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1. GC. Women University, Sialkot .
Assignment Nuclear Chemistry
Submitted To, Ma’am Hafsa
Submitted By, Anan Fatima
Roll No. 20
Session 2014-2018
Semester 6th
Department Chemistry

2. Assignment Physical Chemistry
Topic Nuclear chemistry
Answer the following questions
Question no : 1
a. Why certain isotopes are stable while others are radioactive? Discuss various
factors affecting nuclear stability.
Isotopes are atoms with the same number of protons but different number of neutrons.
As, both protons and neutrons are present inside the nucleus. Neutrons being neutral,
minimizes the proton-proton repulsion. If there are too many protons then the repulsive
force overcomes the nuclear force holding them together or if there are too many
neutrons the atom is said to be unstable. Unstable isotopes then undergo radioactive
decay i.e the emission of radiation. In most cases, elements like to have an equal number
of protons and neutrons because this makes them the most stable.
Example:
Carbon has three isotopes with different number of neutrons; , , . Out of
these three isotopes of carbon, C-14 is unstable and radioactive isotope.
FACTORS AFFECTING NUCLEAR STABILITY:
The factors that affect or determine the nuclear stability are
1. Neutron /Proton Ratio:
The N/Z also determines the nuclear stability. Except in the case of ordinary hydrogen ( H),
all other nuclides contain both neutrons and protons. Stable nuclei have N/Z ratio ≥1.the
ratio is ≈ 1 for light nuclides up to Ca and after this the ratio is > 1 for heavy nuclides .
NM/Z ratio in some stable nuclides
�
�
� � � �
Z 1 10 30 40 50
N 1 10 34 50 70
Z/N 1 1 1.15 1.25 1.40

3. As the atomic number increases, the N/Z also increases of stable nuclei. The stable nuclei are
located in an area of the graph nown as band of stability. Since large no. of elements have
several stable isotopes, the curve is in the nature of a strip or zone which widen out at higher Z
values. All stable nuclei fall within this value
Examples:
2. Magic numbers of nucleons:
Nuclei having 2,8,20,27,28,50,82 or 126 protons or neutrons are more abundant in
nature and nuclei with these magic numbers are more stable. If the nuclei have both proton and
neutron number as magic numbers then these nuclei are very stable.
Examples:
�� , , ,
3-Even-odd rule:
It is also known as even-odd nature of protons and neutrons. The 165 nuclides with even number
of protons and even number of neutrons are stable. Just five nuclei, �, �, �, , with
odd numbers of protons and neutrons are stable. Nuclei with even-odd combination are
intermediate stability
Stable nuclei n:p
�� 1:1
� 1.33:1
� 1.4:1

4. Examples:
�� , , � , �� .
b. Explain the difference between mass defect and binding energy?
Nuclear binding energy is the energy required to split a nucleus of an atom into its
components. The more binding energy, the more stable the nucleus will ne.
The mass defect of a nucleus represents the mass of the energy binding the nuclei
and is the difference between the mass of a nucleus and the sum of the masses of the nucleons of
which it is composed. It is calculated as:
∆m = (mp+mn) -mo
Where mp= mass of total protons (mass of 1proton= 1.00728 amu)
mn = mass of total neutrons(mass of 1neutron= 1.00867 amu)
mo = observed atomic mass
Mass defect and Binding energy can be related by the EINSTEIN’S MASS-ENERGY
EQUATION i.e.
∆E = ∆mc2
where ∆m is the mass defect and ∆E is the binding energy. Both these parameters are inter-
convertible. Binding Energies are usually expressed in MeV.
1amu = 931.5 MeV
So, binding energy can be calcaluted as:
∆E = 9γ1.5 ×∆m
c. Calculate the binding energy of �� in MeV per atom if the exact mass of the
nuclide is 6.01512 amu.

5. Data:
Atomic mass of Li = 6.01512 amu
Binding energy of Li /atom = ?
Solution :
As, Mass of protons = 1.00727 amu
and Mass of neutron = 1.00866 amu
In Li, Mass of protons = 3 × 1.00727 amu = 3.02181 amu
Mass of neutron= 3 × 1.00866 amu =3.02598 amu
So, Mass of nucleo = mass of protons + mass of neutrons
= 3.02181 + 3.02598 = 6.04779amu
Mass defect=∆m = mass of nucleon – atomic mass of Li
= 6.04799 – 6.01512
∆m = 0.0γβ67amu
As, 1amu = 931.5MeV
Binding energy =∆E= ∆m × 9γ1.5
= 0.03267 × 931.5
= 30.4 MeV/atom
Question no : 2
1- What is nuclear reactions?
A reaction is the process in which change in the character of a nucleus take place either
spontaneously or as the result of bombardment by a particle or a ray. A nuclear reaction take
place if a particle able to enter a target nucleus. The particle which is used to strike a target
nucleus called projectile.
Or A nuclear reaction is considered to be the process in which two nuclear
particles interact to produce two or more nuclear particles or ˠ-rays (gamma rays). Thus,
a nuclear reaction must cause a transformation of at least one nuclide to another.

6. Types of nuclear reactions 1-Fission 2-Fusion.
● 1-Nuclear fission occurs when larger, heavier atoms are split into smaller atoms. This is
the type of reaction used in nuclear power plants and in most atomic bombs.
• Nuclear fission of U-235
• 2-Nuclear fusion occurs when two smaller atoms are fused together into a larger one. The
sun generates its power through nuclear fusion reactions.
Nuclear fusion of two hydrogen atoms
1- In nuclear reactions, no breaking or making of bonds is involved while they generally
involve breaking of old bonds and formation of new chemical bonds.
2- Generally nuclear reactions proceed with tremendous release of energy whereas chemical
reactions may involve evolution of absorption of energy.
3- Temperature and pressure do not affect the rates of nuclear reactions whereas the rates of
chemical reaction are affected by temperature and pressure conditions.
4- Nuclear reactions are generally irreversible while chemical reactions can be reversible as
well as irreversible.
5- Nuclear reactions involve the conversion of one nuclide into the other and chemical
reactions simply involve the rearrangement of atoms and do not involve any change in
the nucleus.
6- In nuclear reactions, large amount of energy release while in chemical reaction less
amount of energy release.
7- Mass changes are detectable while in chemical reaction. In chemical reactions mass reactants
= mass product
2- What is atomic bomb?
Definition:
Powerful explosive nuclear weapon fueled by the splitting, or fission, of the nuclei of uranium or
plutonium in a chain reaction.
Principle
An atom bomb works on the principle of nuclear chain reaction ( fission ).

7. Fission is the releases process of splitting an atom into many fragments by bombarding it. This
breaking of nuclear bonds a lot of energy in the form of heat and radiation and neutrons are
produce.
Processes
When a single free neutron strikes the nucleus of an atom of radioactive material like uranium or
plutonium, it knocks two or three more neutrons free. Energy is released when those neutrons
split off from the nucleus, and the newly released neutrons strike other uranium or plutonium
nuclei, splitting them in the same way, releasing more energy and more neutrons. This chain
reaction spreads almost instantaneously.
3- What is nuclear fission? Explain nuclear fission with full detail.
Definition:
“A reaction in which an atomic nucleus of a radioactive element splits by bombardment
from an external source with simultaneous release of large amounts of energy, used for electric
power generation”.
Explanation:
Nuclear fission is an exothermic reaction and excess amount of energy is released in
this process. Nuclear fission may also occur spontaneously in the case of very heavy nuclei. A
“chain reaction” results when the neutrons released during fission cause other nearby nuclei to
break apart.
3 n
3 n
3 n
+ E

8. Nuclear fission reactions can be controllable. Nuclear reactor uses controlled chain
reactions to generate electricity. But, uncontrolled fission chain reactions take place during the
explosion of an atomic bomb.
Example of nuclear fission:
Uranium-235 and Plutonium-239 are two fissionable substances undergoing nuclear
fission reaction. For fission to occur in the Uranium -235 nucleus, it first absorb a neutron.
Then, the nuclei The nucleus undergoing fission splits into smaller nuclei . Barium-141 and
krypton-92 are just two of many possible products of this fission reaction and 2-3 neutrons and
energy is released .These neutrons may go on to start a chain reaction.
U + n Ba + K r + n
4- Why neutrons are the ideal bullets for fission reaction?
Due to the neutrality of neutron particles, they are the ideal bullets for fission reaction.
Neutrons are the ideal bullets for fission reaction because they are neutral particles. As the
nucleus is composed of proton and neutron and is positively charged, repulsion forces are
stronger when the positively charged nucleus is being strike by particle other than neutron like
proton that is also positively charged particle. While neutrons have no charge so, don’t cause
such type of problem.
Question no : 3
a) What is decay constant and half-life? How are these interrelated?
DECAY CONSTANT:
Definition:
The decay constant is the fraction of the number of atoms that decay in 1 second. It is the
probability of decay per unit time. It is also known as “disintegration constant”.
Representation:
It is represented by symbol λ.
Formula:
λ = -N
��
��
Where dN/dt = number of decays per second / Activity
N = number of atoms

9. Unit:
s-1
is the unit of decay constant.
HALF-LIFE:
Definition:
Half-life is a measure of the tendency of the half of the nucleus to "decay" or "disintegrate". It
can also be defined as the time needed to convert half of a reactant into the product.
Representation:
It is represented by t1/2 if the t is the total time to decay whole nucleus.
Formula:
t / =
.
λ
Units:
sec or min are the units of half-life.
RELATIONSHIP BETWEEN HALF-LIFE AND DECAY CONSTANT:
The rate of radioactive decay is typically expressed in terms of either the radioactive half-life, or
the radioactive decay constant. They are related as follows:
Suppose at time “t” , the initial concentration of radioactive element is N0
According to decay’s law:
λ =
.
t
log
N
N
By definition, if time t = t1/2 then N =
N
Put the values in above equation,
λ =
.
t /
log
N
N ⁄
λ =
.
t /
log
λ =
. × .
t /

10. λ =
.
t /
So, the above expression shows the inverse relation of half-life and decay constant.
b) How do half-life and decay constant determine experimentally ?
Half-life and decay constant can be experimentally determined by the device
“Geiger-Muller Counter”. One of the first devices used to detect radioactivity was a Geiger-
Muller tube, which is a gas filled cylinder with a very thin metal wire down its center. A voltage
difference is maintained between the center wire and the cylinder. If radiation interacts with the
gas in the cylinder, ionization of the gas atoms takes place. Because of the voltage difference, the
electrons move toward the center wire and the positive ions move toward the outer cylinder. This
is an electrical discharge producing a pulse of current which can be counted. Each pulse indicates
that a nucleus has decayed and the decay rate or decay constant is measured by the number of
pulses per second.
Before the source is used the background, count rate is measured using a Geiger Muller
tube connected to a counter. The count rate from the source is then measured at regular fixed
intervals over a time period. The background count rate is then subtracted from each
measurement and the actual count rate from the source is measured. A graph of the count rate of
the source against time is plotted. From the graph, the time taken for the count rate to fall by half
is measured. A number of measurements are made and an average value is calculated. The
average value is the half-life of the radioactive source.
c) The half-life of � is 14.3 days. How long it would take for 1g of sample of
� to decay to 0.5g of?
DATA:

11. t1//2 = 14.3days
[N0] = 1g
[N] = 0.5g
t = ?
Solution :
As t1//2 =
.
λ
λ =
.
t /
=
.
.
= 0.0484 /days
t =
.
λ
log
[No]
[N]
=
.
.
log
.
= 47.58 × log 2
= 47.58 × 0.301
= 14.3 days
d) Calculate the half -life of decay of ��
�
if ig of sample decays to 0.125g in
165min.
DATA:
t = 165min
[N0] = 1g
[N] = 0.125g
t1/2 = ?
Solution:

12. As, λ =
.
t
log
[No]
[N]
=
.
log
.
= 0.0139 × log 8
= 0.0139 × 0.903
= 0.0125 /min
t1//2 =
.
λ
=
.
.
= 55.4 min
Question no :4
Comment on the following statements.
1) The future of mankind is in the hands of nuclear scientists.
The nuclear chemistry has become a very important branch of science due to tremendous amount
of energy that liberated during nuclear reactions. The study indicates that most of the prosperous
nations are extracting about 30-40 per cent of power from nuclear -power and it constitutes a
significant part of their clean energy case. It reduces the burden of combating climate change and
the health hazards associated with pollution. But, nuclear scientists can destroy the whole world
into few seconds. The radioactive wastes coming from nuclear power plants, atomic bomb, chain
reaction, all these things are very dangerous for human beings. In addition, Nuclear weapons are
the most powerful and destructive fighting tools the world has ever known. So, it is rightly said
that future of mankind is in the hand of nuclear scientist.
2) Curie is the SI unit of radioactivity.
The older unit for measuring the amount of radioactivity was the Curie that’s was named after
Pierre and Marie Curie. It is the activity of 1 gram of radium isotope Ra. It is represented by
Ci and is defined as:
1 Curie = 3.7x1010
decays per second

13. The curie has been replaced by the SI unit Becquerel after Henri Becquerel. It is defined as
the activity of a quantity of radioactive material in which one nucleus decays per second.it is
represented by Bq.
1 Bq = 1 s−1
The relationship between Curie and Becquerel are given as:
Bq = 2.703x10-11
Ci
Ci = 3.7×1010
Bq
3) Lighter nuclides have more binding energy.
As, Nuclear binding energy is the energy required to split a nucleus of an atom into its
components. More the binding energy, the harder it to split the nuclide and more stable it will be.
There are stronger nuclear forces (short-range attractive) in the lighter nuclides. As the atomic
number (Z) increases, the repulsive electrostatic forces (proton-proton repulsion forces) within
the nucleus increase. To overcome this increased repulsion and maintain stability, the proportion
of neutrons in the nucleus must increase. As the repulsive forces are increasing, less energy must
be supplied to remove a nucleon from the nucleus. In other words, the Binding energy per atom
has decreased.
The above graph shows that as the atomic mass number increases, the binding energy per
nucleon decreases for mass no. > 60. The BE/A curve reaches a maximum value of 8.79 MeV at
A= 56 and decreases to about 7.6 MeV for A = 238. The increase in the Binding energy per
nuclide as the atomic mass number decreases from 260 to 60 is the primary reason for the energy
liberation in the fission process. In addition, the increase in the BE/A as the atomic mass number
increases from 1 to 60 is the reason for the energy liberation in the fusion process, which is the
opposite reaction of fission.

14. 4) Radionuclides are intrinsically unstable.
A radionuclide is an atom that has excess nuclear energy, making it unstable. This excess energy
can be either emitted from the nucleus as gamma radiation, or create and emit from the nucleus a
new particle (α or particle), or transfer this excess energy to one of its electrons, causing that
electron to be ejected as a conversion electron. During those processes, the radionuclide is said to
undergo radioactive decay. These emissions constitute ionizing radiation. The unstable nucleus is
more stable following the emission, but will sometimes undergo further decay. All the nuclides
with atomic number greater than 83 are radioactive and are beyond the band of stability.
EXAMPLES:
Examples of α-decay of radionuclides are given as:
U Th + 
Po Pb + 
5) All radioactive decay follows first-under kinetics.
Radioactive decay is the emission of a particle that results from the spontaneous decomposition
of the unstable nucleus of an atom. A radioactive decay is a first-order process and can be
described in terms of the rate law as:
−
ΔN
Δt
= k N
In radioactive decay, the number of radioactive atoms decaying per unit time is proportional to
the total number of radioactive atoms present at that time. Since the decay rate is proportional to
first power of radioactive atoms present, therefore, radioactive decay is a first order kinetics. As,
radioactive decay is a first-order process, the time required for half of the nuclei in any sample of
a radioactive isotope to decay is a constant, called the half-life of the radioactive nuclides.
6) Nuclear fission is a sustainable reaction.
Nuclear fission technology is the only developed energy source that is capable of delivering the
enormous quantities of energy that will be needed to run modern industrial societies.
Nuclear Fission reaction generates a large amount of nuclear energy and this is sustainable
because it meets all the criteria of sustainability. Fission can be self-sustaining because it
produces more neutrons with the speed required to cause new fissions. Today's commercial
uranium-fueled nuclear power plants can provide the world with clean, economical and reliable
energy well into the next century on the basis of the already-identified uranium deposits.
7) Water is used as moderator in atomic pile.

15. Nuclear reactor is formerly known as atomic pile. Light and heavy water can have dual function.
They can act as both moderator and coolant in nuclear reactor. These moderators slows the fast
(high-energy) neutrons emitted during fission to energies at which they are more likely to induce
fission. In doing so, the moderator helps initiate and sustain a fission chain reaction.
Most commercial nuclear reactors use normal water (also called light water) as a neutron
moderator. Some reactor designs, such as the CANDU reactor, use heavy water. Heavy water is
made from deuterium instead of hydrogen + normal oxygen. Deuterium is much less likely to
absorb neutrons than proton. As a result, heavy water increases the probability of fission with the
fuel material.
8) α –particles have more penetrating power.
This statement is not correct. α –particles have least penetrating power they are stopped by the
sheet of paper or thin Al foil. They are heavier than beta and gamma particles and can be easily
stopped by a few sheets of paper, so have least penetrating power. Beta particles are more
penetrating, but still easily shielded. Gamma rays have greatest penetrating and are the most
difficult to stop and require concrete, lead, or other heavy shielding to block them. So, the
decreasing order of penetration power of radiations is:
-rays > -rays > α –rays
9) β –particle have more ionizing power.
Ionizing power is the ease with which ionizing radiation forms ions. It is directly related to
kinetic energy. -particles have speeds of up to 18 times greater than alpha particles, with a
mass of 7400 times less than alpha particles, the kinetic energies of beta particles are much less

16. than those of α- particles thus has a lower ionizing power than alpha bur more than -rays.
Therefore, the above given statement is incorrect.
The decreasing order of ionizing power of radiations is:
α-rays > -rays > –rays
10) Radiations can damage human skin.
Radiation exposure greater than certain limit, can damage the human body. By the radiations,
rapidly dividing skin cells can be damaged, leading to skin lesions. Acute exposure of radiations
can cause skin redness and burns. and –radiations are the most dangerous radiation sources
because they can penetrate the skin and damage the cells inside. α-particles are the least
dangerous in terms of external exposure because they don't penetrate very deeply into the skin, in
fact, clothing can stop α- particles.
11) Radiations can be used for diagnostic purposes.
There are nearly one hundred radioisotopes whose and –radiation radiations are used in
diagnosis, therapy, or investigations in nuclear medicine. Some of the uses of radiations for
diagnosis are:
❖ Radiotherapy can be used to treat some medical conditions, especially cancer, using
radiation to weaken or destroy particular targeted cells.
❖ Radiation to provide information about the functioning of a person's specific organs or to
treat disease.
❖ In hospitals, ionizing radiations are used for tests in the form of X-ray include:
❖ Radiographs - commonly, known as x-rays.
❖ CT scans - used to be called CAT scans.
❖ Radioactive 131
I, with a half-life of 8 days, is used to diagnose and treat thyroid disorders.
12) Atomic bomb uses nuclear fission reaction.
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. Fission
was much more likely to occur in the uranium-235 isotope. Fission occurs when a neutron strikes
the nucleus of uranium-235 isotope, splitting the nucleus into fragments known as fission
fragments and releasing three new neutrons and tremendous amount of energy. The fission
process becomes self-sustaining as neutrons produced by the splitting of atom strike nearby
nuclei and produce more fission. This is known as a chain reaction and it causes an atomic
explosion.
+ � → � + �� + 2 neutrons + 180MeV

17. 13) H-bomb works on the principle of nuclear fusion.
The hydrogen bomb is a nuclear weapon that uses a mixture of fission and fusion to
produce a massive explosion. It has two cores. One is a classical atomic bomb called primary.
The other core, the secondary is a combination of deuterium, hydrogen, lithium and uranium.
They are mounted inside an x-ray, gamma ray reflecting material. The energy released by the
primary section compresses the secondary through a process called "radiation implosion," at
which point it is heated and undergoes nuclear fusion.
The nuclear fusion releases neutrons much faster than a fission reaction, and these
neutrons then bombard the remaining fissile fuel, causing it to undergo fission much more
rapidly. So, most of the energy comes from fission and fusion only enhances neutron production
contributing little to the explosion.
14) Radiation dosimeters are used to measure the amount of radiation
damaged.
Radiation damage Includes ionizing radiations such as α, , and - rays; X rays; and
protons, neutrons, and other particles. Radiation dosimetry is the calculation and assessment of
the ionizing radiation dose received by the human body due to both external irradiation and the
ingestion or inhalation of radioactive materials. Dose is used to describe the amount of energy
absorbed per unit mass at a site of interest. The SI unit for dose is the gray, Gy: 1 Gy = 1 J/kg =
100 rad. Internal dose is calculated from a variety of physiological techniques, whilst external
dose is measured with a dosimeter or inferred from other radiological protection instruments.
15) Heavy nuclides usually decay by β-decay.
This statement is not true. Heavy nuclides usually decay by α-decay not -decay.
Beta decay can occur in nuclei that are rich in neutrons - that is - the nuclide contains more
neutrons than stable isotopes of the same element. In order to regain some stability, such a
nucleus can decay by converting one of its extra neutrons into a proton, emitting an electron and
an anti-neutrino(ν). The high energy electron emitted in this reaction known as beta particle.
Lighter atoms (Z < 60) are the most likely to undergo -decay.
EXAMPLES:
Na Mg + e
−
+ v
C N + e
−
+ v