Ch8 Radioactivity Flashcards
Who discovered radioactivity
Henri becquerel
What did becquerel find
Radiation was emitted continuously and didn’t require that the uranium be treated with light or heat - ie it was spontaneous
What did henri becquerel observe
That some sort of radiation emitted by uranium was able to penetrate paper and affect a photographic plate
What did henri becquerel do
Left some uranium salts resting on a photographic plate that was wrapped in black paper.
Photographic plate became fogged or darkened in the area near uranium salt
Ore becquerel used
Pitchblende
Two scientists and the elements they discovered
Marie and Pierre curie
Radium polonium
Radioactivity
The spontaneous breaking up of unstable nucleus with the emission of one or more types of radiation.
3 types of radiation
Alpha particles
Beta particles
Gamma radiation
Alpha particles
- groups of 2 protons and 2 neutrons emitted from unstable nucleus
I.e. the same as the nucleus of a helium atom 4 2 He
Alpha particles characteristics
-charge positive 2
-attracted to negative electrode
-have a relatively large mass, travel relatively slow
-low penetrating power, stopped by sheet of paper or few cm of air
Alpha emitter
Americium-241
Polonium-210
Americium-241
Used in smoke detectors
As alpha particles have low penetrating power, smoke alarms do not pose health risks
Polonium-210 poisoning
Alexander Litvinenko
If radioisotopes that emit alpha particles are inhaled or ingested -> harmful
Beta particles
- Beta radiation resulst when within a nucleus a neutron splits into a prótón and an electron
- prótón States in nucleus; electron is ejected from the nucleus
High speed, high energy electron
Beta particles characteristics
-Negative, attracted to positive electrode
-Lighter than alpha particles and are more penetrating therefore
-can penetrate up to 5mm of aluminium
Beta particles emitter
Carbon-14
Carbon-14
Used to find the age of objects -> carbon dating
What did radioactivity dismiss
Daltons theory that atom was a solid sphere
How did the discovery of radioactivity show that the atom is not a solid sphere, but consists of smaller particles?
The only place alpha and beta particles could be coming from is from within the atoms of the radioactive material.
Gamma radiation
- High energy electromagnetic radiation… sim to X-rays
Gamma radiation characteristics
- does not consist of particles (does not have mass)
- does not consist of charged particles - not deflected by electric or magnetic fields
-unstable nucleus emits gamma radiation in order to lose surplus energy
Gamma radiation characteristics
- High penetrating ability - only stopped by thick slab of lead
-most dangerous type of radiation
What can gamma radiation be used for
-can change the structure of the chemicals in our bodies and cause cancer.
-can be used to kill cancer cells by focusing the radiation on the cancerous tissues.
Gamma radiation emitter
Cobalt - 60
Used in hospitals -> gives off gamma rays
Used to detect radioactive radiation
Geiger - Müller tube
-connected to ratemeter
-detects a,b,y radiation
Nuclear reactions
Process that alters the composition, structure or energy of an atomic nucleus.
-radioactive radiation is emitted from the nuclei of unstable atoms… nuclear reaction!
Chemical reactions vs nuclear reactions
Chemical - involves electrons rather than nucleus
Nuclear - changes take place in nucleus and electrons not involved
Chemical - no new element formed/ nuclei of atoms stay same
Nuclear - new element formed from change in nucleus of an element - transmutation
Chemical - no release of nuclear energy
Nuclear - nuclear energy released
Chemical - chemical bonds broken and formed
Nuclear - no chemical bond breaking or bond formation involved
Alpha decay
Atom loses 2 protons and 2 neutrons from its nucleus
-atomic no. Decrease by 2
-atomic mass decrease by 4
Beta decay
When an atom loses a beta particle, the b particle is ejected from the nucleus
-neutron is changed into a proton and an electron
-atomic no increase by 1
-mass number no change
Emission of gamma radiation
Loss of gamma radiation does not give rise to any new atoms
-energy simply lost from the nucleus
Half- Life
Of an element is the time taken for half of the nuclei in any given sample to decay
-emission of radiation is random
-each radioisotope decays at its own rate
QUITE VARIED
What is used to find half lives
Geiger- Müller tube and ratemeter
Where can radioactive elements be found
In the lanthanides and actinides series
Radiocarbon dating
Carbon dating
A technique used to determine the age of an object containing carbon
-based on the ratio of carbon -14 to carbon-12 in the object
Background radiation
Naturally occurring radiation in our environment
(Radon gas produced by decay of uranium and thorium in rocks)
Uses of radioisotopes
-medical uses - radiotherapy, sterilise medical equipment, (gamma radiation)
-archaeology - carbon 14 dating
-agricultural research - eg study uptake of fertilisers by plants
-food irradiation - kills germs
-industry
Radioisotope
Radioactive isotope
