1) What is the first step in problem-solving? A) Writing code B) Debugging C) Understanding the problem D) Optimizing the solution Answer: C 2) Which of these is not a step in the problem-solving process? A) Algorithm development B) Problem analysis C) Random guessing D) Testing and debugging Answer: C 3) What is an algorithm? A) A high-level programming language B) A step-by-step procedure to solve a problem C) A flowchart D) A data structure Answer: B 4) Which of these is the simplest data structure for representing a sequence of elements? A) Dictionary B) List C) Set D) Tuple Answer: B 5) What does a flowchart represent? A) Errors in a program B) A graphical representation of an algorithm C) The final solution to a problem D) A set of Python modules Answer: B 6) What is pseudocode? A) Code written in Python B) Fake code written for fun C) An informal high-level description of an algorithm D) A tool for testing code Answer: C 7) Which of the following tools is NOT commonly used in pr...
Nuclear Physics
* The atomic nucleus was discovered by Earnest Rutherford in 1911. Rutherford’s experiment on scattering of alpha particles proved that the mass of the atom and the positive charge is concentrated in a very small central core called nucleus. The dimension of nucleus is much smaller than the overall dimension of the atom. The nucleus is surrounded by orbiting electrons.
Nucleus
* The nucleus consists of the elementary particles, protons and neutrons which are known as nucleons. A proton has positive
charge of the same magnitude as that of electron and its rest mass is about 1836 times the mass of an electron. A neutron is electrically neutral, whose mass is almost equal to the mass of the proton. The nucleons inside the nucleus are held
together by strong attractive forces called nuclear forces.
* A nucleus of an element is represented as ZXA, where X is the chemical symbol of the element. Zrepresents the atomic number which is equal to the number of
protons and A, the mass number which is equal to the total number of protons and neutrons. The number of neutrons is represented as N which is equal to A−Z. For example, the chlorine nucleus is
represented as 17Cl35. It contains 17 protons and 18 neutrons.
Classification of nuclei
(i) Isotopes
* Isotopes are atoms of the same element having the same atomic number Z but different mass number A. The nuclei 1H1, H2 and H3 are the isotopes of hydrogen. In other words isotopes of an element contain the same number of protons but different number of neutrons. As the atoms of isotopes have identical electronic structure, they have identical chemical properties
(ii) Isobars
* Isobars are atoms of different elements having the same mass number A, but different atomic number Z. The nuclei 8O16 and 7N16represent two isobars. Since isobars are atoms of different elements, they have different physical and
chemical properties.
(iii) Isotones
* Isotones are atoms of different elements having the same number of neutrons. 6C14 and 8O16 are some examples of isotones.
General properties of nucleus
Nuclear size
* measure of nuclear radius, which is approximately 10−15m.(1 Fermi, F = 10−15m)
Nuclear density
The nuclear density is calculated as 1.816 × 1017 kg m−3
Nuclear charge
Proton has a positive charge equal to 1.6 × 10−19C.
Atomic mass unit
* One atomic mass unit is considered as one twelfth of the mass of carbon atom 6C12. Carbon of atomic number 6 and mass number 12 has mass equal to 12 amu.
1 amu = 1.66 × 10−27kg
The mass of a proton, mp = 1.007276
Binding energy
Explanation of binding energy curve
* The binding energy per nucleon increases sharply with mass number 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 even number of protons and neutrons. Example: He4, 4Be8, C12, 8O16, and 10Ne20. The curve becomes almost flat for mass number between 40 and 120. Beyond 120, it decreases slowly as A increases.
* 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.
* The average binding energy per nucleon is about 8.5 MeV for nuclei having mass number ranging between 40 and 120. These elements are comparatively more
stable and non radioactive.
* For higher mass numbers the curve drops slowly and the BE/A is about 7.6 MeV for uranium. Hence, they are unstable and radioactive.
* 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 nuclei are fused to form heavier one (fusion) or if heavier nuclei are split into lighter ones (fission).
Nuclear force
1. Nuclear force is charge independent. It is the same for all the three types of pairs of nucleons (n−n), (p−p) and (n−p). This shows that nuclear force is not electrostatic in nature
2. Nuclear force is the strongest known force in nature.
3. Nuclear force is not a gravitational force. Nuclear force is about 1040 times stronger than the gravitational force.
4. Nuclear force is a short range force. It is very strong between two nucleons which are less than 10−15 m apart and is almost
negligible at a distance greater than this. On the other hand electrostatic, magnetic and gravitational forces are long range forces that can be felt easily. Yukawa suggested that the nuclear force existing
between any two nucleons may be due to the continuous exchange of particles called mesons, just as photons, the exchange particle in electromagnetic interactions. However, the present view is that the nuclear force that binds the
protons and neutrons is not a fundamental force of nature but it is secondary.
Radioactivity
* Radioactivity was discovered by Henri Becquerel in 1896 The phenomenon of spontaneous emission of highly penetrating radiations such as α, β and γ rays by heavy elements having atomic
number greater than 82 is called radioactivity and the substances which emit these radiations are called radioactive elements The radioactive phenomenon is spontaneous and is unaffected by any external agent like temperature, pressure, electric and magnetic fields etc.
Properties of α–rays
1. An α - particle is a helium nucleus consisting of two protons and two neutrons. It carries two units of positive
charge.
2. They move along straight lines with high velocities.
3. They are deflected by electric and magnetic fields.
4. They produce intense ionisation in the gas through which they pass. The ionising power is 100 times greater than that of β-rays and 10,000 times greater than that of γ−rays.
5. They affect photographic plates.
6. They are scattered by heavy elements like gold.
7. They produce fluorescence when they fall on substances like zinc sulphide or barium platinocyanide.
Properties of β – rays
1. β–particles carry one unit of negative charge and mass equal to that of electron.Therefore, they are nothing but electrons.
2. The β–particles emitted from a source have velocities over the range of 0.3 c to 0.99 c, where c is the velocity of light.
3. They are deflected by electric and magnetic fields.
4. The ionisation power is comparatively low
5. They affect photographic plates.
6. They penetrate through thin metal foils and their penetrating power is greater than that of α−rays
7. They produce fluorescence when they fall on substances like barium platinocyanide.
Properties of γ – rays
1. They are electromagnetic waves of very short wavelength.
2. They are not deflected by electric and magnetic fields.
3. They travel with the velocity of light.
4. They produce very less ionisation.
5. They affect photographic plates.
6. They have a very high penetrating power, greater than that of β-rays.
7. They produce fluorescence.
8. They are diffracted by crystals in the same way like X−rays are diffracted.
Half life period
* Since all the radioactive elements have infinite life period, in order to distinguish the activity of one element with another, half life period and mean life period are
introduced. The half life period of a
radioactive element is defined as the time taken for one half of the radioactive element to undergo disintegration.
Neutron
Chadwick in the discovered that the emitted radiation consists of particlesof mass nearly equal to proton and no charge.
4Be9 + 2He4 → 6C12 + 0n1
where on1 represents neutron
Properties of neutrons
1. Neutrons are the constituent particles of all nuclei, except hydrogen.
2. Neutrons are neutral particles with no charge and mass slightly greater than that of protons. Hence, they are not deflected by electric and magnetic fields.
3. Neutrons are stable inside the nucleus. But outside the nucleus they are unstable. The free neutron decays with an emission of proton, electron and antineutrino, with half life of 13 minutes. 0n1→1H1+−1e
0+ν
4. As neutrons are neutral, they can easily penetrate any nucleus.
5. Neutrons are classified according to their kinetic energy as (a) slow neutrons and (b) fast neutrons. Both are capable of penetrating a nucleus causing artificial
transmutation of the nucleus. Neutrons with energies from 0 to 1000 eV are called slow neutrons. The neutrons with an average energy of about 0.025 eV in
thermal equilibrium are called thermal neutrons. Neutrons with energies in the range between 0.5 MeV and 10 MeV are called fast neutrons. In nuclear reactors, fast neutrons are converted into slow
neutrons using moderators.
Artificial radioactivity
* Artificial radioactivity or induced radioactivity was discovered by Irene Curie and F. Joliot in 1934. This is also known as man-made Radioactivity
Applications of radio-isotopes
Medical applications
* In medical field, radio-isotopes are used both in diagnosis and therapy. Radio cobalt (Co60) emitting γ−rays is used in the treatment of cancer. Gamma rays destroy cancer cells to a greater extent. Radio-sodium (Na24) is used to detect the presence of blocks in blood vessels, to check the effective functioning of heart in
pumping blood and maintaining circulation. Radio-iodine (I131) is used in the detection of the nature of thyroid gland and also fortreatment. Radioiodine is also used to locate brain tumours. Radio-iron
(Fe59) is used to diagnose anaemia. An anaemic patient retains iron in the blood longer than normal patient. Radio-phosphorous (P32) is used in the treatment of skindiseases.
(ii) Agriculture
* In agriculture, radio-isotopes help to increase the crop yields. Radio phosphorous (P32) incorporated with phosphate fertilizer is added to the soil. The plant and soil are tested from time to time. Phosphorous is taken by the plant
for its growth and radio-phosphorous is found to increase the yield.
* Sprouting and spoilage of onions, potatoes, grams etc. are prevented by exposure to a very small amount of radiation. Certain perishable cereals remain fresh beyond their normal life span when exposed to radiation.
(iii) Industry
* In Industry, the lubricating oil containing radio-isotopes is used to study the wear and tear of the machinery.
(iv) Molecular biology
* In molecular biology radio-isotopes are used in sterilizing pharmaceutical and surgical instruments.
(v) Radio-carbon dating
* In the upper atmosphere, C14 is continually formed from N14 due to the bombardment by neutrons produced from cosmic rays.
7N14 + 0n1 → 6C14* + 1H1
* The C14 is radioactive with half life of 5570 years. The production and the decay of C14are in equilibrium in atmosphere. The ratio of C14 and C12 atoms in atmosphere is 1 : 106. Hence, carbon dioxide present in the atmosphere contains a small portion of C14.
* Living things take C14 from food and air. However with death, the intake of C14 stops, and the C14 that is already present begins to decay. Hence the amount of C14
in the sample will enable the calculation of time of death i.e, the age of the specimen could be estimated. This is called radio-
carbon dating. This method is employed in the dating of wooden implements, leather
clothes, charcoal used in oil paintings, mummies and so on.
Biological hazards of nuclear radiations
* When γ-ray or any high energy nuclear particle passes through human beings, it disrupts the entire normal functioning of the biological system and the effect may be either pathological or genetic. The
biological effects of nuclear radiation can be divided into three groups
(i) Short term recoverable effects
(ii) Long term irrecoverable effects and
(iii) Genetic effect
The extent to which the human organism is damaged depends upon
(i) The dose and the rate at which the radiation is given and
(ii) The part of the body exposed to it.
Smaller doses of radiation exposure
produce short term effects such as skin
disorder and loss of hair. If the exposure is 100 R*, it may cause diseases like leukemia (death of red blood corpuscle in the blood) or cancer. When the body is exposed to about 600 R, ultimately it causes death. Safe limit of receiving the radiations is about 250 milli roentgen per week. The genetic damage is still worse. The radiations cause injury to genes in the
reproductive cells. This gives rise to
mutations which pass on from generation to generation. The following precautions are to be taken for those, who are working in radiation laboratories.
1. Radioactive materials are kept in thick−walled lead container.
2. Lead aprons and lead gloves are used while working in hazardous area.
3. All radioactive samples are handled by a remote control process.
4. A small micro−film badge is always worn by the person and it is checked periodically for the safety limit of radiation.
Nuclear fission
* In 1939, German scientists Otto Hahn and F. Strassman discovered that when uranium nucleus The process of breaking up of the nucleus of a heavier atom into two fragments with the release of large
amount of energy is called nuclear
fission.
92U235+0n1→56Ba141+36Kr92+3n1+Q
* Atom bomb is based on the principle of uncontrolled fission chain reaction. Natural uranium consists of 99.28% of U238 and 0.72% of U235. U238 is fissionable only by fast neutrons. Hence, it is essential in a bomb that either U235or Pu239 should be used, because they are fissionable by neutrons of all energies
Nuclear reactor
* A nuclear reactor is a device in which the nuclear fission reaction takes place in a self sustained and controlled manner. The first nuclear reactor was built in 1942 at Chicago USA
Fissile material or fuel
* The fissile material or nuclear fuel generally used is 92U235. But this exists only in a small amount (0.7%) in natural uranium. Natural uranium is enriched with more number of 92U235 (2 – 4%) and this
low enriched uranium is used as fuel in some reactors. Other than U235, the fissile isotopes U233 and Pu239 are also used as fuel in some of the reactors.
Moderator
* The function of a moderator is to slow down fast neutrons produced in the fission process having an average energy of about 2 MeV to thermal neutrons with an average energy of about 0.025 eV, which are in thermal equilibrium with the moderator. Ordinary water and heavy water are the commonly used moderators Graphite is also used as a moderator in some countries. In fast breeder reactors, the fission chain reaction is sustained by fast neutrons and hence no moderator is
required.
Neutron source
* A mixture of beryllium with plutonium or radium or polonium is commonly used as a source of neutron
Control rods
* The control rods are used to control the chain reaction. They are very good absorbers of neutrons. The commonly used control rods are made up of elements like boron or cadmium In our country, all the power reactors use boron carbide (B4C), a ceramic material as control rod.
The cooling system
* The cooling system removes the heat generated in the reactor core. Ordinary water, heavy water and liquid sodium are the commonly used coolants. A good coolant must possess large specific heat capacity and high boiling point. Liquid
sodium boiling point is about 1000°C.
Neutron reflectors
Neutron reflectors prevent the leakage of neutrons to a large extent, by reflecting them back
Uses of reactors
a. Nuclear reactors are mostly aimed at power production, because of the large amount of energy evolved with fission.
b. Nuclear reactors are useful to produce radio-isotopes
c. Nuclear reactor acts as a source of neutrons, hence used in the scientific research
Nuclear fusion
* Nuclear fusion is a process in which two or more lighter nuclei combine to form a heavier nucleus. The mass of the product nucleus is always less than the sum of the masses of the individual lighter nuclei. The difference in mass is converted into
energy. The fusion process can be carried out only at a extremely high temperature of the order of 107 KThe nuclear fusion reactions are known as thermo-nuclear reactions
Hydrogen bomb
* The principle of nuclear fusion is used in hydrogen bomb. It is an explosive device to release a very large amount of energy by the fusion of light nuclei.
1H3 + 1H2 → 2He4 + 0n1 + energy
Elementary particles
* The study of the structure of atom reveals that the fundamental particles electron, proton and neutron are the
building blocks of an atom. But the
extensive studies on cosmic rays have
revealed the existence of numerous new nuclear particles like mesons.These particles are classified into four major groups as photons, leptons mesons and baryons.