What is Radioactivity?
and why does it happen?
- The nucleus is composed of protons and
and glued together by a strong attraction
BUT only certain combinations of the n/p ratio seem to be stable (see stability curve graph
on right). Any isotope of any element that does not lie in the
stability band with a stable n/p ratio is likely to be radioactive!
- Radioactivity results from the random and spontaneous breakdown of the unstable nucleus of an atom.
- This breakdown is called radioactive decay
of the unstable nucleus of the atom (radioisotope).
- In the breakdown of the unstable nucleus, energy is released by the emission
(usually) of three types of ionising radiation (nuclear radiation) called alpha
particle radiation, beta particle radiation and gamma
(see diagram below).
- These emissions are ALL high velocity and high
energy particles or radiation.
Alpha particles are
positive, mass 4, 2 protons (+, single plus) combined with 2 neutrons.
Beta particles are negative, mass 1/1850,
a negative electron (charge -, minus), 0-1e
Gamma photon, mass 0 (~zero), radiation is electrically neutral (charge 0 or zero)
- When an unstable nucleus splits a
different nucleus with a different number of protons is formed, as
well as the emission of radiation, and
so a different element is formed (NOT possible in chemical changes, but
this is a nuclear reaction!).
- The breakdown of an unstable atom is referred to as
radioactive decay or radioactive disintegration.
- It is a totally random process meaning it is a
matter of chance which particular nucleus decays.
did they find out there were three types of atomic ionising radiation?
The basic experimental technique for
separating beams of a mixture of particles
A radium source was used, which
also contains other radio-isotopes, and a lead casing was the only
safety precaution used!
- How people like Marie Curie and Ernest
Rutherford etc. survived beyond the age of 60 is a mystery!
- Anyway! it was found that the
original 'emission' from the radioactive radium source was split into three beams
by an electric or magnetic field (diagram on the right).
- (i) The alpha beam was attracted/deflected
towards a negative plate, showing it was positive, since opposite
charges attract/like charges repel - the rules of electric charge
- (ii) The beta (negative electrons) beam bent
towards a positive plate (showing it was negative).
- (iii) The gamma beam passed through
un-deflected (showing it had no charge).
- Note: Although the alpha
particles have the biggest charge of +2, the beta beam (smaller
charge of -1) is more easily deflected because of its much smaller
mass (nearly 8000 x smaller, mass ratio for He2+ : e-
is 4 : 1/1850).
- Note that in other nuclear
particle separation experiments, a proton (+), or any other positive
particle beam, bends towards the negative plate.
- Other experiments have detected positron
(positive electron) emission from beta plus radioactive decay.
TOP OF PAGE
RADIOACTIVITY and NUCLEAR
Atomic structure, fundamental particles and radioactivity
is radioactivity? Why does it happen? What radiations are emitted?
3. Detection of
radioactivity, measurement, dose units, ionising radiation sources,
properties and dangers of alpha, beta & gamma radioactive emission
uses of radioactive Isotopes emitting alpha, beta or gamma radiation
6. Half–life of radioisotopes, how
long does material remain radioactive? Uses of decay data & half–life values
changes in radioactive decay? how to write nuclear
equations? Production of Radioisotopes
Nuclear fusion reactions and the formation of 'heavy elements'
9. Nuclear Fission Reactions, nuclear power energy resources
multiple choice QUIZZES
word-fills on radioactivity
puzzle on radioactivity