Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Inelastic and elastic scattering and absorption.

  1. Feb 1, 2014 #1
    I have to write some training on the following and I really have no idea. Is this correct? Any help is greatly appreciated;)

    Inelastic scattering
    In inelastic scattering, a neutron collides with and is temporarily absorbed by the nucleus of the target particle. This excites the nucleus, causing it to release gamma radiation and another neutron. Both the neutron and the target particle ‘scatter’ in different directions. As the neutron continues to collide with target particles, it loses more energy and is therefore more likely to experience an elastic scattering.

    Elastic scattering
    In elastic scattering, the neutron is at a lower energy state and so bounces off the target nucleus, but in the process it shares its kinetic energy with the target nucleus, causing the neutron to change direction. The target particle to continues on its original trajectory, but at a higher velocity.

    In absorption, the lower energy neutron collides with the nucleus of an atom that has the same mass and as a result is captured forming a heavier nucleus. When a neutron is captured, the heavier nuclear becomes unstable and decays, releasing gamma radiation.

    Inelastic scattering and absorption can be measured by the amount of gamma radiation they release......and because the radioactive emissions of elements are well known, we can compare the spectra of radiation released with known elements, to determine the concentration of elements within a formation.
  2. jcsd
  3. Feb 2, 2014 #2


    User Avatar
    2017 Award

    Staff: Mentor

    That's not right. In particular, the target particle can be at rest before the collision, what is its original trajectory then?
    Momentum is conserved, if the neutron changes its momentum the target has to change its momentum as well.
    If the target particle is moving before the collision, it can slow down and the neutron can gain speed.

    The same mass as what?
    The neutron does not have to be low-energetic, although a lower energy is often useful to get absorption.

    That doesn't have to happen.

    Apart from those points, I think it looks fine.
  4. Feb 2, 2014 #3


    User Avatar
    Gold Member

    From measuring part, one more thing could as well use neutron detectors...
  5. Feb 3, 2014 #4
    I´d group the options as follows:
    1) Elastic scattering
    The neutron and nucleus change their momenta and energies, but remain unchanged in state, and no new particles are formed. In a frame where the momenta of neutron and nucleus are equal and opposite, their values are unchanged and only directions change; in a frame where the momentum of nucleus is zero, the nucleus loses energy and neutron gains it.
    2) Absorption
    Several options:
    Most common is n,γ. If the neutron can be bound in a heavier nucleus, stable or unstable (there are very few longlived nuclei at the beginning on neutron dripline, such as α and t) then n,γ is the simplest way to get rid of the binding energy.
    Simplest but not always the most favourable. Strong interaction is strong. Thus, when strong interaction is possible, like n,p, n,α or n,f, it usually is faster than the parallel n,γ.

    If the neutron has appreciable energy, then 1) and 2) are still possible, usually with smaller cross-section, but there will be extra options
    3) Braking radiation. Nuclei are charged, so when accelerated they may radiate electromagnetic waves. They do not have to, they can scatter elastically, but inelastic scattering is possible
    4) Inelastic scattering with delayed gamma. This requires that the nucleus should possess an excited state with suitable energy
    5) Inelastic scattering with nuclear reaction. Such as n,2n, n,3n, n,np, n,nα et cetera. As well as the reactions listed above under absorption (n,p, n,α or n,f) where the nucleus did not meet the energy threshold with slow neutrons.

    Is that correct?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook