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If a stationary oxygen atom is hit head-on by a neutron, and the oxygen atom now has energy equal to say 20 keV, is there a way to calculate the initial energy of the neutron?

Jackson Hart
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  • Only if you know the initial vector of the neutron and the resultant vectors of both. Or if you know the resultant energy of the neutron you can determine how much it gave to the oxygen using the masses. – Gwydionforge May 02 '17 at 15:11
  • @Gwydionforge Assuming its a direct collision, I'm just wondering the worst case scenario. What is the most energy that could be transferred, approximately? – Jackson Hart May 02 '17 at 15:14
  • I think it would be a ratio of the masses. The mass of oxygen divided the mass of a neutron equals the energy of the oxygen divided by the energy of the neutron. – Gwydionforge May 02 '17 at 15:18
  • Think of it like a marble hitting a billiard ball. The marble will bounce away after imparting some of it's energy to the other. – Gwydionforge May 02 '17 at 15:19
  • I understand, just trying to determine a ballpark number for the initial energy of the neutron – Jackson Hart May 02 '17 at 15:22
  • Also, your solution makes no sense. That says the initial energy of the neutron is less. – Jackson Hart May 02 '17 at 15:25

1 Answers1

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You have two unknowns, the initial neutron velocity (kinetic energy) and the final neutron velocity (kinetic energy).
This means that you need two equations.

No external forces - use conservation of momentum.
Elastic collision - use conservation of kinetic energy.

If the masses had been equal then the transfer of kinetic energy would have been 100 % but if the mass of the target had been very much larger than the incoming particle then the transfer of kinetic energy to the target would be very small with the less massive particle rebounding off the target particle.
To get the required value you will need to do some calculations but from what I have said you might expect the kinetic energy of neutron to be (much) greater than that of the oxygen atom.

Farcher
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  • What if I just assume an initial neutron velocity? – Jackson Hart May 02 '17 at 15:42
  • I just want a ballpark number. What is the energy of a neutron if it gives 20 keV to an oxygen atom – Jackson Hart May 02 '17 at 15:46
  • With the two constraints if you assume the initial neutron velocity the the final velocities of the neutron and oxygen are immediately determined and the kinetic energy of the oxygen atom will not necessarily be 20 keV. – Farcher May 02 '17 at 15:47
  • So assume that the mass of a neutron is 1 unit and that of the oxygen is 16 units and do the sums. – Farcher May 02 '17 at 15:48