Nuclear Chemistry ppt.pptkmkmkmklknklnlnl

NUCLEAR CHEMISTRY
• In ordinary reactions electrons are
involved.
• Nucleus remains unaffected
• In nuclear reaction nucleus under go
changes.
• It is not common because nucleus is
highly stable.

• Atom = nucleus + electrons
• Nucleus = neutrons and protons held together by
“strong interactions”
• Strong nuclear force (interaction) is a
fundamental force of nature
• Range of force is about 10-15
m
• Strong enough to overcome Coulombic repulsion
of protons

• Stability of a nucleus can be explained in
terms of
• Mass defect
• Binding energy
• n/p ratio and
• Packing fraction

Mass defect
• The difference between the mass of an atom and the
sum of the masses of the nucleons and electrons of
which it is composed is called the mass defect.
• The mass defect
• Δm = [Z(mp + me) + (A – Z)mn] – matom
where mp = mass of a proton; mn = mass of a neutron;
me = mass of an electron; matom = Actual mass atom,
Z = atomic number, A = mass number

For example consider
•
– Mass of proton = 1.007825 amu
– Mass of neutron = 1.008665 amu
– Mass of electron = 0.0005485 amu
• Thus:
– 8 protons = 8.0626
– 8 neutrons = 8.06932
– 8 electrons = 0.004388
– Sum = 16.136308
• Actual mass of 16
O on = 15.9949148 amu
• Therefore, mass defect = 0.141394 amu
16
8 O

Binding Energy of Nucleus
• Decrease in mass ie Mass defect is
converted to energy release when atom is
formed, according to Einstein’s equation
i.e.:
• E = mc2
= 0.141394 x 10-3
kg x (3 x 108
ms-1
)2
/6.023 x 1023
= 2.1128 x 10-11
J
• But 1 eV = 1.6021 x 10-19
J
• Thus E = 131.9 MeV
or Binding energy= 8.24 MeV per
nucleon

Binding Energy of Nucleus
• Indication of how strongly the nucleus is bound
together
• Energy liberated in formation of nucleus from its
nucleons is a measure of its stability
• High binding energy = stable nucleus
• Plot binding energy per nucleon vs. mass number is
given in next slide

Nuclear Chemistry ppt.pptkmkmkmklknklnlnl

• Greater the mass defect, greater is the
binding energy and greater is the stability.
• В.Е per nucleon first increases, reaches a
maximum and then decreases
• Binding energy of a stable nucleus varies
from 7-8 MeV.
• 56
Fe have a binding energy per nucleon
value of approximately 8.8 MeV. It's one of
the most stable nuclides that exist.

• Isotopes having intermediate mass
numbers (between 40 & 60) are more
stable.
• Isotopes of low mass number and high
mass number are unstable

n/p Ratio
• n/p ratio represents the ratio of no: of neutrons to no: of
protons in an atom.
• When a graph is drawn between the number of neutrons
and no: of protons in the nucleus of different atoms, we
get a belt of stability or zone of stability.
• Elements with atomic number upto 20 have n/p ratio =1
• All elements which lie within the belt are stable.

Packing Fraction
• The atomic masses (isotopic mass) of elements are
close to but not exactly equal to whole numbers.
• But mass numbers are whole numbers.
• The variation of isotopic mass from whole numbers
is expressed in terms of packing fraction.
• This variation occurs due to mass defect.

• Packing fractions can have negative or positive values.
• Negative value means that isotopic mass is less than
mass number and that some mass is lost during its
formation as energy.
• Hence greater the negative value of packing fraction,
greater is the binding energy and stability.
• Low value of packing fraction indicates greater stability.

• Positive value of packing fraction indicates lesser
stability.
• But this is always not true with elements of low
mass numbers.
• For example,
hydrogen, helium and carbon have positive
packing fractions, but they have low positive
values and are stable.

variation of packing fraction with mass number.

From the graph
• Packing fraction decreases with mass number.
But increases for heavy elements
• Elements with mass number near 45 have
lowest packing fractions. They are highly stable.
• Beyond mass number 200, packing fractions are
positive and these elements are unstable.
(radioactive)

Magic Numbers
• It is seen that nuclei having 2, 8, 20, 50, 82, 126
numbers of protons or neutrons or both protons and
neutrons are extra stable.
• In such nuclei, nucleons exist as pairs and they are
said to have a closed shell.
• They have high B.E.
• e.g.
4
2He, 16
8O, 40
20Ca, 208
82Pb

NUCLEAR FORCES
• The protons and neutrons are packed together in a very small nuclear
space.
• If electrostatic forces alone were involved, the nucleus is unstable and
liable to disintegrations.
• But this does not happen except in the case of heavier elements which are
radioactive.
• This indicates that there must be some attractive forces between proton
and proton which must be stronger than the repulsive forces.
• These attractive forces which hold the nuclear particles together are called
nuclear forces.

Radioactivity
• Radioactivity is the phenomenon of the
disintegration of unstable atomic nucleus into
more energetically stable atomic nucleus..
• All atoms are not radioactive.
• Only atoms with unstable nucleus will be
radioactive.

Natural Radioactivity.
• If the radioactivity is spontaneous it is called natural
radioactivity.
• All naturally occurring elements with atomic number
greater than 83 are found to be radioactive.
• The disintegration occure by emitting radiations
consisting of mainly alpha(α), beta(β) and
gamma(γ) radiations.

Artificial Radioactivity
• The process by which a stable nucleus which is
not radioactive is transformed into radioactive
nucleus by bombarding with suitable subatomic
particles (Eg.Neutron) is called artificial
radioactivity or induced radioactivity.
• The process of converting one element into
another by artificial means is called artificial
transmutation.

Comparison between Natural
and Artificial Radioactivity

alpha(α), beta(β) and gamma(γ)
radiations
• An alpha particle is a helium nucleus ie 2He4
.
• Its mass is four times that of hydrogen.
• Because of high mass, an alpha particle has low
speed and low penetration power.
• It has high ionizing power, because of
two positive charges.

beta particle
• A beta particle is a high energy electron.
• Its mass is1/1850 that of hydrogen.
• It has high energy and medium penetrating
power.
•
Its ionizing power is medium since it has only
one negative charge.

Gamma particles
• Gamma particles are electro magnetic
radiations.
• They are high energy radiations with very
low mass and high speed.
•
• They have high penetration power, but low
ionizing power, since it is a neutral particle.

GROUP DISPLACEMENT LAW
OR
Soddy & Fajan Law
• consists of two parts.
• PART-1.
• The emission of an alpha particle from an atom
will cause the mass number to decrease by four
and the atomic number to decrease by two.
• The new element formed will be two places to
the left of parent element in the periodic table.

• PART-2.
• The emission of beta particle will cause no
change in mass number and the atomic
number will increase by one.
• The new element formed will be one place
to the right of parent element in the
periodic table.

Problem.
• Qn. How many alpha and beta particles are
emitted during the transformation of 84Po218
to
83Bi214
?
• An. One Alpha followed by one beta
84Po218
82Pb214
-α
82Pb214
83Bi214
-β

DETECTION OF RADIOACTIVITY
• The radioactivity of a substance can be detected and
measured by the ionization of gases caused by the
particles (alpha,beta and gamma) emitted by the
substance.
• The most common instrument to detect radioactivity
is a Geiger Muller (GM) Counter.
• They are mainly used for the detection of beta and
gamma radiations.

• GM counter consist of a cylindrical sealed
glass tube enclosing a copper cylinder serving as
the cathode.
•
• A very thin metal wire placed along the axis of the
cylinder, usually of tungsten, acts as the anode.
• The tube is filled with an inert gas like
argon mixed with ethyl alcohol at a low pressure

• The radioactive substance is placed outside the tube close to the
window.
• When the ionizing radiation from the radioactive substance enters the
tube, it causes ionization of argon molecules.
• This creates positively charged ions and electrons. The positive ions
move towards the cathode and the electrons move towards the anode.
• This produces a pulse of current in a circuit connected to the tube.
This pulse is amplified and counted.

UNITS OF RADIOACTIVITY
• Radioactivity is expressed as the number of radioactive events
occurring per unit time.
• 1. Curie (Ci): It is the amount of radioactive substance that undergoes 3.7 x 1010
disintegrations per second.
• 2. Rutherford (Rd): Quantity of substance which gives 106
disintegrations per second.
• 3. Becquerel (Bq): It is the SI unit of radioactivity. One decay per second is called one
becquerel (Bq).
• 1 Curie = 3.7 x 1010
Bq &
• 1 Rd = 106
Bq
• .

Isotopes, Isobars & Isotones
• Isotopes: Atoms having the same number of protons (Atomic number)
but different number of neutrons (Mass number) are isotopes. For
example, the isotopes of hydrogen may be written: 1
1H, 2
1H, 3
1H.
• Isobars: Atoms having the same mass number are isobars. Eg. 11Na24
& 12Mg24
• Isotones: Atoms having the same number of neutrons are isotones.
Eg.6C13
& 7N14

Rate Of Radioactive Disintegration
• Rate of radioactive disintegration is the amount of
radioactive element that disintegrates in unit time.
• All radioactive elements disintegrate at a characteristic
rate.
• It is independent of external factors like temperature,
pressure or state of combination.
• The law of radioactive disintegration states that the rate
of of radioactive disintegration is proportional to the
amount of radioactive element present.

• Radioactive decay is a first order reaction.
• It depends only on the concentration or amount of
disintegrating species.
• Consider a nuclear process in which atoms of A
disintegrate to atoms of B.
• Number of atoms of A originally present = No
• Number of atoms of A present at any time(t) = N
• Thus, when t = 0, number of atoms of A = No
and when t = t, number of atoms of A = N.

• Rate of change of A to B is given by,
• where λ is the decay constant or disintegration
constant.
• On rearranging
• On integration
• ln N = - λt + C ( C is the integration constant)……(1)
• when t = 0, N = No
• Therefore ln No = - λ x 0 + C or C = ln No ………(2)

• Using equ…..1 and equ…..2
• ln N = - λt + ln No
• Or
• λt = ln No - ln N
= ln No/N
λ = 1/t x ln No/N
When changing the base of the Logarithm from e to 10
ie multiply by 2.303
• This equation is called rate equation for radioactivity.

Half life period
• The time required for the disintegration of half of the
original amount of radioactive substance is called its
half life period.(symbol t1⁄2)
• Thus when t = t1⁄2
half of the atoms of the radioactive substance will
disintegrate ie

• The relationship between the half-life, t1/2, and the
decay constant λ is given by t1/2 = 0.693/λ.
• Half-life period of a radioactive element is independent
of its initial concentration and depends only on decay
constant.
• Half-life period is inversely proportional to decay
constant.
• The value of half-life, t1/2 is a constant for a given
element.

Average Life Period
• Reciprocal of decay constant or disintegration
constant (λ) of a radioactive element is called its
average life period.
• It is represented by Tau
• Tau =1/ λ
• t1/2 = 0.693 / λ
• λ = 0.693 / t1/2
• Average life (τ) =1.44×t1/2

Problem-1
• Qn.The half life period of a radioactive element is 2.75
days. Calculate the percentage of the radioactive
element after 11 days.
• An. In 2.75 days 100% become 50%.
In next 2.75 days (2.75+2.75 = 5.5 days)
50% become 25%
After another 2.75 days (2.75+2.75+2.75=8.25 days)
25% become 12.5%.
After 11days(2.75+2.75+2.75+2.75)
12.5% become 6.25 %

Problem 2
• Qn. Half life period of a radioactive element is 10
years. Calculate its disintegration constant &
average life?
• An.
• Given, t1/2 =10 years
• λ = 0.693 / t1/2 = 0.693 / 10
• λ = 0.0693 years1
• Average life = 1.44 × t1/2=1.44×10
• Average life = 14.4 years

Problem-3
• Qn. The half-life of a radioactive element is 24 days.
Calculate the decay constant and the time it will take
to reduce itself to 1/10th
of the initial amount.
• An.
λ = 0.693 / t1/2 = 0.693 / 24 = 0.0289 days-1
N0 = 100
N = 10
t = 2.303 / λ x log(N0/N)
= 2.303 / 0.0289 x log(100/10)
= 2.303 / 0.0289 x log(10)
= 2.303 / 0.0289 x 1 = 79.69 days

• Qn. A common isotope of radium-226, has a half-life of
1620 years. Knowing this, calculate the rate constant for
the decay of radium-226 and the fraction of a sample of
this isotope remaining after 100 years.
• An.
• λ = 0.693/t1/2
• = 0.693/1620 years = 4.28 x 10-4
/year
• log10 N0/N = λ t/2.30
• log10 N0/N = (4.28 x 10-4
/year)/2.30 x 100 years = 0.0186
• Taking antilogs: N0/N = 1.044( But N0=1)
• N= 0.958 = 95.8% of the isotope remains
•

• Qn. Calculate the average life of a radioactive
substance whose half life period is 1650 years.
• An
• Average life =1.44×t1/2
=1.44×1650=2376 years
• Home Work
• Qn. Half life of a radioactive element
is 10 days. What percentage of the element
will remain undecayed after 100 days?
• A) 10%, B) 1%, C) 99%, D) 0.1%

Nuclear Reactions
• 1.Nuclear Fission Reaction
• 2. Nuclear Fusion Reaction

NUCLEAR FISSION
• Nuclear fission is either a nuclear reaction or a
radioactive decay process in which the nucleus of an atom
splits into smaller parts (lighter nuclei).
• The fission process often produces free neutrons and
gamma photons, and releases a very large amount of
energy.
• Nuclear fission is accompanied by mass defect i.e. the
total mass of products of fission is less than the total mass
of the atom undergoing fission and the neutrons.
• The loss of mass appears in the form of energy according
to Einstein's mass-energy relation, E=mc2

FISSION REACTION OF 92U235
92U235 + 1n —› Ba141 + Kr92 + 3 1n + E
Where E is the energy released in this reaction

FISSION CHAIN REACTION
• A chain reaction is a sequence of reactions where a
reactive product or by-product causes additional
reactions to take place.
• An atom of uranium-235 to undergo fission by
bombarding it with neutrons.
• Along with barium and krypton, three neutrons are
released during the fission process. These neutrons
can hit further U-235 atoms and split them, releasing
yet more neutrons. This is called a chain reaction.

• Critical Mass
• The minimum mass of fissionable material
required for a self sustaining chain reaction is
called critical mass.
• A subcritical mass is a mass of fissionable material
that does not have the ability to sustain a fission chain
reaction.
• A supercritical mass is one in which, once fission has
started, it will proceed at an increasing rate.

Neutron Multiplication Factor (k)
• The average number of neutrons released per fission
event that go on to cause another fission event rather
than being absorbed or leaving the material is known
as multiplication factor (k).
• When k = 1, The chain reaction is self-sustaining.
Eg. Nuclear Reactor (Controlled chain reaction)
• When k >1, The chain reaction is uncontrolled one.
Eg. Atom Bomb
• When k <1, No chain reaction is occure.

Atom Bomb
• Atomic bombs are nuclear weapons that use the
energetic output of nuclear fission to produce massive
explosions.
• Atomic bombs are made up of a fissile element, such
as uranium
• When a free neutron hits the nucleus of a fissile atom
like uranium-235 (235
U), the uranium splits into two
smaller atoms called fission fragments, plus more
neutrons.
• Fission can be self-sustaining because it produces
more neutrons with the speed required to cause new
fissions. This creates the chain reaction.

• In fission weapons, a subcritical mass of fissile material
(uranium) is assembled into a supercritical mass
• In order to start an exponentially growing nuclear chain
reaction.
• This is accomplished either by shooting one piece of
sub-critical material into another, termed the “gun”
method,
• Or by compressing a sub-critical sphere of material
using chemical explosives to many times its original
density, called the “implosion” method.

• Neutrons entering this supercritical mass from a
Radium-Beryllium mixture to initiate a rapid chain
reaction.
• The energy released raises the temperature to the
order of about 107
Degree Celsius and preasure
several million times of atmosphere.

Nuclear Reactor
• The principle used in nuclear reactor is nuclear
fission reaction.
• A nuclear reactor is a device to initiate, and control,
a sustained nuclear chain reaction.
• The most common use of nuclear reactors is for the
generation of electrical power ( Nuclear power) and for
the power in some ships.

Components of a nuclear reactor
• The main components are :
• 1. Fuel:
• Fissionable material used in nuclear reactor.
Eg. Uranium-235, Thorium-232
• 2. Moderator.
• Material in the core which slows down the neutrons released
from fission so that they cause more fission. It is usually
water, but may be heavy water or graphite.
• 3. Control rods. These are made with neutron-absorbing
material such as cadmium, hafnium or boron, and are inserted
or withdrawn from the core to control the rate of reaction

• 4.Coolant. A fluid circulating through the core so as
to transfer the heat from it. In light water reactors
the water moderator functions also as primary
coolant.
• 5.Shields. The structure around the reactor and
associated steam generators which is designed to
protect it from outside intrusion and to protect those
outside from the effects of radiation in case of any
serious malfunction inside. It is typically a meter-
thick concrete and steel structure.

Breeder reactors
• Breeder reactors are a type of nuclear reactor which
produce more fissile materials than they consume.
• They are designed to extend the nuclear fuel supply
for the generation of electricity
• They use, by irradiation of a fertile material, such
as uranium-238 or thorium-232 that is loaded into the
reactor along with fissile fuel.

Why Are We Interested?
• There are great challenges that are associated with
fusion, but there are also very large possible benefits
• A coal power plant uses 9000 tons of coal a day to
produce 1000 MW and emits many pollutants including
30,000 tons of carbon dioxide
• The amount of lithium contained in a single computer
battery along with about half of a bathtub full of water
can produce as much energy as 40 tons of coal

What is Nuclear Fusion?
• Fusion is the process of light atoms
uniting to form heavier atoms
• This releases energy
• Nuclei are positively charged so they
repel each other
• Energy has to be input to overcome this
repulsive force
+ +
F
F

• The nucleus made by fusion is heavier than either
of the starting nuclei.
• However,it is not as heavy as the combination of
the original mass of the starting nuclei.
• This lost mass is changed into lots of energy.
• This is shown in Einstein's famous E=mc2
equation.
• Fusion happens in the middle of stars, like the Sun.

What are the Challenges?
• For fusion to occur, reactor temperatures would have to be on
the order of 200 million degrees Celsius
• No material on earth can withstand 200 million degrees without
melting
• Two basic strategies:
1) Magnetic Confinement: Confine the plasma with magnetic
fields so that the plasma will not touch the containment walls
2) Inertial Confinement: Supply large amounts of energy very
quickly (i.e. shoot with lasers) so that the fuel is burned before
it has time to expand and touch the walls

What is the Goal?
• Currently more energy has to be supplied to get
the fusion reactions going than is output by fusion
• Breakeven is the point in which the energy
supplied equals or exceeds the energy output
• Ignition is the point in which the energy from
fusion supplies the heat necessary to sustain the
reaction without external sources

Is it Safe and Environmentally
Friendly?
• Fission reactors could meltdown because the fuel is in the
reactor at all times and the reaction must be stopped to
cool the reactor down
• Fusion reactors cannot meltdown because there is very
little fuel in the reactor at a time
• Fission produces radioactive waste that needs to decay for
10,000 years before it can be buried
• The structure will only need to be stored for 100 years and
constitutes much less material than nuclear fission

Advantage
• Environment friendly as no greenhouse gases
are produced.
• Stocks are supposed to last for a really long
time.
• No chain reaction. So no chances of major
accidents as the reactions can be stopped
anytime by just cutting off the supply of the fuel.

• The cost of the fuel is very low.
• Can be used for interstellar space where solar
energy is not available.
• Many problems like fresh water shortages can
also be solved because they exist mainly
because of the power shortages.

Disadvantage
• Unproven till now at a commercial scale.
• Initial experiments have been very costly.
• The energy required to initiate is greater than
what’s generated.
• The material for setups has to be worked upon
so that it can take the excessive temperatures
produced during the process.

Hydrogen Bomb
• The principle behind hydrogen bomb is fusion
reactions of hydrogen to form helium
producing huge amounts of energy.
• Energy is released due to mass defect. But, this
reaction can occur only at very high
temperatures.
• This temperature is first produced by exploding
an atom bomb.

• In the preparation of a hydrogen bomb, a
suitable fissionable material likeU-235 is
arranged at the core.
• It is surrounded by a suitable quantity of a
mixture of deuterium and lithium isotope.
• A chain reaction is allowed to set in at the core
by bombarding with neutrons.
.

• Because of this, an enormous amount of energy is
released and the temperature increases to several
million degree
• This provides an atmosphere of the required
temperature to initiate the fusion reaction of
deuterium and lithium.
Hydrogen bomb is more powerful than
an atom bomb

APPLICATIONS OF
RADIOACTIVE ISOTOPES
• 14
C DATING OR CARBON DATING
• Carbon-14 is one of the isotope of carbon.
• It is formed by cosmic rays bombardment with nitrogen.
• C-14 undergoes β decay with a half life of 5770 years gives
N-14.
• 14
C undergoes Oxidation in atmosphere to form 14
CO2
• In the atmosphere, it mixes with non radioactive carbon
dioxide: 12
CO2.
• Quantity of 14
C and 14
CO2 in the atmosphere has been
constant over long periods of years.

• During photosynthesis 14
CO2 and 12
CO2 are absorbed
by plants and in turn, it reaches animals.
• Hence, the concentration of C-14 in all living
organisms remains constant during their life time.
• But, when the organism dies, they cannot take up CO2
from atmosphere.
• The C-14 content in the animal body now begins to
decay by emitting β particle.
• The concentration of C-14 in the body starts
decreasing.
• Hence, the age of a dead animal or a sample of wood
can be determined knowing that the half life period of
C-14 (5770 years).

• Using the equation
• No = Amount of C-14 in a fresh sample
• N = Amount of C-14 in a old sample

ROCK DATING OR URANIUM
DATING
• This technique is used to predict the age of earth
rocks.
• Rocks contain U-238.It is radioactive and disintegrates
with the emission of radiations forming a stable
product s Pb-206.
• Thus, a sample of rock contains both U-238 and
Pb-206; by measuring the amount of these two in a
rock sample, its age can be determined.
• The amount of Pb-206 is equal to the amount of U-238
that has disintegrated over time, t i.e. (N)

• The sum of amounts of U-238 and Pb-206 gives the
amount of U-238 present in the rock initially (N0)
• The age of the rock is calculated by the equation

Radioisotopes in Medicine
• In medicine, radioisotopes are used in
diagnosis and treatment.
• Co-60 used in the treatment of cancer.
• Radioactive iodine, I-131 is used to diagnose
and treat hyper thyroidism.
• Radioactive Na, Fe and P is used in the
treatment of blood related problems.

Radioisotopes in Agriculture
• Using radioisotopes, transportation of nutrients from
roots to leaves within plants can be studied.
• If fertilizers containing radio nitrogen, potassium and
phosphorous are mixed with soil, it is possible to find
out the plants which absorb a particular fertilizer.
• Thus, the correct timing for the application of fertilizers
can be known.
• Control of pests can be done using P-12 and Co-60
isotopes.

• The amount of micronutrients like B, Co, Cu, Mn, Zn
and Mo required for the plant and their functions can
be understood with the help of radioisotopes.
• Seeds can be irradiated with radiations to effect
desirable changes and produce superior quality
seeds.
• On irradiation, the chromosomes in their cells undergo
changes.
• This is called mutation.

RADIO DIAGNOSIS
• Radio diagnosis is a branch of medical
science which uses radiations like X-rays,
gamma rays, ultrasound and magnetic
resonance in medical practices.
• It relates to anatomy, pathology,
physiology and interventional procedure.

RADIOTHERAPY
• Radiotherapy is a treatment used against cancer and
thyroid disease, blood disorders and noncancerous
growths.
• Radiotherapy uses high-energy rays, usually x-rays
and similar rays to treat disease.
• It destroys cancer cells in the area that is
treated.
• Normal cells can also be damaged by radiotherapy.

• But normal cells can usually repair themselves,
whereas cancer cells cannot.
• Radiotherapy is carefully planned so that it avoids as
much healthy tissue as possible. But, there will always
be some health tissue that is affected by the treatment
and this will cause side effect.
• Radiotherapy can be given both externally and
internally. External beam radiotherapy aims high-
energy X-rays at the affected area using a machine.
Internal radiotherapy involves placing the radioactive
material inside the body.

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