Disintegration Energy of Beta Plus Decay

[xoxomae]

Homework Statement

The radionuclide ¹¹C decays according to
¹¹₆C → ¹¹₅B + e⁺ + v
Show that the disintegration energy is given by
Q = (m_C - m_B - 2m_e) c²

Homework Equations

Q = (m_i - m_f) c²

The Attempt at a Solution

[/B]
Q= (m_C - m_B - m_e) c²

Im probably missing something obvious but I can't see where the 2m_e comes from.

 

[TSny]

The key is to remember that the given masses m_C and m_B are atomic masses, not nuclear masses.

 

[xoxomae]

But that leads me to
Q = ((m_C+6m_E) - (m_B + 5m_E + m_E))c²

Which gives me
Q= (m_C + m_B)c²

 

[TSny]

To get the nuclear mass of the carbon, should you add 6 electrons to the atomic mass?

 

[xoxomae]

Ah i think I understand

Q = ((mC- 6mE) - (mB - 5mE + mE))c2

Q = (mC - mB - 2me) c2

Is this right?

 

[TSny]

Looks right. Good.

 

[xoxomae]

Thank You :)