picture of detectors

Lead Shielding of Muons

(Yazi Takaki and Derek Hamersly)

This experiment sought to evaluate the effect of lead shielding on muon flux by placing numerous lead bricks between the scintillator detectors. By factoring in multiple variables, the experimenters were able to calculate the expected decrement and compare it to their experimental finding.

Question: Will muons be blocked by lead bricks? If some of them are, how much energy do they lose per layer of lead bricks? We spent the first two weeks planning how we would do an experiment to answer these questions. To learn about shielding effects on muons, we did background research and made estimates of how much energy muons would lose through x centimeters of lead using online sources. Then we were ready to start experimenting.

Setup: We put one muon detector on top of a table and three others on the floor. Then we stacked lead bricks on a platform above the floor detectors and below the table detector. We were using 4 detectors in order to make sure that each event that was recorded by the detectors was actually a muon and not an accident in the PMT (Photomultiplier Tube), which detects photons.

Results: As we hypothesized, the number of muons that made it through the lead was significantly less than the number of muons that reached the detectors when there was no lead. For only one layer of lead (5cm thick), we saw a 15% decrease in the flux rate, or the amount of muons hitting the detectors over time. When we added more layers, there were less dramatic decreases in the flux rate, indicating that the first layer of lead bricks must have knocked out a large portion of the total muon population, and that that large portion was on the low end of the muon energy spectrum.