Transcript Lecture 8: Rad Safety

Lecture 8
Instruments and Calibration
Area Surveys and Leak Tests
Audits/Inspections
Review of Take home midterm
Regions
• Recombination: If the voltage is too low, the ions
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recombine before reaching the electrodes.
Ionization (Ion Chambers) Size of pulse directly
related to energy deposited. Thus, can measure
exposure in Roentgens.
Proportional Basically the same as Ion except
stronger signal. Probably better in lower radiation
areas where you still want exposure
measurements.
Regions
• Geiger-Mueller (The Geiger counter) Very
sensitive to small amounts of radiation. Best
calibrated for cpm and to locate radiation.
• Use ion chamber for exposure (hence dose)
Survey Meters
Excellent Reference
on Survey Meters
• http://www.ndted.org/EducationResources/CommunityColleg
e/RadiationSafety/radiation_safety_equipment/
SurveyMeters.htm
Scintillation Detectors.
• The most sensitive to radiation. Calibrated in
cpm.
• Can detect very small amounts.
• The type of survey meter that is used at
landfills
Examples of Some Survey Meters
Multichannel Analyzers
• It should be easy to differentiate between the types of
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radiation if there exists a relationship between energy
deposited in a crystal, and size of pulse.
Therefore, one can discriminate between various
energy levels.
Very useful for the identification of types of radiation.
In imaging, isolates the energy used for imaging, such
as Tc-99m
Portable MCA
MCA PC DISPLAY
Dose Calibrator
• Dose Calibrators are Shielded Ion chambers
with preset settings(which can be manually
adjusted) for specific isotopes, which can
give an apporximate yet prompt reading
based upon the preprogramed settings. It is
very useful in the clinical environment due
to it's immediate readings.
Dose Calibrator
Calibration Tests
Daily Constancy and Channel
Check
Quarterly Linearity
Annual Accuracy
Geometry
Well counter
Usually employing a sodium iodide crystal
detector, that is used for measuring
radioactivity in small samples (sodium iodide
well counter). The well counter is so called
because the samples are inserted into a well
within the crystal in order to maximize
sensitivity by collecting as many of the emitted
gamma rays are possible.
Well Counter
“Gamma Counter”
Modern well counters can automatically record
activity in many different samples sequentially.
Samples are placed in test tubes which are then
inserted into the well, one sample at a time, and
counted for a predetermined time. Results are
presented as a graph, and, if required,
corrected for the decay of the sample from a
specified time point.
Gamma Counter
Well Counter
Calibration Tests
Daily Constancy
Annual Efficiency
Radiation Safety Audits
Mid-Term
Polar Mapping
Polar Map Display