Cross Sections for Neutron Scattering in Different Frames

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In summary, the cross sections provided on http://www.nndc.bnl.gov/sigma/ are given in the lab frame and not the center-of-mass frame. For heavy nuclides, this distinction does not matter, but for lighter elements like hydrogen, it is important to note. A 1 MeV neutron in the lab frame will have an incident energy of 1 MeV, while the same neutron in the center-of-mass frame will have an incident energy of 250 keV. The angular distribution, however, is given in the center-of-mass frame. This information is important to consider when using this data for Monte Carlo simulations.
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vanesch
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This is probably a very dumb question, but I'm stuck with it.
The cross sections one finds on http://www.nndc.bnl.gov/sigma/ as a function of incident energy, is that energy given in the lab frame or in the cog frame ?
For heavy a nuclide, this doesn't matter, but for hydrogen for instance ?
If I have a (lab frame) neutron at 1MeV impinging on (thermal) hydrogen, do I read the table at 1MeV or at 250KeV ?

Thanks,
cheers,
Patrick.
 
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As far as I know, one uses the lab frame, i.e. a 1 MeV neutron has incident energy of 1 MeV.

Where did the 250 keV come from? COM?
 
  • #3
Astronuc said:
As far as I know, one uses the lab frame, i.e. a 1 MeV neutron has incident energy of 1 MeV.

Where did the 250 keV come from? COM?

Yes: half the speed (for hydrogen), hence 1/4 the KE...

Thanks for the answer !

In fact, this is how I wrote a Monte Carlo, and then I got worried that the energy might be given in the COM frame, because the angular distribution is, as far as I understand, given in the COM frame.
 
  • #4

1. What are tables of cross sections used for?

Tables of cross sections are used in various fields of science, engineering, and mathematics to represent the area or shape of an object or phenomenon. They are commonly used in physics, chemistry, and biology to analyze and understand the properties of particles and molecules.

2. How are tables of cross sections created?

Tables of cross sections are created through experimental observations or mathematical calculations. In experiments, scientists measure the physical dimensions of an object or phenomenon and use mathematical equations to calculate the cross-sectional area. In theoretical calculations, mathematical models and equations are used to determine the cross-sectional area of an object or phenomenon.

3. What is the difference between a one-dimensional and two-dimensional table of cross sections?

A one-dimensional table of cross sections represents the cross-sectional area of an object or phenomenon along a single axis. This is commonly used for linear objects such as wires or beams. A two-dimensional table of cross sections represents the cross-sectional area of an object or phenomenon along two axes, and is commonly used for 2D shapes such as circles or squares.

4. How can tables of cross sections be used in real-world applications?

Tables of cross sections can be used in a variety of real-world applications, such as designing buildings and structures, analyzing the aerodynamics of airplanes and cars, and understanding the behavior of particles in particle accelerators. They can also be used in medical imaging to determine the shape and size of organs and tissues.

5. Can tables of cross sections be used to compare different objects or materials?

Yes, tables of cross sections can be used to compare the cross-sectional areas of different objects or materials. This can provide valuable insights into the properties and behavior of these objects or materials, and can help in making informed decisions in various fields such as materials engineering and product design.

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