Professor Nigel Mason

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Radiation -- Friend or Foe ?

• Professor Nigel Mason
• The Open University

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Typical Radiation exposures

• You are exposed to radiation every day !
• From sunlight

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Typical Radiation exposures

• Most dangerous exposures
• in UK often come from
• Skiing !!!

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Typical Radiation exposures

• You are exposed to radiation every day !
• To natural radioactivity

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Typical Radiation exposures

• You are exposed to radiation every day !
• And what about your mobile ??

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Typical Radiation exposures

• The unit of radioactivity is the rad
• It is a unit of absorbed radiation dose in terms
  of the energy actually deposited in the tissue.
• The rad is defined as an absorbed dose of 0.01
  joules of energy per kilogram of tissue.
• The SI unit is the gray, which is defined as
  1joule of deposited energy per kilogram of
  tissue.

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Typical Radiation exposures

• The biologically effective dose in rems is the
• radiation dose in rads multiplied by a "quality
• factor" which is an assessment of the
  effectiveness
• of that particular type and energy of radiation.
• The sievert is equal to 100 rems.

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Typical Radiation exposures

• Radiation doses (milli Seiverts)
• UK yearly dose 2.6
• Chest x-ray .02
• Fortnight in Cornwall 0.2
• Bag of Brazil nuts a week 0.2 !
• Jar of Mussels a week 0.25
• Frequent flyer 0.4 (100 hours per year)
• Apparently you will receive a 2 mrem
  dose sleeping next to someone for 8 hours (from
  your K) !!!
• 100 mrem 1 millisievert

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So what is radiation ?
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Why is radiation dangerous ?

• Many forms of radiation have enough energy to
• damage molecules in your body most particularly
• your DNA
• DNA tries to repair itself, but if it does so
• incorrectly then it can lead to CANCER
• 1/3 of us will suffer from cancer in our lives

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Why is radiation dangerous ?

• Skin Cancer
• More than 90 of skin cancer is caused by sun
  exposure.
• Unprotected exposure to UV rays can be from being
  outdoors, tanning booths, and even through your
  car or home windows.

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Why is radiation dangerous ?

• Skin cancer data from UK
• Over 65,000 cases of skin cancer were reported in
  1999
• The number of skin cancer cases has more than
  doubled since the early 80s
• Over 2,000 people die from skin cancer each year

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Why is radiation dangerous ?

• Cancer
• More often it is the effect of ionizing radiation
  that can penetrate the body that causes cancers
• Radiation emitted by radioactive atoms

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Radiation damage of biomolecules
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Biological effectiveness radiation type
Energetic X-rays
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Biological effectiveness radiation type
Energetic X-rays
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Biological effectiveness radiation type
a-particles
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DNA is most sensitive genetic material to
radiation damage

• Long chain
• Ladder-like

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DNA structure Double helix

• The original model of DNA by Francis Crick and
  James Watson

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(No Transcript)
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DNA Damage
single-strand break
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DNA Damage
double-strand break
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DNA Damage
complex damage
Locally multiply damaged sites (LMDS)
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DNA Damage
double-strand break
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What is radioactivity ?

• Decay of atomic nucleus leads to emission of
• three types of radiation
• Alpha
• Beta
• Gamma

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What is radioactivity ?

• Alpha decay helium nucleus

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What is radioactivity ?

• Beta decay --- Electron and positron

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What is radioactivity ?

• Gamma decay --- photon

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Dangers of radioactvity

• Alpha particles are absorped by piece of paper
• Beta by thin piece of aluminium
• Gamma by few cms of lead
• So alpha and beta are usually only dangerous by
  ingestion
• Smoking may lead to dose of up to 16,000 mrems

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Radiation your friend

• High doses of radiation can lead to cancer BUT
• It can also play a key role in its treatment
• Radiotherapy high doses of radiation to kill
  cancer cells and stop them from spreading.

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Radiation your friend

• High doses of gamma radiation are directed into
  the tumour.
• The tumour has absorbed chemicals which are
  radiosensitive.
• Tumours cells are killed healthy cells
  survive/repair

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Radiation your friend

• Health effects of UV radiation
• Small amounts of UV are essential in the
  production of vitamin D.
• UV radiation is also used to treat several
  diseases, including rickets, psoriasis, eczema
  and jaundice.

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Radiation your friend

• Sterilisation
• Food may be sterilised using
• gamma radiation in order
• to increase its shelf-life.
• The gamma rays kill micro
• organisms, such as bacteria,
• that may be harmful to
• humans

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Radiation your friend

• Locating the tumours ! Radioisotopes (tracers)
  can be injected into humans in order to locate
  cancerous tumours and other medical problems.
• The picture on the left shows the image from a
  'gamma camera' immediately after a human has been
  injected with Technetium-99. The picture on the
  right shows an image six hours later. You can see
  cancerous cells as a yellow glow (lung cancer

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Radiation your friend

• Another use of
• radioisotopes in
• industry is in
• the thickness
• control of
• materials such as
• paper, cardboard
• and metal
• (e.g. tin foil).

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Radiation your friend

• Smoke Detectors
• Include a tiny mass of radioactive
• americium-241 alpha radiation. The
• radiation passes an air-filled space
• between two electrodes, and permits a
• small, constant current to flow between
• the electrodes. Any smoke that enters the
• chamber absorbs the alpha particles,
• which reduces the ionization and
• interrupts this flow of current, setting off the
  alarm.

Approximately 0.2 milligrams of Am-241 is used,
which has a half life of 432.2 years. This means
that it does not have to be replaced very often,
alpha particles have high ionization (so
sufficient air particles will be ionized for the
current to flow), and they have low penetrative
power - meaning they will be stopped by the
plastic of the smoke detector and/or the air.
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Radiation your friend

• Maybe even a little
• radiation is good for you !!
• Radiation hormesis is the
• hypothesis that ionizing
• radiation can be beneficial.
• This is in contrast to the linear
• no threshold (LNT) model
• which states that the negative
• health effects of ionizing
• radiation are proportional to
• the dose.

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Radiation your friend

• Radiation causes Mutagenesis
• changes in DNA
• Was it necessary for the development of life ?

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The Interstellar Medium is rich in molecules
from the simplest molecule (H2) to those
necessary for the formation of life
Credit R.Ruiterkamp
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gt140 Interstellar Molecules
Glycine ?
Acetic Acid
Benzene
Glycolaldehyde
Cyanopolyynes
Formic Acid
National Radio Astronomy Observatory
http//www.cv.nrao.edu/awootten/allmols.html
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Radiation Chemistry on Dust grains

• Large grains of dust between the stars are where
  molecules form in space
• These Dust grains are covered with an icy mantle
• These ices are irradiated and undergo chemical
  changes.
• Is this where molecules of life are formed ?

• The ices in the mantle are bombarded with cosmic
  rays, Ions, solar UV, electrons.
• Chemical modification occurs.

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Building blocks of life are then transported
to Earth like planets by comets etc
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But .

• There are known knowns
• Known unknowns
• and
• Unknown unknowns

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This is the science of Astrobiology

• But that is another talk .

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Astrobiology has come of age

• And it is an exciting (the most exciting ?) area
  of scientific research.
• Bringing together researchers in a truly
  interdisciplinary programme ! INTERNATIONALLY !!!

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Radiation -- Friend or Foe ?

• YOU DECIDE !!