www.sakshieducation.com
MODERN PHYSICS
The word ‘atom’ derived from Greek work which literally means ‘indivisible’. The picture of
atom underwent significant modifications from Dalton to Erwin Schrodinger…..
Different models namely, Dalton model, Thomson’s model, Rutherford’s model, Bohr’s
model, Somerfield’s concept of elliptical orbits, De Broglie’s concept of Dual nature of
atom, Schrodinger’s wave equation etc lead to unveil the structure of atom. (Details will be
discussed in chemistry)
Constituents of Atom
Atom consists Central particle named as Nucleus. Nucleus consists Protons, and Neutrons.
Electrons revolve around the nucleus.
Proton is positively charged, electron is negatively charged, and neutron has no charge.
Protons and neutrons are collectively known as Nucleons.
Atomic number (Z):
The number of protons in an atom is defined as Atomic number.
Atomic mass or Mass number (A)
The total number of protons (Z) and neutrons(N) in an atom is defined as its atomic mass
number or mass number (A)
A=Z+N
Atomic mass unit (amu)
The amu is defined as 1/12th of mass of a neutral Carbon atom.
1 amu = 1.66054021 x 10-27 Kg.
Atom symbol:
ZX
A
X atom
Z Atomic number (number of protons) A
Mass number (Z + N)
MASS DEFECT (∆m)
Mass defect is defined as the difference between the sum of the individual
masses of constituents in a nucleus and the mass of the nucleus itself.
www.sakshieducation.com
www.sakshieducation.com
∆m = Sum of individual masses of Constituents of the nucleus
Actual mass of the nucleus
Ex: Let us calculate the ∆m Helium (2He4) atom
4
2He
Consists 2 protons and 2 neutrons in its nucleus.
Mass of proton (mp) = 1.0078amu, Mass of neutron (mn) = 1.0087amu
Total mass of 2 protons = 2 x 1.0078 = 2.0156 amu
Total mass of 2 neutrons = 2 x 1.0087 = 2.0174 amu
---------4.0330 amu
-----------∆m = 4.0330 - 4 = 0.330 amu
The magnitude of mass defect is a measure of the stability of the nucleus.
MASS ENERGY EQUIVALENCE ( E)
The relation between Mass & Energy conversion was postulated by Albert Einstein (1879 1955) in 1905.
“Mass and Energy are mutually convertible”.
The principle of mass energy equivalence is given by
E = ∆m c2
Where
∆m is the mass defect
C is the velocity of light (3 x108m/sec)
Albert Einstein (1879 - 1955)
Thus the mass defect of Helium nucleus to be 0.0304 amu has been converted a energy the
energy is utilized to bind two protons and two neutrons together and is called Binding
Energy (B.E)
B.E of nucleus = ∆m x 931.5 Mev.
NATURAL RADIO ACTIVITY
Radio activity was accidentally discovered by A.H Becquerel.
www.sakshieducation.com
www.sakshieducation.com
“The self disintegrating spontaneous activity in the form of emission & radiation by some
unstable nuclei with atomic number greater than 83 is called natural radio activity”
A.H. BECQUERAL
CLASSIFICATIONS OF RADIATIONS FROM RADIOACTIVE SUBSTANCES
A small quantity of radioactive material is kept in a deep
cavity of thick block of lead.A strong electic and
Magnetic field are applied and the nature of radiations are
studied. Three types of emissions are observed on the
three photographic plated placed on the three sides of the
Lead cavity.The three types of radiations are α, β, and γ The
characteristics are as follows.
PROPERTIES OF α , β, AND γ, RADIATIONS
PROPERTY
NATURE
CHARGE
Speed
Ionization power
Penetrating
power
Effect of electric
field
Effect of
magnetic field
(α ) radation
It consists of two
protons and two
neutrons
Positive
107m/sec
Very high
Very low
Deflected
towards cathode
Deflected
(β ) radiation
These are
electrons
(γ )radiation
These are electro
magnetic
radiations
Negative
No charge
8
10 m/sec
3 x 108m/xec
Less than α, more Very less
than γ
More than α, less Very high
than γ
Deflected
No deflection
towards anode
Deflected
No deflection
RADIOACTIVE TRANSFORMATIONS:
Since α, and β are charged particles, the emission of these particles from a nucleus should
convert it into different nucleus, which would be stable or unstable.
The disintegration of an unstable nucleus resulting in another nucleus is called
RADIOACTIVE TRANSFORMATION
www.sakshieducation.com
www.sakshieducation.com
Ejection of α particle
When α - particle is emitted the atomic number of the original nucleus is reduced by 2 and its
mass number by 4 units.
Ex:
238
92U
Th234
90
-
+ 2He4
Ejection of β particle:
Ejection of β particle from nuclear results in the increase of atomic number by 1 unit.
Ex:
90Th
234
91
Pa234 + +1 β0
Ejection of γ particle:
The emissions of γ ray doesnot alter either the atomic number or the mass number of the
atom.
RADIOACTIVE SERIES
The sequential decay of a given nuclei results in the production of a nuclei or element. This
series of elements thus formed is known as a radioactive decay series.
There are 3 radioactive series depending on the original progenitor.
1) uranium series
2) Actinium series
3) Thorium series
The important features of the radioactive series:
1) In every one of these three series radioactivity finally ceases with a stable lead
Isotope.
2) Only Inert gas formed in these series are Radon (Rn) Z = 86
3) In all the d series wherever there is a change in mass number, it alters by 4 only.
4) Depending upon the masses of the element, the series are named as
Uranium (4n + 2 )
Thorium ( 4n )
Actinium ( 4n + 3 )
5) There is another artificially produced radioactive series called as Neptunium ( 93
Np237 ) or ( 4n + 1 ) series.
HALF LIFE PERIOD (T )
www.sakshieducation.com
www.sakshieducation.com
The half life period (T) of a radioactive substance is defined as the time required for half of its
atom to disintegrate.
If 1gm of radioactive element reduced to ½ gm in a time T, ¼ gm in 2T 1/8 gm in 3T and so
on……….
The radioactive decay constant (λ) is also used do describe the activity of a radioactive
element λ = 0.693/T
ISOTOPES
Aston established the concept of isotopes.
Atoms of the same element having same atomic number but different mass number are called
Isotopes of that element.
Ex:
1) 1H1 , 1H2 , 1H3
2) 10Ne20, 10Ne21, 10Ne22 etc.
ISOBARS
Atoms of different elements having same mass number but different atomic numbers are
called Isobars.
Ex : 1)
2)
ISOTONES
40
, 20Ca40
13
6C , 7N etc.
19K
13
Isotones are the atoms with their nuclei having same number of neutrons but different
number of protons.
Ex:
www.sakshieducation.com
www.sakshieducation.com
ELEMENT Z
Si
14
P
15
A
31
32
N
17
17
ARTIFICIAL RADIOACTIVITY
ARTIFICIAL TRANSMUTATION:
The process of transformation of one element into another by artificial means of
bombarding it with high energy particles is known as ARTIFICIAL TRANSMUTATION.
Rutherford’s experiment:
+
1
O17 +
1H
(Alpha particle) (Nitrogen) (Oxygen) (Proton)
Here α particle is used as projectile, then Proton is released.
2He
4
7N
14
8
ARTIFICIAL TRANSMUTATION BY PROTONS
Cockcroft and Walton attempted to transmute elements by using Proton as projectile.
Ex:
1H
1
+
11Na
23
10
Ne20 +
(proton)
2He
4
(Alpha particle)
Here α particle is released.
ARTIFICIAL RADIOACTIVITY
The product nuclei formed in the above transmutations, found to be radioactive, which is
undergoing disintegration by emitting positron (positton is an elementary particle with a positive
charge and mass equal to the mass of electron) this radioactivity is known as
Artificial radioactivity.
It was first discovered by Curie in 1934. Their experiments is
bombardment of Aluminium with α
Particle.
27
13Al
15 30
+ 2He4
Q
P * + 0n1 +
(Alpha particle)
(Neutrino) (energy)
www.sakshieducation.com
www.sakshieducation.com
30
15P
30
*
14Si
+ 1e0 (Positron)
Madam curie
A NUCLEAR PROCESS IN WHICH A STABLE ELEMENT IS CONVERTED INTO
ANOTHER ELEMTN WHICH IS RADIOACTIVE IN NATURE IS CALLED
ARTIFICIAL OR INDUCED RADIOACTIVITY.
About 500 radioactive Isotopes have been artificially produced by bombardment of stable
elements with α particle.
USES OF RADIO ISOTOPES
a) In medicine:
1) Radio Sodium (11Na24) is used to detect a clot in the blood of a human body
2) Radio Cobalt (27Co60 ) is used to kill cancer cells.
3) Radio Iodine (53I131 ) is used to test the functioning of Thyroid.
b) In Industry
1) Radio Cobalt (27Co60 ) is used to detect internal flaws of cast material.
2) Radiation from radio Isotopes is used to dispel the static electricity acquired
by some material.
c) Agriculture
1) Unnecessary mutations of plants can be prevented by irradiating seeds using
radio Isotopes.
d) Meteorology
1) The course of Monsoon and the changes they undergo can be studied by
injecting radioactive gases into atmosphere and they are followed with
suitable detectors.
e) Radio active dating
1) The age of ancient biological materials (Fossils) can be determined by using
radio Carbon (6C14).
2) The age of rocks can be determined by using Uranium isotope.
PROPERTIES OF α, β, AND γ, RADIATIONS
CHARGE
Speed
Ionization power
(α ) radation
It consists of two
protons and two
neutrons
Positive
107m/sec
Very high
Penetrating
Very low
PROPERTY
NATURE
(β ) radiation
These are
electrons
(γ )radiation
These are electro
magnetic
radiations
Negative
No charge
108m/sec
3 x 108m/xec
Less than α, more Very less
than γ
More than α, less Very high
www.sakshieducation.com
www.sakshieducation.com
power
Effect of electric
field
Effect of
magnetic field
Deflected
towards cathode
Deflected
than γ
Deflected
towards anode
Deflected
No deflection
No deflection
NUCLEAR REACTIONS
There are two types of Nuclear reactions. They are 1) Nuclear fission, 2) Nuclear
Fusion.
NUCLEAR FISSION
It was first discovered by OTTO HANN IN 1939.
OTTO HANN
“A Heavy unstable Nucleus such as Uranium when bombarded with slow neutrons
explode into two more or less equal fragments, which fly apart with very great energy of
about 200Mev. Such a nuclear disruption has been named ad FISSION’.
235
92U
+ 0n1
[92U236]
(Combined nucleus)
56Ba
141
+ 36Kr92 + 30n1 + Q (Energy)
This phenomenon was explained by Neils Bohr and wheeler on the
basis of liquid drop model of nucleus.
CHAIN REACTION
A CHAIN REACTION is a series of nuclear fission where by the neutron produced in each
fission causes additional fissions.
www.sakshieducation.com
www.sakshieducation.com
If a nucleus of 92U235 is bombarded in this process energy is liberated and also two or three
neutrons are released. These neutrons in turn would be captured by the nucleus of nearby
Uranium atom and they, in turn, would split, liberating fresh neutrons, which participate in
further fission reaction.
CONTROLLED CHAIN REACTION
The control and harnessing of the energy becomes possible if the number of neutrons in
the immediate environment of Uranium nuclei is limited by some means
NUCLEAR REACTOR
PRINCIPLE:
The controlled chain reaction is the basic principle on which nuclear reactor functions.
These are the sources for the generation of electric power.
The first nuclear reactor was put into operation in Chicago (USA) in 1942.
The essential features of a nuclear reactor are
1) The fuel,
2) Moderator
3) Control rods
4) Radioactive Shielding
5) The coolant.
SCHEMATIC DIAGRAM OF NUCLEAR REACTOR:
www.sakshieducation.com
www.sakshieducation.com
1) FUEL:
The fissionable material used in the reactor is called fuel. Isotopes of Uranium,
Plutonium, and Thorium are commonly used fuels. The rods of these fuels are
tightly sealed in aluminum cylinders.
2) MODERATOR:
The purpose of using moderator is to slowdown the fast moving neutrons during the
fission process. Heavy water or graphite or beryllium, or Hydro carbon
plastics are some of the suitable material used as moderator.
3) CONTROL RODS:
These absorb the neutrons and control the chain reaction. Cadmium or Boron
rods are generally used for this purpose.
4) RADIATION SHIELDING:
Lead blocks, Concrete walls of thickness 10m are used to prevent spreading of
radioactive effect to the space around the nuclear reactor. This is called
radiation shielding.
5) COOLANT:
The substance used to absorb heat generated in the reactor is called the coolant.
Generally Water with pumps is used as coolant.
WORKING
www.sakshieducation.com
www.sakshieducation.com
The reactor core (consisting Moderator and Fuel rods) and pump are in contact with a heat
exchanger which is generally water. This water changes into steam which is utilized to turn
the turbine.
IN THIS NUCLEAR REACTOR, IF THE CHAIN REACTION IS UNCONTROLLED,
THE DEVICE IN TURNS AN ATOM BOMB.
NUCLEAR POWER PLANT:
ATOMIC EXPLOSION:
NUCLEAR FUSION
A nuclear reaction in which lighter nuclei are combined together to form heavier product
nuclei with the release of enormous amount of energy is called FUSION.
EX: Two Hydrogen nuclei combine to form Helium Isotope.
www.sakshieducation.com
www.sakshieducation.com
2 +1e0 +
2 0ν0 + Q
(positron) (neutrino) (energy)
The energy released is 27.67 Mev.
4 1 H1
2
He4 +
The above reactions are called proton - proton cycle. The proton cycles are responsible for
energies of the stars like Sun.
HYDROGEN BOMB:
Uncontrolled fusion is the principle of Hydrogen Bomb.
IMPORTANT CONSTANTS
1)
2)
3)
4)
5)
6)
7)
8)
9)
Radius of nucleus:
2.4 x 10-15m
1 amu = 1.66054021 x 10-27 Kg
Nucleus density = 2.92 x 1017 Kg/m3
Charge of electron (e)
= 1.6 x 10-19 Coulombs
Mass of electron (m) = 9.11 x 10-31 Kg
e/m of electron = 1.76 x 1011 C/Kg
1 amu = 931.5 Mev (or) 931.5 x 106 ev
∆m in case of He atom = 0.0304 amu (or) 1.5 x 10 -10Joules (or)
6.24 x 1012 Mev
16
1 Kg = 9 x 10 Joules
www.sakshieducation.com
www.sakshieducation.com
1 Joule = 1.15 x 10-17 Kg
1 Mev = 1.6 x 10-13 J
Mass of proton (mp ) = 1.0078 amu
Mass of Neutron (mn) = 1.0087 amu
Speed of α particle = 107 m/sec
Speed of β particle = 108 m/sec
Speed of γ particle = 3 x 108 m/sec = speed of light
Energy released in fission reaction of Uranium = 200Mev
Energy released in Fusion of Hydrogen = 27.67 Mev
Energy required to start a fusion reaction = 0.01Mev (or)
80 x106 degrees Kelvin
20) Energy of Thermo neutrons = 0.04ev.
10)
11)
12)
13)
14)
15)
16)
17)
18)
19)
IMPORTANT QUESTIONS
1 MARK:
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
Define Mass defect?
What is natural radioactivity?
What is radioactive transformation?
State the law of radioactive disintegration?
What is moderator?
Define nuclear fission?
What is a chain reaction?
Define nuclear fusion?
State the law of Einstein’s mass energy equivalence?
What happens when an α partcle is ejected from a radioactive element?
What happens when a β partcle is ejected from a radioactive element?
What happens when a γ partcle is ejected from a radioactive element?
2 MARKS:
1)
2)
3)
4)
Define Isotopes? Give examples?
Define Isobars? Give examples?
Define Isotones? Give examples?
Differentiate between artificial and natural radioactivity?
4 MARKS:
1)
2)
3)
4)
5)
What are the properties of α, β, and γ radiations?
What is radioactive dating? Explain?
Mention the uses of Radio Isotopes in medicine, industry, agriculture and
meteorology?
What are the components of a nuclear reactor? What are their functions?
What is the principle of nuclear reactor? How is a chain reaction controlled in a
nuclear reactor?
5 MARKS:
www.sakshieducation.com
www.sakshieducation.com
1)
Draw a neat labeled diagram of Nuclear reactor?
BITS
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
14)
15)
16)
17)
18)
19)
20)
21)
22)
23)
24)
25)
26)
27)
28)
29)
30)
31)
The description of the distribution of mass and positive and negative charges in an
atom is called an ______________________
Alpha particle is _________ charged particle.
Mass of the electron is __________ of mass of alpha particle
________ discovered neutron in 1932.
Protons and neutrons are collectively called ____
The amu is defined as 1/12th of the mass a ________ atom.
The difference between the sum of the individual masses of the constituents of
nucleus and the mass of the nucleus is called __
The mass defect of Helium atom is ______
The magnitude of the mass defect is a measure of ____ of nucleus
The mass energy equivalence was given by _____
The mass energy equivalence E = ___
The energy used to bind the protons and neutrons in a nucleus is called ____
Binding energy = mass defect x _____
Electron volt is a unit of _____
The ability of certain substances to transform incident ultraviolet radiations into
visible light is called ____
The self disintegrating spontaneous activity in the form of emission of radiations
by some unstable nucleus with atomic number greater than 83 is called ______
_____ can absorb the radioactive rays given by radioactive substance.
_____ are doubly ionized Helium atom
______ particles have high ionization extent of the gases through which they pass.
_______ rays are electromagnetic radiations in radioactive emission.
Γ rays travel with the speed of ________
_________ rays have low Ionization power.
_______ rays have high penetrating power.
______ rays are used in treatment of cancer.
The disintegration of an unstable nucleus resulting in another nucleus is called
_______
After α decay, the position of the element shifts _____ places left in the periodic
table.
After α decay, the atomic number of the parent nucleus decrease by _ and its mass
number by ________
238
90
92U
Th 234 + _________
In β decay the element changes into another element of _____ mass number and
atomic number increases by ______
The sequential decay of a given nucleus results in the production of a series of
nuclei of elements known as _________
In transformation series, radioactivity finally ceases with a stable ____ isotope as
the end product.
www.sakshieducation.com
www.sakshieducation.com
32) The inert gas present each series is _____
33) In the radioactive series whenever the mass number changes it changes by _____ 34)
The time required for half of the atoms of a radioactive substance to disintegrate is
known as _____
35) The decay constant λ = _____
36) Atoms of different elements having same mass number but different atomic
number are called ________
37) Atoms with nuclei having same number of neutrons but different number of
protons are called _______
38) Atoms of same element having same atomic number but different mass number are
called _________
39) Speed of β particles is ______
40) 1 Mev = _____ Joules.
41) Radius of nucleus _______
42) _________ Isotope is used to determine the age of fossils
43) ________ is used as moderator in Nuclear reactor.
44) In a nuclear reactor, the part which consists the moderator and fuel rods is known
as __________
MATCHING
1)
2)
3)
4)
5)
Uranium series
Thorium series
Actinium series
Neptunium series
Age of rocks
ANSWERS:
1)
2)
3)
4)
5)
1)
B
Atomic number
Mass defect
Mass number
Atomic mass unit
Units of energy
ANSWERS;
1) C
2)
(
(
(
(
(
)
)
)
)
)
A)
B)
C)
D)
E)
F)
4n+1
4n + 2
4n
U Isotope
4n + 3
Carbon Isotope
2)
C
3)
E
(
(
(
(
(
)
)
)
)
)
A) Stability of an atom
B) amu
C) Number of protons
D) ev
E) Sum of protons and neutrons
A
3) E
4) B
4) A
5) F
5) D
ANSWERS FOR BITS
1)
Atomic model 2) Positively 3) 1/7000 4) Chadwick 5) Nucleons
6) Carbon 7) mass defect 8) 0.0304 amu 9) Stability 10) Einstein
11) ∆mc2 12) binding energy 13) 931.5 Mev 14) Energy 15) Flourosence
16) Natural radioactivity 17) Lead 18) α particles 19) α particles
www.sakshieducation.com
www.sakshieducation.com
20) γ particles 21) Light 22) γ rays 23) γ rays 24) γ rays
25) Radioactive disintegration 26) 2 27) 2, 4 28) α particle
29) same, 1 30) Radioactive series 31) Lead 32) Radon
33) decrease by 4 units 34) Half life period (T) 35) 0.693/T 36) Isobars
37) Isotones 38) Isotopes 39) 108 m/sec 40) 1.6 x 10-13 Joules
41) 10-13 Cm 42) Carbon 43) Heavy water or Graphite 44) Reactor core
www.sakshieducation.com