1000 Solved Problems in Modern Physics

(Tina Meador) #1

3.3 Solutions 245


σ(θ)=

1

4

(

z 1 z 2 e^2
μv^2

) 2

1

sin^4


2

) (Rutherford scattering formula)

3.119 By Problem 3.116


F(q^2 )=

3

q^2 R^2

(

sinqR
qR

−cosqR

)

(1)

R=roA^1 /^3 = 1. 3 ×(64)^1 /^3 = 5 .2fm
q= 2 posin(θ/2)

qR= 2 cpoRsin(θ/2)/c=^2 ×^300 ×

5. 2 ×sin 6◦
197. 3
= 1 .653 radians (2)
sinqR= 0. 9966 ,cosqR=− 0. 0819 (3)
Inserting (2) and (3) in (1), we findF(q)= 0. 75 ,F^2 ≈ 0 .57. Thus Mott’s
scattering is reduced by 57%.

3.120 F(q^2 )= 1 −q


2
6 ^2 <r

(^2) >+···
q= 2 posin(θ/2)= 2 × 200 ×(sin 7◦)MeV/c= 48 .75 MeV/c
<r^2 >=


6 ^2

q^2

[1−F(q^2 )]

= 6 ×

(197.3)^2

(48.75)^2

(1− 0 .6) fm^2

= 39. 3
∴Root mean square radius= 6 .27 fm

3.121 F(q)=(4π/q)


∫∞

0

ρ(r)sin(qr)rdr

=(4π/π^3 /^2 b^3 q)

∫∞

0

e−r

(^2) /b 2
sin(qr)rdr
=(− 4 /π^1 /^2 b^3 q)



∂q

∫∞

0

e−r

(^2) /b 2
cos(qr)dr
=(− 4 /π^1 /^2 b^3 q)



∂q

[

1

2

(πb^2 )^1 /^2 e−b

(^2) q (^2) / 4


]

F(q)=exp(−b^2 q^2 /4)

<r^2 >=

∫∞

0 r

(^2) ρ(r)4πr (^2) dr

ρ(r)4πr^2 dr


=

∫∞

0 r

(^4) er^2 /b^2 dr
∫∞
0 r
(^2) e−r^2 /b^2 dr
where we have putρ(r)=(1/π^3 /^2 b^3 )e−r
(^2) /b 2
dr
With the change of variabler^2 /b^2 =x, we get
<r^2 >=
b^2


∫∞

0 x

3 / (^2) e−xdx
∫∞
0 x
1 / (^2) e−xdx =


Γ

( 5

2

)

b^2
Γ

( 3

2

) =

3 b^2
2
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