1) Answer the following questions:

1. 1. What it is a thermal neutron?
   2. Neutrons are produced with high energy. How do you reduce their energy without losing them?
   3. What is a neutron moderator and what is a neutron absorbent? Give two examples of both.
   4. Neutrons are often detected by gas- detectors filled with ³He. Why is ³He used and not ⁴He?
   5. Neutral radiation is detected by making charged particles. Which reaction happens when tubes filled ³He is used as neutron detectors?
   6. What is the Q-value of the reaction in 5)? Is the reaction endothermic or exothermic?
   7. Two charged particles are created in the reactions, which particles?
   8. What energy does each of the two particles receive when a thermal neutron reacts?

2) One of the quite few nuclear reactions that happened during the birth of the universe (“big bang”) is: n + p → d + γ.

1. 1. Calculate the Q-value of the reaction.
   2. What is the energy of the gamma ray?
   3. What is the energy of the deuterium? Assume a thermal neutron.

3) The most important process for fusion in the sun is, in total 4p → α + 2e⁺ + 2 μ. Calculate the Q-values and determine the end products for these reactions:

1. 1. ⁴⁰Ca(alpha,gamma)
   2. ⁵²Cr(alpha,gamma)
   3. ⁵⁶Fe(alpha,gamma)
   4. ⁵⁸Ni(alpha,gamma)

4) Use Nuclear Wallet Cards to do the following calculations:

1. 1. The maximum kinetic energy of the positron/electron for ¹⁴C.
   2. The maximum kinetic energy of the positron/electron for the neutron.
   3. The maximum kinetic energy of the positron/electron for ¹⁸F.
   4. The maximum kinetic energy of the positron/electron for ⁶⁴Cu (both disintegrations).
   5. Nuclei that decays by both beta minus and beta plus are of a special type. Why is this?
   6. Calculate the mass of ²²⁸Ra from information from the Chart of the Nuclides.

5) In a breeder-reactor a new fissile atom is created from each atom that fission. Breeder-reactors can be made from thorium and uranium as starting material.

1. 1. Write down the nuclear reactions which give new fissile atoms in a uranium-breeder reactor and in a thorium-breeder reactor.
   2. Calculate the work (in watt) that is generated when one kg of uranium metal is irradiated in a neutron flux of 10¹⁴ neutrons/(cm²s).

6) Borium has a high cross-section to absorb thermal neutrons.

1. 1. Write down the nuclear reaction that happens.
   2. Calculate the Q-value for the reaction.
   3. A flux of 10¹⁴ neutrons/(cm²s) striking an area of 100 cm² is completely stopped by a wall of borium. Calculate the work (in watt).

7) The radionuclide ⁸⁹Zr has a half-life of 78 hours and is often generated in hospitals by a cyclotron. It is generated by the nuclear reaction ⁸⁹Y(p,n)⁸⁹Zr. The cross section for this reaction is 0.8 b with 12 MeV protons.

1. 1. Calculate the Q-value for this reaction.
   2. Find a production speed that is able to generate a sample of 1 GBq of ⁸⁹Zr with 6 hours of irradiation time.
   3. In this case the target material is cheap and there is no need to regenerate it. Why is it so?