Atomic Physics

Atomic Physics

isotope

An atom with the same number of protons and a different number of neutrons from other atoms of the same element.

ion

charged particles formed when atoms gain/lose electrons

how was radioactivity discovered (and who by)?

-Henry Becquerel, he placed uranium sample in drawer which also contained a photographic plate inside of an envelope; when he returned, the plate had developed

background radiation

nuclear radiation that occurs naturally in the environment

natural background radiation examples

51%- radon in atmosphere

14%- ground + buildings

12%- food + drink

10% cosmic rays

artificial background radiation examples

12%- medical usage

0.4%- fallout from weapons tests

0.2%- TV sets, etc

0.2%- non-medical industry uses

0.1%- nuclear power discharges

measurement of the radiation dosage someone receives

millisieverts (mSv)

biggest danger of radiation

ionisation

ionisation of radiation

to give an atom/molecule a charge, which will then react with something else, leading to mutations

safety procedures for small quantities of radioactive substances

-only those authorised can use it (sign in + out)

-users may wear special badge which shows radiation exposure

-gloves worn + tongs used to touch the substance

-never direct the source towards others/yourself

-put source in lead lined box when not in use

Geiger-Muller counter

an instrument that detects radiation by counting electric pulses carried by gas ionised by radiation

why is background radiation measured before an experiment with a radioactive substance?

so the background radiation can be subtracted from any measurement taken (don't want naturally occurring radioactive particles to interfere

overall charge, neutrons + protons +electrons found in ALPHA RADIATION

neutrons= 2

protons= 2

overall charge= 2+

ALPHA RADIATION speed

0.1x the speed of light (3x10^8ms^-1)

ALPHA RADIOATION ionisation

highly/strongly ionising

ALPHA RADIATION penetration

cant penetrate far, 6cm range in air before stopped

overall charge, neutrons + protons + electrons of BETA RADIATION

electrons= 1

overall charge= -1

BETA RADIATION speed

0.9x speed of light

BETA RADIATION ionisation

moderately ionising

BETA RADIATION penetration

moderately far penetration, 50cm to a few metres range

5mm aluminium sheet to stop it

overall charge, protons + neutrons of GAMMA RADIATION

0 mass

0 charge

often emitted after alpha or beta radiation

electromagnetic wave

GAMMA RADIATION speed

speed of light

GAMMA RADIATION ionisation

Very weak ionising effect

GAMMA RADIATION penetration

almost infinite range, stopped by thick sheets of lead

ALPHA PARTICLE mass

4 amu

BETA PARTICLE mass

1/2000

GAMMA PARTICLE mass

0

alpha decay

isotope decays by alpha emission, an alpha particle is lost from the nucleus (2p, 2n) + energy released

mass number decreases by 4, atomic number decreased by 2

beta decay

neutron splits into 2 smaller particles- proton + electron

proton remains in nucleus, electron (beta) released with energy

mass number doesn't change, atomic number increases by 1

gamma decay

only emit energy. no mass/charge so mass + atomic number stays the same

half life

length of time required for half of the radioactive atoms in a sample to decay

time taken for the number of radioactive nuclei in a sample to halve

time taken for the count rate of a sample to halve

if the half life is shorter, is the decay faster/slower?

faster the decay

what can the count rate be measured in

counts per minute (cpm), counts per second (cps), Becquerels (Bq)

irradiation

occurs when there is exposure to ionising radiation from the radioactive source

contamination

occurs when the radioactive source itself is spread

damage + mutation of cells

caused by ionising radiation which damages the molecules that make up the cells of living tissues; constant exposure to ionising radiation can kill the cells or make them mutate, can cause cancer

radioactive medical tracers

radioactive substance injected into the bloodstream/taken orally

substance works its way around the body

special camera scans the body, detecting the radiation and forming an image

radiation type that should be used in medical tracers

low ionising (gamma)

radiotherapy

gamma knife may be used to destroy cancerous cells so they are no longer able to reproduce

precautions for radiotherapy and gamma knife

go to a different room

wear lead clothes

take care when aiming the gamma ray- dont aim at other parts of the body

CT scan

computerised tomography; series of x rays taken from different angles/directions that are then assembled into a 3d model of the subject

MRI scan

magnetic resonance imaging; create images of the body using a large magnet and radio waves

DOES NOT USE RADIOACTIVE ISOTOPES

medical uses of radiation

-radioactive medical tracers

-radiotherapy

-CT scan

-MRI scan

non-medical uses of radiation

-smoke detector

-thickness measurement

-keeping food fresh

-sterilisation

-fault detection

-non-medical tracers

-radiocarbon dating

-atomic bomb

nuclear fission

the act of splitting a larger nucleus into two smaller ones

where is nuclear fission found

inside nuclear power plants/stations

nuclear chain reaction

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

fuel rods

packed with pellets of uranium-235 or plutonium-239; helps start the reaction

most common element used for nuclear fission

uranium, plutonium (can also be used but not nearly as common as it doesn't occur in nature)

how is nuclear fission controlled

Control rods are lowered into a nuclear reactor which absorbs neutrons to slow a reaction

how is safety ensured in nuclear fission power plants

substance known as the moderator surrounds the fuel and control rods

example of a moderator

graphite or water

what does the moderator do in nuclear fission

slows down the neutrons, making the chain reaction more efficient, as the neutrons need to travel at the right speed to prevent them from being absorbed

radioactive waste

any material that is either radioactive itself or is contaminated by radioactivity, for which no further use is envisaged.

nuclear disasters

Three Mile Island, Chernobyl, Fukushima

radiocarbon dating

a chemical analysis used to determine the age of organic materials based on their content of the radioisotope carbon-14

atomic bomb

uncontrolled chain reaction, extreme heat + pressure, radioactive fallout

eg. Hiroshima and Nagasaki

nuclear fusion

The process by which two or more small nuclei fuse to make a bigger nucleus

nuclear fusion in stars

process by which stars give off huge amounts of energy in the form of heat and light

benefits of using nuclear fusion

-fuels are relatively abundant

-renewable

-energy density four times greater than uranium

-not a chain reaction, can be controlled and safe

what are the most common fuels for nulear fusion

hydrogen-2 and hydrogen-3

what does the deuterium-tritium reaction produce

helium-4

why do we not use fusion power?

-requires large amounts of energy to start

-temperatures in excess of 10,000,000

-inefficient, requires a larger energy input than output, although technology is developing to improve this

risks for nuclear fission

leaks of radioactive material (eg. chernobyl)

risks for nuclear fusion

very high temperatures