Sodium-21 will emit positrons each having an energy of 4.0 × 10^-13 J. What is this energy in MeV? A) 4.0 × 10^-7 MeV B) 2.5 MeV C) 40 MeV D) 2.5 × 10⁶ MeV E) None of these choices are correct.

Question

Quizplus · Accepted Answer

We can use the conversion 1 MeV = 1.602 × 10^-13 J to convert the energy given in J to MeV.

(4.0 × 10^-13 J) / (1.602 × 10^-13 J/MeV) = 2.49 MeV

Rounding to three significant figures, we get 2.50 MeV, which is closest to choice B.

Sodium-21 Will Emit Positrons Each Having an Energy of 4