[khwcm]

Chadwick, the chemist who discovered the neutron, use the following method to produce neutron:
Alpha particle hit to a thin sheet of beryllium, a neutron will be given off.
i wonder that: the neutron came from beryllium or alpha particle, and why?

[gippgig]

When ⁴He (an alpha particle) hits (with sufficient energy) ⁹Be it can form an excited state of ¹³C, which deexcites by emitting a neutron. The compound nucleus is formed before the neutron is emitted so the source of the neutron is the compound nucleus, not either of the starting nuclei.

[khwcm]

since 9Be + 4He --> 13C
so do u mean that when C-13 deexcited, it is possible that the neutrons given out were came from alpha particles?(because there are 2 neutron from He-4 in C-13)

[Borek]

Neutrons are indistinguishable.

[khwcm]

i am not asking for the prove =.='''
i am just asking: is it POSSIBLE to be a neutron from alpha particle.
(just like probability, ie: electronic diagram -- we cannot see the s orbital/distinguish a particular electron at particular place, but we may have may found the electron with 90% in it)

[sjb]

As Borek has said, for the minute neutrons are indistinguishable. As there are 7 neutrons in ¹³C, and 2 have come from the alpha particle, I guess Occam's razor would suggest that there is 2/7 chance the ejected neutron has come from the alpha particle.

[khwcm]

thanks....i finally got the answer...
btw....the prob should be 2/13 rather than 2/7, isnt it?

[sjb]

Why do you think it is 2/13?

[Borek]

What does 13 in ¹³C mean?

[khwcm]

ar...i think i got it !..thanks