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Long Answer Questions · Q15

Q.Describe alpha, beta and gamma decays and write down the formulae for the energies generated in each of these decays.

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Alpha decay is the emission of a helium-4 nucleus from a (typically very heavy, A > 210) parent nucleus: ZAX→ Z−2A−4Y+ 24He_Z^AX\rightarrow\,_{Z-2}^{A-4}Y+\,_2^4He; its Q-value (energy released, appearing as kinetic energy of the products) is Q=[mX−mY−mHe]c2Q=[m_X-m_Y-m_{He}]c^2, using atomic masses throughout. Beta decay converts one type of nucleon into another: in β−\beta^- decay a neutron becomes a proton, ZAX→ Z+1AY+e−+νˉ_Z^AX\rightarrow\,_{Z+1}^AY+e^-+\bar\nu, while in β+\beta^+ decay a (bound) proton becomes a neutron, ZAX→ Z−1AY+e++ν_Z^AX\rightarrow\,_{Z-1}^AY+e^++\nu; in both cases the mass number A stays fixed, and the Q-value, Q=[mX−mY−me]c2Q=[m_X-m_Y-m_e]c^2, gives the maximum kinetic energy shared between the emitted electron/positron and the accompanying (anti)neutrino. Gamma decay involves no change in either Z or A at all -- the parent and daughter are the same nuclide -- instead, a nucleon inside a nucleus already left in an excited state (typically by a preceding alpha or beta decay) drops to a …

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