# Problem set 5

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# Particles and Nuclear Reactions

'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 is often detected by gas- detektors filled with 3He. Why 3He 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 e)? is the reaction endothermic or exothermic.
7. Two charged particles are created in the reactions, which particles.
8. What energy does each of the to 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 this one: n+p → d+γ.

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 proses for solar energy is, in total 4p → α + 2e++ 2neutrino. Calculate the Q-values and determine the end products for these reactions:

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

4: Use nuclear wallet cards to calculate:

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 228 Ra from information from the nuclide chart.

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

1. Write down the nuclear reactions which gives 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. Uranium-metall is radiated in a neutron fluks 10^14 neutrons/(cm2s).

6: Borium is a good absorbent of thermal neutrons.

1. Write down the nuclear reaction that happens.
2. Calculate the Q-value of the reaction.
3. A fluks of 10^14 neutrons/Cm^2s striking a area of 100 cm^2 is completely stopped in a 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 of this reaction is 0.8 b when a proton energy of 12Mev is used.

1. Calculate the Q-value of this reaction.
2. What must the production speed be to generate a sample of 1Gbq of 89Zr when the target is radiated for 6 hours.
3. The target material is cheap in this case and there is no need to regenerate it. Explain why.