[mjfranklin]

The homework question reads:

"Use the semiempirical mass equation to compute, for given A, the relation between Z and N for a nucleus that has S_n=0 (the neutron "drip line").  Compute N/Z for A=100."

Using S_n=B_tot(A,Z) - B_tot(A-1,Z), I have been trying to manipulate the equation so that I can plug in A=N+Z for one of the A values to get N/Z=some A dependent expression.  I and several other students have spent hours manipulating the equation every way we can think of, and nothing looks even close to useful for getting an N/Z relationship. 

Are we missing something?

Any suggestions would be really appreciated.

[Mitch]

You just need an equation in terms of N's and Z's only. You do not need to manipulate the equation into something that looks like N/Z = blah...blah...

[Mitch]

The N/Z is brought up since we know stable nuclei at around A=100 typically have an N/Z ratio of ~1.3. But, at the neutron drip line the ratio becomes roughly ~1.7. This is the point the problem is subtly trying to make you discover from first princibles.

[timmy04jc]

  Hey, Mitch. I'm also having much trouble with #7 of problem set #3. It gets much messier and longer than I thought. You've worked it out already, right? Could you give us any suggestions for making the math shorter/cleaner? Thanks.

[Mitch]

You just need an equation in terms of N's and Z's only.

You do not need to manipulate the equation into something that looks like N/Z = blah...blah...