I need help with this assignment please

11. Both Iodine-131 and Cs-137 are radioactive isotopes dangerous to human life. The latter isotope emits radiation of lower energy than the former but is as dangerous because a) it has a shorter half-life b) it has a longer half-life

c) there is more of it d) actually, no one really knows

12. The mass of an atomic nucleus is (greater than, less than, equal to) the sum of the masses of the nucleons it contains.

13. The mass defect is defined as

a) the mass of a nucleus b) the difference between the sum of the masses of the nucleons in a nucleus and that of the nucleus itself c) the sum of masses of the nucleons in a nucleus d) the difference between the mass of a proton and the mass of a neutron

14. Nuclear energy is related to the mass defect according to the formula_______________, which is the quantity called the __________ energy.

15. In a sample of naturally occurring uranium, such as from a mine, most of it is the isotope Uranium-238. What is the other isotope that is present and what percentage is it of the whole sample? __________________________.

16. What level of enrichment of Uranium with this fissile isotope is required for the operation of a nuclear reactor? a) 30-40% b) 0.7% c) 10% d) 3-5%

17. A moderator in a nuclear reactor serves the purpose of a) slowing down neutrons so they can be captured by the uranium-235 nuclei b) absorbing neutrons in order to stop the fission reaction c) preventing the reactor core from cooling d) none of these

18. Of the two primary types of reactors used for electric power generation, boiling water reactors (BWRs) and pressurized water reactors (PWRs), the type using a heat exchanger in the reactor containment building to make the steam to drive the turbine generating electricity is the ____________type.

19. Perhaps the most important environmental issue associated with nuclear power is

a) what to do with the hot water generated b) the problem of preventing a nuclear explosion at a power plant c) the emission radioactive materials from the reactor d) the storage of radioactive waste

20. Provide a simple sketch to illustrate the idea of a chain reaction for the generation of nuclear energy by the fission of U-235 nuclei.