TRB PG PHYSICS :Question No.28 in 'B' series A,B,C,D நான்கு விடைகளுக்கும் மதிப்பெண் வழங்க சென்னை உயர்னீதி மன்றம் உத்தரவு- முக்கிய பகுதிகள்
3. I have heard the learned counsel appearing for the petitioner and the learned Special Government Pleader appearing for the respondent. I have also perused the records carefully.
4. Question No.28 in 'B' series reads as follows:-
Q.No.28. Fermi Selection rule for B-transition to occur is
(A) ?I=0 ; ?P=0 (B) ?I=+1 ; ?P=0
(C) ?I=-1 ; ?P=0 (D) ?I=+1 ; ?P=0
5. According to the key answer Option 'D' is the right answer and thus TRB has decided to give marks to those candidates who have chosen option 'D' as the right answer. But, according to the petitioner, option 'A' is the right answer.
6. Today, three experts in the Physics subject are present before this Court who are (1) Dr.A.Subbiah Pandi, Associate Professor, Department of Physics, Presidency College, Chennai, (2) Dr.K.Chitra, Associate Professor, Department of Physics, Bharathi Women's College, Chennai and (3) Dr.B.Uma Maheswari, Associate Professor, Department of Physics, Bharathi Women's College, Chennai. This Court had the benefit of hearing them also.
7. According to the experts, the question relates to selection rules in beta processes. For beta transition to occur initial and final states of the nucleus are supposed to satisfy certain definite conditions. The conditions to be satisfied are related with the conservation of angular momentum and parity and are called selection rules for allowed transitions. The selection rules have been classified as Fermi selection rule and Gamow Teller selection rule.
8. It is the admitted case of the petitioner as well as the experts that in Fermi Selection Rule, it includes those transitions in which neither the angular momentum nor the parity undergoes a change, i.e., ?I=0 and ?P=0. Here 'I' refers to for angular momentum and 'P' refers to parity. From the text book and the submissions made by the experts it is seen that if electron and neutrino are emitted with their intrinsic spins anti-parallel (singlet state), the change in nuclear spin ?I must be strictly zero, if these are emitted with their spins parallel (triplet state), ?I may be +1, 0 or -1 (but no Ii=0 to If=0), where subscripts 'i' and 'f' refer to the initial and final nuclear states. The former selection rule was one originally proposed by Fermi, the latter was subsequently suggested by Gamow and Teller. The experts would say that in the question it is not specified whether the electron and neutrino are emitted with their intrinsic spins anti-parallel (singlet state) or spins parallel (triplet state). So, the experts would submit that if the question specifically refers to singlet state then certainly option 'A' is the right answer and if the question refers to triplet state then ?I may be +1 or 0 or -1, in which case, options 'B', 'C' and 'D' are all right answers.
9. As I have understood, as explained by the experts, in case of singlet state ?I must be zero but in the case of triplet state ?I shall be either +1, 0 or -1. The question whether fermi selection rule applies to singlet state and not to triplet state has to be decided based on the opinion offered by the three experts before me, who would state that Fermi Selection Rule relates both the singlet state and well as triplet state.
10. But in this case, since it is not specifically mentioned as to whether the question refers to singlet state or triplet state, all the four options are correct answer. The experts have placed some authoritative books in support of their opinion.
11. But the petitioner would say that Fermi Selection Rule refers only to singlet state and not to triplet state. She would further state that if it is triplet state i.e. allowed transition, then it must be Gamow and Teller Selection Rule. The petitioner would also rely on standard text books in support of her contention.
12. In my considered opinion, when three experts who are very seasoned experienced professors, based on authoritative text books would state before this Court that in the absence of specific mention as to whether the question refers to singlet state or triplet state all the four answers may be awarded marks, I have to necessarily agree with them.
13. In such view of the matter, the TRB is directed to award mark to all the candidates who have answered either option 'A' or 'B' or 'C' or 'D' as right answer. This direction is applicable to all the candidates and therefore TRB shall revalue the physics paper by awarding mark to this question.
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