Radiation Detection

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Radiation Detection

• By
• Kelly Garnes
• Michelle Green
• Shilpa Goyal
• Anand Jain
• Okechukwu Nwogu

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History of Radiation Detection
The early pioneers equipped only with crudely
constructed, large scale machines, their human
senses, and classical theory were seeking to see
into into the interiors of atoms. Were it not
for the spinthrascopes and cloud chambers of
their time, atomic theory could never have
advanced as rapidly as it did.
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The X-RAY
The x-ray, discovered by German physicist Wilhelm
Konrad Roentgen on November 8, 1895, was
reported to the world shortly after the first of
the year 1896. Roentgen's discovery was a
scientific bombshell, and was received with
extraordinary interest by both scientist and
laymen. The X-Ray brought harmful radiation
into the scientific scope.
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THE ERA
With the discovery of harmful types of radiation,
protection and detection efforts became
prevalent. Here is the early chronology of
radiation protection efforts. Pioneer Era
(1895-1905), briefly described above, in which
recognition of the gross somatic hazard
occurred, and relatively simple means devised to
cope. Dormant Era (1905-1925), in which the
major concern was toward applications, but in
which great gains were made in technical and
biological knowledge which were later applied to
protection. Era of Progress (1925-1945), which
saw the development of radiation protection as a
science in its own right along with the birth of
health physics in the Manhattan District.
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The Progressive Era was by far the most
important portion of the radiation protection
movement. It was the Manhattan District of U.S.
Army Corps of Engineers that the name "health
physics" was born, and great advances were made
in radiation safety. From the onset, the leaders
of the Manhattan District recognized that a new
and intense source of radiation and
radioactivity would be created, and thus, in the
summer of 19424, asked Ernest O. Wollan, a
cosmic ray physicist at the University of
Chicago, to form a group to study and control
radiation hazards. Thus, Wollan was the first to
bear the title of health physicist. He was soon
joined by Carl G. Gamertsfelder, recently
graduated physics baccalaureate, and Herbert M.
Parker, the noted British-American medical
physicist. By mid 1943, six others had been
added Karl Z. Morgan, James C. Hart, Robert R.
Coveyou, O.G. Landsverk, L.A. Pardue and John E.
Rose.
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The Manhattan District

• Their activities included development of
  appropriate monitoring instruments, developing
  physical controls, administrative procedures,
  monitoring areas and personnel, radioactive
  waste disposal.
• It was in the Manhattan District that many of the
  modern concepts of protection were born,
  including the rem unit, which took into account
  the biological effectiveness of the radiation,
  and the maximum permissible concentration (MPC)
  for inhaled radioactivity.
• It was in the Manhattan District that modern day
  radiation protection effects, born in the early
  days of x-ray and radium, realized their maturity.

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Radiation Detection and the Future

• Radiation detection
  instrumentation over the past 100 yrs
• has played a significant role in ushering in the
  atomic age
• and the numerous outreaching applications which
  followed.
• While largely unnoticed by the public at large,
  radiation
• detection instrumentation has revolutionized the
  world we
• live in today and will most likely continue to go
  
• undetected in the future as it leads us in our
  endeavor to
• restore the environment.

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Natural Radiation
There are many sources of Natural Radiation.
Randon gas exists in most parts of US at
different levels and is produced from naturally
occurring Uranimum-238 in the soil. It can be a
problem in some areas since the gas can enter the
house through basement. Another gas called
Thorium-232 also exists in the soil. Both Uranium
and Thorium decay into numerous other radioactive
isotopes before decaying into a stable element,
lead.
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Types of Detectable Radiation
There are three types of radiation that may be
detected with a Geiger counter Alpha
Particles Helium nuclei, generally emitted from
heavy elements such as uranium and thorium. Alpha
particles only travel a few inches in the air,
and can be stopped by a piece of paper. Special
Geiger tubes with a mica window are necessary to
detect them, as other windows will stop alpha
particles. Beta Rays Electrons moving at
extremely high (often relativistic) speeds. They
are more penetrating than alpha particles. They
can pass through light elements, such as paper
and aluminum (but only small thicknesses). Gamma
Rays Electromagnetic waves, similar to light,
but at a much higher energy. Much more
penetrating than alpha or beta radiations.
High-energy gamma rays can pass through several
inches of metal. Note that X-Rays and Gamma Rays
are really the same thing, the term X-Ray is used
when the radiation is produced by electrons
striking a material, such as in an X-Ray tube.
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Types of Radiation Detectors
The two types of radiation detectors are GM-10
and GM-45. These are sensitive and affordable
ionizing radiation detectors and are called
Geiger counters. They are capable of detecting
extremely small amounts of radiation. They can
connect to almost any personal computer and
this allows you to measure, record, and display
radiation readings over any time period. GM-10
and GM-45 Geiger counters are also self powered
off the computers serial port and therefore, are
ideal for use in the filed or any location.
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The Geiger counter detects the ionization
produced by a radioactive particle. The counter
records as a particle is detected each time. The
number of events recorded over a period of time
indicates the amount of radiation present. When
this is done over one minute intervals, it is
called counter per minute or CPM. The higher
the CPM, the higher the radiation levels.
The difference between the GM-10 and GM-45 is the
size of the radiation sensor. The GM-45 sensor
has 24 times the surface area of that in the
GM-10 making it more sensitive, especially for
alpha and beta radiation sources. That means that
it can detect weaker levels of radiation.
GM-10
The typical background levels that are detected
with the GM-10 are about 10 CPM which can be
higher in the basement of homes with randon
levels. A GM-10 on an airplane flight recorded a
level of over 400 CPM and this is only due to the
larger amount of cosmic radiation that is present
at high altitudes.
GM-45
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Specifications of Detectors
There is a size difference between the GM-10 and
GM-45 detectors. The surface area of the GM-45
detector is 24 times as large. This means that it
is much more sensitive for alpha and beta
radiation, and somewhat more sensitive for gamma
/ x-ray radiation. That is, it will be able to
detect much smaller (weaker) levels of such
radiation.
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Bringin down the house

• Noise and radiation detection

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• Radiation detector output signals are usually
  weak and require amplification before they can be
  used.
• The nature of the input pulse and discriminator
  determines the characteristics that the
  preamplifier and amplifier must have.
• Two stage amplification is usually used to
  increase the signal-to-noise ratio.

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One and Two stage amplification
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Dad, where does noise come from?

• The detector is away from the readout.
• A shielded cable transmits the output to the
  amplifier. The output signal may be 0.01 volts.
• A gain of 1000 is needed to increase this to 10
  volts (a usable output pulse voltage).
• There is always a pickup of noise in the long
  cable run this noise can amount to 0.001 volts.

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• If all amplification were done at the remote
  amplifier, the 0.01-volt pulse signal would be 10
  volts, and the 0.001 noise signal would be 1
  volt, for a signal-to-noise ratio of 10.
• Dividing the total gain between two stages of
  amplification will reduce the ratio.
• A preamplifier near the detector eliminates cable
  noise because of the short cable length.

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Dad, where does noise come from?

• Radiation impinges on a sensor and creates an
  electrical signal.
• The signal level is low and must be amplified to
  allow digitization and storage.
• Both the sensor and amplifiers cause noise.
• 1. Fluctuations in signal introduced by sensor
• 2. Noise from electronics
• The detection limit and measurement accuracy are
  determined by the signal-to-noise ratio.

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Sure sounds good, but does it do?

• Electronic noise affects all measurements
• Detect presence of hit
• Noise level determines minimum threshold, so that
  if the threshold is too low, the output signal is
  dominated by noise hits.
• 2. Energy measurement
• Noise smears signal amplitude.
• 3. Time measurement
• Noise alters time dependence of signal pulse

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Signal-to-Noise Ratio

• How to optimize the signal-to-noise ratio?
• Increase signal (amplification) and reduce noise
• 2. For a given sensor and signal reduce
  electronic noise

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Its noise to you, but fluctuations within a
power spectrum to me.

• All signals exhibit undesirable fluctuations that
  are called noise the frequency of noise is a
  power spectrum.
• Noise can be periodic or nonperiodic.
• - Periodic noise is high frequency
• - Nonperiodic noise is low frequency and white
  noise

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So many to choose from!

• Detector noise originates in the detector and can
  be classified as
• - Thermal due to the thermal agitation of
  current carriers in a resistive element.
• - the most common example of noise due to
  velocity fluctuations
• Temperature noise is due to fluctuations of the
  electric signal through heat exchange.
• Generation-recombination noise due to
  generation-recombination processes.

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• Contact noise due to current fluctuations across
  electrical contacts.
• Radiation noise due to statistical fluctuations
  in the "arrival" of the photons.
• Dark current noise due to the sum of noise
  currents in the absence of a signal, including
• fluctuations of thermionic emission, of leakage
  current, of corona discharge charge carriers and
  other physical effects.
• Shot noise is the sum of the radiation noise and
  the statistical component of the dark current
  noise.

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Finding resolution

• Resolution distinguishing signal levels
• - recognize structure and improve sensitivity
• - signal to background ratio improves with
  better resolution as signal counts compete with
  fewer background counts
• Signal variance is greater than baseline variance
  - resolution is determined by signal and noise.
• Baseline fluctuations can have many origins but
  noise is the basic limit.

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• Solution
• Tailor frequency response of measurement system
  to optimize signal-to-noise ratio.
• Frequency response of measurement system affects
  both signal amplitude and noise.
• Apply a filter to make the noise spectrum
  white (constant over frequency).
• Then the optimum filter has an impulse response
  that is the signal pulse mirrored in time and
  shifted by the measurement time.

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• This is an acausal filter, i.e. it must act
  before the signal appears.
• - only useful if the time of arrival is known
  in advance.
• - Not good for random events
• need time delay buffer memory ? adds
  complexity!

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Hidden Detectors?

• Radiation and Terrorism
• A 34-year-old man was treated for Graves
  disease. Twenty-four hours after treatment, his
  radioactive iodine uptake was 63. Later that
  week, he was strip-searched twice at Manhattan
  subway stations. Police identified him as
  emitting radiation and detained him for further
  questioning.

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Radiation Badges

• NJ Company develops radiation badges
• Laboratory has created a small device that can
  detect if someone was exposed to radiation.
• Price of 5.

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Radiation Pills

• Radiation Plant Workers Offered Pill
• Tiny pill known as potassium iodide that blocks
  the thyroid from radioactive iodine.
• Pills are available at pharmacies and on the
  Internet, no matter where you live. Cost about
  16 for a package of 14 pills.

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Current Threat of Radiation

• What is a dirty bomb?
• A radiation threat or "Dirty Bomb" is the use of
  common explosives to spread radioactive materials
  over a targeted area.
• A dirty bomb, also known as a radiological
  weapon, is a conventional explosive such as
  dynamite packaged with radioactive material that
  scatters when the bomb goes off.
• A dirty bomb kills or injures through the initial
  blast of the conventional explosive and by
  airborne radiation and contaminationhence the
  term dirty.
• Such bombs could be miniature devices or as big
  as a truck bomb.

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Dirty Bomb Description

• It is not a nuclear blast.
• The force of the explosion and radioactive
  contamination will be more localized.
• While the blast will be immediately obvious, the
  presence of radiation will not be clearly defined
  until trained personnel with specialized
  equipment are on the scene.
• As with any radiation, you want to try to limit
  exposure.

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Radiation Threat
3. Shielding If you have a thick shield between
yourself and the radioactive materials more of
the radiation will be absorbed by the thick
shield, and you will be exposed to less.
2. It is not a nuclear blast. The force of the
explosion and radioactive contamination will be
more localized. In order to limit the amount of
radiation you are exposed to, think about
shielding, distance and time.
1. A radiation threat or "Dirty Bomb" is the use
of common explosives to spread radioactive
materials.
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Radiation Threat (Cont)
4. Distance The farther away you are from the
radiation the lower your exposure.
6. Local authorities may not be able to
immediately provide information on what is
happening and what you should do. However, you
should watch TV, listen to the radio, or check
the Internet often for official news and
information as it becomes available.
5. Time Minimizing time spent exposed will also
reduce your risk.
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Thank you. Hope you enjoyed it!