Chapter 9
Particle Physics – I
9.1 Basic Concepts and Formulae
Interactions and decay
Probability for scattering
P = t/λ
(9.1)
where t is the thickness and λ is the mean free path.
Attenuation of beam intensity due to interaction
I = I o e
−μx
(9.2)
The absorption coefficient μ is in metre
−1 if x is in metre.
μ is in cm
2
/g if x is in g/cm
2
.
x in g/cm
2
= (x in cm)(density in g/cm
3 )
μ = Σ(macroscopic cross - section)
Σ = σ N 0 ρ/A
(9.3)
where σ = microscopic cross-section, N o = Avogadro’s number, ρ = density and
A = Atomic or molecular weight.
Attenuation of beam intensity due to decay
I = I o e
−t/τ
= I o e
−s/νγ τ 0
(9.4)
where ν = βc is the particle velocity, γ is the Lorentz factor, s is the distance
travelled and τ o is the proper life time, that is the life time in the rest frame of the
particle.
485
Particle Physics – I
9.1 Basic Concepts and Formulae
Interactions and decay
Probability for scattering
P = t/λ
(9.1)
where t is the thickness and λ is the mean free path.
Attenuation of beam intensity due to interaction
I = I o e
−μx
(9.2)
The absorption coefficient μ is in metre
−1 if x is in metre.
μ is in cm
2
/g if x is in g/cm
2
.
x in g/cm
2
= (x in cm)(density in g/cm
3 )
μ = Σ(macroscopic cross - section)
Σ = σ N 0 ρ/A
(9.3)
where σ = microscopic cross-section, N o = Avogadro’s number, ρ = density and
A = Atomic or molecular weight.
Attenuation of beam intensity due to decay
I = I o e
−t/τ
= I o e
−s/νγ τ 0
(9.4)
where ν = βc is the particle velocity, γ is the Lorentz factor, s is the distance
travelled and τ o is the proper life time, that is the life time in the rest frame of the
particle.
485