INDEX
TOPIC –
NUCLEI

INTRODUCTION

NUCLEAR PROPERTIES

SIZE AND SAHAPE OF
NUCLEUS

BINDING ENGERY PER
NUCLEUS

MASS DEFECT

RADIOACTIVITY
INTRODUCTION
Nucleus is a small central,
massive and positively
charged core surrounded
by orbits of electron. The
size of nucleus is 104m i.e.
10,000 times smaller than
atom. Nucleus is made of
two types of elementary particles.
1. PROTONS – Proton is positively charged particles
having magnitude +1.6×10-19 Coulombs . Protons is
1836.1 times heavier than electrons . Mass of
protons mp= 1.6725×10-27 kg. it possess ½ spin and
have small magnetic movement mp =1.07277 amu
discovered goidstein.
NUTRONES – Neutrons is a neutral particle . ist
also possess half spin its mass is mn= 1.6748×1027kg .i, m = 1.008665amu
n
Proton and neutrons are collectively called
nucleons.
Nuclear Properties
o The nuclear charge is +e times the number
(Z) of protons.
o Atoms with the same Z, but different
mass number A, are called isotopes.
Examples:- Hydrogen’s isotopes:
 Deuterium: Heavy hydrogen. Has a neutron
as well as a proton in its nucleus.
 Tritium: Has two neutrons and one proton.
 The nuclei of the deuterium and tritium
atoms are called deuterons and tritons.
o The symbol of an atomic nucleus is
.
where Z = atomic number (number of protons)
N = neutron number (number of neutrons)
A = mass number (Z + N)
X = chemical element symbol
o Each nuclear species with a given Z and A is
called a nuclide.
o Z characterizes a chemical element.
o The dependence of the chemical properties on
N is negligible.
o Nuclides with the same neutron number are
called isotones and the same value of A are
called isobars.
o Both neutrons and protons, collectively called
nucleons, are constructed of other particles
called quarks
Sizes and Shapes of
Nucleus
 Rutherford concluded that the range of the nuclear
force must be less than about 10−14 m.
 Assume that nuclei are spheres of radius R.
 Particles (electrons, protons, neutrons, and alphas)
scatter when projected close to the nucleus.
 It is not obvious whether the maximum interaction
distance refers to the nuclear size (matter radius),
or whether the nuclear force extends beyond the
nuclear matter (force radius).
 The nuclear force is often called the strong force.
Nuclear force radius ≈ mass radius ≈ charge
radius
 The nuclear radius may be approximated to be R
= r0A1/3
Where r0 ≈ 1.2 × 10−15 m.
 Nuclear size:- nucleas is nearly spherical.
Volume of nucleas is directly propotional to
mass no A
V = 4/3πR3 α A
→
R3 α A or R α A1/3
→
R = RoA1/3
Binding Energy Per
Nucleon
 Use
this
to
compare
the
relative
stability of different nuclides.
It peaks near A = 56.
The curve increases rapidly, demonstrating the
saturation effect of nuclear force.
Sharp peaks for the even-even nuclides 4He, 12C,
and 16O tight bound.
Binding Energy Per Nucleon
MASS
DEFECT
The nucleus of the atom
is held together by a
STRONG NUCLEAR
FORCE.
The more stable the
nucleus, the more energy needed to break it apart.
Energy need to break to break the nucleus into
protons and neutrons is called the Binding Energy
Einstein discovered that the mass of the separated
particles is greater than the mass of the intact
stable nucleus to begin with. This difference in mass
(Dm) is called the mass defect.
Mass Defect - Explained
The extra mass turns into
energy holding the atom
together
Mass Defect –Example
Radioactivity
When an unstable nucleus releases energy and/or
particles.
Radioactive Decay
There are 4 basicRadioactive Decay types of
radioactive decay
 Alpha – Ejected Helium
 Beta – Ejected Electron
 Positron – Ejected Anti-Beta particle
4
2
He
0
1
0
1
e
e
0
0

You may encounter protons and neutrons being
1
emitted as well
1
p
1
0
n
 Gamma – Ejected Energy
Gamma Decay
240
94
Pu Pu  
240
94
0
0
Fission Bomb
One class of nuclear weapon, a fission
bomb (not to be confused with the
fusion bomb), otherwise known as
an atomic bomb or atom bomb, is a
fission reactor designed to liberate
as much energy as possible as
rapidly as possible, before the
released energy causes the reactor
to explode (and the chain reaction to
stop).
A nuclear reactor is a device in
which nuclear chain fission reactions
are initiated, controlled, and
sustained at a steady rate, as
opposed to a nuclear bomb, in which
the chain reaction occurs in a
fraction of a second and is
uncontrolled causing an explosion.