Biological Effects of Radiation Ionizing radiation consists of photons and/or moving particles that have sufficient energy to knock and electron out of an atom or molecule, thus forming an ion. Exposure is a measure of the ionizing radiation produced in air by X-rays or γ -rays. In passing through the air, the beam produces positive ions whose total charge is q . Exposure is the charge per unit mass of the air.
Absorbed Dose For biological purposes, the absorbed dose is a more suitable quantity because it is the energy absorbed from the radiation per unit mass of the absorbing material: gray
Differences in effect To compare the damage produced by different types of radiation, the relative biological effectiveness (RBE) is used.
Effect on Organisms The product of the absorbed dose and the RBE is the biologically equivalent dose:
32.1.1. Ionizing radiation can be harmful to living things because of which of the following reasons? a) Cells may be destroyed by the thermal energy released by radioactive decay. b) Cells may be damaged by nuclear fusion occurring within them. c) Cells may be damaged by nuclear fission occurring within them. d) Cells may be damaged by fast moving helium nuclei, electrons, or very high frequency photons. e) Cells may be damaged by the beta decay of .
32.1.2. What is the absorbed dose of fast neutrons (RBE = 9.5) that is biologically equivalent to 75 rad of slow neutrons (RBE = 2.0)? a) 350 rad b) 120 rad c) 16 rad d) 48 rad e) 5.0 rad
Nuclear Reaction vs Decay A nuclear reaction is said to occur whenever the incident nucleus, particle, or photon causes a change to occur in the target nucleus.
Example 3 An Induced Nuclear Transmutation An alpha particle strikes an aluminum nucleus. As a result, and unknown nucleus and a neutron are produced.
Induced Nuclear Reaction An induced nuclear reaction in which uranium is transmuted into plutonium.
32.2.1. Consider the following nuclear reaction: . The symbol “ d ” indicates a deuterium nucleus . Which one of the following statements is true concerning particle X in this reaction? a) X must be an alpha particle. b) X must be a photon. c) X must be two protons. d) X must be two neutrons. e) X must also be a deuterium nucleus.
32.2.2. Consider the following nuclear reaction: . Which one of the following statements is true concerning particle X in this reaction? a) X must be an alpha particle. b) X must be a photon. c) X must be a proton. d) X must be a neutron. e) X must be an electron.
Nuclear Fission A slowly moving neutron causes the uranium nucleus to fission into barium, krypton, and three neutrons.
Conceptual Example 5 Thermal Neutrons Versus Thermal Protons or Alpha Particles Why is it possible for a thermal neutron to penetrate a nucleus, whereas a proton or alpha particle would need a much larger amount of energy? Neutron has not electromagnetic repulsion
Chain Reaction In a controlled chain reaction, only one neutron, on average, causes another neutron to fission.
32.3.1. In the process known as nuclear fission, which of the following occurs? a) Two nuclei with atomic numbers less than that of iron are combined. b) Two nuclei with atomic numbers greater than that of iron are combined. c) A nucleus with an atomic number less than that of iron is split. d) A nucleus with an atomic number greater than that of iron is split. e) A nucleus with an atomic number much greater than that of iron is split by an alpha particle or a very low frequency photon.
32.3.2. Consider the following nuclear reaction: What is X in this reaction? a) b) c) d) e)
32.3.3. How many neutrons are released in the following reaction: a) 1 b) 3 c) 6 d) 8 e) 12
32.3.4. How much energy is released in the following reaction: a) 78.2 MeV b) 96.1 MeV c) 126.5 MeV d) 140.8 MeV e) 177.9 MeV
32.3.5. Why is it that neutrons induce nuclear fission reactions better than protons do? a) The nucleus exerts a repulsive force on the proton, but not on the neutron. b) With more mass, neutrons have greater momentum than protons. c) It is difficult to produce enough protons for the reaction to occur. d) Neutrons experience the attractive strong nuclear force, whereas protons do not experience this force.
32.3.6. Which one of the following quantities is not necessarily conserved in nuclear reactions? a) number of protons b) electric charge c) angular momentum d) linear momentum e) number of protons and neutrons
32.3.7.What is the origin of the energy that is released in a nuclear fission process? a) electrostatic repulsion of neutrons b) weak nuclear force c) Coulomb energy of protons and electrons d) electrostatic repulsion of protons e) energy of the thermal neutrons
32.3.8. Which one of the following statements best explains why light nuclei do not undergo nuclear fission? a) Light nuclei cannot be radioactive. b) Light nuclei cannot absorb thermal neutrons. c) Light nuclei do not have neutrons. d) Light nuclei have a much higher binding energy than heavy nuclei. e) Fission of a light nucleus would result in a reduction of the binding energy, rather than an increase.
Nuclear Reactors A nuclear reactor consists of fuel elements, control rods, and a moderator.
Nuclear Reactors The moderator slows neutrons and the control rods absorb neutrons.
32.4.1. Which one of the following statements concerning a nuclear reactor is true? a) Nuclear energy is converted to thermal energy within the reactor. b) Binding energy is converted to nuclear energy within the reactor. c) Binding energy is created within the reactor. d) Thermal energy is converted to nuclear energy within the reactor. e) Energy is created in the fission reactions that occur within the reactor.
32.4.2. What is the purpose of the moderator in a fission reactor? a) The moderator prevents heat loss from the reactor core. b) The moderator decreases the speed of fast neutrons. c) The moderator absorbs slow neutrons. d) The moderator absorbs gamma rays. e) The moderator prevents the reactor from reaching a critical state.
32.4.3. A nuclear power plant is constructed to generate 6.0 × 10 8 W. If the nuclear fission reaction used in the reactor produces 150 MeV per fission, how many fissions per second are required? a) 6.0 × 10 23 b) 2.5 × 10 19 c) 6.4 × 10 18 d) 1.1 × 10 18 e) 4.0 × 10 17
32.5.1. In a fusion reaction in which two helium nuclei are fused, what nucleus is produced? a) b) c) d) e)
32.5.2. Consider the following nuclear reaction: + X . Identify particle X . a) a photon b) a proton c) a neutron d) an electron e) No such particle is produced in this reaction.
32.5.3. Under what circumstances can a fusion reaction be self-sustaining? a) Unlike fission, there are no circumstances in which fusion can be self-sustaining. b) A fusion reaction can be self-sustaining if the reaction produces heavier nuclei from lighter nuclei. c) A fusion reaction can be self-sustaining if the reaction produces lighter nuclei from heavier nuclei. d) A fusion reaction can be self-sustaining if the reaction produces nuclei with larger binding energy per nucleon. e) A fusion reaction can be self-sustaining if the reaction produces nuclei with smaller binding energy per nucleon
32.5.4. A certain fission reaction releases three neutrons. How many of these neutrons must go on to produce a subsequent fission if a chain reaction is to be sustained? a) 1 b) 2 c) 3 d) It could be zero as long as there are other neutrons from other fission processes available.
32.5.5. Is there some minimum requirement of mass of fissile material, such as uranium, for a chain reaction to be sustained? a) No, a small number of atoms is sufficient. b) Yes, there must be enough material to prevent neutrons from escaping and defeating the chain reaction. c) Yes, there must be enough fissions to continue the chain reaction. d) Yes, there must be enough energy to continue the chain reaction.
Units of Matter The current view of how matter is composed of basic units.
32.6.1. In what way are photons related to charged particles, such as electrons and protons? a) Photons, also having a charge, are members of the same family as other charged particles. b) Charged particles, such as electrons and protons, interact with each other via photons. c) Charged particles, such as electrons and protons, are composed of photons. d) Photons interact with each other via charged particles, such as electrons and protons. e) There is no relationship between these particles; and that is why photons have a family all to themselves.
32.6.2. Which one of the following kinds of particles is most closely related to an electron? a) muon b) quark c) proton d) kaon e) neutrino
32.6.3. Which one of the following statements concerning the antiparticle of the proton is true? a) The antiproton has a positive charge and a negative mass. b) The antiproton has no charge and a positive mass. c) The antiproton has a negative charge and a negative mass. d) The antiproton has no charge and a negative mass. e) The antiproton has a negative charge and a positive mass.
32.6.4. Within the theoretical framework called the Standard Model, which one of the following is not considered an elementary particle? a) quark b) electron c) proton d) antiquark e) neutrino
32.6.5. Which one of the following particles is not composed of quarks? a) proton b) neutron c) kaon d) pion e) muon
32.7.1. The cosmic background radiation of the universe was produced at what point in the history of the universe? a) a few billion years ago when the universe had cooled to about 3 K b) about 12 billion years ago when the first atoms formed c) after the first one hundred thousand years when protons, electrons, and neutrons were formed d) after the first 10 35 s e) at the Big Bang
32.7.2. Which one of the following forces is the most difficult to unify with the other three fundamental forces? a) weak nuclear force b) strong nuclear force c) electromagnetic force d) gravitational force e) normal force
32.7.3. Why is the gravitational force so difficult to reconcile with the other three fundamental forces into a single grand unified force? a) It has infinite reach. b) It is much weaker than the other forces. c) It involves mass. d) The universal gravitational constant cannot be accurately measured. e) Gravitons have only been produced in small numbers in laboratories.