P5 - Radioactive Materials Flashcards
Describe the structure of a nucleus
The nucleus is positively charged and is
made of protons (positive) and neutrons
(neutral).
What are the relative charges of protons,
electrons and neutrons?
Protons: +1
Electrons: -1
Neutrons: 0
What are the relative masses of protons,
electrons and neutrons?
Protons: 1
Electrons: 0 (0.0005)
Neutrons: 1
Give an estimate for the radius of an
atom
1x10^−10m
Describe the arrangement of electrons in
an atom
Electrons are arranged at different
energy levels, different distances from
the nucleus.
How can electrons arrangement
change?
If an atom absorbs EM radiation,
electrons can move to higher energy
levels or leave the atoms entirely.
Describe Dalton’s atomic model
Everything is made of tiny spheres
(atoms) which could not be divided into
anything smaller.
(1800)
Describe JJ Thompson’s atomic model
The Plum Pudding Model: the overall
charge of an atom is neutral, so it
consists of a positive sphere (“pudding”)
with embedded negative electrons.
(1897)
Describe Rutherford’s experiment
● Alpha particles (charge +2) were fired at a thin
sheet of gold foil.
● Most particles went straight through.
● Some particles were deflected by small angles
(< 90o).
● A few particles were deflected by large angles
(> 90o).
What are the conclusions of Rutherford’s
experiment?
● Most of an atom is empty space.
● The nucleus has a positive charge.
● Most of the mass is concentrated in
the nucleus.
Describe Rutherford’s atomic model
There is a positive nucleus at the centre
of an atom, with negative electrons
existing in a “cloud”/region around the
nucleus.
(1913)
Describe Bohr’s atomic model
Bohr’s model was very similar to the Rutherford model, but he described electrons as existing in fixed orbitals/shells/energy levels around the nucleus.
What is an isotope?
Atoms of the same element, with the
same number of protons, but a different
number of neutrons so therefore different
masses.
What do all atoms of the same element
share?
The same number of protons (atomic
number).
When is an atom neutral?
When proton number = electron number.
When does radioactive decay occur?
When an atomic nucleus is unstable; it
gives off radiation to become more
stable.
Define activity
The rate of decay of a source of unstable
nuclei; the number of decays per
second.
What is activity measured in?
Becquerels, Bq
Define count rate
The number of decays per second.
How can count rate be measured?
Using a Geiger-Muller Tube.
Describe α radiation
● 1 particle is 2 protons, 2 neutrons (same as a helium nucleus). ● Highly ionising. ● Weakly penetrating (blocked by ~5cm of air).
Give the equation for an α particle
α4/2
Describe ß radiation
● 1 particle is a single electron.
● Medium ionising effect.
● Medium penetration (blocked by
~50cm of air or a sheet of metal).
Give the equation for a ß particle
ß0/-1
