# Question about differential cross section

Clara Chung
Homework Statement:
Attached below
Relevant Equations:
Attached below

I have attached the two pages in my notes and I have the following question.
1. Where have the n_t*l gone in 9.9? (According to 9.5 why do they disappear?)
2. Why J_s=sigma_tot J_i? The dimension of flux is per m^2 and sigma is per area too, the dimension is not right...

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View attachment 242124
View attachment 242125
I have attached the two pages in my notes and I have the following question.
1. Where have the n_t*l gone in 9.9? (According to 9.5 why do they disappear?)
2. Why J_s=sigma_tot J_i? The dimension of flux is per m^2 and sigma is per area too, the dimension is not right...
Looks like an error to me...

Clara Chung
Mentor
Yes, insert ##n_t l## into (9.9) in such a way that the units are consistent on both sides.

A physical reality check: if ##l = 0## or ##n_t = 0##, i.e. the target disappears completely, what should we expect ##J_s## to be, regardless of ##J_i##?

Clara Chung
Clara Chung
Yes, insert ##n_t l## into (9.9) in such a way that the units are consistent on both sides.

A physical reality check: if ##l = 0## or ##n_t = 0##, i.e. the target disappears completely, what should we expect ##J_s## to be, regardless of ##J_i##?
Yes, it should be zero :)