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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: ZXA X atomZ 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.



∆m = Sum of individual masses of - Actual mass of the nucleus Constituents of the nucleus

Ex: Let us calculate the ∆m Helium (2He4) atom

2He4 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.



“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 (α ) radation (β ) radiation (γ )radiationNATURE It consists of

twoprotons and

These areelectrons

These are electromagnetic

CHARGE Positive Negative No chargeSpeed 107m/sec 108m/sec 3 x 108m/xecIonization power

Very high Less than α, more

Very less

Penetratingpower

Very low More than α, less

Very high

Effect of electric

Deflectedtowards

Deflectedtowards anode

No deflection

Effect ofmagnetic field

Deflected 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.comEjection 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: 92U238- Th23490 + 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 )



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 arecalled Isobars.

Ex : 1) 19K40, 20Ca402) 6C13 , 7N13 etc.

ISOTONES

Isotones are the atoms with their nuclei having same number of neutrons but different number of protons.

Ex: www.sakshieducation.com


ELEMENT Z A NSi 14 31 17P 15 32 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:

2He4 + 7N14 8O17 + 1H1(Alpha particle) (Nitrogen) (Oxygen) (Proton)Here α particle is used as projectile, then Proton is released.

ARTIFICIAL TRANSMUTATION BY PROTONS

Cockcroft and Walton attempted to transmute elements by using Proton as projectile.

Ex: 1H1 + 11Na23 10Ne20 + 2He4(proton) (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.

13Al27 + 2He4 15P30 * + 0n1 + Q(Alpha particle) (Neutrino) (energy)



15P30 * 14Si30 + 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

PROPERTY (α ) radation (β ) radiation (γ )radiationNATURE It consists of

twoprotons and

These areelectrons

These are electromagnetic

CHARGE Positive Negative No chargeSpeed 107m/sec 108m/sec 3 x 108m/xecIonization power

Very high Less than α, more

Very less

Penetrating Very low More than α, Very highwww.sakshieducation.com

www.sakshieducation.com power than γEffect of electric

Deflectedtowards

Deflectedtowards anode

No deflection

Effect ofmagnetic field

Deflected Deflected 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’.

92U235 + 0n1 [92U236] 56Ba141 + 36Kr92 + 30n1 + Q (Energy)(Combined nucleus)

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.



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:



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 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.



4 1H1 2He4 + 2 +1e0 + 2 0ν0 + Q(positron) (neutrino) (energy)

The energy released is 27.67 Mev.

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) Radius of nucleus: 2.4 x 10-15m2) 1 amu = 1.66054021 x 10-27 Kg3) Nucleus density = 2.92 x 1017 Kg/m3

4) Charge of electron (e) = 1.6 x 10-19 Coulombs5) Mass of electron (m) = 9.11 x 10-31 Kg6) e/m of electron = 1.76 x 1011 C/Kg7) 1 amu = 931.5 Mev (or) 931.5 x 106 ev8) ∆m in case of He atom = 0.0304 amu (or) 1.5 x 10-10Joules (or)

6.24 x 1012 Mev 9) 1 Kg = 9 x 1016 Joules



10) 1 Joule = 1.15 x 10-17 Kg11) 1 Mev = 1.6 x 10-13 J12) Mass of proton (mp ) = 1.0078 amu13) Mass of Neutron (mn) = 1.0087 amu14) Speed of α particle = 107 m/sec15) Speed of β particle = 108 m/sec16) Speed of γ particle = 3 x 108 m/sec = speed of light17) Energy released in fission reaction of Uranium = 200Mev18) Energy released in Fusion of Hydrogen = 27.67 Mev19) Energy required to start a fusion reaction = 0.01Mev (or)

80 x106 degrees Kelvin 20) Energy of Thermo neutrons = 0.04ev.

IMPORTANT QUESTIONS 1 MARK:

1) Define Mass defect?2) What is natural radioactivity?3) What is radioactive transformation?4) State the law of radioactive disintegration?5) What is moderator?6) Define nuclear fission?7) What is a chain reaction?8) Define nuclear fusion?9) State the law of Einstein’s mass energy equivalence?10) What happens when an α partcle is ejected from a radioactive element?11) What happens when a β partcle is ejected from a radioactive element?12) What happens when a γ partcle is ejected from a radioactive element?

2 MARKS:

1) Define Isotopes? Give examples?2) Define Isobars? Give examples?3) Define Isotones? Give examples?4) Differentiate between artificial and natural radioactivity?

4 MARKS:

1) What are the properties of α, β, and γ radiations?2) What is radioactive dating? Explain?3) Mention the uses of Radio Isotopes in medicine, industry, agriculture and

meteorology?4) What are the components of a nuclear reactor? What are their functions?5) What is the principle of nuclear reactor? How is a chain reaction controlled in a

nuclear reactor?

5 MARKS: www.sakshieducation.com


1) Draw a neat labeled diagram of Nuclear reactor?

BITS

1) The description of the distribution of mass and positive and negative charges in anatom is called an ______________________

2) Alpha particle is _________ charged particle.3) Mass of the electron is __________ of mass of alpha particle4) ________ discovered neutron in 1932.5) Protons and neutrons are collectively called ____6) The amu is defined as 1/12th of the mass a ________ atom.7) The difference between the sum of the individual masses of the constituents of

nucleus and the mass of the nucleus is called __8) The mass defect of Helium atom is ______9) The magnitude of the mass defect is a measure of ____ of nucleus10) The mass energy equivalence was given by _____11) The mass energy equivalence E = ___12) The energy used to bind the protons and neutrons in a nucleus is called ____13) Binding energy = mass defect x _____14) Electron volt is a unit of _____15) The ability of certain substances to transform incident ultraviolet radiations into

visible light is called ____16) The self disintegrating spontaneous activity in the form of emission of radiations

by some unstable nucleus with atomic number greater than 83 is called ______17) _____ can absorb the radioactive rays given by radioactive substance.18) _____ are doubly ionized Helium atom19) ______ particles have high ionization extent of the gases through which they pass.20) _______ rays are electromagnetic radiations in radioactive emission.21) Γ rays travel with the speed of ________22) _________ rays have low Ionization power.23) _______ rays have high penetrating power.24) ______ rays are used in treatment of cancer.25) The disintegration of an unstable nucleus resulting in another nucleus is called

_______ 26) After α decay, the position of the element shifts _____ places left in the periodic

table. 27) After α decay, the atomic number of the parent nucleus decrease by _ and its mass

number by ________ 28) 92U238 90Th 234 + _________29) In β decay the element changes into another element of _____ mass number and

atomic number increases by ______ 30) The sequential decay of a given nucleus results in the production of a series of

nuclei of elements known as _________ 31) In transformation series, radioactivity finally ceases with a stable ____ isotope as

the end product.



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 fossils43) ________ 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) Uranium series ( ) A) 4n+12) Thorium series ( ) B) 4n + 23) Actinium series ( ) C) 4n4) Neptunium series ( ) D) U Isotope5) Age of rocks ( ) E) 4n + 3

F) Carbon Isotope

ANSWERS: 1) B 2) C 3) E 4) A 5) F

1) Atomic number ( ) A) Stability of an atom2) Mass defect ( ) B) amu3) Mass number ( ) C) Number of protons4) Atomic mass unit ( ) D) ev5) Units of energy ( ) E) Sum of protons and neutrons

ANSWERS; 1) C 2) A 3) E 4) B 5) D

ANSWERS FOR BITS

1) Atomic model 2) Positively 3) 1/7000 4) Chadwick 5) Nucleons6) Carbon 7) mass defect 8) 0.0304 amu 9) Stability 10) Einstein11) ∆mc2 12) binding energy 13) 931.5 Mev 14) Energy 15) Flourosence16) Natural radioactivity 17) Lead 18) α particles 19) α particles



20) γ particles 21) Light 22) γ rays 23) γ rays 24) γ rays25) Radioactive disintegration 26) 2 27) 2, 4 28) α particle29) same, 1 30) Radioactive series 31) Lead 32) Radon33) decrease by 4 units 34) Half life period (T) 35) 0.693/T 36) Isobars37) Isotones 38) Isotopes 39) 108 m/sec 40) 1.6 x 10-13 Joules41) 10-13 Cm 42) Carbon 43) Heavy water or Graphite 44) Reactor core


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picsciences.weebly.compicsciences.weebly.com/uploads/1/8/8/4/18842038/10-modernph… · Web vie . MODERN PHYSICS . The word ‘atom’ derived from Greek work which literally means