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Transcript
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COMPOSSED AND WRITTEN BY PROF. NAJEEB MUGHAL. GOVT. MUSLIM SCIENCE DEGREE COLLEGE HYD.
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CHAPTER19
THE ATOMIC NUCLEUS
Contents:
1.
discovery of Nucleus
2.
Isotopes, Atomic Number: Atomic, Mass number
3.
Radioactivity, Disintegration , Law of radioactive elements
4.
Half-life of radioactive elements Binding energy and mass defect
5.
Nuclear Fission and Nuclear Fusion
6.
Nuclear reactions
7.
Nuclear reactor
8.
EQUATIONS.
9.
DIMENSIONS
10.
SHORT QUESTIONS AND ANSWERS
DESCRIPTIVE
PART
1: Introduction about discovery of Nucleus:
Aristotle disbelieved the ancient Greek theory of atoms being of different sizes, regular
geometric shapes and being in constant motion. He didn't think atoms could be in constant motion in
an empty space. Aristotle’s theory was used for almost 2000 years, until after the scientific revolution,
when other theories prevailed
John Dalton's in 1803 gave the atomic theory. According to this theory,
1. All matter is made up of undividable particles called atoms
2. There is a void, which is empty space between atoms
3. Atoms are completely solid
4. Atoms are homogeneous with no internal structure
5. Atoms vary in size, shape and weight
Sir Joseph J. Thomson, who had done so much to investigate the structure of the atom
experimentally, wanted to devise an atomic model that would explain all the known properties of
atoms. In 1897 Thomson proposed the atomic model. Thomson made the first discovery of sub-atomic
particles with the electron. He proved this with his “cathode ray” experiment. He found that the
charge-to-mass ratio was very high, as such it was either very highly charged or it was very light.
Thomson atomic model failed to explain the scattering of -Particles.
1. Cathode rays are charged particles (which he called "corpuscles").
2. These corpuscles are constituents of the atom.
3. These corpuscles are the only constituents of the atom
In 1909 Lord Ernest Rutherford helped in understanding the atomic structure of the atom. He
investigated the scattering of -particles by thin films of metals of high atomic mass, such as gold foil.
He was correct in proving that atoms have a small center which contained most of its mass and is
positively charged (nucleus). He discovered nucleus has only positive charge and a cloud of electrons
covering the atom were assumed to be circulating around the nucleus. He calculated that a neutral
atom has a diameter of about 1x 10-8 cm, and the nucleus has a diameter of 1x10-13 cm
In 1909 R.A.Millikan determined charge on an electron by oil drop experiment that, e = 1.6x10-19C.
Although Rutherford’s experiment proved that the majority of an atom consists of space it was
Neils Bohr in 1913, which disproved Rutherford’s view for the electron. Rutherford thought that
electrons covered the atom in motion. This couldn’t work because the electrons would produce
electromagnetic radiation as they orbited the nucleus. Gradually the electrons would lose energy and
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spiral down and collapse on the nucleus. Neils Bohr overcame with his model of how
electrons orbited the nucleus. His two main ideas were:
1. Not every orbit is possible but only certain specific ones, at certain specific distances
from the nucleus
2. The electrons will not slowly lose energy as they travel, and hence will remain in
stable, non-decaying orbits
After Bohr’s explanation of how electrons move in orbits Erwin Schrödinger was
fascinated and explored if the movement of the atom could be better explained as a wave.
Schrödinger’s equation explains the electron like a wave rather than a particle; it also explained more
technically what different phenomena that Bohr failed to explain himself.
In 1920 Werner Heisenberg suggested the uncertainty principle; that is, it is impossible to
simultaneously know the precise location and energy of an electron.
In 1932 a scientist named Chadwick found discovers the neutron. He found it to measure slightly
heavier than the proton with a mass of 1840 electrons and with no charge (neutral). The proton-neutron
together, received the name, "nucleon." It had about the same mass as the proton but carried no charge.
The new particle is known as “Neutron”. He verified experimentally by scattering the -Particles from
Beryllium.
In 1932 in experiments with cosmic rays, Carl Anderson discovered the anti-electron, which
proved Dirac's equations. Physicists call it the positron. The neutrons and protons together are known
as “Nucleon number A”. The number of protons in the nucleus is known as “Atomic number Z”. The
nucleus has conventional symbol ZXA. The number of neutrons, N = A – Z.
The masses of proton and neutron are,
m p = 1.67x10-27kg = 1.00727 a.m.u.
And, m n = 1.675x10-27kg = 1.00866 a.m.u.
Where, 1a.m.u = 1.6605x10-27kg.
In 1932 C.D. Anderson found that a “Positron”, a positive electron, a new fundamental particle
discovered in the nucleus. An Italian physicist Enrico Fermi in 1934 was invented a new particle known
as “Neutrino” has zero mass and travels close to the speed of light. He gave a theory, postulated
existence of the fourth force in nature, which we call the “weak nuclear force”.
+
Protons (p )
1. positively charged subatomic particle located in nucleus of an atom
2. mass = 1.673 x10 - 24 g or 1.0073 u
3. always moving (atomic vibration)
Neutrons (n)
1. subatomic particle located in nucleus that has no electrical charge
2. mass = 1.675 x10 -24 g or 1.0087 u
3. free neutron decays into proton, electron, and electron anti-neutrino
4. half-life of free neutron is about 890 seconds
5. From Standard Model theory, the neutron is composed of 3 quarks, the weak force converts one of
the Down quarks into an Up quark, turning the neutron into proton . A third particle, known as Wboson is emitted as a result of the conversion process. This W boson decays into an electron and the
electron-antineutrino.
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-
Electron (e )
1. very small negatively charged subatomic particle found in orbit around nucleus
2. mass = 1.1 x10 -29 g or 0.000 549 u
3. mass is 1/1836 that of proton
4. moves very rapidly and is rather easily accelerated
2: Ions:
Atoms that have lost or gained electrons.
For example: calcium atoms tend to lose 2 electrons in reactions calcium starts with 20 protons and 20
2+
electrons so that by losing 2 electrons it now is an ion and is written as Ca (it has 2 more protons than
electrons). Similarly oxygen tends to gain 2 electrons in reactions oxygen starts with 8 protons and 8
2-
electrons and when it gains those 2 electrons it becomes an ion that is written as: O (2 more electrons
than protons)
3: Isotopes:;
These are atoms of the same element that have different numbers of neutrons in the
nucleus. Their mass numbers will be different but atomic number is the same.
The same charge but different mass is called “Isotope of the Element”. Hydrogen has 3 forms: natural
hydrogen with 1 proton and 1 electron, deuterium with 1 proton, 1 neutron, and 1 electron, and tritium
with 1 proton, 2 neutrons, and 1 electron. The atomic no. (Proton) say Z determines the chemical
properties of the element.
The masses of nuclei have been measured by a device accurately is known as “Mass Spectrograph”.
A scientist named F.W.Aston designed this device.
4: Atomic Number:
The number of protons in an atom is called “Charge Number” or “Atomic
Number”, denoted by “Z”.
5: Atomic Mass number:
The sum of the number of protons and neutrons is called “Mass
Number”, “A” denotes it.
6: Radioactivity:
A phenomenon of radiation of three different particles say,  and  rays from
radioactive elements is called “Radioactivity”.
Introduction:
Radioactivity was discovered by accident by Henry Becquerel in 1896. Other experiments with
radium by Marie and Pierre Curie proved that some elements emit invisible
radiation. This phenomenon was named as radioactivity by Marie Curie.
All those nuclei having atomic number larger than 83 are unstable known
as “Radioactive elements”. The nuclei of radioactive elements under go
change by ejecting radiations. Hence, such property is known as
“Radioactivity”. The radiations are named,  and  rays or particles known
to be Helium nuclei, electrons and photons respectively.
Description:
Radioactivity is the result of disintegration or decay of unstable
nucleus. Certain isotopes are unstable under the action of nuclear force and
they decay with the emission of some type of radiation. Such radioactivity is called “natural
radioactivity”. Other unstable isotopes can be produced in the laboratory by
nuclear reaction, these are said to produce artificially, and have “artificial radioactivity”.
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Experiment:
A radioactive substance like uranium that emits , and - radiations in a lead
container. Let the lead container, a pot have a small hole through which the radiation is
able to come out. A thick wall of lead can stop radiations. Thus with this arrangement,
the , and - radiations come out only from hole. Keep the lead pot with the
radioactive substance in a chamber which is evacuated.
Let plates connected to a battery the P1 acquires a negative charge and P2 acquires a positive
charge. Keep a photographic plate parallel to the hole in the lead pot so that the radiation coming out
from the radioactive substance is incident on the photographic plate.
Expose the photographic plate to the radiation and develop the plate. Notice three dots. These indicate
that there are three types of radiation. The central dot shows that this particular radiation is not affected
by the presence of an electric field. This is called the  - radiation. Of the other two dots, one is deviated
towards the positive plate P2. This shows that this particular radiation is negatively charged. This
radiation is called the - radiation. The last dot is seen to be deviated towards the negatively charged
plate P1. This radiation is called the - radiation.
Properties of -Radiation:
1.
Being charged particles, they are deflected by both electric and magnetic fields.
2.
They possess low penetrating power as their mass is high.
3.
They possess high ionizing power.
4.
They are positively charged particles. Their charge is 2e.
5.
They effect onto the photographic plate.
6.
They are helium nuclei. The mass of a  particle is 4 times the mass of proton and the charge is
twice the charge of proton
7.
While  decay the charge number decreases by 2 and mass number decreases by 4. Hence new
nucleus is produced.
8.
These particles are emitted with very high speed of order 1.6x107 m / sec.
9.
Charge of particles is 3.19 x 10-19 coulombs and mass 6.62 x 10-27 kg
Properties of -Radiation:
1. They are deflected in magnetic and electric field.
2. They are made of two types: - particles are electrons. They are negatively charged. +
Particles are positrons. They are positively charged.
3. They are generally emitted with high energies.
4. The penetrating power of  particles is larger than that observed for the - particles. But
the penetration is less than that seen for the -rays.
5. Their ionizing power while passing through any matter is relatively small. Since the mass
of the  particles is small,
6. They effect onto the photographic plate.
7. They are electrons. The charge of  particles is 1.6x10-19 C and mass 9.11x10-31kg.
Emission of  particles leads to change in the atomic number Z, but the atomic mass
number a remains unchanged.
8. They are emitted with different speeds some value is 0.9995 that of light.
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Properties of -Radiation:
1.
They are deflected in magnetic and electric field.
2.
They possess very high penetrating power.
3.
They possess very low ionizing power.
4.
They effect onto the photographic plate.
5.
They are high frequency photons.
6.
They are electromagnetic in nature. Their wavelength is very small ~ 10-10m.
7.
During “” decay neither charge number nor mass number changes.
8.
The nucleus comes from excited state to normal state.
9.
The element remains unchanged.
Disintegration of radioactive elements:
If radioactive element decays by given  particles then its atomic mass (A) decreases by 4 and
the atomic number Z decreases by 2. The new element thus formed is known as “Daughter element” or
“Daughter nucleus”. The original element is known as “Parent element” or “Parent nucleus”.
When a parent nucleus AZXN emits a - radiation, the atomic mass number A and the proton number
Z as well as the neutron number N remains unchanged. The nucleons jump from higher excited levels
to lower level and emit a
- radiation only.
A
ZX

Parent Element
(Nucleus)
A
Z
Daughter element
(Nucleus)
X
+γ
When the parent nucleus emits a or a positron, the mass number A remains the same, but the
atomic number Z decreases by one to Z - 1.
When the parent nucleus emits a
or an electron, the mass number A remains the same, but
the atomic number Z increases by one to Z + 1.
A
A

+ β - (electron)
ZX
Z+1 X
Parent Element
(Nucleus)
Daughter element
(Nucleus)
.
When an - particle is emitted, the atomic number Z reduces by 2 and the neutron number N
reduces by 2 atomic mass A reduces by 4. This is because an - particle is nothing but doubly ionized
helium atom (or helium nucleus).
A
A-4

+ 2 He 4  α- particles 
ZX
Z-2 X
Parent Element
(Nucleus)
Daughter element
(Nucleus)
A daughter nucleus is unstable nucleus, undergoes further disintegration till it attains stable nucleus.
88Ra226  86Rn222 + 2He4.
If radioactive element decays by giving  particle then its atomic mass does not change but its atomic
number increases by 1. Thus new element formed is called “Isobar” of the original element.
Law of radioactive elements:
The rate of disintegration of a radioactive element decreases with time. The rate of disintegration is
the characteristic property of the radioactive isotope. The fact for the process is that,
i) The number of atoms under going decay is very large. It is not possible to study a single nucleus.
ii) This is random process. It is impossible to say, which nucleus is going to disintegrate.
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iii) The rate of disintegration is directly proportional to the number of nuclei present at
that time.
Suppose “N” is the total number of nuclei of an element at instant “t”. After t
N
time, the number of nuclei left will be
(N - N). The rate of disintegration is
.
t
Thus according to this law,
N
 N
t
N
= -N
t
Where,  is called “decay Constant” or “Disintegration Constant”, its unit is sec-1. The negative sign
indicates that the no. of nuclei's decreases with increase of time.
7: Half-life of radioactive elements:
The time taken for a substance or collection of particles to decay by half of its original amount.
Half-life, denoted T½, is a useful concept by which to express the rate of radioactive decay. After one
half-life, half of the original number of atoms of a radioactive element will remain. After two half-lives,
one-quarter (= ½ × ½) will remain. After three half-lives, 1/8 (= ½ × ½ × ½) will remain, and so on.
When  and  particles are emitted from the nuclei then element changes. The original nucleus is
called “Parent nuclei” whereas the new nucleus formed from the parent nuclei is called “Daughter
nuclei”. The time in which half of the parent nuclei decay into daughter element is called “Half life of
an element”. The half-life varies for different radioactive atoms. The Uranium has half-life 4500 million
years, Radium has 1600 years, and Polonium has 138 days.
T1  = 0.693
2
Where T1 is called “Half Life of Radioactive Element”. If there are 3.7x1010 disintegration per second in
2
the radioactive sample then its activity is called “1 Curie”.
8: Binding energy:
The protons and neutrons in the nucleus of an atom are called “nucleons”. The amount of energy
released when a particular isotope is formed. Protons and neutron are held together by the strong force,
which only acts over very small distances but is able to overcome the electrostatic repulsion between
protons. The strength of the bonding is measured by the binding energy per nucleon where "nucleon" is
a collective name for neutrons and protons
Mass defect:
The mass energy relation follows that, the total mass of the nucleus is less than the sum of the mass
of the individual neutrons and protons that formed it. The difference in mass is equivalent to the
energy released in forming the nucleus.
The difference in mass is called “mass defect” and is measured by the binding energy.
Some times, the binding energy is called mass defect per nucleon .
9: Nuclear Fission:
In 1938 the German scientist Otto Hahn and Fritz Strassmann made a discovery
that, the nucleus of an element is broken into two nearly equal fragments the masses of
the product is found to be less than that of original nucleus. This difference in mass is
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converted into energy. The process is called “Nuclear Fission” or “Fission reaction”.
Thus, when the uranium is bombarded by neutron sometimes produced smaller nuclei,
which were half the size of original uranium nucleus. Therefore, a very slow neutron
collides with the isotope of Uranium 92U235, the unstable nuclei (more unstable than the
common use 92U238 nuclei)) of uranium 92U236 called “compound nucleus” is to be
formed, after absorbing neutron. Thus, the nucleus is to be broken into two intermediate
nuclei called “fission fragments” with the release of large
energy along with three neutrons. If such a process is once
started, it will continue by itself till all the nuclei will be
disintegrated. This is called “fission chain reaction”.
The fission fragments Barium and Krypton are the two
intermediate nuclei, the reaction can be written as,
92U235 + 0n1  92U236  56Ba141+36Kr92 + 3on1 + Q
In the above fission reaction, the neutrons emitted have
thousand times greater velocity as compared with the
incident slow neutron. The emitted neutrons go head- on
collision with the Uranium atoms. This produces fission
chain reaction so the process multiplies. If this reaction is
produced rapidly then huge “atomic explosion” is to be
produced. This fission chain reaction controlled by placing Cadmium plates.
An uncontrolled fission chain reaction is called an atom bomb. To sustain a chain reaction, a minimum
quantity of fissionable material is needed.
10: Nuclear Fusion:
The mass of every stable nucleus is less than the sum of the masses of its protons and
neutrons. This mass loss is the source of release of a large amount of energy. The process of building
two light nuclei with each other to form new heavy nuclei in this process some mass is converted into
energy. Such process is called “Nuclear Fusion”.
Suppose in the fusion of deuterium 1H2, an isotope of hydrogen known as heavy hydrogen and its
nucleus is called “Deuteron”. The process of two deuterons can result in helium nucleus.
1H2 + 1H2  2He3 + 0n1.
In this process, mass of two deuterons 2 x 2.015 = 4.030 a.m.u.
And mass of helium and neutron 3.017 + 1.009 = 4.026 a.m.u.
Therefore mass is converted into energy by fusion is 0.004 a.m.u.
Hence, 0.004 a.m.u. x 931MeV = 3.7 MeV energy is to be released.
Other fusion reaction can release much more energy. For example, the fusion of deuterium and tritium,
isotopes of hydrogen,
H2 + 1H3  2He4 + 0n1 + 17.6MeV.
Another nuclear fusion reaction is,
1H2 + 1H2  1H3 + 1H1 + 4.0MeV.
2He3 +2He3  2He4+1H1+1H1+12.86 MeV
One set of fusion reaction that is supposed to be source of solar energy.
1H1 + 1H1  1H2 + + + (neutrino).
1H1 + 1H2  2He3 + 
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+ 2He3  2He4 + + + (neutrino)
This is known as proton- proton cycle.
In the fusion reaction four protons are combined to obtain helium nucleus.
41H1  2He4 + 2+ + 2 + 
In this nuclear reaction 25MeV energy is to be released.
Sun gives out a large amount of energy continuously. Before the discovery of nuclear
fusion reaction it was not possible to understand the source of
this energy. Scientist Bethe tried to explain the origin of
amount of energy. The energy liberated in this fusion process,
which further increases, the temperature. This nuclear fusion
process is taken the source on sun energy. Once the star has
exhausted all its hydrogen fuel, the helium fusion starts to
take place. From 126C other nuclei are produced by fusion.
This is the reason why this cycle is known as carbon-carbon
cycle. According to Bethe, the energy in the sun is produced as a result of hydrogen, carbon-helium,
and chain reaction. The carbon cycle is given by,
6C12 + 1H1  7N13 + 
7N13  6C13 + + + 
6C13 + 1H1  7N14 + 
7N14 + 1H1  8O15 + 
8O15  7N15 + + + 
7N15 + 1H1  6C12 + 2He4 .
It is believed that many of elements in the universe were original formed through the process of
fusion and that today; fusion is taking place with in the stars, including our sun.
11: Nuclear reactions:
When a nucleus undergoes  and decays, the daughter nucleus is that of
different elements from the parent. The transformation of one element into another, called
“transformation” also occurs by means of nuclear reactions. A “nuclear reaction “ said to occur r when
a given nucleus is struck by another nucleus or by neutron, so tat interaction takes place. In 1919
Rutherford observed that by passing particles through nitrogen gas were absorbed and proton
emitted.
7N14 +2He4 8O17 +1H1
Where 2He4 is  particle and 1H1 is proton.
The nuclear reactions in which  and  particles are emitted by unstable nuclei. These nuclear reactions
are however spontaneous and uncontrollable. Hence, Lithium absorbs a proton two helium particles
are formed.
3Li7 + 1H1  22He4
3Li6 + 1H2  22He4
Neutron captures:
The reaction of a neutron by a proton to form a deuteron is given by,
1H1 + 0n1  1H2 + 
Neutron when incident on carbon can eject another neutron from the nucleus.
1H1
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6C12 + 0n1  6C11+
2 0n1
Neutrons are ideal projectile for the nuclear bombardments, having no charge and no
electrical repulsion.
Proton captures:
The reaction of lithium by a proton to form a two alpha say helium nucleus is given by,
3Li7 + 1H1  2He4 + 2He4
This reaction is very important because Einstein, mass-energy relation is revivified with the same.
Deuteron captures:
The reaction of lithium by a bombardment of deuteron to form a two alpha nucleus is given by,
3Li6 + 1H2  2He4 + 2He4
Gamma captures:
The reaction of bombardment of gamma process is photo disintegration, is given by,
13Al27 + 1H2 +   11Na25 + 21H1
12: Nuclear reactor:
A nuclear reactor is a device in which a chain reaction involving nuclear fission can be
initiated and controlled. A reactor is a very efficient source of energy. The energy used in a nuclear
reactor is display as heat and it can be extracted by circulating a suitable liquid or gaseous coolant
through the reactor‘s interior.
In design of reactor there are two problems: one is the loss of neutron through the reactor surface and
loss by absorbing without inducing fission. Increasing the reactor size can solve this problem. Second
problem is natural uranium contain only 0.7 percent of fissionable isotope U235. The U238 captures fast
neutrons but usually does not undergo fission as a result. Where as U235 for slow neutron – induced
fission. A substance used in reactor to slow down the
neutrons is known as “moderator”. The moderator will
consist of atoms whose mass is as close as possible to that
of neutrons. 1H2 does not absorb many neutrons and thus
an ideal moderator. Either 1H1 or 1H2 can be used in the
form of water.
Nuclear reactors have been built for use in
research and produce electric power. Fission produces
many neutrons and a “research reactor” is basically an
intense source of neutrons. These neutrons are used, as
projectiles in nuclear reactions to produce nuclides not
found in nature, including isotopes used as tracer and for
medical therapy.
A “power reactor” is used to produce electric
power. The energy released in fission process appears as
heat, which is used to boil water and produce steam to derive turbine connected to an electric
generator. The core of nuclear reactor consists of the fuel and moderator .The fuel is usually uranium
enriched so that it contains 2 to 4 percent 92U235.Water is allowed to flow through the core. The thermal
energy it absorbs is used to produce steam in the heat exchanger, so the fissionable fuel acts as heat
input for the heat engine.
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A “breeder reactor” is one in which some of the neutron produced in the
fission
are absorbed by 92U238 , and 94Pu239 is produced via the set of reaction .
94Pu238 is fissionable with slow neutron, so after separation it can be used as fuel in a
nuclear reactor. Thus breeder reactor “breeds” new fuel (94Pu239) from useless 92U238.
Since natural uranium is 99.3percent 92U238, this means that the supply of fissionable
fuel could increase by more than a factor 100. Plutonium produced in a reactor can be
used in a bomb.
EQUATIONS
01. T½ = 0.693 02. N  t = -½ N 03. Activity = ½ N 04. Activity = ½ t 05. E = m c2
06. ZXA  Z-2XA-4 + [ 2He4 ] 07. ZXA  Z+1XA + -(electron). 08. ZXA  Z-1XA + 
(positron).
DI
MENSIONS
PHYSICAL QUANTITY & SYMBOL
DIMENSION
UNIT
Activity | Radioactivity Bq
bequerel. [Events]/[Time].
s-1
-3
Irradiance
[Power]/[Area].
kg.s = W.m-2
Exposure
[Charge]/[Mass]. For ionising radiations
kg-1.s.A= C.kg-1
Half life
typically of a radioactive substance
s
SHORT QUESTIONS AND ANSWERS
Q: No: 1 After four half lives what percent of a sample remains?
Answer:
½  ½  ½  ½  percent remains, after four half lives.
Q: No: 2 A slow neutron will cause fission in 92U234, 92 U235, 92U238 .
Answer:
A slow neutron will cause fission in 92 U235 .
Q: No: 3
complete the reaction:
i) ZXA +? = Z-1 XA-3 + 2He4
ii) ZXA  Z+1XA +?
iii) ZXA  Z-1XA +?
iv) 92U238  ? + 2  
v) 90Th232  ? + 4  3
vi) 3Li8  ? + 2  
vii) 51Sb133  ? + 3
viii) 88Ra226  ? + 2He4
ix) 20Ca45  ? + - + 
x) 29Cu58  ? + 
xi) 24Cr46  23V46 +?
xii) 94Pu234  ? + 
xiii) 9\3Np239 92U239 +?
xiv) 11Na22  ? + 
xv) 11Na24  ? + 
xvi) 84Po210  ? + 
xvii) 16S35  ? + 
xviii) 83Bi211  ? + 
xix) 15P32  ? + 
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Answer:
i) ZXA + 1H1 = Z-1 XA-3 + 2He4
ii) ZXA  Z+1XA +  (electron decay)
iii) ZXA  Z-1XA +  (positron decay)
iv) 92U238  90Th230 + 2  
v) 90Th232  88Ra220 + 4  3
vi) 3Li8  3Li4 + 2  
vii) 51Sb133  54Xe133 + 3
viii) 88Ra226  86Rn222 + 2He4
ix) 20Ca45  21Sc45 + - + 
x) 29Cu58  29Cu58 +  + Q
xi) 24Cr46  23V46 + +
xii) 94Pu234  92U230 + 
xiii) 93Np239 92U239 + +
xiv) 11Na22  10Ne22 + 
xv) 11Na24  12Mg22 + 
xvi) 84Po210  84Po210 +  + Q
xvii) 16S35  17Cl36 + 
xviii) 83Bi211  81Tl207 + 
xix) 15P32  16S32 + 
Q: No: 4 The core of how many neutrons and protons do the following nuclei contain:
4Be10, 16s36, 10Ne22, 56Ba138, 82Pb207,13Al27, 16Ar40, 92U238.36Kr92
Answer:
For,4Be10 Nucleus, A = 10, Z = 4 .
Hence, No. of proton( Z ) = 4 & No. of neutron = A - Z= 6
For,16s36 Nucleus, A = 36, Z =16.
Hence, No. of proton( Z ) = 16 & No. of neutron = A - Z = 20
For,10Ne22 Nucleus, A = 22, Z =10.
Hence, No. of proton( Z ) = 10 & No. of neutron = A – Z = 12
For,56Ba138 Nucleus, A =138, Z = 56.
Hence, No. of proton( Z ) = 56 & No. of neutron = A - Z = 82
For,82Pb207 Nucleus, A = 207, Z = 82.
Hence, No. of proton( Z ) = 82 & No. of neutron = A – Z = 125
For,13Al27 Nucleus, A = 27, Z = 13.
Hence, No. of proton( Z ) = 13 & No. of neutron = A – Z = 14
For,16Ar40 Nucleus, A = 40, Z = 16 .
Hence, No. of proton( Z ) = 16 & No. of neutron = A – Z = 24
For,92U238 Nucleus, A = 238, Z = 92.
Hence, No. of proton( Z ) = 92 & No. of neutron = A - Z =146
For,36Kr92 Nucleus, A = 92, Z = 36.
Hence, No. of proton( Z ) = 36 & No. of neutron = A – Z = 56
Q: No: 5 How does Cl35 differ from Cl37. When they are considered to be chemically identical even
though their nuclei are not he same?
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Answer:
We know that, 17Cl35 and 17Cl37 have the same number of protons but
different number of neutrons. The chemical properties depend upon the number of
electrons. So that Cl35 and Cl37 are chemically same.
Q: No: 6 Do , , and  rays come from same elements? Why d we find three in many
radioactive elements?
Answer:
No,,, and  rays are coming from different elements. Because, any
radioactive element cannot emit such radiation at a same time.

ZXA 
Z-2YA - 4 +  - particle
Z - 2 YA - 4 
Z - 2YA - 4 +  - Particle
Z - 2 YA - 4 
Z - 1WA - 4 +  - particle
Z - 1WA - 4  Z - 1WA - 4 +  - particle
Z - 1WA - 4  Z - 3YA - 8 + - particle
This series of reactions shows that  and  are coming from different elements, on the other hand “” is
coming from the same element. It is also found that daughter elements of many radioactive elements
are also radioactive, till a stable nucleus reached.
Q: No:7 It is more difficult to start a fusion reaction than a fission reaction .Why?
Answer:
The fusion reaction releases energy which is ten times more than fission process.
Moreover there are no radioactive by-products that need to be disposed.
In the fusion reaction two nuclei are fused and form a single nucleus. The nuclei are positively
charged and with greater repulsive. Thus, maximum energy is required to overcome this force, at very
high temperature.
In the fission reaction a slow neutron enters nucleus easily, because no repulsive force between them.
Thus nucleus split up into fragments. So tat fission reaction can occur at low temperature.
Thus, it is more difficult to start fusion reaction than fission reaction.
Q: No: 8 How mass number and charge number of radioactive element ZXA change when, a) 
participle is emitted b)  particles are emitted.

Answer:
ZXA  Z -1XA   (positron)
This shows that atomic number decreases by one and mass number remain same.

ZXA  Z  1XA   (electron)
This shows that atomic number increased by one and mass number remains same.
Q: No: 9 What is mass defect?
Answer:
In general, all nuclei have masses that are less than the masses of constituent protons
and neutrons together in Free State. The apparent loss of mass is called “mass defect”.
Q: No: 10 In radioactive decay, if the probability of decay per unit time is double, the half-life will
be double. Comment.
Answer: We know that, N / t  N
N  t =  N,
T½ = 0.693
 = 0.693  T½
Therefore, N / t = [ 0.693  T½ ] N
This shows that, in radioactive decay, if the probability of decay per unit time is double, the half-life
will be double.
Q: No: 11 what is meant by half life of a radioactive element
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Answer:
The number of radioactive atoms of a material that decay to one half of the
total number of atoms, in a time. Such time is called “Half life (T½ )” of radioactive
elements. T½ = 0.693 / 
Q: No: 12 What is the difference between nuclear force and binding energy?
Answer:
The difference is that binding energy is created by fusion. And most nuclear
forces are created by Fission. Fission is when a single neutron is sent to an unstable
element, like uranium, making it even more unstable, making the atom split, and
releasing a lot of energy.
Q: No: 13 how would you use a Geiger counter to determine the count rate of alpha particle?
Answer:
A Geiger counter has a gas filled tube ( inert ) which becomes conductive to electricity
when a photon passes through it as when " radiated " from an Isotope. A cascade effect is used to
amplify the signal which is then shown on a needle or by clicks.
Q: No: 14 What is a Van de Graff generator?
Answer:
The Van de Graff generator was named after Van de Graff, who invented it.
A Van de Graff generator is a device used to store an enormous amount of electric charge (either
positive or negative) on a metallic sphere so that a very strong electric field can be produced. This
strong electric field can be used to accelerate charged particles like protons, alpha particles etc.
In the Van de Graff generator, charges from an electric battery are separated and stored on a metallic
sphere which is mounted on an insulating pillar.
Q: No: 15 What is a neutron?
Answer:
Uncharged elementary particle of slightly greater mass than the proton.
Q: No: 16 What is a phonon?
Answer:
phonon , quantum of vibrational energy. The atoms of any crystal are in a state of
vibration, their average kinetic energy being measured by the absolute temperature of the crystal.
Q: No: 17 What is one half-life?
Answer:
One half-life is the time required for one half of any given quantity of the substance to
decay.
Q: No: 18 What is a half-life of a radioactive isotope?
Answer:
The half-life of a radioactive isotope is a characteristic of that isotope and is not
affected by any change in physical or chemical conditions.
Q: No: 19 What are cosmic rays?
Answer: Cosmic rays charged particles moving at nearly the speed of light reaching the earth from
outer space.
Q: No: 20 What is the nucleon?
Answer:
The nucleon may be considered a single particle, of which the proton and the neutron are
two different states.
Q: No: 21 Define nuclear fusion reaction.
Answer: Nuclear fusion is a reaction in which two or more light nuclei combine to form a heavier
nucleus releasing an enormous amount of energy.
Q: No: 22 What is the weight of an electron?
Answer:
The electron is the lightest particle having a non-zero rest mass
Q: No: 23 What is a neutrino?
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Answer: Elementary particle with no electric charge and a very small mass emitted
during the decay of certain other particles.
Q: No: 24 What are a leptons?
Answer:
Leptons are elementary particles, and are classified as fermions. There are
six different types of lepton, which are known as flavours. These are:- electron,- muon,tauon,- electron-neutrino,- muon-neutrino,- tauon-neutrino
Q: No: 25 What is a quark?
Answer: A quark is an elementary particle, and is classified as a fermion.
There are six different types of quark, which are known as flavours.
Q: No: 26 Write two differences between nuclear fission and fusion reactions.
Answer:
Nuclear Fission
A heavy nucleus splits up into two or more light nuclei
Harmful nuclear radiations are emitted and this causes pollution
Nuclear Fusion
Two light nuclei combine together to form a heavy nucleus
No harmful radiations are emitted and hence pollution free
Q: No: 27 What is nuclear fission reaction?
Answer: The process of splitting of a heavy nucleus into a number of light nuclei with the liberation of
tremendous amount of energy and two or three neutrons is called nuclear fission
Q: No: 28 What is a nuclear reactor?
Answer: A nuclear reactor is a device or a furnace where controlled fission chain reaction is carried out
and the energy released is used to generate electricity
The following charts list the various particle groupings:
LEPTONS (spin 1/2, mass < mesons)
NAME
MASS
LIEFTIME
SPIN
Electron
0.5511 MeV
Stable
CHARGE
-1
Positron
0.5511 MeV
Stable
+1
1/2
105.6 MeV
2 x 10-6 s
-1
+1
1/2
1/2
1.78 GeV
< 50 eV
291 x 10-15s
0
0
1/2
1/2
0 (?)
<.05 MeV
Stable (?)
0
0
1/2
1/2
Muon &
Antimuon
Tau &
Antitau
Muon
neutrino &
1/2
Antineutrino
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Tau neutrino
&
0 (?)
<70 MeV
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Stable (?)
0
0
1/2
1/2
Antineutrino
NAME
Up &
Antiup
Down &
Antidown
Strange &
Antistrange
Charm &
Anticharm
Botton &
Antibottom
Top &
QUARKS (particles with 1/3 or 2/3 charge)
MASS
LIFETIME
CHARGE
SPIN
1.5-4.5
MeV
Stable *
+2/3
-2/3
1/2
1/2
5.0-8.5
MeV
Variable *
-1/3
+1/3
1/2
1/2
~100
MeV
Variable *
-1/3
+1/3
1/2
1/2
~1.2 GeV
Variable *
+2/3
-2/3
1/2
1/2
~4.2 GeV
Variable *
-1/3
+1/3
1/2
1/2
175
GeV
Variable *
+2/3
-2/3
1/2
1/2
Antitop
* As quarks occur only in pairs or triplets, their lifetimes vary
BOSONS (force carrying particles)
NAME
NATURE
MASS
LIFETIME
CHARGE
Photon
Electromagnetic
0
Stable
0
W-plus
+1
Weak force
80.4 GeV
10-25 s
-1
W-minus
Z
Weak force
91.2 GeV
10-25 s
0
Gluon
Strong force
0
Stable
0
Graviton*
Gravity
0
Stable
0
* Undetected at the time of this writing
MESONS (masses between the electron and proton)
NAME
MASS
LIFETIME
CHARGE
SPIN
-16
Pion (pi-zero)
135 MeV
0.8 x 10 s
0
0
Pion (pi-plus)
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2.6 x 10-8 s
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-1
SPIN
1
1
1
1
1
2
0
0
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Pion(pi-minus)
Kaon (K-zero)
498 MeV
10-10 s
5 x 10-8 s
0
0
494 MeV
1.2 x 10-8 s
0
0
3.1 GeV
10-20 s
0
1
1.87 GeV
10-12 s
4 x 10-13 s
0
+1
0
0
1
MASS
10-20 s
BARYONS
LIFETIME
938.3 MeV
938.3 MeV
Stable (?)
Stable (?)
Kaon (K-plus)
Kaon (Kminus)
J/PSI
D (D-zero)
D (D-plus)
UPSILON
NAME
Proton
Antiproton
Neutron
Antineutron
Lambda
Antilambda
Sigma (sigma +)
Sigma (sigma -)
Sigma (sigma 0 )
XI (xi-minus)
9.46 GeV
939.6 MeV Stable in nuclei
939.6 MeV
15 Min. free
SPIN
+1
-1
1/2
1/2
0
0
1/2
1/2
1.115 GeV
1.115 GeV
2.6 x 10-10 s
0
0
1/2
1/2
1.189 GeV
1.197 GeV
1.192 GeV
0.8 x 10-10 s
1.5 x 10-10 s
6 x 10-20 s
+1
-1
0
1/2
1/2
1/2
1.321 GeV
1.315 GeV
1.6 x 10-10 s
3 x 10-10 s
-1
0
1/2
1/2
0.8 x 10-10 s
2 x 10-13 s
-1
1
3/2
1/2
XI (xi-zero)
Omega minus 1.672 GeV
Charmed lambda
2.28 GeV
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Quark flavor properties
Name Symbol
Antiparticle
symbol
C
S
T
B′ Antiparticle
First generation
+2⁄3 +1⁄2
0
1
1
1
+ ⁄3 − ⁄3 − ⁄2
0
Second generation
0
0
0
0
0
0
Antiup
Antidown
u
d
Mass (MeV/c2)*
J
B
+1⁄3
Q
I3
Up
Down
u
d
1.7 to 3.3
4.1 to 5.8
1⁄
2
Charm
c
1,270+70
1⁄
2
+1⁄3
+2⁄3
0
+1
0
0
0
Anticharm
c
Strange
s
101+29
1⁄
2
+1⁄3
−1⁄3
0
0
−1
0
0
Antistrange
s
1⁄
2
+1⁄3
Top
t
−90
−21
1⁄
2
Third generation
+2⁄3
0
0
172,000±900 ±1,300
0
+1
0
Antitop
t
4,190+180
1⁄
Bottom
b
+1⁄3 −1⁄3
0
0
0
0
−1 Antibottom
b
2
−60
J = total angular momentum, B = baryon number, Q = electric charge, I3 = isospin, C = charm,
S = strangeness, T = topness, B′ = bottomness.
* Notation such as 4,190+180
−60 denotes measurement uncertainty. In the case of the top quark, the first uncertainty is statistical in
nature, and the second is systematic.
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Binding Energy
The nucleus of an atom consists of positively charged protons and neutral neutrons. Collectively, these
nuclear particles are known as nucleons. Protons repel each other electrically, so why doesn't the
nucleus fly apart? There is another force which holds nucleons together, known as the strong nuclear
force. This extremely strong force overcomes the electrical repulsion of the protons, but it is only
effective over very small distances.
Because nucleons are held together by the strong nuclear force, you must add energy to the system to
break apart the nucleus. The energy required to break apart the nucleus is known as the binding
energy of the nucleus.
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If measured carefully, we find that the mass of a stable nucleus is actually slightly less
than the mass of its indivudal component nucleons. The difference in mass between the
entire nucleus and the sum of its component parts is known as the mass defect ( m).
The binding energy of the nucleus, therefore, must be the energy equivalent of the mass
defect due to the law of conservation of mass-energy:
.
Fission & Fusion
Fission is the process in which a nucleus splits into two or more nuclei. For heavy (larger) nuclei such
as Uranium-235, the mass of the original nucleus is greater than the sum of the mass of the fission
products. Where did this mass go? It is released as energy! A commonly used fission reaction involves
shooting a neutron at an atom of Uranium-235, which briefly becomes Uranium-236, an unstable
isotope. The Uranium-236 atom then fissions into a Barium-141 atom and a Krypton-92 atom, releasing
its excess energy while also sending out three more neutrons to continue a chain reaction! This process
is responsible for our nuclear power plants, and is also the basis (in an uncontrolled reaction) of atomic
fission bombs.
Fusion, on the other hand, is the process of combining two or more smaller nuclei into a larger nucleus.
If this occurs with small nuclei, the product of the reaction may have a smaller mass its precursors,
thereby releasing energy as part of the reaction. This is the basic nuclear reaction that fuels our sun and
the stars as hydrogen atoms combine to form helium. This is also the basis of atomic hydrogen bombs.
Nuclear fusion holds tremendous potential as a clean source of power with widely available source
material (we can create hydrogen from water). The most promising fusion reaction for controlled
energy production fuses two isotopes of hydrogen known as deuterium and tritium to form a helium
nucleus and a neutron, as well as an extra neutron, while releasing a considerable amount of energy.
Currently, creating a sustainable, controlled fusion reaction that outputs more energy than is required
to start the reaction has not yet been demonstrated, but remains an area of focus for scientists and
engineers.
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