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Electronics

Once the radiation deposits it energy in the detector and the detector converts the energy into an electrical pulse, the system electronics process the information into a useable form, either as a count rate for gross counting systems or as an energy spectrum for nuclide identification and spectroscopy. The basic components in the electronics include the preamplifier, the main amplifier and either one or more discriminators and counters (for gross counting) or an analog to digital converter and histogram memory (for spectroscopy).


Preamplifier


The functions of the preamplifier are:


  1. conversion from current to voltage
  2. inear amplification
  3. providing circuitry close to the diode to minimize the capacitive loading of the diode
  4. allowing matching of diode impedances.


Linear Amplifier


The purposes of the amplifier are:


  1. amplification
  2. pulse shaping


The input pulse to the amplifier is the voltage output from the preamplifier and the output from the amplifier is an amplified and shaped pulse. The gain of the amplifier is defined as:

gain = output voltage / input voltage, so a gain of 100 would result in an output  of 10 V from an input  of 0.1 V.


Differential Discriminator

The purpose of the discriminator is to create a logic signal output only if the input signal is between a lower and upper discriminator setting corresponding to a low and high reference voltage.


Counter

A counter is incremented by one for each output signal from the discriminator.

For gross counting of gamma rays, a total count of an energy range may be reported, for example from 25 to 3000 keV for gamma rays. However, because gamma rays associated with a given radionuclide have specific energy and because some gamma ray detectors can measure this energy more precisely than others, it is possible to look at specific energy intervals and improve the sensitivity. Sensitivity is determined by the signal to background ratio. This is true for radiation measurements as it is true for many electronic measurements. Nucsafe gross counting systems for gamma rays utilize at least 6 separate regions of interest (ROI) plus a total of all 6 ROI.


Channel

Data

Abbreviation

Comments

0,0

Total Energy

gS

0-3 MeV or full energy scale

0,1

ROI 1

g1

0-500 keV

0,2

ROI 2

g2

500-1000 keV

0,3

ROI 3

g3

1000-1500 keV

0,4

ROI 4

g4

1500-2000 keV

0,5

ROI 5

g5

2000-2500 keV

0,6

ROI 6

g6

2500-3000 KeV

0,7

ROI 7

g7

>3000 KeV

 

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