This document discusses various methods for detecting radiation. It outlines passive detectors like photographic film, electroscopes, dosimeters, and thermoluminescent dosimeters (TLDs) which do not require a power source. Active detectors mentioned include Geiger-Muller tubes and scintillation detectors, which need a constant energy supply. Both types detect radiation indirectly by ionizing matter and detecting the ions produced, though active detectors provide more information about the radiation type and energy.

1. Radiation
Detection

2. Detection
• Now that we know the
characteristics of atomic
structure and radioactivity, we
now need to discuss methods of
detecting radioactivity
• Since radiations are
submicroscopic and cannot be
seen, they must be detected
indirectly

3. Detection
• This is accomplished through
the fact that radiations ionize
matter
• Since we cannot detect the
radiations directly we detect the
ions that it produces
• Consequently, most radiation
detectors work on the process
of ionization

4. Detection
• There are two types of
detectors
– Passive
– Active
• Passive detectors do not require
a constant source of energy, i.e.
“plugged in”, batteries, etc.
• Active detectors require a
constant energy source

5. Detection
• Passive detectors – The first
passive detector we need to
discuss is the first ever
radiation detector…
Photographic Film
• In 1895 Wilhelm Roentgen used
photographic film to record the
first X-Rays

6. Detection
• In 1896 Henri Becquerel used
photographic film to discover
natural radioactivity
• Photographic film is a mixture of
silver nitrate, when silver nitrate
is ionized, they change color
• Photographic film is still the
most commonly used detector

7. Detection
• Both x-rays used the medical
field and PMD (personnel
monitoring device) i.e. Film
Badge
• The quantity of radiation
determines the darkness of the
film exposure
• The type of radiation can be
determined by the use of filters
placed in front of the film

9. Detection
• The advantages of photographic
film are…
– Cost effective
• Cheap
• Length of use
– Requires no user interaction
• Disadvantages of film
– Not immediate results
– Not reusable

10. Detection
• Another passive detector not
used anymore was called an
electroscope
• Electroscopes used the
charging and uncharging of ions
to show the presence of
radiation

12. Detection
• The rate at which the
electroscope discharges, tells
how strong the radiation source
is
• Advantages of electroscopes
– Reusable
• Disadvantage
– Not qualitative (what kind of
radiation)
– Not accurately quantitative (how
much)

13. Detection
• Dosimeters are yet another type
of passive detectors
• Dosimeters work like a
miniature electroscope, inside
there is a small ion chamber
• This chamber contains a Mylar
fiber that works like the gold
leaf of the electroscope

14. Detection
• The dosimeter is charged by
placing the contact point on a
corresponding charging contact
on a dosimeter charger
• They are used for personnel
monitoring
• They are used where the
potential for higher doses of
radiation are possible i.e.
Nuclear Power Plants

15. Detection
• Advantages of dosimeters
– Reusable
– Accurately Quantitative (How
Much)
– Immediate results
• Disadvantages of dosimeters
– Expensive (initial cost)

17. Detection
• The next passive detector we
need to look at are TLD’s
– (Thermo Luminescent Dosimetery)
• Early on in the study of radiation
it was learned that radiation has
very unique affects on
crystalline structures
• Radiation energy causes
electrons to move in these
structures

18. Detection
• When electrons are moved to
higher energy levels, they store
energy
• In many cases this causes a
color change in crystal i.e.
brown glass
• Gemologists learn of this effect
and used it to enhance the color
of gem stones

19. Detection
• Consequently approximately 6
thousand metric tons of
gemstones are irradiated each
year
• Approximately 85% of all the
dark blue topaz sold in the US
has been irradiated
• Other effects to gemstones
include turning yellow into
green diamonds

20. Detection
• Some crystals when heated and
the electrons move back to their
original positions, will give off
visible light
• The amount of light given off is
proportional to the amount of
radiation received i.e. lithium
fluoride

21. Detection
• Consequently, crystals can be
used as personnel monitoring
devices
• The advantages of TLD’s
– Readers are inexpensive
– They are reusable
• Disadvantages of TLD’s
– More quantitative than qualitative

22. Detection
• Cloud Chambers are another
passive detector
• The work on the process of a
gas changing to a liquid
• They are similar to that of a jet
airplane giving off a vapor trail
at high altitude
• In a cloud chamber the cold
area is at the bottom

23. Detection
• The atmosphere is made up of
ethyl alcohol which is slightly
heavier than air
• As the ethyl alcohol sinks
towards the bottom, it gets cold
and wants to condense
• It condenses on the trails of
ions created by the radiation,
therefore you see the effects of
ionization

24. Detection

25. Detection
• Advantages of cloud chambers
– You can physically see the effects
of the radiation
• Disadvantages
– Clouds don’t stay long
• Bubble Chambers work on the
process of liquid changing to
gas… opposite of a cloud
chambers

26. Detection
• They use a chamber of liquid
hydrogen, as the radiation
passes through the liquid, it
causes the atoms to move and
the friction changes the liquid to
a gas
• We do not do bubble chambers
because hydrogen is explosive
and tough to keep in a liquid
state

28. Detection
• Advantages
– Once the bubbles are created, they
are frozen in position, therefore
you can study bubble tracks…
• Disadvantages we discussed
already…
• The final passive detector is the
“missing link” between passive
and active detectors

29. Detection
• A spark chamber contains many
metal plates with a gap between
them
• The plates all have alternating
charges (+ - + - +)
• Inside the chamber and around
the plates is an easily ionized
gas

30. Detection
• As the radiation passes through
the chamber, it creates ions
that bridged the gap and creates
trails of sparks

31. Detection

32. GM Tube
• Detects Alpha, Beta, and
Gamma
• Low efficiency
• But won’t tell you what kind of
radiation

33. Detection

34. Scintillation
• Only Gamma
• And will differentiate between
low and high energy gamma