Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

I have a question which asks me to determine what x is for the following nuclear transition

$$^{29}Si(\alpha, n)X$$

But I don't have any idea what this notation implies.

Another example:


share|improve this question

1 Answer 1

up vote 2 down vote accepted

$^{29}Si(\alpha, n)X$ means the nuclear reaction starting with $^{29}Si$, having an $\alpha$ particle go in and a neutron come out to produce $X$. That means the atomic number must increase by 2 and atomic weight by 3.

Similarly $^{111}Cd(n,x)^{112}Cd$ means the reaction starts with $^{111}Cd$, a neutron goes in, something comes out and you end up with $^{112}Cd$.

share|improve this answer
Is it mean of me to complain about the fecklessness of modern students and point out that just Googling "29Si(α,n)X" gets the answer as the second result? :-) –  John Rennie Mar 7 '13 at 10:59
No, but to be fair this notation is quite awful - almost as unintuitive as the stuff we use in astronomy –  Chris White Mar 7 '13 at 16:38
@Chris: That notation carries rather more information to an experimenter than John describes here, it's just that none of it is relevant to this particular question. It's the information on what is and is not measured that this form is preferred over, say, $^{29}\mathrm{Si} + \alpha \to n + X$. –  dmckee Mar 7 '13 at 16:52
@dmckee Oh I agree it has more information, but I contend it's something of an abuse of parentheses and commas - they take on meanings here very much unaligned with their typical interpretations (grouping of inputs, separating things whose order isn't physically important, etc.) –  Chris White Mar 7 '13 at 17:06

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.