Solutions 5

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  1. Thermal neutrons have a kinetic energy of about 0.025eV
  2. Fast neutrons are “braked” with elastic collisions with particles with the same size as the neutrons. A moderator also needs to have a low cross-section for absorbing neutrons.
  3. A moderator is a material that brakes the neutrons, for instance H2O, D2O, C, Be. A neutron absorbent catches the neutrons and reacts with the neutron. Good absorbants are borium and gadolinium.
  4. From the nuclide carte we can see that 3He has a high cross-section for the n,p-reaction.
  5. The reaction 3He+n arrow 3H++1H(+2e-). The charged particles from the reaction creates more ionisations when they travel towards the anode and the cathode, this gives a electric signal.
  6. The Q-value from the reaction is 764 keV, the reaction is exothermic.
  7. 3H+ and 1H+ is created.
  8. The two products in the reaction recives opposing recoils 180 degrees. Conversion of momentum m1v1=m2v2 gives:

[math]m_{1}^{2}v_{1}^{2}=m_{2}^{2}v_{2}^{2}\rightarrow m_{1}E_{1}=m_{2}E_{2}\rightarrow E_{1}=\frac{m_{2}}{m{1}}E_{2}=\frac{1}{3}E_{2}[/math]

[math]E_{1}+E_{2}=Q=764 keV\rightarrow E_{1} = 190 Kev, E_{2}=570 keV[/math]