Scintillators, DAQ boards, and PMTs

Getting Familiarized With the Equipment

By Melissa Sussmann and Alex Bonnifield

Scintillators

Scintillators are substances that absorb energy from fast-moving particles to ultimately detect cosmic rays in our atmosphere.

Our Scintillators are made out of a hard plastic containing an organic dye. They are meant to detect particles, particularly muons in our atmosphere. As the energy from the muons is absorbed, the scintillator produces a quick flash of light, which is detected by a photomultiplier tube

Photomultiplier Tubes (PMTs)

Photomultiplier tubes detect the light from the scintillator. They then use that energy to produce a small amount of electricity.

How is it done??? The light from the scintillator is detected by the

photocathode and turned into electricity. Then, the electrons produced by the photocathode are

bounced from dynode to dynode. Dynodes are a kind of electrode that multiplies the number of electrons for every dynode they touch.

The more dynodes in a PMT, the more electrons are produced.

Another electrode, called an anode flows electric current to the DAQ board

Photomultiplier Tubes (PMTs)

For a more visual approach, click here

Data Acquisition Board (DAQ board)

O The data acquisition board basically counts the time it takes for a scintillation to occur.

O It then discriminates between muons and other particles or forms of error.

O The board then transmits that data to a PC

Data Acquisition Board (DAQ board)

First the electricity goes from the PM tubes through the input of the DAQ board.

It is then pre-amplified to a factor set by resistors

The small, amplified voltage then has to go under a set threshold voltage (from 0 to 750 mV) in order to be detected by the discriminators. If it is not detected, one can assume that the voltage that was produced was not caused by a muon.

Data Acquisition Board (DAQ board)

Data Acquisition Board (DAQ board)

The TDC then receives the feed from the discriminator outputs.

It measures the time a PMT pulse is below the voltage threshold.

This information is then passed through the CPLD, better known as the “fast logic” board.

It is called “fast logic”, because it has the capability of taking information from the TDC at very fast rates, in this case, nanoseconds.

Data Acquisition Board (DAQ board)

The information from the fast logic board is then transmitted to the microcontroller.

The microcontroller is referred to as the “MCU” or the “slow logic”. It is called the “slow logic” board, because it measures time in microseconds; not nanoseconds.

The MCU makes the information given by the CPLD readable for the PC. This information is then displayed on your computer and therefore made accessible to the user.

Data Acquisition Board (DAQ board)

Bibliography

http://microscopy.fsu.edu/primer/flash/photomultiplier/

http://en.wikipedia.org/wiki/Photomultiplier

http://ea.grolier.com/cgi-bin/article?assetid=0348390-00

QuarkNet/Walta/CROP Cosmic Ray Detectors User’s Manual