YouTube Lecture # 103

1. 1
The neutrons produced in a
reactor are known as thermal
neutrons, because their kinetic
energies have been reduced (by
collisions) until K = 3/2 (kT),
where T is room temperature
(293 K). (a) What is the kinetic
energy of such neutrons? (b)
What is their de Broglie
wavelength? Because this
wavelength is of the same order
as the lattice spacing of the
atoms of a solid, neutron
diffraction (like X-ray and
electron diffraction) is a useful
means of studying solid lattices.
Helping Tools
No.1

2. 2
No.2
No.3

3. 3
No.4
OR
OR
OR

4. 4
Solution
5
5
( )
We know that
3
2
3
8.617 10 293
2
3787.1715 10
0.037871715
a
K kT
eV
X X X K
K
X eV
eV
−
−
=
=
=
=

5. 5
2
2
2 2
2
2 2
6
2
6 2
2
6 2
2
2
3
( )
1
K &
2 2
2
2 2
2 939.6 10 0.038
71.41 10 ( )
71.41 10 ( )
8.45 10
b Now
p
mv p mv K
m
c mc K
p mK mKX
c c
X X eVX eV
c
X eV
c
X eV
p
c
X eV
p
c
= =  =
 = = =
=
=
 =
 =

6. 6
15
3
18
18 8
10 9
,
4.136 10 .
8.45 10
0.4895 10 .
0.4895 10 2.998 10 .
1.47 10 0.147 10
0.147
Also
E hf h
p
c c
h X eV s
eV
p X
c
X c s
m
X X X s
s
X m X m
nm


−
−
−
− −
= = =
 = =
=
=
= =
=