Title 13. NUCLEI.pdf ✅

+ +→ + 22 4 11 2 H H He Q . U [OEB] 4. What do you mean by mass defect of a nucleus? U [OEB] 5. In the following nuclear reaction, identify unknown labelled X. 11 22 10 22 Na e + X → ν Ne + U [SQP 2020-21] Short Answer Type Questions-I (2 marks each) 1. What is the nuclear radius of 125Fe ,if that of 27Al is 3.6 fermi? [SQP 2023 - 24] Ans. R = R0A1/3, where R0 is a constant and A is the mass number of a nucleus 1⁄2 R R Fe Al = A A Fe Al       1 3/ = 125 27 1 3       / 1⁄2 RFe = 5 3 RAl 1⁄2 = 5 3 × 3 6. 1⁄2 = 6 fermi 2. (i) Distinguish between isotopes and isobars. (ii) Two nuclei have different mass numbers A1 and A2. Are these nuclei necessarily the isotopes of the same element? Explain. [Term-2, 2022] Ans. (i) Isotope Isobar Same element. Different element. Same atomic number. Different atomic number. Different mass number. Same mass number. Numbers of protons are same in isotopes. Numbers of protons are different in isobars. (ii) No, only when the two nuclei have same atomic number then they are known as isotopes. Otherwise they may be isobars also. Isobars have same mass numbers. 3. A heavy nucleus P of mass number 240 and binding energy 7.6 MeV per nucleon splits in to two nuclei Q and R of mass numbers 110 and 130 and binding energy per nucleon 8.5 MeV and 8.4 MeV, respectively. Calculate the energy released in the fission. Ap [Delhi Set-1, 2020] 4. Explain the processes of nuclear fission and nuclear fusion by using the plot of binding energy per nucleon (BE/A) versus the mass number A. U [Board 2018] Concept Applied Elements with A > 200 are prone to fission and elements with A < 20 are prone to fusion. Ans. The plot of (B.E. / nucleon) verses mass number is as shown. 1 [Note :Also accept the diagram that just shows the general shape of the graph]. From the plot we note that (i) During nuclear fission A heavy nucleus in the larger mass region (A>200) breaks into two middle level nuclei, resulting in an increase in B.E/nucleon. This results in a release of energy. 1⁄2 (ii) During nuclear fusion Lighter nuclei in the lower mass region (A<20) fuse to form a nucleus having higher B.E. / nucleon. Hence, energy gets released. 1⁄2 [Alternatively : As per the plot, during nuclear fission as well as nuclear fusion, the final value of B.E/nucleon is more than its initial value. Hence, energy gets released in both these processes. ] [Marking Scheme, 2018] Commonly Made Error Many students do not refer to mass no. of elements and just mention heavy nucleus and light nucleus. Since it has been asked to refer the A vs. BE/A plot then the fission and fusion should be related with A. Answering Tip 5. Calculate the energy in fusion reaction : 1 2 1 2 2 3 H H + → He +n where, BE of 1 2 = 2 2. 3H MeV and 2 3He = 7 7. 3 MeV. E [Delhi Set 1, 2016] Short Answer Type Questions-II (3 marks each) 1. A given coin has a mass of 3.0g. Calculate the nuclear energy that would be required to separate all the neutrons and protons from each other. For