|Message: Re: neutron stimulated gamma spectrum||Not Logged In (login)|
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Thanks a lot. But I still don't understand why this happened. Under a classic view, it is just like bullets (neutrons) shooting balls (nucleus). The only explanation that there is less gammas coming out of Fe seems to be some of the Fe are blocked by copper. But that is very unlikely because the density is really small. The size of Fe nucleus is close to 1 barn (E-24 cm2) and there are only about E+17 Fe nucleus in 1cm3 cube. So the possibility that one nucleus blocking another one is really small. I am wondering if this result has ever been verified by experiment.
On Thu, 17 Jan 2013 16:54:42 GMT, michel maire wrote:
> On Tue, 15 Jan 2013 02:47:56 GMT, Tuoyu Cao wrote: > > > Hi All, > > > > I had simulated the characteristic gamma spectrum from neutron inelastic > > scattering. I shoot 2.5 MeV neutron beam to water Iron mixture cube > > (1cm3). The Iron concentration is very small, about 60 ppm. I can get > > about 20 gammas on 847keV peak from 1 million incident neutron. However > > after I add other elements to the mixture, for example 60 ppm Cu, the > > number of gammas on the Iron peak decreases a lot. In other words, the > > precence of other elements (even very small amount), can affect neutron > > scattering cross section of Iron. I don't understand the mechanism here > > and I am not sure if the result makes sense. Thanks a lot for any > > explanation. > > > > Playing with example Hadr03 (and QBBC physics), one get following informations: > cross section n + Fe56 : 0.96 barn > cross section n + Cu63 : 1.24 barn, eg. the same order of magnitude. > > Therefore, in a mixture Fe-Cu (50%-50%), about half of neutron beam will interact with Cu instead of Fe, as it can be seen in the attached log file. > I also attach plot of gamma spectrum (low and high energy parts) > > Attachment: > http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/01/17/08.50-58404-Fe_Cu.log.txt > http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/01/17/08.50-7406-gamma1.gif > http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/01/17/08.50-57577-gamma2.gif >