Measurement and instrumentation Flashcards
What is the operational voltage for a Gieger-Muller counter?
900-1000 volts
What is the scintillation process?
The absorption of energy by a substance and its re-emission as visible or near visible light. (photoluminescence, thermoluminescence, phosphorescence)
Equation for resolving time correction
N= n/(1-nt) N=true count rate n=observed count rate t= resolved time ex: t=200 sec; n= 6x10^4 cpm; N=7.5x10^4 cpm
What is dead time?
The interval of time for GM tubes where no pulse can be formed.
What is resolving time?
The interval of time which is required between two successive signals, so that both may be analyzed
Equation for resolving time correction
N= n/(1-nt) N=true count rate n=observed count rate t= resolved time ex: t=200 sec; n= 6x10^4 cpm; N=7.5x10^4 cpm
What is Recovery Time?
the period from the time a pulse can be formed (end of dead time) until the time the pulse size is large enough to be passed by the discriminator and be counted.
Common gases used in proportional counters
- 90% argon, 10% methane
- Propane
- BF3
What is exposure?
the correspondence to the amount of ionization charge collected per unit of mass of air
What is absorbed dose?
The measurement of ionization produced by radiation considering its avg energy needed to create an ion pair in the detector.
What is Dose Equivalent?
The true dose imparted to matter. Takes into account the quality factor for the type of radiation exposed.
Which factors affect detector response?
Temperature, humidity, and pressure
What is the process of radiation being detected?
Radiation goes into the detector, interacts with the scintillator, creates secondary electrons, secondary electrons interact with dynodes, electrons progressively multiply until it reaches 10^6 electrons, signal goes through pre-amp, then amp, the discriminator, then pulse shaper, lastly scaler/analyzer
What factors affect detector efficiency?
Geometry, backscatter, housing/other scatter, self-absorption, other absorption, intrinsic efficiency
How to calculate detector efficiency?
E= (# counts)
—————————
(# disintegrations)