2. (a) A radioactive nucleus 180
72 X undergoes a series of radioactive α, β−, α, γ radiations and successively decays into X1, X2, X3 and X4. What are A and Z of the final nucleus X4.
(b) What is pair production? Explain why pair production cannot occur bellow an energy of
1.02MeV .
(c) Consider the following nuclear reactions. Classify all the elementary particles involved and
tell which of the two reactions is allowed / not allowed and explain why?.
i. p + ¯νe −→ n + µ
+
ii. p + ¯νe −→ n + e
+
(d) How much time (in years) will be required for 5 mg of 22Na (T1/2 = 2.60yrs) to reduce to 1
mg?.
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