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1
Calculate the
impact parameter
for scattering a
7.7-MeV a particle
from gold at an
angle of
(a) 1° and
(b) 90°.
Solution
Alpha Particle
Alpha particles, also called alpha
rays or alpha radiation, consist of
two protons and two
neutrons bound together into a
particle identical to a helium-4
nucleus.
Gold
Gold is a chemical element; it has
symbol Au (from Latin Aurum 'gold')
and atomic number 79.

2
Atomic Number
(Proton Number) Symbol Z. The
number of protons in the nucleus of
an atom. The atomic number is
equal to the number of electrons
orbiting the nucleus in a neutral
atom.
Nucleon Number
(Mass Number) Symbol A. The
number of nucleons in an atomic
nucleus of a particular nuclide.

3
2
1 2
0
The relation between the
impact parameter b and
scattering angle for
Coulomb scattering is
cot (1)
8 2
Z Z e
b
K



   
1 2
2
0
(a)
Using
2, 79, 1 ,
7.7 ,
1.440 .
4
in eq.(1), weget
Z Z
K MeV
e
MeV fm


  



4
15
15
12
2 79 1.440 .
cot0.5
2 7.7
14.77 10 114.59
1692.96 10
1.69296 10
X X MeV fm
b
X MeV
X mX
X m
X m







12
12
12
14
( )
90
1.69296 10
45
0.5
1.69296 10
1
114.59
0.0147 10
1.47 10
b
b X mX
Cot
Cot
X mX
X m
X m











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