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Is there any element that does not absorb neutrons?

by Nitro Squared
Tags: absorb, element, neutrons
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Nitro Squared
#1
Aug4-14, 08:58 PM
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Recently I have been researching the topic and I have not found any completely clear answer.
To restate my question (as I asked in the title), is there any element that would not absorb neutrons and if not which element has the lowest neutron absorption rate?
Thank you.
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Simon Bridge
#2
Aug4-14, 10:12 PM
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Welcome to PF;
Is there any element that does not absorb neutrons?
Short answer: No.
Executive answer: it depends.

which element has the lowest neutron absorption rate?
Oxygen

The quantity you are looking for is called "neutron absorption crossection"
The crossection depends on the configuration of the atoms and the energy of the neutrons - which is probably why you are having trouble finding a clear answer: there isn't one.
i.e. for thermal neutrons.
-- Kenneth Barbalace: EnvironmentalChemistry.com. 1995 - 2014. Accessed on-line: 8/4/2014
OmCheeto
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Aug4-14, 10:29 PM
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Quote Quote by Nitro Squared View Post
Recently I have been researching the topic and I have not found any completely clear answer.
To restate my question (as I asked in the title), is there any element that would not absorb neutrons
All of them. Otherwise the x axis of the chart of nuclides would go on forever.
and if not which element has the lowest neutron absorption rate?
Once again, all of the nuclides on the right hand edge of the chart. According to wiki, Hydrogen-7 had to be synthesized using heavy helium atoms bombarding a hydrogen atom, so it may not even have a defined neutron absorption rate.

Hydrogen-7
7H consists of a proton and six neutrons. It was first synthesised in 2003 by a group of Russian, Japanese and French scientists at RIKEN's RI Beam Science Laboratory by bombarding hydrogen with helium-8 atoms. In the resulting reaction, all six of the helium-8's neutrons were donated to the hydrogen's nucleus. The two remaining protons were detected by the "RIKEN telescope", a device composed of several layers of sensors, positioned behind the target of the RI Beam cyclotron.
On the chart of the nuclides link above, they have a hyperlink labeled σ(n,y). All of the nuclides greyed out have undefined cross sections.

All of the colored nucleons on the chart have defined cross sections. Xenon-135 appears to have the largest at 2.665E+6 barns.

Thank you.

Simon Bridge
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Aug4-14, 10:55 PM
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Is there any element that does not absorb neutrons?

All of them. Otherwise the x axis of the chart of nuclides would go on forever.
i.e. for every element there exists an isotope that will not absorb any more neutrons... at least, not without fissioning.

Probably another reason there is no clear answer to the question ;)
OmCheeto
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Aug4-14, 11:24 PM
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Quote Quote by Simon Bridge View Post
i.e. for every element there exists an isotope that will not absorb any more neutrons... at least, not without fissioning.
I believe the nuke nerds would claim that that would be only for fissionable isotopes. The rest just decay. Beta, gamma, and alpha are the only decay modes I remember.
Probably another reason there is no clear answer to the question ;)
NoSimon Bridge + Yes(All of them)OmCheeto = it depends.



ps. This doesn't strike me as a chemistry question. Should this thread be moved to the "High Energy, Nuclear, Particle Physics" forum?
Simon Bridge
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Aug5-14, 12:01 AM
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The ;link I gave in post #2 is to a chemistry site, so it seems this is something that gets covered in a chemistry classes.
We don't know enough to call it "high energy".
Need the context - is OP looking for a material especially transparent to neutrons in some energy range?


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