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Given the masses of various atomic particles m_p = 1.0072u, m_n = 1.0087u, m_e = 0.000548u, m_v = 0, m_d = 2.0141u, where p = proton, n = neutron, e = electron, v = antineutrino and d = deuteron. Which of the following process is allowed by momentum and energy conservation? (1) n + p → d + γ (2) e^+ + e^- → γ (3) n + n → deuterium atom (electron bound to the nucleus) (4) p → n + e^+ + v

1. (1)
2. (2)
3. (3)
4. (4)

Correct answer: (1)

Solution

The reaction n + p → d + γ is allowed because the total mass-energy of the initial particles (neutron and proton) is greater than the mass-energy of the final products (deuteron and photon), satisfying both momentum and energy conservation.

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