HPGe Gamma-Ray Spectrometer

The detector is the center piece of the gamma spectroscopy system.

The gamma photons interact with the detection material producing electrons.

Why Hyper-Pure Germanium (HPGe)?








e- must go from the valence to conduction band by gaining energy, above energy gap (Eg), from heat or photon
e- transfer will be more efficient if detector has less impurities

Ge are purified


Detector
Multichannel Analyzer (MCA)


Multichannel Analyzer (MCA)
The heart of most experimental measurement.

Sorts analog data according to height then converts them to digital 'channels' via Analog-to-Digital Converter (ADC)

The number of pulse counts as a function of channel number is called a 'pulse height spectrum'.
Pulse height spectrum




Thank you
Parts of a Gamma-Ray Spectrometer

Amplifier
It shapes and magnifies the amplitude of the preamp's output pulse from mV to 0.1- to 10-V range
Due to the linear nature of amp, the pulse height is proportional to the gamma-ray energy absorbed
Amplifier


Preamplifier
Collects the charge created within the detector after photon interaction

It converts the collected charge pulse to a voltage pulse


Attenuates background radiation before reaching the detector.

Composed of layers of high-density and large-atomic number like lead and aluminum.
Detector Shielding
Cooling system


Cooling system
Due to low band gap, HPGe must be cooled to reduce the production of electrons from heat absorption.

These electrons (noise) destroy the detector's energy resolution.

To avoid this, the detector must operate in very cold conditions.

LN2 is the common cooling medium given these conditions.
Preamplifier


Detector



Gamma Spectrometer System



Samples have radionuclides that emit
gamma photons at known energies.

These photons interact with the detector which are processed into
Samples have radionuclides that emit gamma photons at known energies.

These photons interact with the detector which are processed into a photopeak spectrum
HPGe Gamma-Ray Spectrometer

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The detector is the center piece of the gamma
spectroscopy system. The gamma photons interact
with the detection materia
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Background radiation like terrestrial gamma-ray or cosmic radiation
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LN2 which has a temperature of 77°K or –196 °C is the common cooling medium
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their form carefully manipulated to
eliminate problems with electronic noise, and pulses "riding"
on the tails of those preceding them.
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