the alarm to sound

How is radiation used in checking thickness?

Beta radiation is mildly penetrating, and can just pass through paper

A source and receiver are placed either side of the paper during its production

If there is a drop or rise in received electrons, then that means the thickness of the paper has changed

What are the 2 effects radiation can have on cells?

Kill cells - radiation burns and tissue damage caused by large amounts of radiation

Mutate cells - if cells mutate they can then grow into a tumour, caused by small amounts of radiation over a long time

What is a key requirement for the half-life of medical radiation isotopes?

It must be short enough to minimize the dose of potentially harmful radiation given to the patient.

What is another requirement for the half-life of medical radiation isotopes?

It must be long enough to produce the required image or kill cancer cells.

Irradiation

Exposure to nuclear radiation without becoming radioactive

What is contamination in the context of radiation?

The source of radiation is transferred to an object.

What happens when you touch radioactive material?

Its atoms are now on you.

What does PET stand for in medical imaging?

Positron Emission Tomography

What does a PET scan visualize?

Brain activity

What substance does a PET scan use to detect brain activity?

A radioactive form of glucose

What does a PET scan measure while the brain performs a task?

Where the radioactive form of glucose goes

How does a PET scan work?

1. inject radioactive tracer (glucose)

2. Glucose emits positronn

3. positron reacts with electrons

4. 2 gamma rays are produced going in opposite directions

5. PET scan picks up those gamma rays

internal radiotherapy

Treatment of cancer by putting a radioactive source inside the body.

Nuclear power

Energy that is harnessed from reactions among radioactive isotopes

advantages of nuclear power

Stores a lot more energy per 1g than other fuels

Produces no polluting gases

Reliable - provides power whatever the weather

disadvantages of nuclear power

Pollution from accidents can contaminate land for decades

Produces radioactive waste that is very difficult and expensive to dispose

Nuclear fission

large nuclei (uranium-235) break up to form smaller nuclei and energy

nuclear chain reaction

the continued process of atoms splitting and releasing neutrons that trigger more atoms to split

how to control the chain reaction in nuclear power plants?

By using control rods which slows the reaction down by absorbing more of the neutrons, or moved up so that fewer of the neutrons are absorbed, which means that the reaction remains constant and explosions do not occur.

Control rods

neutron-absorbing rods that help control the reaction by limiting the number of free neutrons

fuel rods

a uranium rod that undergoes fission in a nuclear reactor

moderator

used to slow down the fast neutrons produced by fission

How to generate electricity from a reactor core?

Thermal energy from the core is is used to heat water pumped through the reactor. The heated water is pumped to a heat exchanger where it turns to steam. The steam turns a turbine which turns a generator. The generator transfers kinetic energy to electrical which is then transferred through the national grid

nuclear fusion

2 small nuclei fuse to form a larger nucleus