1000 Solved Problems in Modern Physics

Chapter 9

Particle Physics – I

9.1 Basic Concepts and Formulae ................................

Interactions and decay

Probability for scattering

P=t/λ (9.1)

wheretis the thickness andλis the mean free path.

Attenuation of beam intensity due to interaction

I=Ioe−μx (9.2)

The absorption coefficientμis in metre−^1 ifxis in metre.

μis in cm^2 /gifxis in g/cm^2.

xin g/cm^2 =(xin cm)(density in g/cm^3 )

μ=Σ(macroscopic cross - section)

Σ=σN 0 ρ/A

(9.3)

whereσ=microscopic cross-section,No=Avogadro’s number,ρ=density and

A=Atomic or molecular weight.

Attenuation of beam intensity due to decay

I=Ioe−t/τ=Ioe−s/νγτ^0 (9.4)

whereν=βcis the particle velocity,γ is the Lorentz factor,sis the distance

travelled andτois the proper life time, that is the life time in the rest frame of the

particle.

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