Hazards of Radiation

1
Hazards of Radiation

• Radioactivity

2
Learning Objectives

• Recap properties of a, ß, ? radiation.
• Describe and explain the relative hazards to
  humans when exposed to a, ß, ? radiation.
• Recap the inverse square law of radiation.
• Describe how this applies to the safe handling of
  radioactive sources.

3
Quick Recap

• Complete the table (in pencil) that describes the
  properties of the three common radiations-

Radiation Particle Range in air Stopped By



4
Recap - Answers
Radiation Particle Range in air Stopped By
Alpha Helium nucleus (P) Few mm (P) Paper (P)
Beta High speed electron (P) Few cm (P) Aluminium sheet (P)
Gamma Energetic photon (P) Infinite (P) Several cm lead (P)
5
Ionisation

• What is ionisation?
• Which do you think is the most ionising?

6
Ionisation

• a - Intense, ionises about 10,000 atoms per alpha
  particle. (because strongly ve and large)
• ß - Less intense than a, about 100 ionisations
  per particle. (because lower charge, but higher
  speed)
• ? - Weak interaction about 1 ionisation per mm.

7
Hazards

• a Once it gets in it is highly damaging to body
  tissue.
• Luckily cant pass through skin but could be
  inhaled or ingested. Considered less damaging
  than gamma rays or alpha particles.
• ß Lower interaction rate means it is much less
  damaging to body tissue than alpha. Used as
  medical tracers.
• ? - can be a dangerous form of radiation, as they
  are very penetrating.  Needs intense or prolonged
  radiation to cause damage to cells.

8
Annoying Question (10 mins)

• Explain the dangers associated with radioactive
  sources (8 marks).
• Write a mark scheme for this question i.e. assign
  1 mark each to 8 short but relevant statements.

9
Possible Mark Scheme

• Alpha is intensely ionising.
• Although short range and kept out by skin
• Ingestion of alpha emitters can do immense damage
  to the cells.
• Beta is less ionising
• But can penetrate the body
• Gamma is highly penetrating
• But causes little ionisation.
• Long term exposure leads to damage to DNA

10
Spare Question

• Alpha and beta particles lose about 5 10-18 J
  of kinetic energy in each collision they make
  with an air molecule.  An alpha particle makes
  about 105 collisions per cm with air molecules,
  while a beta particle makes about 103
  collisions.  What is the range of an alpha
  particle and a beta particle if both start off
  with an energy of 4.8 10-13 J?

11
Spare Question Answer

• Both particles lose all their energy in 4.8
  10-13 J 5 10-18 J (P)   96 000 collisions
  (P)  
• The alpha particle has a range of 96000 105
  cm-1 0.96 cm (P)  
• The beta particle has a range of 96000 1000
  cm-1 96 cm. (P)

12
Inverse Square Law for ?
When taking a reading of intensity, I, at a
distance x from the source, I0 is the intensity
at the source and k is a constant. Intensity
(number of photons per unit area) decreases by
the square of the distance. So doubling distance
from source means only a quarter of radiation
reaches you so keep them at a distance! -tongs

• Can be written as-
• or-

13
Learning Objectives

• Recap properties of a, ß, ? radiation.
• Describe and explain the relative hazards to
  humans when exposed to a, ß, ? radiation.
• Recap the inverse square law of radiation.
• Describe how this applies to the safe handling of
  radioactive sources.