A muon is a sub-atomic particle (a member of the lepton family) that is unstable
PHYSICS · Multi-part · A Level · Physics · Turning points in physics · Turning points in physics
Problem
A muon is a sub-atomic particle (a member of the lepton family) that is unstable. It has a half-life of t21=3.1μs when measured in a frame of reference where the muon is at rest.Muons are produced in large numbers in the Earth's upper atmosphere, at an altitude of about 15 km, by cosmic rays colliding with atoms to produce pions. These pions then decay into muons (and muon neutrinos). When produced, muons travel at a speed of 0.97c towards the Earth's surface, where they are detected.
(1) According to an observer on the Earth, what is the muon's half-life?
(2) According to an observer on the Earth, how far do muons travel through the atmosphere in one half-life?
(3) Show that, in the muon's frame of reference, the muon's proper half-life and the distance it travels in this time are consistent with it moving at a speed of 0.97c relative to the Earth.
(4) How many half-lives must pass before the muons reach the Earth's surface?
(5) Outline why so many muons are observed at the Earth's surface.