Radioactivity: Evidence for the Nucleus
Yafaa Chaudhary PHYSICS 5 NOTES
Physics 5
3.5.1 Radioactivity
Evidence for the nucleus
Qualitative study for the Rutherford scattering.
Rutherford directed a narrow beam of α-particles, all of the same kinetic energy, in an evacuated container at a thin gold film, in order to identify the structure of an atom:
The α-particles need to be of the same kinetic energy otherwise slow α-particles would be deflected more than faster α-particles on the same initial path.
The container needs to be evacuated as otherwise the α-particles would be stopped by air particles.
Observations:
Most α-particles passed through
A few α-particles deflected – some more than 90° (bounce back)
Interpretation:
Most of the atom’s mass is concentrated in a small region, the nucleus, at the centre of the atom.
The nucleus is positively charged because it repels α-particles
The nucleus itself is small since very few α-particles are deflected are deflected by much.
α, β and ϒ radiation
Their properties and experimental identification using simple absorption experiments; applications
e.g. to relative hazards of exposure to humans.
Radiation
Alpha- α
Beta- β
-
Gamma- ϒ
Range
Ionising
Strongly
Slow
1m
Weakly
Fast
Follows inverse law
Very
Weakly
Speed of
Light
Alpha:
Beta (-):
Beta (+):
Gamma:
Speed
100mm
no change
Electron Capture:
Penetrating Power
Absorbed by paper or a few cm of air Absorbed by approximately 3mm of aluminium
Absorbed by many cm of lead, or several m of concrete
Application
Fire Alarms
Thickness of paper, fill up of bottle Diagnostic techniques is medicine, sterilising equipment
Yafaa Chaudhary PHYSICS 5 NOTES
Hazards of exposure to humans:
Affects living cells because:
It can destroy cell membranes which cause cells to die.
Damage DNA.
As a result of ionising radiation, living cells die or grow uncontrollably or mutate. This can affect patient’s health, possibly affecting future generation because of genetic disorders. Mutations can lead
to
Physics 5
3.5.1 Radioactivity
Evidence for the nucleus
Qualitative study for the Rutherford scattering.
Rutherford directed a narrow beam of α-particles, all of the same kinetic energy, in an evacuated container at a thin gold film, in order to identify the structure of an atom:
The α-particles need to be of the same kinetic energy otherwise slow α-particles would be deflected more than faster α-particles on the same initial path.
The container needs to be evacuated as otherwise the α-particles would be stopped by air particles.
Observations:
Most α-particles passed through
A few α-particles deflected – some more than 90° (bounce back)
Interpretation:
Most of the atom’s mass is concentrated in a small region, the nucleus, at the centre of the atom.
The nucleus is positively charged because it repels α-particles
The nucleus itself is small since very few α-particles are deflected are deflected by much.
α, β and ϒ radiation
Their properties and experimental identification using simple absorption experiments; applications
e.g. to relative hazards of exposure to humans.
Radiation
Alpha- α
Beta- β
-
Gamma- ϒ
Range
Ionising
Strongly
Slow
1m
Weakly
Fast
Follows inverse law
Very
Weakly
Speed of
Light
Alpha:
Beta (-):
Beta (+):
Gamma:
Speed
100mm
no change
Electron Capture:
Penetrating Power
Absorbed by paper or a few cm of air Absorbed by approximately 3mm of aluminium
Absorbed by many cm of lead, or several m of concrete
Application
Fire Alarms
Thickness of paper, fill up of bottle Diagnostic techniques is medicine, sterilising equipment
Yafaa Chaudhary PHYSICS 5 NOTES
Hazards of exposure to humans:
Affects living cells because:
It can destroy cell membranes which cause cells to die.
Damage DNA.
As a result of ionising radiation, living cells die or grow uncontrollably or mutate. This can affect patient’s health, possibly affecting future generation because of genetic disorders. Mutations can lead
to