HW7-7ii - 6-6 Binary Nuclear Reactions Chap. 6 The neutron...

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Unformatted text preview: 6-6 Binary Nuclear Reactions Chap. 6 The neutron threshold energy for thjs reaction is found from Eq. (6.15) 8. The isotope 18Fis a radionuclide used in medical diagnosesof tumors and, although usually produced by the 180(p,n)18F reaction, it can also be produced by irradiating lithium carbonate (Li2CO3) with neutrons. The neutrons interact with 6Li to produce tritons (nuclei of 3H) which in turn interact with the oxygen to produce 18F. (a) What are the two nuclear reactions? (b) Calculate the Q-value for eachreaction. (c) Calculate the threshold energy for each reaction. (d) Can thermal neutrons be used to create 18F? Solution: (a) The first reaction is 6Li(n,t)4He followed by 160(t,n)18F. (b) Using the massesin Ap. B, the Q-values for these reactions are 6Li(n,t)4He: Q = [M(gLi) +mn -M(~He) -M(~H)]C2 = 4.78 MeV, and for the second reaction 160(t,n)18F: Q = [MrgO) + M(~H) -mn -Mr~F)]~ = 1.27 MeV. (c) Because both reactions are exoergic, there are no kinematic thresholds. However, the 160(t,n)18F reaction has a Coulombic threshold. From Eq. (6.19), the minimum energy of the triton Ef needed to cause this reaction is Ef ~ 1.2A;/3ZxZx1j3 ..31/32 =1 +A (1)(8) = 2.42 MeV. + 161/3 (d) The energy of the triton produced by a thermal neutron induced 6Li{n,t)4He reaction is given by Eq. (6.12), namely Et =Q I This is greater than Ef, and hence thermal neutrons can be used. July 24, 2002 ~ ...
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This note was uploaded on 02/01/2010 for the course ECE 4130 taught by Professor Cady during the Spring '06 term at Cornell University (Engineering School).

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