Nuclear & Particle Physics - Cosmic Rays

In experiments located deep underground the two types of cosmic rays that most commonly reach the experimental apparatus are

A. alpha particles and neutrons
B. protons and electrons
C. iron nuclei and carbon nuclei
D. muons and neutrinos
E. positrons and electrons

(GR9277 #25)

Solution:

Since the experiment is located deep underground, the particles must be essentially massless and able to pass through or do not interact with matter easily → muons and neutrinos.

Muon:

• "heavy" electron (200 times the mass of the electrons)
• highly penetrating

Neutrinos:

• almost no mass
• travel close to the speed of light
• weakly interact with other

Answer: D



Notes:

• Alpha particles and neutrons have high kinetic energy but very short penetrating depth because they are quite massive, can't go through the Earth.
• Protons and electrons don’t penetrate much as they interact easily with matter. Protons are also pretty massive.
• Iron and carbon nuclei are very heavy and interact very easily with matter.
• Positrons and electrons have the same mass and are highly interacting with matter. Positron also has a very short life span.