# Determining Threshold Voltage and Plateau from experimental data

I’ve been trying to figure out how to interpret the following data from the Geiger muller tube

There are only seven data points. Where does the plateau begin? Has the data collection begun after the number of counts has reached the plateau? What does this say and the threshold voltage. I feel like it’s ambiguous.

• What you need to include are the error bars in the count rate. If the total count is $N$ then the error due to statistical fluctuations is $\sqrt N$. – Farcher May 16 '18 at 8:08
• The plateau runs up to 700 or 750 volt. The GM works at least at 500 volts. So 600 V is a good voltage to run this device on. That is usually the quantity that one is interested in. – Pieter May 16 '18 at 11:44

• I have updated the picture, its just a sketch. I have done a weighted linear regression ($\sigma _{CountRate} = \sqrt{\frac{N}{t^2}} = \sqrt{N}, ~ as~t = 1$). I then did a chi squared value GOF test which output a very large number (p-val < 0.001) if I use the first 5 or 6 points. I suppose I will simply have to explain why the experiment deviates from the theory as you said – frozenbooger May 16 '18 at 15:19
• @dmckee I agree, there seems to be significant systematic error. This data was given to me to analyze with no detail as to any errors in the collection process. The only error I am aware of is that counts will follow a poisson distribution, thus $\sigma_{counts} = \sqrt{N}$ – frozenbooger May 16 '18 at 17:59