Nuclear Physics Online Test 10th Science Lesson 6 Questions in English

Humans are very much interested in knowing about atoms. Things around us are made up of atoms. A Greek Philosopher 'Democritus' in 400 BC(BCE) believed that matter is made up of tiny indestructible units called atoms.

In 1803, John Dalton considered that elements consist of atoms, which are identical in nature.

In 1896, French physicist Henri Becquerel finished his research for the week and stored a certain amount of uranium compound away in a drawer for the week end. By chance, an unexposed photographic plate was also stored in the same drawer. After a week he returned and noticed that the film had been exposed to some radiation. He discovered that he could reproduce the effect whenever he placed uranium near a photographic film.

The uranium radiated something that could affect a photographic plate. This phenomenon was called as Radioactivity. Uranium was identified to be a radioactive element.

The Polish physicist Marie Curie and her husband Pierre Curie detected radioactivity in 'Pitchblende', a tiny black substance. They were not surprised at the radioactivity of pitchblende, which is known as an ore of uranium. Later, they discovered that the radiation was more intense from pure uranium. Also, it was found that the pitchblende had less concentration of uranium.

Marie Curie and her husband Pierre Curie concluded that some other substance was present in pitchblende. After separating this new substance, they discovered that it had unknown chemical properties and it also emitted radiations spontaneously like uranium. They named this new substance as 'Radium'. The radioactive elements emit harmful radioactive radiations like alpha rays or beta rays or gamma rays.

The elements such as uranium and radium undergo radioactivity and emit the radiations on their own without any human intervention. This phenomenon of spontaneous emission of radiation from certain elements on their own is called 'natural radioactivity'. The elements whose atomic number is more than 82 undergo spontaneous radioactivity.

Gallium is not the radioactive element.

There are only two elements, which have been identified as radioactive substances with atomic number less than 82. They are technetium (Tc) with atomic number 43 and promethium (Pm) with atomic number 61.

The phenomenon by which even light elements are made radioactive, by artificial or induced methods, is called 'artificial radioactivity' or 'man-made radioactivity'. This kind of radioactivity was discovered by Irene Curie and Fredric Joliot in 1934.

During such a disintegration, the nucleus which undergoes disintegration is called 'parent nucleus' and that which is produced after the disintegration is called a 'daughter nucleus'. When the projectile hits the parent nucleus, it is converted into an unstable nucleus, which in turn decays spontaneously emitting the daughter nucleus along with an ejected particle.

There have been 29 radioactive substances discovered so far. Most of them are rare earth metals and transition metals.

The particle, which is used to induce the artificial disintegration is termed as projectile and the particle which is produced after the disintegration is termed as ejected particle.

Natural radioactivity properties are 1. Emission of radiation due to self-disintegration of a nucleus, 2. Alpha, beta and gamma radiations are emitted, 3. It is a spontaneous process, 4. Exhibited by elements with atomic number more than 83 and 5. This cannot be controlled.

The units of Radioactivity are 1. Curie, 2. Rutherford, 3. Becquerel and 4. Roentgen.

The SI unit of radioactivity is becquerel. It is defined as the quantity of one disintegration per second.

The radiation exposure of γ and x-rays is measured by another unit called roentgen. One roentgen is defined as the quantity of radioactive substance which produces a charge of 2.58 × 10-4 coulomb in 1 kg of air under standard conditions of pressure, temperature and humidity.

Rutherford (Rd) is another unit of radioactivity. It is defined as the quantity of a radioactive substance, which produces 106 disintegrations in one second.

The property of Artificial radioactivity is 1. Emission of radiation due to disintegration of a nucleus through induced process, 2. Mostly elementary particles such as neutron, positron, etc. are emitted, 3. It is an induced process, 4. Exhibited by elements with atomic number less than 83 and 5. This can be controlled.

Curie is the traditional unit of radioactivity. It is defined as the quantity of a radioactive substance which undergoes 3.7 × 1010 disintegrations in one second. This is actually close to the activity of 1 g of radium 226. 1 curie = 3.7 × 1010 disintegrations per second.

When a radioactive nucleus undergoes radioactivity, it emits harmful radiations. These radiations are usually comprised of any of the three types of particles. They are alpha(α), beta (β) and gamma(γ) rays.

Uranium, named after the planet Uranus, was discovered by Martin Klaproth, a German chemist in a mineral called pitchblende.

Low penetrating power (even stopped by a thick paper). Ionising power is 100 time greater than β rays and 10,000 times greater than γ rays.

Neutral particles. Charge of each gamma particle = zero. Very less ionization power

Deflected by both the fields; but the direction of deflection is opposite to that for alpha rays. (in accordance with Fleming’s left hand rule). Penetrating power is greater than that of α rays. They can penetrate through a thin metal foil. Penetrating

β rays speed can go up to 9/10 times the speed of light. γ rays travel with the speed of light.

92U238 >>> 90Th234 +2He4

In a γ - decay, only the energy level of the nucleus changes. The atomic number and mass number of the radioactive nucleus remain the same.

In 1939, German Scientist Otto Hahn and F. Strassman discovered that when a uranium nucleus is bombarded with a neutron, it breaks up into two smaller nuclei of comparable mass along with the emission of a few neutrons and energy.

The process of breaking (splitting) up of a heavier nucleus into two smaller nuclei with the release of a large amount of energy and a few neutrons is called ‘nuclear fission'.

Nuclear fission of a uranium nucleus (U235): 92U235 + 0n1 >>> 56Ba141 + 36Kr92 + 30n1 + Q. The average energy released in each fission process is about 3.2 × 10-11 J. Nuclear fission is pictorially represented.

All isotopes of uranium do not undergo nuclear fission when they absorb a neutron. For example, natural uranium consists of 99.28 % of 92U238 and 0.72 % of 92U235. Of these two, U238 does not undergo fission whereas U235 undergoes fission. Hence, U235 is a fissionable material and U238 is non fissionable.

There are some radioactive elements, which can be converted into fissionable material. They are called as fertile materials. E.g.: Uranium-238, Thorium-232, Plutonium-240.

Two kinds of chain reactions are possible. They are: (i) controlled chain reaction and (ii)uncontrolled chain reaction.

A uranium nucleus (U-235) when bombarded with a neutron undergoes fission producing three neutrons. These three neutrons in turn can cause fission in three other uranium nuclei present in the sample, thus producing nine neutrons. These nine neutrons in turn may produce twenty-seven neutrons and so on. This is known as 'chain reaction'. A chain reaction is a self-propagating process in which the number of neutrons goes on multiplying rapidly almost in a geometrical progression.

The energy released due to a controlled chain reaction can be utilized for constructive purposes. Controlled chain reaction is used in a nuclear reactor to produce energy in a sustained and controlled manner.

In the uncontrolled chain reaction, the number of neutrons multiplies indefinitely and causes fission in a large amount of the fissile material. This results in the release of a huge amount of energy within a fraction of a second. This kind of chain reaction is used in the atom bomb to produce an explosion.

If the mass of the fissile material is less than the critical mass, it is termed as 'subcritical'.

If the mass of the fissile material is more than the critical mass, it is termed as 'supercritical'.

During this explosion tremendous amount of energy in the form of heat, light and radiation is released. A region of very high temperature and pressure is formed in a fraction of a second along with the emission of hazardous radiation like γ rays, which adversely affect the living creatures. This type of atom bombs was exploded in 1945 at Hiroshima and Nagasaki in Japan during the World War II.

Electron Volt (eV) is the unit used in nuclear physics to measure the energy of small particles. It is nothing but the energy of one electron when it is accelerated using an electric potential of one volt. 1eV = 1.602 × 10-19 joule. 1 million electron volt = 1 MeV = 106 eV (mega electron volt). The energy released in a nuclear fission process is about 200 MeV.

The energy can be produced when two lighter nuclei combine to form a heavier nucleus. This phenomenon is known as nuclear fusion.

Here, 1 H2 represents an isotope of hydrogen known as 'deuterium'. The average energy released in each fusion reaction is about 3.84 × 10-12 J.

The mass of the daughter nucleus formed during a nuclear reaction (fission and fusion) is lesser than the sum of the masses of the two parent nuclei. This difference in mass is called mass defect. This mass is converted into energy, according to the mass-energy equivalence.

J J Thomson discovered cathode rays, known as electrons, experimentally.

Goldstein discovered positive rays, which were named as protons by Rutherford.

The concept of mass-energy equivalence was proposed by Einstein in 1905. It stated that mass can be converted into energy and vice versa. The relation between mass and energy proposed by Einstein is E = mc2 where c is the velocity of light in vacuum and is equal to 3 × 108 m s–1.

The nuclear bomb that was dropped in Hiroshima during World War II was called as 'Little boy'. It was a gun-type bomb which used a uranium core.

Nuclear fusion is possible only at an extremely high temperature of the order of 107 to 109 K and a high pressure to push the hydrogen nuclei closer to fuse with each other. Hence, it is named as 'Thermonuclear reaction'.

Nuclear fusion is the combination of two lighter nuclei. The charge of both nuclei is positive. According to electrostatic theory, when they come closer, they tend to repel each other.

The stars like our Sun emit a large amount of energy in the form of light and heat. This energy is termed as the stellar energy. All stars contain a large amount of hydrogen. The surface temperature of the stars is very high which is sufficient to induce fusion of the hydrogen nuclei. Fusion reaction that takes place in the cores of the Sun and other stars results in an enormous amount of energy, which is called as 'stellar energy. Thus, nuclear fusion or thermonuclear reaction is the source of light and heat energy in the Sun and other stars.

The bomb, which was subsequently dropped over Nagasaki was called as 'Fat man'. It was an explosion type bomb, which used a plutonium core.

Nuclear Fission Can be performed at room temperature.

In 1932, James Chadwick discovered the chargeless particles called neutrons. Presently, a large number of elementary particles like photon, meson, positron and neutrino have been discovered.

In 1911, the British scientist, Ernest Rutherford explained that the mass of an atom is concentrated in its central part called Nucleus.

In Nuclear Fusion Only light and heat energy is emitted.

The radio isotope of phosphorous (P-32) helps to increase the productivity of crops. The radiations from the radio isotopes can be used to kill the insects and parasites and prevent the wastage of agricultural products. Certain perishable cereals exposed to radiations remain fresh beyond their normal life, enhancing the storage time. Very small doses of radiation prevent sprouting and spoilage of onions, potatoes and gram.

Radio sodium (Na24) is used for the effective functioning of heart.

Medical applications of radio isotopes can be divided into two parts: i) Diagnosis ii) Therapy. Radio isotopes are used as tracers to diagnose the nature of circulatory disorders of blood, defects of bone metabolism, to locate tumours, etc. Some of the radio isotopes which are used as tracers are: hydrogen, carbon, nitrogen, sulphur, etc.

Radio - Iodine (I131) is used to cure goitre. Radio-iron is (Fe59) is used to diagnose anaemia and also to provide treatment for the same. Radio phosphorous (P32) is used in the treatment of skin diseases. Radio cobalt (Co60) and radio-gold (Au198) are used in the treatment of skin cancer. Radiations are used to sterilize the surgical devices as they can kill the germs and microbes.

An isotope of californium (Cf 252) is used in the airlines to detect the explosives in the luggage.

An isotope of Americium (Am241) is used in many industries as a smoke detector.

13Al27 + 2He4--------> 15P30 + 0n1 12Mg24 + 0n1 --------> 11Na24 + 1 H1 92U238 + 0n1 --------> 93Np239 + –1e0

The International Commission on Radiological Protection (ICRP) has recommended certain maximum permissible exposure limits to radiation that is believed to be safe without producing any appreciable injury to a person

According to International Commission on Radiological Protection (ICRP) the Safe limit of overall exposure to radiation is given as 20 milli sievert per year. In terms of roentgen, the safe limit of receiving the radiation is about 100 m R per week.

Dosimeter is a device used to detect the levels of exposure to an ionizing radiation. It is frequently used in the environments where exposure to radiation may occur such as nuclear power plants and medical imaging facilities. Pocket dosimeter is used to provide the wearer with an immediate reading of his/her exposure to X-rays and γ rays.

Lead coated aprons and lead gloves should be used while working with hazardous radioactive materials. You should avoid eating while handling radioactive materials.

A Nuclear reactor is a device in which the nuclear fission reaction takes place in a self-sustained and controlled manner to produce electricity. The first nuclear reactor was built in 1942 at Chicago, USA.

1 Bq = one disintegration per second one curie = 3.7 × 1010 Bq 1 Bq = 13.7 ×1010 Curie ∴ 3.7 × 103 G Bq = 3.7 × 103 × 10 9 ×13.71010 = 100 Curie.

Breeder reactor, fast breeder reactor, pressurized water reactor, pressurized heavy water reactor, boiling water reactor, water cooled reactor, gas-cooled reactor, fusion reactor and thermal reactor are some types of nuclear reactors, which are used in different places world-wide.

The essential components of a nuclear reactor are (i) fuel, (ii) moderator, (iii) control rod, (iv) coolant and (v) protection wall.

Let X and Y be the resulting nucleus after the emission of the alpha and beta particles respectively. 92 U235 α decay → 90X231 + 2He4 0X231 β decay→ 91Y231 + -1e0 Number of neutrons = Mass number – Atomic number = 231 – 91 = 140.

A moderator is used to slow down the high energy neutrons to provide slow neutrons.

A fissile material is used as the fuel. The commonly used fuel material is uranium.

Graphite and heavy water are the commonly used moderators.

Control rods are used to control the number of neutrons in order to have sustained chain reaction. Mostly boron or cadmium rods are used as control rods. They absorb the neutrons.

Water, air and helium are some of the coolants. Nuclear reactors are widely used in power generation. They are also used to produce radio isotopes, which are used in a variety of applications. Some reactors help us to do research in the field of nuclear physics.

Breeder reactors are used to convert non-fissionable materials into fissionable materials.

Mass defect in the reaction (m) = 2 kg Velocity of light (c) = 3 × 108 m s-1 By Einstein’s equation, Energy released E = mc2 So, E = 2 × (3 × 108) 2 = 1.8 × 1017 J.

Indian Atomic Energy Commission (AEC) was established in August 1948 by the Department of Indian Scientific Research committee.

Dr. Homi Jahangir Bhabha was the first chairman of Indian Atomic Energy Commission. Now, it is known as Bhabha Atomic Research Centre (BARC).

Nuclear power is the fifth largest source of power in India. Tarapur Atomic Power Station is India’s first nuclear power station.

Tamil Nadu is the only state with two atomic power station in Kalpakkam and Kudankulam

Now, there are a total of seven power stations, one each in Maharashtra, Rajasthan, Gujarat, Uttar Pradesh and two in Tamil Nadu. In Tamil Nadu, we have nuclear power stations in Kalpakkam and Kudankulam.

Apsara was the first nuclear reactor built in India and Asia.

Now, there are 22 nuclear reactors which are operating in India.

Some operating reactors in India are 1. Cirus, 2. Dhuruva and 3. Purnima.

Indian Atomic Energy Commission (AEC) was established in August 1948 at Bombay (now Mumbai) in Maharashtra. It is the nodal agency for all the research done in the field of atomic energy.