In reply to Jones Beene's message of Tue, 10 May 2011 15:07:19 -0700: Hi, [snip]
From http://atom.kaeri.re.kr/cgi-bin/nuclide?nuc=Ni-62&n=2 one can see that the cross section for neutron absorption by Ni62 at thermal energies (~ 2E-8 MeV) is about 14 barn. Dividing this into the atomic volume of Nickel yields an average travel distance of about 7.8 mm before absorption takes place. This will vary depending on the element/isotope involved. (For Ni58 it's about 4.5 barn, and the corresponding distance is about 24 mm). For B10 it's 3837 barn, and the travel distance is 0.1 mm (taking into account that B10 is only 20% of Boron). >Craig, > >I don't if this helps, but most metals tend to be relatively transparent to >neutrons, due to the scattering cross-section which is caused by spin, not by >anything related to charge. The Coulomb barrier is not involved AFIK with >neutrons. > >A few metals like cadmium will absorb neutrons of the correct velocity to >nullify spin effects, but in general neutrons must be slowed way-down >(thermalized) before they can interact with say nickel; and usually they >easily would escape the reactor long before that happens unless they are >extremely "cold" - low velocity. Thus the W&L "ULM", which because it is >cold/slow can stay around longer and have a much better chance of an >interaction. > >IOW the approaching neutron will only interact at a significant rate if it >extraordinarily slow in velocity. > >Jones > > >-----Original Message----- >From: Craig Haynie > >Hello all! > >I've got a question that I believe you could help me with: > >I understand that the coulomb barrier is the point at which the Strong >Force will become dominant, and overcome the natural repulsion of two >nuclei as they are moved closer together. But can neutrons penetrate the >coulomb barrier without any problem, since they are not repelled by the >positive charge in the nucleus? Is this why the Widom-Larsen hypothesis >posits the entry of weak neutrons into the nucleus? > >Craig Haynie >Manchester, NH > > > Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/project.html
