Physics - Radioactivity Flashcards
radius of a nucleus compared to radius of atom
nucleus radius = 100,000 times smaller than atom radius
reasons for unstable nuclei
- nucleus is too large
- number of protons is very different to number of neutrons
- nucleus has a lot of energy
what happens when nuclei is stabilised
radiation emitted
types of ionising radiation
- alpha decay
- beta decay
- gamma decay
what is alpha decay
- when alpha particle emitted from nucleus
- alpha particle is made up of 2 protons and 2 neutrons (helium nucleus)
- highly ionising, slow moving and low penetrance due to large size
- stopped by a few cm of air
- due to the loss of 2 protons and 2 neutrons, element emitting alpha particle is a new particle
what is beta decay
- when beta particle is emitted from nucleus
- when neutron is converted to a proton and an electron
- element gains a proton in beta emission, hence a new element
- beta negative decay - electron emitted
- possible for positron to be emitted instead of an electron
- beta particles are smaller than alpha and are moderately ionising, fast moving, moderate penetrance (stopped by foil)
what is a positron
- positively charged antiparticle of electron
- when positron is emitted, proton changes into a neutron thereby creating a new element
what is gamma decay
- occurs when a gamma ray is emitted
- gamma ray is a high energy photon
- mass and atomic number of element remain unchanged
- weakly ionising, highly penetrating (stopped by thick lead)
uses of alpha particles
smoke alarms
- alpha emitter in smoke alarms produces alpha particles which ionise air molecules.
- ionised molecules carry current and complete a circuit in the smoke alarm
- smoke particles prevent ionisation of air molecules, hence breaking the circuit
dangers of
alpha particles
due to them being highly ionising - can damage dna of cells and tissues
low penetrance so have to be inhaled or digested
uses of beta particles
tracers/material quality control
used to measure thickness of paper/aluminium - if material is too thick, fewer beta particles will penetrate
medial uses - imaged certain body parts - POSITRON EMISSION TOMOGRAPHY
danger of beta particles
moderately penetrating so present a hazard if inhaled, ingested or direct exposure without barrier
uses of gamma particles
sterilising medical equipment/food/radiotherapy
radiotherapy - multiple angles are used to maximise tumour exposure to gamma rays whilst simultaneously minimising damage to non-cancerous tissue
dangers of gamma particles
weakly ionising so gamma rays aren’t particularly dangerous provided the dose is low enough
highly penetrating so only thick lead/concrete will prevent exposure
half life
time taken for 50% of sample to decay
what does half life depend on
decay constant
what is half life measured in
becquerels using a geiger counter
one becquerel =
one decay per second
nuclear fission
nuclear reaction which heavy nucleus splits spontaneously into smaller nuclei with the release of energy
how do power plants use nuclear fission
- uranium-235
- in a fission reactor
- uranium-235 absorbs a neutron producing the unstable isotope uranium-236
- uranium-236 splits into two random smaller nuclei releasing neutrons and energy in the process
- three neutrons can then be absorbed by other uranium-235 atoms in chain reaction that needs to be controlled in a nuclear reactor through the use of neutron absorbing control rods to prevent nuclear explosion
nuclear fusion
- nuclear reaction which atomic nuclei of low atomic number fuse to form a heavier nuclei with release of energy
- fusion requires an incredible amount of energy to occur as mutual repulsion of nuclei needs to be overcome
nuclear fusion in the sun
fusion mainly occurs between hydrogen and deuterium to produce helium
