Radioactivity and nuclear reactions are very delicate chemical processes that are usually carried out in controlled environment owing to the health hazards associated with such reactions such as genetic mutation and cancer. However, radioactivity and the nuclear reactions associated with it have found use in the generation of electricity, in the production of nuclear weapons, in the treatment of diseases. It also found application in sterilization of hospital surgical instruments and in agriculture.
Students and researchers in the area of radioactivity are often faced with some challenging questions on nuclear reactions and radioactivity in academic tests or examination rooms in schools or other research institutes. These 25 important test questions on radioactivity, radiation and nuclear reactions have been carefully compiled to give the student a good resource base to practice for examinations or carryout out research findings. The questions covers a wide area of radioactivity including half-life calculations, radioactive decay, detection of radioactive substances, conditions for nuclear activity, radioactive elements, nuclear particles, radioactive isotopes among several other terms.
Important Research and Exam Questions on Radioactivity
1. If the half-life of radium is 1620 years, what is its radioactive decay constant? What will be the rate of disintegration of 1g of radium in terms of atoms disintegrating per second? How many curies is this? How many grammes of radium represent 1 curie?
2. If the decay constant for radium is 1.356×10-11 calculate the time required for (a) 10 percent, (b) 90 percent of a sample of radium to disintegrate.
3. If 1 curie of radium of isotopic weight 226 and half-life 1620 year is 1.02g, how many grammes of cobalt 60, of half-life 5.2 year will represent 1 curie? If 1 curie of potassium 40 is 146kg, what is its half-life?
4. Radon has a half-life of 3.8 day. Plot a graph of the percentage of a sample of radon which has decayed against the time in the days.
5. Prove that the mass of a radioactive isotope required to give 1 curie of radiation is equal to 8.87x 10-14x M x t
6. If a sample of a radioactive isotope of half-life 3.11 hour has an activity of 1000s-1 at a certain time, what will be its activity one hour later?
7. What is the percentage loss in the activity of a radioactive element after 1, 10 and 100 half-life periods?
8. The period of average life for a radioactive substance is the time within which the whole of the substance would disintegrate if the initial disintegration rate remained constant. How is the period of average life related to the disintegration constant?
9. Explain why it is that the determining factor for the detection of a radioactive substance by the measurement of its radiation is the product of the amount of the substance and its disintegration constant.
10. The ratio by mass of radium of uranium 1 in old minerals is 3.3 x 10-7. In such equilibrium with the radium. If the disintegration constant for radium is 1.39. x10-11 s-1, what is the value of the disintegration constant for uranium 1?
11. Give an account of the early work on radioactivity of Rutherford, Rusell and Soddy.
12. 238U emits an α-particle to form UX This, in turn, emits a β-particle to give UX2. What are the atomic and mass numbers of UX1 and UX2?
13. Np emits a β-particle to give an isotope which then decays to 235 What particle is emitted in the final day?
14. 238U decomposes by emitting (a) and forming 234Th. This isotope undergoes decomposition with β-emission forming (b). What are (a) and (b)?
15. The thorium, uranium and actinium disintegration series are sometimes known as the 4n, 4n + 3, series respectively. Why is this? What isotopes might exist in the 4n + 1 series?
16. Write symbols showing the mass number and the atomic number for an electron, a proton, a neutron, a positron, a deuteron and an α-particle.
17. Write symbols showing the mass number and the atomic number of the atoms formed when (a) Ra loses an α-particles, (b)
18. What is (a) an α-particle, (b) a β-ray (c) a y-ray? Show how the position of an element in the periodic table is affected by (d) the loss of an α-particle, and (e) the emission of a β-ray from the nucleus.
Radium (atomic number 88, atomic weight 226) is placed in Group 2 of the periodic classification. The following is a consecutive series of elements produced by its radioactive disintegration together with their respective atomic weights: radium emanation, 222; radium A, 218; radium B, 214; radium C, 214 radium c’, 214; radium D, 210; radium F, 210; radium G, 206.
Construct a small table showing (i) their atomic numbers, (ii) their main group placing in the periodic table, (iii) the type of radiation emitted at each stage of their disintegration. Identify any sets of isotopes which occur in the series (W.S.)
19. Three kinds of fundamental particles are of great importance in chemical theory. Name them and give their relative masses and charges.
What is meant by (a) the atomic number (z) and (b) the relative atomic mass (M) of an element? For sodium Z =11 and M=23; how must the nucleus of this atom be built up? How is the fractional relative atomic mass of chlorine of the nature of atoms and which other of his postulates concerning elements are no longer acceptable? (N.)
21. Explain why it is that the charge/mass ratio for cathode rays independent of the nature of the gas in the discharge tube, whilst the charge/mass ratio for positive rays is smaller than that for cathode rays and depends on the nature of the gas in the tube.
22. If natural oxygen consists of 99.758 per cent of an isotope of mass 16, 0.0373 per cent of a n isotope of mass 17.004534 and 0.2039 per cent of an isotope of mass 18.004844, calculate the average mass of an atom in natural oxygen.
23. Compare the functioning of Aston’s mass spectrograph with that of an achromatic prism.
24. Give an account of some typical uses of isotopes.
25. It has been suggested sodium chloride obtained from the depths of the sea might be richer in 37Cl than sodium chloride found on the earth’s surface. Is there any validity in this?
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