# Which of the SEMF terms account for low A binding energy?

1. May 16, 2015

### Flucky

1. The problem statement, all variables and given/known data
Which of the semi-empirical mass formula terms accounts for a drop in stability at low A and why?

2. Relevant equations
B = avA - asA$\frac{2}{3}$ -acZ(Z-1)A$\frac{-1}{3}$ -aa(A-2Z)2A-1 ± apA$\frac{3}{4}$

3. The attempt at a solution
I'm struggling getting my head around this one.

The Coulomb term will decrease the binding energy as Z increases so I've ruled that out.

The asymmetric term decreases the binding energy as N>Z (more stable when N ≈ Z) so I've ruled that out.

All the rest are only dependent on A, so I would guess that it is the first term (volume term) that is the cause of low A instability. However the volume term increases linearly with A and it's such a dramatic change when looking at the binding energy per nucleon curve.

I can't explain why it would be the volume term if it is.

Any ideas?

2. May 21, 2015