Thermal Neutron Absorption Rate in Water?

[bran_1]

Homework Statement

"The 2200 m/s flux in an ordinary water reactor is 1.5*10^13 neutrons/cm^2*s. At what rate are the thermal neutrons absorbed by the water?"

Homework Equations

(unsure)

The Attempt at a Solution

I know that absorption of a thermal neutron (a neutron in thermal equilibrium) is a type of radiative capture, and is therefore exothermic and considered an absorption reaction.

Where I'm stuck is how I can relate this information to the flux at the given neutron energy (velocity), as I don't see how I can get anywhere with the information given.

Any and all help would be greatly appreciated!

 

[drvrm]

Any and all help would be greatly appreciated!

you must get a relation between the rate of absorption and the generated flux of neutrons in water medium in say a reactor..

pl. consult your textbook.

i think the relation ship will involve the 'mean free path of absorption' and
for water, heavy water, graphite its given in nuclear reactor data table.

 

[bran_1]

you must get a relation between the rate of absorption and the generated flux of neutrons in water medium in say a reactor..

pl. consult your textbook.

i think the relation ship will involve the 'mean free path of absorption' and
for water, heavy water, graphite its given in nuclear reactor data table.

I have consulted it, it doesn't seem to elaborate beyond the definition of the mean free path. There is nothing mentioned about the mean free path of absorption

 

[drvrm]

I have consulted it, it doesn't seem to elaborate beyond the definition of the mean free path. There is nothing mentioned about the mean free path of absorption

i have seen discussion in the following reference...<.http://nvlpubs.nist.gov/nistpubs/jres/51/jresv51n4p203_a1b.pdf >i think you can use the introduction to understand and apply the process of neutron absorption in water

 

[bran_1]

i have seen discussion in the following reference...<.http://nvlpubs.nist.gov/nistpubs/jres/51/jresv51n4p203_a1b.pdf >i think you can use the introduction to understand and apply the process of neutron absorption in water

So based on that:

absorption = n * v / lambda ,
lambda = 1 / sigma,
sigma = lowercase_sigma * N,
phi = n * v = flux

I'm given the flux, but how would I get lowercase_sigma? Also, I know N to be the atom density, so how does that change for a molecule vs an atom, since the units are in neutrons/cm^3?

 

[drvrm]

I'm given the flux, but how would I get lowercase_sigma? Also, I know N to be the atom density, so how does that change for a molecule vs an atom, since the units are in neutrons/cm^3?

if you wish to have cross section for neutron absorption then you can use the absorption data .
moreover N the no. of atoms/nuclei involved can also be calculated using avogadro number and density of water.

you may see a text (ref given below) which discusses the shielding and the variation of cross sections with neutron energy
<http://mragheb.com/NPRE 402 ME 405 Nuclear Power Engineering/Neutron Cross Sections.pdf>