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# Physics/About bombardment of lithium with neutron

Question
QUESTION: When neutron bombards lithium-7, it becomes tritium and helium with the emission of neutron. Can this neutron initiate chain reaction, causing the fission of lithium and thus release energy? If it can be done, what is it critical mass? If it cannot be done, why?

ANSWER: You mean Lithium 6, not 7.  And that does not release another neutron, unless you mix it with Be.  (Berylium), but that would only cause a neutron-releasing reaction once in about 100,000 times.  It can't be used to create a critical mass.  And 6Li is the rare isotope, it's very expensive because most of it goes to the bomb-making industry.

---------- FOLLOW-UP ----------

QUESTION: Then what about the bombardment of beryllium-9 by neutron, causing it to break into two helium nucleus and two neutrons? This process also releases energy, so can chain reaction happens when the neutrons from continuously breaks apart beryllium-9, releasing energy as a result?

That's normal, but the cross section (i.e. probability) and energy release is too low to create a chain reaction like you'd see in a weapon or a reactor.  Especially the probability of neutron capture without an n-gamma reaction and/or (especially) neutron escape.  You don't understand the massive probability of neutron escape without (or even with) a proper moderator structure.  That's just crazy, to even quote a "critical mass" without a deuterium scattering moderator.

Physics

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#### Dr. Stephen O. Nelson

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