P6

Define Isotope

Define Isotope

Isotopes have the same number of protons but different number of neutrons.

Difference between mass and atomic number

Mass/Nucleon number- number of protons and neutrons in an atom

Atomic number- Number of protons/electrons in an atom

How is radiation emitted

Radioactive atoms have an unstable nucleus
Unstable nuclei emit ionising radiation in an attempt to become more stable

What are the 3 types of radiation and their properties

Alpha radiation- Two protons and neutrons (helium nucleus), Moves at 10% of the speed of light
Beta radiation- Fast-moving electron moving at 90% of the speed of light. (Neutron turns into a proton and electron)
Gamma radiation- High energy electromagnetic wave (not a particle)

How does one detect ionising Radiation

Measured using a GM tube to measure count rate or activity of a radioactive sample (number of decays per second in Becquerels)

Penetrating Properties of the 3 types of radiation

Alpha- Stopped by 3-5cm of air, paper or skin, Least penetrating but most ionising)
Beta- 30-50cm of air or 3mm of aluminium, Fairly penetrating and fairly ionising
Gamma- Reduced by several cm of lead or several metres of concrete, Most penetrating but Least ionising due to no mass and charge

Difference between irradiation and contamination

Irradiation- Exposure to ionising radiation, used in sterlising medical equipment and food to kill bacteria. Can ionise cell atoms which causes sickness and increase chance of cancer

Contamination- Radioactive substance has been transferred (infected), Can happen due to nuclear weapons or power stations exploding

When does radioactive decay occur

Radioactive decay is both spontaneous and random
(Can’t predict which nucleus decays and when)

Define half life

Half-life: Time taken for half of the radioactive unstable nuclei present to decay (constant)

How do smoke detectors work?

Contains alpha source with long half-life, Alpha particles ionise the air to create electric current
If smoke particles enter detector, smoke absorb some of the ionising radiation
Less current flows, causing alarm to sound

How does carbon dating work?

Amount of carbon-14 in the atmosphere is constant
When an organism dies, it no longer takes in carbon-14
Amount of carbon-14 in organism decreases as it undergoes beta decay (Half life of 5700 years)
Use info. about amounts of carbon-14 to work out when organism passed away

How do medical tracers work?

Radioactive substance (beta or gamma radiation) is ingested or injected into body
Attached to chemicals which absorbed by organ system being studied
Path of radioactive source observed by detecting radiation using a GM detector outside the body

How does nuclear fission work?

Neutron fired at uranium nucleus which absorbs neutron
Nucelus becomes unstable and splits into two smaller nuclei, releasing 2 or 3 neutrons
Causes mass to be converted into heat energy as products lighter than reactants

What is a chain reaction?

Neutrons released during fission can cause further fission if they lose some eneergy before striking another nucleus
Chain reaction grows exponentially unless neutrons safely absorbed by stable materials

How do fission power stations work

Use enriched Uranium-235 to generate heat energy through fission
Heat turns water to steam via moderator , which turns turbine which drives generator which generates electricity
Reaction mainted or reduced by control rods which saffely absorb spare neutrons

How does nuclear fusion work

Two small nuclei fuse together to form a larger nucleus, converting mass into energy
Requires very high pressure and temp. Conditions needed to overcome repulsive forces between positively charged nuclei.
All stars release energy due to nuclear fusion in cores

What are energy levels

Energy levels are like shells, electrons can only exist at certain distances from nucleus

How does excitation work

If an electron is struck by a photon of light with the correct energy, it is absorbed and electron transitions to higher energy level
If photon has too much or too little, it won’t be absorbed

How does de-excitation work?

Electrons are unstable in higher energy levels and will de-excite spontaneously releasing a photon of light
Photons released will always match the energy difference between energy levels

What is an energy level diagram

Like a cross section of the orbit
Difference in energies used to calculate energy required for an electron to transition between them

What is ionisation energy

If electron struck by hgih energy photon, can gain enough energy to leave the atom
Energy level values show amount of energy required to ionise from that level

Describe how an absorption spectrum shows energy levels of an atom

White light contains all frequencies where each frequency corresponds to specific energy
When a photon with energy that matches difference between energy levels enters the atom, it’s absorbed by electron
Electron becomes excited (moves up)
Electron is unstable, de-excites, emits photon of same energy
Missing wavelengths match energy level groups, remaining frequencies pass through gas