Conceptual Questions: 2, 5, 7, 11
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2. The signs of the charges of alpha, beta, and gamma rays could have been determined by tracking the trajectory of particles emitted into a region of constant magnetic field. The direction of deflection, or the lack of deflection for the case of the neutral gamma ray, would indicate the sign of the charge. The radius of curvature of the particle’s track can be used to determine the charge to mass ratio of each particle. You've already done this in problems from previous chapters.
5. There is a mass "defect" due to the binding energy of atomic electrons but it is several orders of magnitude smaller than the binding energy of the nucleus and may thus be omitted without significant loss of accuracy. Remember that the energy needed to ionize a hydrogen atom is about 13 eV, while a nuclear binding energy is on the order of millions of eV (MeV).
7. The nucleus is so much smaller than the atom and much much smaller than the gaps between atoms that there is no potential overlap of nucleon wavelengths between the nuclei of neighboring atoms.
11. Alpha particles emitted in radioactive decay usually have enough energy to ionize many molecules, so they are potentially very damaging. They do not penetrate to very great depths however, which makes them less dangerous outside the body. A few centimeters of air or less than a millimeter of human tissue is sufficient to stop them, so they do not penetrate the skin. An alpha emitter that is ingested or inhaled is much more dangerous because the softer tissue inside the body—the lungs or digestive tract—is exposed directly to the radiation, and all of the energy of the alpha decay is deposited to local cells in the body.
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