In: Physics
calculate the mass collision stopping power for a 20-MeV proton in lead, without the shell correction.
Answer: 11.6 MeV cm^2/g
Bethe's formula for stopping power of charged particle
z =1 for proton , charge on the charged particle
Iev - average excitation energy of the medium
= 52.8ev + 8.71*z ev , approx.
= 52.8ev + 8.71*82 = 767 ev ( z= 82 for lead)
= v/c , v is the speed of the particle
relativistic kinetic energy of proton mc2 / (1-2 )1/2 - mc2 = 20 Mev
mc2 = 931.5 Mev , rest mass of proton
2 = 0.0416
F() = 10.65
n: electron density of lead
density of Pb = 11.34 gm/cc
z= 82 ; 82 electrons per atom 1 mol of Pb = 207 gm
per gm = 6.02e+23/207 * 82 = 2.385e+23 electrons /gm
per cu.m n= 2.385e+23 *11.34e+6 = 2.704e+30
dE/dx = 5.08e-31 *1*2.704e+30 / 0.0416 * (10.65 - ln(767) ) = -131.55 Mev/cm
- linear stopping power
mass stopping power = 1/ * dE/dx = 131.55/11.34 = 11.60 Mev-cm2/gm