dRic2
Gold Member
 441
 77
Hi, I'm reading chapter 63 of Lamarsh's book "Introduction to Nuclear Reactor Theory". Here it is discussed the very idealistic case of Hydrogen being used as a Moderator (without adsorption).
The moderator is:
 infinte
 homogeneous
 with uniformly distributed source emitting at constant rate ##S## and constant energy ##E_0##
 (of course) made of Hydrogen
 the nuclei are considered at rest.
In the book it is said that the emitted neutrons hit the Hydrogen atoms and so they lose energy (this I understand perfectly). As a consequence the author assumes that the only possible outcome of a collision is the slowing down of neutrons.
I do not fully agree and I was looking for some help to better understand this.
My thought about what is "missing":
Neutrons emitted from the source have an amount ##E_0## of kinetic energy and they hit the Hydrogen nuclei at rest so that they transfer to them some of their staring kinetic energy thus they (neutrons) slow down (to an energy level ##E##). BUT the Hydrogen atoms have gained some kinetic energy (and this isn't something to be neglected because Hydrogen nuclei and neutron have the same mass!) and so they (Hydrogen nuclei) are now moving with some velocity and kinetic energy. Now that the nucleus in no more at rest if it collides with a neutron it (the nucleus) may "give back" some of the energy he stole in the previous collision and in this way the new neutron could be accelerated instead.
My possible explanation:
The author doesn't seem to care about the kinetic energy of the nuclei (ie the temperature of the moderator) so I guess he assumes that once the collision has occurred the recoiling nucleus is somehow "stopped" (ie the moderator is cooled) otherwise there would be a loss of energy in the system.
What do you think? Can you help me figure it out?
PS: I also like to know why neutronneutron scattering is totally neglected. Is that so rare ?
(I upload the first page of the chapter for completeness)
The moderator is:
 infinte
 homogeneous
 with uniformly distributed source emitting at constant rate ##S## and constant energy ##E_0##
 (of course) made of Hydrogen
 the nuclei are considered at rest.
In the book it is said that the emitted neutrons hit the Hydrogen atoms and so they lose energy (this I understand perfectly). As a consequence the author assumes that the only possible outcome of a collision is the slowing down of neutrons.
I do not fully agree and I was looking for some help to better understand this.
My thought about what is "missing":
Neutrons emitted from the source have an amount ##E_0## of kinetic energy and they hit the Hydrogen nuclei at rest so that they transfer to them some of their staring kinetic energy thus they (neutrons) slow down (to an energy level ##E##). BUT the Hydrogen atoms have gained some kinetic energy (and this isn't something to be neglected because Hydrogen nuclei and neutron have the same mass!) and so they (Hydrogen nuclei) are now moving with some velocity and kinetic energy. Now that the nucleus in no more at rest if it collides with a neutron it (the nucleus) may "give back" some of the energy he stole in the previous collision and in this way the new neutron could be accelerated instead.
My possible explanation:
The author doesn't seem to care about the kinetic energy of the nuclei (ie the temperature of the moderator) so I guess he assumes that once the collision has occurred the recoiling nucleus is somehow "stopped" (ie the moderator is cooled) otherwise there would be a loss of energy in the system.
What do you think? Can you help me figure it out?
PS: I also like to know why neutronneutron scattering is totally neglected. Is that so rare ?
(I upload the first page of the chapter for completeness)
Attachments

395.2 KB Views: 56