42 Questions
What is the conventional unit of measuring exposure to x-rays?
Roentgen
What is the best way to count the x-ray photons incident across an area?
Extrapolating their number from the ionizations they are causing within air molecules
What is generated within the air when x-ray photons interact with it?
An electric charge
What is the limitation of the Roentgen unit?
It is not a good indicator of the biological impact of radiation exposure
What is the common component of all radiation detectors?
A transducer (radiation sensitive region)
What happens to the electrons freed by ionization in a detection device?
They are attracted to the positive anode of a detection device
What is the primary function of a portable survey instrument in environmental radiation?
To detect radiation contamination on work surfaces
What happens when valence electrons return to their normal position in scintillation?
They scintillate
What is required for a material to scintillate?
A particular crystalline structure
What determines the amount of light emitted in scintillation?
The amount of energy absorbed by the material
What type of detector converts x-rays to light?
Scintillation detector
What is the purpose of a photocathode in a scintillation detector?
To convert light to electrons
What is the basis of radiation detection instruments?
The ionization of atoms
What determines whether ionization or excitation is favored in a radiation detector?
The physical state and density of the transducer
What is the purpose of the electronic component in a radiation detector?
To convert the radiation effect in the transducer into a useful electronic signal
What is the main difference between instruments designed for detection and those designed for measurement?
The mode of operation
What is the main advantage of using the integrate mode in radiation detection?
It provides a precise measurement of radiation exposure over a set period of time
What is the unit of measurement for radiation exposure in the integrate mode?
Millisieverts (mSv)
What is the main factor that affects the accuracy of radiation detection devices?
The actual printed scale behind the needle of a meter
How can the sensitivity of a radiation detection instrument be improved?
By increasing the electronic amplification of the incoming signal
What is the definition of sensitivity in radiation detection?
The ability to detect small amounts of radiation
What is the purpose of a photomultiplier tube in radiation detection?
To increase the sensitivity of the instrument
What can cause the read-out of a radiation detection device to be higher than the real exposure?
Electronic noise
Why do integrate mode detectors have less chance of missing photons?
They are less susceptible to dead times
What is the problem with using a Geiger counter on a diagnostic x-ray machine?
It overloads the circuits of the counter
What happens if the range of a detection instrument is set too high for the intensities of radiation expected?
Low intensities will not be picked up and adequately displayed on the read-out
What is required for a transducer to have a high quantum detection efficiency?
Sufficient stopping power and optimal positioning
What is the effect of increasing the density of a transducer on its absolute detection efficiency?
It increases
What is the definition of absolute efficiency of a radiation detector?
The ratio of the number of radiation events detected to the number of photons emitted
What is the reason for the low absolute efficiency of gas-filled detectors?
They are based on ionization of gas
What is the result of increasing the resolving time of a radiation detector?
It decreases the accuracy of the instrument
What is the condition necessary for a radiation detection device to produce a valid and accurate reading?
The sensitivity of the device must be matched to the expected intensity levels and type of radiation
What occurs when radiation passes through gas in a detector?
Ion pairs are created
What is the purpose of the anode in a gas filled detector?
To attract and detect electrons freed from the gas
What is the characteristic of ionization chambers that makes them suitable for radiation surveys?
Portability
What is the 'cascade' effect in proportional counters?
The electron ejected from the first event has energy to knock other electrons out
What is the main difference between proportional counters and Geiger-Mueller tubes?
Cascade effect vs saturation process
What is the purpose of quenching agents in Geiger-Mueller tubes?
To restore the gas molecules to their original state
What is the characteristic of Geiger-Mueller tubes that makes them suitable for detecting small amounts of radiation?
High sensitivity
What is the disadvantage of Geiger-Mueller tubes?
Dead time
What is the result of the saturation process in Geiger-Mueller tubes?
The ionization of all gas molecules in the chamber
What is the advantage of ionization chambers over proportional counters?
Higher accuracy
Test your knowledge of radiation units, exposure, and detection in radiologic science. Covers the Roentgen unit, radiation intensity, and x-ray photon counting.
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