Why Are We Bombarded by Muons? Muons are unstable subatomic particles that decay to electrons with a mean lifetime of 2.2 μs. They are produced when cosmic rays bombard the upper atmosphere about 10 km above the earth's surface, and they travel very close to the speed of light. The problem we want to address is why we see any of them at the earth's surface. (a) What is the greatest distance a muon could travel during its 2.2 μs lifetime? (b) According to your answer in part (a), it would seem that muons could never make it to the ground. But the 2.2 μs lifetime is measured in the frame of the muon, and muons are moving very fast. At a speed of 0.999c, what is the mean lifetime of a muon as measured by an observer at rest on the earth? How far would the muon travel in this time? Does this result explain why we find muons in cosmic rays? (c) From the point of view of the muon, it still lives for only 2.2 μs, so how does it make it to the ground? What is the thickness of the 10 km of atmosphere through which the muon must travel, as measured by the muon? Is it now clear how the muon is able to reach the ground?
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1. Intro to Physics Units
Introduction to Units
Problem 21
Textbook Question
X rays with an initial wavelength of m undergo Compton scattering. For what scattering angle is the wavelength of the scattered x rays greater by than that of the incident x rays?

1
Determine the relationship between the change in wavelength (Δλ) and the scattering angle (θ) using the Compton wavelength shift formula: Δλ = (h / (m_e * c)) * (1 - cos(θ)), where h is Planck's constant, m_e is the electron mass, and c is the speed of light.
Calculate the change in wavelength (Δλ) as 1.0% of the initial wavelength: Δλ = 0.01 * 0.900 × 10^-10 m.
Substitute the known values of Δλ, h, m_e, and c into the Compton formula to isolate the term (1 - cos(θ)): (1 - cos(θ)) = Δλ / (h / (m_e * c)).
Solve for cos(θ) using the equation: cos(θ) = 1 - (Δλ / (h / (m_e * c))).
Finally, calculate the scattering angle θ by taking the inverse cosine (arccos) of the result: θ = arccos(cos(θ)).

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Compton Scattering
Compton scattering is a phenomenon where X-rays or gamma rays collide with matter, resulting in a change in the wavelength of the radiation. This effect occurs due to the interaction between photons and electrons, leading to the transfer of energy and momentum. The change in wavelength is dependent on the scattering angle, which can be calculated using the Compton wavelength shift equation.
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Wavelength Shift
The wavelength shift in Compton scattering refers to the difference in wavelength between the incident and scattered X-rays. It can be quantified using the formula Δλ = λ' - λ = (h/m_ec)(1 - cos(θ)), where h is Planck's constant, m_e is the electron mass, c is the speed of light, and θ is the scattering angle. A 1% increase in wavelength indicates a specific relationship between the initial and final wavelengths that must be calculated.
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Scattering Angle
The scattering angle is the angle at which a photon is deflected after colliding with an electron. It plays a crucial role in determining the change in wavelength during Compton scattering. By analyzing the relationship between the scattering angle and the resulting wavelength shift, one can derive the angle that corresponds to a specific increase in wavelength, such as the 1% increase mentioned in the question.
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