Hydrogen neutron capture

[Pheo1986]

Hi all. I am going to be doing an experiment involving neutron scatter. I am going to be firing fast neutrons into water and then detecting the thermal neutrons scattered. I am also going to look into thermal neutron capture where the hydrogen atom captures the thermal neutron and gives off a promt gamma ray.

i was wondering that when the hydrogen atom captures the neutron does this turn it into deuterium and if so does this now mean that my targeted water has turned into heavy water? would this have any affect on my experiment in the long run? or is my understanding of physics/chemistry way off?

any help is much appreciated

 

[Bob S]

When a hydrogen atom captures a thermal neutron, it turns into deuterium with the release of a 2.1-MeV gamma ray. The cross section is about 330 millibarns (not very large). To turn 18 grams (1 mole) of water to heavy water, about 2 moles (12 x 10²³) of neutrons are required, and 2 moles (12 x 10²³) of 2.1-MeV gammas are released. If your neutron flux is 10¹⁴ n/cm²-sec, you will need to wait ~4 years to get a 1% concentration of deuterium in your water. What is your neutron flux? How long are you willing to wait to create 20 grams (1 mole) of heavy water?

Bob S

 

[Pheo1986]

wow cheers for the indepth explanation Bob. I am not to sure what my neutron flux will be yet but my experiment will no way last as long as 4 years so I am sure i won't be having any problems with deuterium.

Thanks

 

[Bob S]

Here is the thermal neutron flux in the core of a 20 MW research reactor. See especially the plot vs. distance from core:

http://www.frm2.tum.de/en/technik/reactor/neutron-flux-density/index.html [Broken]

It is ~ 1 x 10¹⁴neutrons/cm²-sec at 1 meter from the core.

Bob S