PET stands for Positron-electron tomography. These scans use radioactive tracers, to see where gamma rays are given off. In the city where I live, there are several portable PET scanners. The only radioactive part of the procedure should be the patient injucted with radiotracers. In order to get the information needed for dose, I took 3, 10 minute measurements at 5 step intervals(using my feet as measurement) stepping away from the PET scanner. The closest trial had a mean of 3266.11 CPS. The farthest trial had a mean of 344.09 CPS when peaks are taken away. (Peak count rates were detected when a person walked by, their body containing the various sources I explore in this paper) Using that, we can conclude that I was originally 4.8 feet away from the source. If we assume that 40 CPS is normal background, then it would take approximately 43 feet to get back to background. I’d also like to mention that in some trials there were inconsistencies in radiation detection, sometimes the background level was higher, and sometimes a person with the source wouldn’t be detected as a spike.

From there we can also figure out what radioactive source specifically was being used, that also might there be on a more consistent basis, because the data showed a consistent level of counts besides people walking past. We can do this by figuring out the half life, from a fitted line of Ae-λt+b.(this is the equation for half life decay) This gave us a slope of the exponential of 0.000489. This is manipulated to give us a half life of 1417.47 seconds, or 23.62 minutes. This is extremely close to the true half-life of carbon 11 --20 minutes. They often use carbon 11 for PET scans.

Historically planes are known to have higher levels of radiation, going so far as to have regulations for people whose jobs include flying extremely often. This is because the higher altitude you have, the more exposure to cosmic rays you are getting, especially the closer to the poles you are. I got the opportunity to fly in a Cessna over the summer, so I brought the CsI detector with me in the air. The main discoveries we found were that the CsI detector cannot detect the most common cosmic rays. This is shown in the fact that we got less than background levels while at an altitude of around 5500 feet, seeing the drop off of the gamma rays reflected from the ground. From there we were able to show the actual correlations that could be picked up by the CsI.

I found online data that tracked our planes altitude, vs time. This had to be calibrated to our time on the device. Unfortunately, the device's time wasn’t accurate because it hadn’t connected to the internet before. This meant that I had to first change all the times to the accurate epoch time, and then convert all the times from the website into the same format. The other problem was that their timing in between data points wasn’t the same, so a pandas data frame resample was used to fix that. Lastly, there were some problems with delays that contributed to uncertainty with the take off and landing times correlated to the graph in terms of background radiation, so the data was shifted to account for that. Doing all this, gives us a correlation of around -0.85 between Radiation Counts and Altitude, showing how only the altitude was contributing to radiation differences!

Correlation graph between Radiation Counts, and Altitude over Time

Next, we made a scatterplot to look at the specific data points. We focused on the region below 4000 ft, but above the ground because we wouldn’t expect fluctuations on the groups to be related to change in altitude, and above a certain altitude. (It flattens off around 4000 ft) For that specific section, there was a very strong correlation of -0.95. The p-value was also minuscule enough that it showed up at 0.0000, meaning that there is a 0% chance that such a correlation was due to random chance, proving a statistically significant correlation.

Scatterplot with Altitude vs Radiation Counts