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 × 10 ⁶ MeV E)None of these choices are correct.

Question

Quizplus · Accepted Answer

We can use the formula E = mc² to convert from J to MeV. First, we need to find the mass of the positron:

E = mc²
4.0 × 10¹¹ J = (m)(3.0 × 10⁸ m/s)²
m = 4.44 × 10⁻²⁷ kg

Now we can convert the energy to MeV:

E = (4.0 × 10¹¹ J)(1 MeV/1.602 × 10⁻¹³ J)
E = 2.49 × 10¹⁰ MeV
E ≈ 2.5 MeV

Therefore, the answer is B.

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