# Homework Help: Pulsing an LED during muon detection

1. Dec 6, 2016

### rmiller70015

1. The problem statement, all variables and given/known data
For my lab physics class I was in a group doing the classic muon detection assignment. We ran the equipment for about two days and during the time we had a pulsing (100 Hz) LED inside the scintillator chamber. This gave some measurements that were extremely low (about 0.6 μs) and I was wondering why the pulsing light caused the results. Would it be due to the scintillator material absorbing some of the photons from the LED or would it be due to the photomultiplier tube catching these photons or some other effect. Also, what are the LED pulsers used for?

2. Relevant equations

3. The attempt at a solution

2. Dec 6, 2016

### Simon Bridge

... what were you measuring and how? Some time period I'm guessing but what time period?
Without knowing the details of the setup I cannot say. What makes you think the pulsating light caused anything?
All or none of these - what measures were used to prevent this?
You did the experiment - what did you use it for?
Did you just blindly follow instructions? What do the instructions say about it?

Basically - there is no way tot ell what is going on unless you provide a detailed description of the experiment. I am unlikely to be familiar with what counts as standard for this assignment in your country. To my mind "the classic muon detection" thing involves a bunch of guys travelling the the top of Mt Washington, and a lot of effort was made to block out all light from the scintilator and the photomultiplier. I have ever done an experiment which deliberately introduced another light source during the test run. The only time another source is used is for calibration... you switch it off during the run.

3. Dec 6, 2016

### rmiller70015

We were measuring the mean lifetime of a muon. The pulsing light was accidentally turned on by someone and caused mean lifetime of about 1/4 of the expected value. By classic muon experiment I mean the experiment most undergraduate students do to detect muons and measure their life time with a scintillator and photomultiplier.The light shouldn't have been used so I'm guessing its for the time dilation experiment not the mean lifetime experiment that comes in the users manual for the muon phyics equipment.

4. Dec 6, 2016

### Simon Bridge

The time dilation experiment involves measuring the mean lifetime of the muons ... the LED is most likely for calibration.
Can light from the LED get to the scintilator and can it get to the photomultiplier?

Note:
... this statement is nonsense: you don't know that the LED has any effect on the muon's mean life and you do not know of any mechanism for this to happen either so don't say this. What you have written here is a conclusion when you should be writing observations.

Say only what you know first - then speculate.
What you know is that you got a bunch of signals from the equipment.
If you assume that all the pulses come from muons, then use the data to work out the muon mean-life, you get a low number.
However, some pulses come from the LED by some mechanism that depends on stuff you have not told me about how the equipment was set up.
You could maybe rescue the experiment by using what you know about how the LED and equipment interact (which you have also not told me) to take account of this as a kind of background pattern. ie if you know the LED pulses at 1Hz you should be able to remove the resulting artifacts with reasonable confidence.
But if you don't know how the LED interacts with the rest of the equipment, then the experiment is a wash. You have no useful data.