Radiation Detectorrs

1
Radiation Detectorrs

• Two main Groups 1. Thermal (wide response)
• 2. Photoelectric
  (narrow response)
• Detector Characteristics
• Responsivity (RE) Ratio of detector output to
  detector input.
• RE can be determined over a single Wavelength or
  a range of wavelengths.

2
Radiation Detectors

• 2. NEP noise equivalent power
• - all detectors generate noise
• - NEP is the point of applied power
  where the signal output equals the noise output
  .
• - Also the point where S/N 1.

3
Radiation Detectors

• Summary
• What is the relationship between BW (bandwidth)
  and noise?
• Detector area and RE are inversely proportional.
• The lower the NEP the more sensitive the
  detector is.

4
Radiation Detectors

• 3. Detectivity the measure of sensitivity of a
  detector to respond to lower levels of radiation.
• - the reciprocal of NEP
• - detectivity also depends on noise
  bandwidth and detector area.
• (dee-star) detectivity normalized to a
  detector with an area of 1 .

5
Radiation Detectors

• 5. Quantum efficiency- relates to intrinsic
  efficiency of a photodetector.
• - ratio of the number of photoelectrons
  released to the number if incident quanta
  absorbed at a particular wavelength.
• 6. Response Time expressed as time constant
  when response is exponential. (time to reach 63
  of response magnitude)
• - expressed as rise and fall time when
  non-exponential.(10 to 90).

6
Radiation Detectors

• Noise
• Johnson noise thermal in nature
• Shot noise
• Recombination noise
• Flicker noise