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]


  1. Q-Value 2.224MeV
  2.  And 3. The energy of the deuterium is not calculated relativistic but the γ-ray is completely relativistic, we then get: [math]m_{d}v_{d}=\frac{E_{\gamma}}{c}\rightarrow m_{d}^{2}=\frac{E_{\gamma}^{2}}{c^{2}}\rightarrow \frac{1}{2}m_{d}^{2}v_{d}^{2}=\frac{E^{2}_{\gamma}}{2c^{2}}[/math]

         Inserting the energy of the deuterium we get:


         we know that [math]E_{d}+E_{\gamma}=Q=2.2224\, MeV[/math] solving for this:

         [math]E_{d}=0.0013\, MeV,\, E_{\gamma}=2.2226\, MeV[/math]

3: Q-Values

  • 40Ca: M(40Ca)+M(α)-M(44Ti)=5.126 MeV
  • 22Cr: 7.61 MeV
  • 56Fe: 6.29 MeV
  • 58Ni: 3.367 MeV

4: For ground state transitions assuming zero momentum to the neutrino

  1. 0.16 MeV
  2. 0.78 MeV
  3. 1.655 MeV subtracting the mass of a electron and a positron we end up at 0.633 MeV.
  4. β- :0.579 for 64Zn,   β+ : 0.653 MeV for 64Ni.
  5. The cause of this effect is the even-even/odd-odd addition to the energy
  6. 228Ra is created with desintigration of 232Th: 232Th arrow 228ra + α +Q this gives
    M(228Ra) = M(230Th)-M(α)-Q
    All of the naural thorium that exist is 232Th. The mass that is given for thorium is therefore more or less equal to the mass 232Th 232.0381 u. It is much the same for helium where the mass is 4.002602 u. To find M(228Ra) we need to find the Q-value. The excess energy (Q-value) is distributed as kinetic energy on the products 228Ra and alpha. The alpha particle has very little mass compared to 228Ra, and the alpha particle by conversion of momentum will receive almost all the kinetic energy:

[math]E_{228Ra} M_{228Ra} =E_{\alpha} M_{\alpha} \rightarrow E_{288Ra} \cdot 288 = E_{\alpha} \cdot 4 \rightarrow E_{228Ra} = E_{\alpha} \cdot \frac{4}{228}[/math]

Eα is know ( using the most powerfull α for transition to groundstate), and the Q value is found with: [math]Q=E_{228Ra}+E_{\alpha}=4.013 \, MeV \cdot \left(1+\frac{4}{228}\right)[/math]

This gives [math]M(^{228}Ra)=232.0381 \, u-4.002602 \, u - \frac{4.775\, Mev \left(1+\frac{4}{288}\right)}{931.5 \, Mev/u}=228.03\, u[/math]


  1. [math].^{232}Th(n,\gamma ) ^232Th \stackrel{\beta}{\rightarrow}[/math]<span class="texhtml"