Week 8 Blog Post

Hi everybody!

Welcome to week 6 of my senior project. This week, I talk about radiation spectrum peaks and progress on my project.

Nuclear Physics Weekly

Last week, we discussed the Compton continuum that radiation peaks sit on. Now, let’s shift our focus to the peaks themselves.

Bell-Curve Peaks
When a gamma ray interacts with a CsI crystal, it produces a flash of light whose energy is measured and converted to a voltage reading. Over many events, you’ll see that the pulses corresponding to a particular gamma-ray energy cluster around a mean voltage, but they’re not all identical—instead, they form a symmetric, bell-shaped peak in the spectrum.

This bell shape comes from a combination of small, random fluctuations in the light yield, the photodetector gain, and the electronics. Each individual measurement of a pulse is subject to these errors and the result is a peak that is spread out a bit. Therefore, if we want to find the number of counts at, say, 1000 keV, we need to sum up the counts in a range from, say, 995 to 1005 keV. To model these bell-shaped curves, we use something called a Gaussian Distribution

Gaussian (Normal) Distributions
The Gaussian, or normal distribution, is the go-to model whenever you have many small, independent sources of variation adding together. Usually, it’s seen in the context of probability distribution (PDF) functions, which model the probability of different events occurring. A lot of random events tend to shape themselves in a Gaussian distribution, so using it here is an appropriate choice. Once we get the shape of the gaussian, we simply take the area under the gaussian to determine the number of decays that happened at the peak energy of the gaussian. 

Project Progress

The end of the project is nearing, and I’m mostly wrapping up work at this point. I didn’t write much new code this week, but did a lot of cleaning up and organizing existing code into readable chunks. I’m also trying to get my hands on a portable detector, but if that’s not possible, I’ll be running my code on a simulation. Next week, I’ll start writing my presentation and wrapping up!

See you all next week!