chapter7nuclearphysics-131023012324-phpapp01.ppt

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Chapter 7:

NUCLEAR

PHYSICS

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SCOPE OF STUDY

11 main sub topics students should learn and understand in this

chapter are :

Structure and Properties of the Nucleus

Discovery of Neutrons

The Nuclear Forces

Atomic Number and Mass Number

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SCOPE OF STUDY

Mass Defect

Binding Energy per Nucleon

Mass-Energy Equation

Isotopes of an Element

Mass Spectrometer

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MASS NUMBER, A

It symbols by A.

A and Z sufficient to specify a nuclide. Nuclide are symbolized by symbol :

X is the chemical symbol for the element.

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Composition of Nucleus:

Every atomic nucleus except that of Hydrogen has two types of particles – protons and neutrons. (Nucleus of Hydrogen contains only one proton)

Proton is a fundamental particle with positive charge 1.6 x 10-19_{C and} mass 1.67 x 10-27_{kg (}_{1836 times heavier than an electron}_).

Neutron is also a fundamental particle with no charge and mass 1.675 x 10-27_{kg (1840 times heavier than an electron).}

Atomic Number (Z):

The number of protons in a nucleus of an atom is called atomic number.

Atomic Mass Number (A):

The sum of number of protons and number of neutrons in a nucleus of an atom is called atomic mass number.

A = Z + N

Atomic Mass Unit (amu):

Atomic Mass Unit (amu) is (1 / 12)th of mass of 1 atom of carbon.

1 amu = 1 12

12 x

6.023 x 1023 g = 1.66 x 10

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MASS NUMBER, A

DEFINITION

Total number of protons and neutrons

(nucleons) in the nucleus

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Classification of nuclei

•

Isotopes are atoms of the same element

having the same Z but different A.

•

1H1, 1H2 and 1H3 are the isotopes of H 2.

•

These contain the same A but different N.

•

As the atoms of isotopes have identical

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•

Isobars

•

Same mass number A, but different atomic

number Z.

•

The nuclei 8O16 and 7N16 represent two

isobars.

•

Since isobars are atoms of different elements,

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•

(iii) Isotones

•

Isotones are atoms of different elements

having the same number

•

of neutrons. 6C14 and 8O16 are some

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ISOTOPES OF

ELEMENT

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Size of Nucleus:

Nucleus does not have a sharp or well-defined boundary. However, the radius of nucleus can be given by

R = R₀ A⅓ _{where R}

0 = 1.2 x 10-5 m is a constant which is the

same for all nuclei and A is the mass number of the nucleus.

Radius of nucleus ranges from 1 fm to 10 fm. Nuclear Volume, V = (4/3) π R3_{= (4/3) π R}

03 A

V α A Nucleus Density:

Mass of nucleus, M = A amu = A x 1.66 x 10-27_kg

Nuclear Volume, V = (4/3) π R3_{= (4/3) π R}

03 A

4 3

22 7

x

= x (1.3 x 10-15₎3_{A m}3

= 7.24 x 10-45_{A m}3

Nucleus Density, ρ = M / V = 2.29 x 1017_{kg / m}3

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General properties of nucleus

•

Nuclear size

•

Nuclear density

•

Nuclear charge

•

Atomic mass unit

•

Nuclear mass

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Nuclear size

The distance of the closest approach of α − particle to the nucleus was taken as a measure of nuclear radius (10−15m).

If the nucleus is assumed to be spherical An empirical relation is found to hold good



1

.

3

10

15

m



A

1 3

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Nuclear density

•

The nuclear density is calculated as 1.816 × 10

17 kg m−3

•

Is almost a constant for all the nuclei

irrespective of its size.

•

The high value shows that the nuclear matter

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Nuclear charge

•

The charge of a nucleus is due to the protons

present in it.

•

Each proton has a positive charge equal to 1.6

× 10−19 C.

•

∴

The nuclear charge = Ze, where Z is the

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•

When the protons and neutrons combine to

form a nucleus, the mass that disappears

(mass defect, Δm) is converted into an

equivalent amount of energy (Δmc2).

•

This energy is called the binding energy of the

nucleus.

•

∴

Binding energy = [ZmP + Nmn – m] c2

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•

The binding energy of a nucleus determines its

stability against disintegration.

•

In other words, if the binding energy is large,

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BINDING ENERGY PER

NUCLEON

BINDING ENERGY

The energy needed to break the nucleus into its

constituent protons and neutrons ( nucleons).

The energy needed to break the nucleus into its

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BINDING ENERGY PER

NUCLEON

Because of the strong nuclear force, the nucleons in a stable nucleus are held tightly together.

Thus, energy is required to separate a stable nucleus into its constituent nucleons.

The more stable the nucleus is, the greater is the amount of energy needed to break it apart.

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BINDING ENERGY PER

NUCLEON



Mass

defect



2

 

2

energy

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BINDING ENERGY PER

NUCLEON

BINDING ENERGY PER NUCLEON

The total binding energy of a nucleus divided by

mass number, A

The total binding energy of a nucleus divided by

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BINDING ENERGY PER

NUCLEON

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BINDING ENERGY PER

NUCLEON

Example: Binding energy for iron.

Calculate the total binding energy and the binding energy per nucleon for , the most common stable isotope of iron.

Solution:

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•

Example: 2He4, 4Be8, 6C12, 8O16, and

10Ne20.

•

The curve becomes almost flat for mass

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Explanation of binding energy

curve

•

The B.E per nucleon ↑ sharply with A upto 20.

It increases slowly after A = 20.

•

For A<20, there exists recurrence of peaks

corresponding to those nuclei,

•

whose mass numbers are multiples of four

and they contain not only equal but also

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(ii) The binding energy per nucleon reaches a

maximum of 8.8 MeV at A=56, corresponding to

the iron nucleus (26Fe56). Hence, iron nucleus

is the most stable.

(iii) The average binding energy per nucleon is

about 8.5 MeV for nuclei having mass number

ranging between 40 and 120.

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(iv) For higher mass numbers the curve drops slowly

and the BE/A is about 7.6 MeV for uranium. (they are

unstable and radioactive.)

(v) The lesser amount of binding energy for lighter and

heavier nuclei explains nuclear fusion and fission

respectively.



A large amount of energy will be liberated if lighter

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STRUCTURE &

PROPERTIES OF

NUCLEUS

Nucleus consists of protons and neutrons.

A proton is the nucleus of the simplest atom hydrogen. Proton has positive charge.

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STRUCTURE &

PROPERTIES OF

NUCLEUS

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STRUCTURE &

PROPERTIES OF

NUCLEUS

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DISCOVERY OF

NEUTRONS

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DISCOVERY OF

NEUTRONS

In 1932, Chadwick proved the existence of neutrons - elementary particles devoid of any electrical charge.

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DISCOVERY OF

NEUTRONS

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DISCOVERY OF

NEUTRONS

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NUCLEAR FORCES

Two types : Strong nuclear forces and weak nuclear forces.

Strong nuclear force is an attractive force that acts between all nucleons (protons and neutrons alike).

Protons attract each other via strong nuclear force at the same time they repel each other via electric force.

Strong nuclear force > electric force.

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NUCLEAR FORCES

Strong nuclear force is a short-range force. It acts only over a very short distance.

It is very strong between 2 nucleons if they are < 10-15 m apart. It is 0 if they are separated by a distance > 10-15 m apart.

Electric and gravitational forces are long-range forces.

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NUCLEAR FORCES

Nuclei stable – have the same number of protons as neutrons (N=Z) up to about A = 30.

Beyond this, stable nuclei contain more neutrons and protons.

As Z increase, electric repulsion increase, greater number of neutrons require to maintain stability.

For very large Z, no number of neutrons can overcome the greatly increased electric repulsion. (Above Z = 82, no completely stable nuclide).

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NUCLEAR FORCES

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ATOMIC NUMBER,

Z

DEFINITION

Number of protons in the nucleus

To establish the chemical identity of the atom.

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ATOMIC MASS UNIT

It is symbolized by amu or u.

It is a unit to specify the nuclear masses because the very small size of protons it is not convenient to express the mass of nuclei and atomic particles in the conventional unit of kilograms.

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ATOMIC MASS UNIT

The relationship between the atomic mass unit and kilogram is :

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ATOMIC MASS UNIT

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MASS DEFECT, ∆m

DEFINITION

The amount by which the sum of the individual masses

of the protons and neutrons exceeds the mass of intact

nucleus

The amount by which the sum of the individual masses

of the protons and neutrons exceeds the mass of intact

nucleus

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MASS-ENERGY

EQUATION

The energy change in a nuclear reaction is considerably greater than that of a normal chemical reaction.

This change can be calculated using Einstein's equation:

where ΔE is the change in energy, Δm is the change in mass,

c is the speed of light (3.00 x 108 m/s).

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ISOTOPES OF

ELEMENT

DEFINITION

Nuclei that contain the same number of protons but

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ISOTOPES OF

ELEMENT

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ISOTOPES OF

ELEMENT

Every nuclide is an isotope of some other nuclide.

Most elements have several isotopes.

In most cases some of the isotopes of a given element are stable (not radioactive), and some are radioactive.

For example, iodine has 23 known isotopes with mass numbers ranging from 117 to 139.

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ISOTOPES OF

ELEMENT

The relationship between the two nuclides is that they are isotopes. I-131 is an isotope of I-127, and I-127 is also an isotope of I-131.

For most elements the most common or most abundant form is the stable isotope.

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MASS

SPECTROMETER

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MASS

SPECTROMETER

DEFINITION

An instrument which can measure the masses and

relative concentrations of atoms and molecules. It

makes use of the basic magnetic force on a moving

charged particle.

An instrument which can measure the masses and

relative concentrations of atoms and molecules. It

makes use of the basic magnetic force on a moving

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MASS

SPECTROMETER

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DETECTION OF

PRESENCE OF

ISOTOPES

Two radioactive isotopes of sodium—sodium-22 and sodium-24—are used in medicine and other applications. They can be used as tracers to follow sodium in a person's body. A tracer is a radioactive isotope whose presence in a system can easily be detected. The isotope is injected into the system at some point. Inside the system, the isotope gives off radiation. That radiation can be followed by means of detectors placed around the system. Two radioactive isotopes of sodium—sodium-22 and sodium-24—are used in medicine and other applications. They can be used as tracers to follow sodium in a person's body. A tracer is a radioactive isotope whose presence in a system can easily be detected. The isotope is injected into the system at some point. Inside the system, the isotope gives off radiation. That radiation can be followed by means of detectors placed around the system.

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DETECTION OF

PRESENCE OF

ISOTOPES

Sodium-24 also has non-medical applications. For example, it is used to test for leaks in oil pipe lines. These pipe lines are usually buried underground. It may be difficult to tell when a pipe begins to leak. One way to locate a leak is to add some sodium-24 to the oil. If oil leaks out of the pipe, so does the 24. The leaking oil may not be visible, but the leaking sodium-24 is easily detected. It is located by instruments that are designed to detect radiation.

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THE END

~~ THE END ~~

“ Write it on ur heart that every

day is the best day in the year”

~Ralph Wardo