Photomultiplier tubes (PMTs) are often used in
scintillation detection of radiation, and Cremat
products can be used to read out signals from PMTs.
There are two different ways to use PMTs with Cremat products, and
these will be described below.
1) PMT
readout using a charge sensitive preamplifier & shaping
amplifier:
This setup
has the advantage that it uses a charge sensitive
preamplifier to read out the PMT, so the gain of the
amplification system is fixed (independent of input
capacitance). The anode of the PMT can be connected
directly to the input of a
CR-150 evaluation board having a
charge sensitive preamplifier
module installed. It does not matter whether
the anode is at ground potential or at positive bias,
because the input to the CR-150 board is protected by a HV
blocking capacitor. The CR-150 board has a "bias in"
connection, which should be unconnected for PMT use. The output
of the CSP is routed to a Gaussian shaping amplifier,
which will amplify the signal from the CSP and shape the
signal pulses into a Gaussian shape. The Cremat
Gaussian shaping amplifier is a
CR-160 evaluation
board having a CR-200
shaping amplifier module installed. A figure showing the
configuration is shown below:
2) PMT
readout using only a Gaussian shaping amplifier:
As implied above, charge
sensitive preamplifiers are not always necessary to
obtain good Gaussian pulses from a PMT. It is possible
to simplify the circuitry a bit by omitting the
preamplifier from the configuration shown above, while
adding only a couple capacitors. A descriptive diagram
is shown below. This configuration will work
for PMTs biased in either polarity because there is a HV blocking capacitor
protecting the shaping amplifier input from the voltage
at the PMT anode. However, if the PMT anode is at ground
potential, then the circuit can be further simplified by
replacing the 0.01uF
HV blocking capacitor with a direct connection (wire)
between the anode and the 0.10uF
capacitor.
