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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