Fig.1 Nuclear energy to generate electricity. Matter can undergo three types of changes or reactions, Namely,
- Atoms and Isotopes All matter, living or non living, are made up of only a few more than 100 types of atoms. They are all listed in the Periodic table. An Atom An atom ,basically has 3 kinds of sub atomic particles. They are electrons, protons and neutrons.
Fig.2 Sub atomic particles in an atom.
Isotopes Fig.3 Three isotopes of the same element carbon. An element is identified by the number of protons. Hydrogen 1, Helium 4, Carbon 12 and so on. The chemical properties of an element depend on the number of electrons, which is equal to the number of protons. The neutron number can vary in the same element, The diagram shows 3 types of carbon atoms. As the neutrons have a mass their mass number varies. When using symbols , mass number is at the top while the atomic number is below. Out of the 3 naturally occurring carbon isotopes only Carbon 14 is radioactive. Nuclear Changes.
There are two kinds of nuclear reactions. 1. Fission:- One element can change into two or more elements. 2. Fusion:-Two elements can fuse together to form a new substance. Radioactivity This is a term given by Marie Curie for the nuclear reactions that spontaneously take place in nature. But this process was discovered by Henri Becquerel. The rays given out were earlier called Becquerel rays. In 1896 Henri Becquerel placed a uranium salt above some photographic paper, covered in a light proof manner and found that the papers behaved as they got exposed to light. On further testing he discovered that the uranium salt was producing some hitherto unknown kind of rays. Detecting radioactive rays. Now there are many methods to detect these invisible rays. 1. Photographic paper:- This is what Becquerel discovered. 2. Cloud chamber: Fig.3 Wilson's cloud chamber. This is a vessel containing a saturated, or super saturated vapur; usually of alcohol. The trail of particles or rays become visible due to the condensation of the vapor. 3. Fluorescent screen:- 4. Geiger counter:-
Fig.4.Geiger counter. When ionising rays enter the tube through the mica window, the gas molecules ionize and allow the current to flow. Nature of rays and particles produced by Nuclear Reactions.
Fig.5 Deflection of rays by electrical charges. Uranium nucleus breaks down emitting powerful rays. They actually consist of three types; Alpha, Beta and Gamma. Their properties are summarized in a table below. Comparing α , β and γ Rays .
Comparing α , β and γ Rays . Fig.6 Penetrating power of the rays.
Alpha emission. The nuclear reaction is given here. Uranium-235 isotope → Helium nucleus + Thorium-231 isotope. In symbols:- .......... 92U235 → 2α4 + 90Th231 Emitting an alpha particle , (sometimes called an alpha ray), reduces the mass number by 4 and the Atomic number by 2. Alpha could not have been the rays that damaged the photo papers of Becquerel, because they have very low penetrating power; unable to go through paper or skin. Then what rays exposed the photo papers? Whenever a nuclear reaction takes place high frequency electromagnetic waves are also produced. These are called Gamma rays γ , and possess a very high penetrating ability, similar to X rays. Emitting electromagnetic rays do not change the Mass number or the Atomic number Moreover the Thorium produced would have undergone further decay emitting Beta β particles. Beta emission. Thorium- 231 → Beta particle + Protactinium -231. In symbols.............. 90Th231→ -1β0 + 91Pa231 Emitting a β particle does not change the mass number but it increases the atomic number by 1.
Radium This is an amazing substance that glows in the dark emitting various rays for over thousand years. .Marie Sklodowska,(Polish) and her husband Pierre Curie..Fr., after months of processing tons of Uranium rich ore, called ,pitchblende, obtained a speck of Radium chloride. A ton of ore contains only about 0.14 grams of radium. Fig.7 Ra. was used freely prior to 1960 not knowing the hazards. Discovering the structure of the atom Ernest Rutherford used the rays from Radium to get the structure of the atom. Fig. 5 The plan of the Geiger Marsden experiment that showed the presence of a nucleus inside atoms. Click Ernest Rutherford year 1907. Transmutation When they understood the natural process of changing Uranium to Thorium, Soddy shouted, “This is transmutation, Ernest!” Rutherford said,”Don’t shout Freddy. They’ll call us alchemists” The year was 1902. Fifteen years later Rutherford was able to perform transmutation by bombarding alpha particles into the nucleus of Nitrogen atoms. Nuclear Reaction:- Nitrogen-14 + Alpha=4 → Oxygen-17 + Proton-1 In symbols:- 7N14 +2α4 → 8O17 +1p1In 1934 Joliot-Curie, son-in-law of Marie Curie, at the Curie Radium Institute in Paris, obtained Nitrogen -13 and Phosphorous -30 by shooting alpha to Aluminium. “This was the first instance a ‘radioactive isotope’ had been made by man". 2He4 + 13Al37 → 15P30 + 0n1 Half Life. This is defined as the time it takes for one-half of the atoms of a radioactive material to disintegrate. Radioactivity or disintegration of atoms is measured in Becquerels. One becquerel = 1 radioactive decay per second. You should be able to determine the half life of this isotope from the graph. Answer...50 years. .... To see the answer high light along the dots
Uses of nuclear changes. Using Radio-isotopes.
The first picture in this lesson shows a plant converting nuclear energy to produce electricity.The first nuclear power plant using the uranium fission began in 1954 in USSR..Today about 17% of the world's electricity is nuclear-generated. The basic reaction that supply heat to work the turbines is the chain reaction of Uranium-235. Fig.6.One way of splitting uranium-235. When a fast emerging neutron from a radioactive material is aimed at the nucleus of a U-235 nuclide, it becomes a u-236 nuclide. This is unstable and undergo fission in different ways. (A nuclide is a nucleus of an isotope) 2. Using Radio-isotopes
Sometime it may be necessary to find out where some water goes; it may be in a river, pipe or inside a plant. It is possible to replace one of the H-1 molecules with a H-3 molecule which has a half life of 12 years. A geiger counter can detect these mulecules even after a few years. Carbon-14, having a half life of 5730 years was used to understand the chemical reactions involved in photosynthesis. This isotope is also used for dating ancient onjects.
Fig.7. Marie Curie and her daughter Irène at the Hoogstade Hospital in Belgium, when Radiographic equipment was installed in 1915.. Courtesey Nobel Prize.org.
From the time Pierre Curie damaged his skin by carrying a radium sample in his pocket, Rays from radium had been used to kill cancer cells.
C. Home and industry
. Fig.8.Using Americium-241, an alpha source, to detect smoke.Courtesy Bitesize BBC D. Uses in agriculture. Fig.9. Phosphorous -32 isotope used to study absorption of fertilizers. Q.1.0 Identify these:- Find the most suitable definition for these terms. 2.Nuclear reaction. Nuclear fusion,
4x5=20 marks
Select from the following. A- Radiation, B - Fusion. C- Transmutation. 4x5=20 marks Q. 3.0Complete these reactions and give a name to describe the type.
4x5=20 marks Q.4.0
4x5=20 marks Q.5.0 Half life of a nuclide is 86X210 is 3.7. Answer the following.
4x5- =20 marks 5.0
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