discovered new subatomic particle -neutron Bethe and Bekker O The Joliot-Curie Enrico Fermi James Chadwick

Data from the appendices and the periodic table may be needed for these problems. What fraction of the 40K mat was on Earth when it formed 4.5109 years ago is left today?

Unreasonable Results A frazzled theoretical physicist reckons that all conservation laws are obeyed in the decay of a proton into a neutron, positron, and neutrino (as in (+ decay of a nucleus) and sends a paper to a journal to announce the reaction as a possible end of the universe due to the spontaneous decay of protons. (a) What energy is released in this decay? (b) What is unreasonable about this result? (c) What assumption is responsible?

(a) An aspiring physicist wants to build a scale model of a hydrogen atom for her science fair project. If the atom is 1.00 m in diameter, how big should she try to make the nucleus? (b) How easy will this be to do?

The purpose of this problem is to show in three ways that the binding energy at the election in a hydrogen atom is negligible compared with the masses of the proton and electron. (a) Calculate the mass equivalent in u of the 13.6eV binding energy of an electron in a hydrogen atom, and compete this with the mass of the hydrogen atom obtained from Appendix A. (b) Subtract the mass at the proton given in Table 31.2 from the mass at the hydrogen atom given in Appendix A. You will find the difference is equal to the electron’s mass to three digits, implying the binding energy is small in comparison. (c) Take the ratio of the binding energy at the electron (13.6 eV) to the energy equivalent of the electron's mass (0.511 MeV). (d) Discuss how your answers confirm the stated purpose of this problem.

Data from the appendices and the periodic table may be needed for these problems. (a) Natural potassium contains 40K, which has a halflife of 1.277109y. What mass of 40K in a person would have a decay rate of 4140 Bq? (b) What is the fraction of 40K in natural potassium, given that the person has 140 g in his body? (These numbers are typical for a 70kg adult.)

Unreasonable Results A physicist scatters (rays from a substance and sees evidence of a nucleus 7.51013m in radius. (a) Find the atomic mass of such a nucleus. (b) What is unreasonable about this result? (c) What is unreasonable about the assumption?

Explain how an (particle can have a larger range in air than a (particle with the same energy in lead.

Integrated Concepts: (a) What temperature gas would have atoms moving fast enough to bring two 3He nuclei into contact? Note that, because both are moving, the average kinetic energy only needs to be half the electric potential energy of these doubly charged nuclei when just in contact with one another. (b) Does this high temperature imply practical difficulties for doing this in controlled fusion?

Large amounts of depleted uranium (238U)are available as a by-product of uranium processing for reactor fuel and weapons. Uranium is very dense and makes good counter weights for aircraft. Suppose you have a 4000-kg block of 238U . (a) Find its activity, (b) How many calories per day are generated by thermalization of the decay energy? (c) Do you think you could detect this as heat? Explain.