Efficiency curves

From MariachiWiki

A Mariachi coincidence box can be used to measure an efficiency curve. This curve shows the efficiency of a detector, i.e. the fraction of times it detects a charge particle going through it (as opposed to missing the particle), as a function of voltage applied to it. The efficiency curve helps to choose a correct operation point which is defined by a few factors: it should be on a plateau of the efficiency curve, the efficiency at that point should be >90%, the noise level should be relatively small <500Hz.

How do you know the fraction of times a detector detects a particle ? You have to separately count how many times particles hit the detector and how many times it reacts (produce a pulse detectable by our electronics). How can you know that a paricle hit a detector ? If you put it between two other counters and these two are hit in the same time (a coincidence is detected) it's extremely likely that this is coused by a cosmic ray particle passed through them. From a pure geometry the same particle should pass through the middle counter (one in question) as well. And you detect how many times the detector reacted by counting triple coincidences (all three detectors produce signals in the same time). Two additional counters are called trigger counters.

The mariachi coincidence box (also refered as the board) designed to detect muliple coincidence fits well for this task. All you need to do is to plug triggers counters to inputs 1 and 2 of the box and plug the testing counter to input 3, power everything on and run the Data Acquistion Program. It shows the number of double coicidences (trigger counters, the denominator for calculating the efficiency) and triple coicidences (all counters, the nominator) for a given amount of time. It also gives you the total number of pulsed detected by each of the detectors which are mostly noise.

Here are more detail instruction:

1. Power everything on following this instructions (you don't need all equipment described there)
2. Load the program to the coincidence box if necessary
3. Set voltage on the power line to the detector to 5.2V
4. Run the DAQ Program and write down the number of double and triple coincidences and the total number of counts from the testing detector (noise). We would suggest you to write this to an Excel spreadsheet).
5. Increase the voltage by 0.1-0.2V and repeat the previous step. Keep doing that until you reach 6.0V.
6. Using an Excel plot the efficiency curve and a level of noise for the testing counter. You should get something like this.

You might want to proceed and install a resistor to the box to make the detector permanently operating from the box at this voltage.

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