GENERAL PHYSICS III
GENERAL PHYSICS III
Optics
&
Quantum Physics
Chapter XXIII
Chapter XXIII
Nuclear Physics
Nuclear Physics
§1. The structure and properties of nuclei
§2. Nuclear binding energy and nuclear force
§3. Nuclear stability and radioactivity
It is well known for you that every atom contains as its center
a nucleus that is:
positively charged
much smaller in size than the atom
carrying almost the total mass of the atom
This chapter provides deeper knowledge about NUCLEI
§1. The structure and properties of nuclei:
1.1 The structure of nuclei:
• Nucleus consist of two sorts of particles: protons (p) and neutrons (n).
(the common name: nucleons)
• The mass of nuleons:
m
p
= 1.007276xu; m
n
= 1.008665xu; (Note: m
e
= 0.000548580 x u).
where 1u = 1.66053873x10

27



N
: the nuclear magneton
(It is 1386 times smaller than the Bohr magneton)
•• An application of the proton spin:An application of the proton spin: Magnetic Resonance ImagingMagnetic Resonance Imaging
In order to image tissue of various types, Magnetic Resonance
Imaging detects the small difference in the numbers of “up” and
“down” hydrogen proton spins generated when the object studied is
placed in a magnetic field.
Magnetic resonance imaging (MRI) depends
on the absorption of electromagnetic radiation
by the nuclear spin of the hydrogen atoms
in our bodies (in water molecules).
The nucleus is a proton with
spin ½, so in a magnetic field B there are only
two possible spin directions with definite energy.
The energy difference between these states is
E=2
p
B, with 
p
= 1.41 x 10
-26
J /Tesla.
= 2.82 x 10
-26
J

• We have for a nucleus: A = Z + N
The mass number =
the total number of
protons and neutrons
The atomic number =
the ordinal numeral of the
element in the Periodic Table
= the charge number
= the number of protons
The number
of neutrons
Denote a nucleus by the symbol:
Z
X
A
(
1
H
1
,
2
He
4
,
8
O
16
,… )
• The isotopes of an element: the nuclei that have the same Z (that is
belong to the same element), but different A


m)10(1fermi
15

§2. Nuclear binding energy and nuclear force:
The component paricles (protons, neutrons) of a nucleus bind strongly
together inside it. The evidence for this is that we must spend an amount
of energy (to bombard the nucleus by other particles) to separate a
nucleus to individual protons and neutrons.
Thus we have for the nuclear binding energy E
B
the following equation:
E
B
= { [Z.m
p
+ (A-Z).m
n
] – M }.c
2
The total mass of separate nucleons
The mass of nucleus
>
2.1 Nuclear binding energy: