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42 Cards in this Set
- Front
- Back
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How does a gass filled detector work?
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radiation sensed by depcting ionization of gas molecules during their passage through the detector
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energy required to knock an e- out of orbit
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ionizing radiation
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gas has what charge in the detector?
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positive
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a gas molecule and an e- produced as a result of ionization
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ion pair
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parts of a gas filled detector
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2 electrodes
gas Voltage Current measurin device |
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name 2 types of electrodes in the gas detector
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anode (+)
cathode (-) |
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What types of gas are used in detectors?
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He
Ne Ar H air |
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Why use a dense noble gas?
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inc. density; inc interaction; inc. efficiency
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how many atmospheres is gas increased by
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5-12 atmospheres
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What is produced when an ion pair reaches an electrode
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Current (AMPs)
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3 types of GFD's
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1. ionization chamber
2. proportional counters 3. GM detectors |
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6 regions of a voltage curve
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recombination
ionization proportional non-proportional Geiger-Mueller Continuous discharge |
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In voltage curve regions 1-4 what 3 types of radiation have curves shown
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alpha
beta gamma |
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How many volts in recombination region of voltage curve?
What detectors operate in this region? |
0 volts
None |
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IHow many volts in ionization region of voltage curve?
What detectors operate in this region? |
100-400V
dose rate meters dose meters (high radiation area) |
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A cutie pie and ionization dose rate meter are examples of ?
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dose rate meters
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These meters measure only amount of radiation present in Ci or Bq
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Dose meters(operate in ionization region)
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Dose calibrator & pocket dosimeters are examples of?
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Dose meters
(operate in ionization region) |
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How many volts in proportional region of voltage curve?
What detectors operate in this region? |
400-800V
Proportional counter |
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Causes more ion pairs to be produced
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Gas amplification
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Avalanche
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a primary ion starts and a secondary ion is produced and collected
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Proportional region represents (more, less) radiation than actually enters the chamber
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More;
it's a factor of current detected |
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Non-proportional region of voltage curve?
What detectors operate in this region? |
800-1000V;
None |
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Geiger-Mueller region of voltage curve?
What detectors operate in this region? |
1000-1500V
Geiger-mueller counter |
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Adding an impurity to Gm attracts energy release on recombination is called?
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Quenching
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Most commonly added gas in quenching? Why?
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Halogen gas It has unlimited use
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Organic gases are not used in quenching normally because of?
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5 year lifetime
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What type of gas amplification is seen in the Gm region of the voltage curve?
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MAX gas amplification
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what rate does the GM region measure intensity in?
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mR/hr.
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How often should constancy be checked? How much should it be within?
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Daily, by nuc med tech, 10%
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Formula for determining slope of GM calibration curve
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Slope=C2-C1/V2-V1
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Slope of GM calibration curve should be <
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<0.15
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Best slope is?
Worst slope is? |
best=0 (horizontal)
worst= 1 (verticle |
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Continuous discharge region of voltage curve?
What detectors operate in this region? |
1500V
None |
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What shape is the dose calibrator
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4pi
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What determines efficiency in a dose calibrator?
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Shape, determined by number of sides
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What does the geometry test?
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Tests different size, volume, and sources to make sure hey read teh same activity
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Sources of error got dose calibrator?
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Wrong setting
contamination location of source |
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4 QC tests; what % must all test be within
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Constancy
Linearity Accuracy Geometry 10% |
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Constancy verifies?
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d.c consistency reproducible on day to day basis
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Linearity verifies
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d.c.reads accuratly over entire range of activities used
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2 linearity tests
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decay method(200Uci-10uCi q 2-6h)
Lead shield |
