Phys 115 1st Edition Lecture 23Outline of Last Lecture I. PhotonsII. Quantum StatesIII. AbsorptionIV. FluorescenceV. PhosphorescenceVI. BioluminescenceOutline of Current Lecture I. Nuclear structureII. Nuclear stabilityIII. Forces and energy in the nucleusIV. Radiation and radioactivityV. Nuclear decay and half-livesCurrent Lecture- Nuclear Structureo The nucleus is composed of protons and neutrons. o Together they are referred to as nucleons.- Nuclear Structureo Each element is characterized by its atomic number, Z, which indicates the number of protons in the nucleus.o Isotopeso Elements which have the same atomic number, Z, but different mass numbers, A, are referred to as isotopes.- Classroom Response Question 1o The isotope 3He has _____ neutronso A: 0o B: 1o C: 2o D: 3o E: 4- Atomic Mass- Atomic masses are specified in terms of the atomic mass unit u, defined such that the atomic mass of isotope 12C is exactly 12u.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- 1 u = 1.6605 x 10-27 kg- We can used Einstein’s energy and mass equivalence equation (E = mc2) to determine the energy equivalent of 1 u of mass: - Atomic Masso We can write 1 u in the following form as well:o MeV/c2 are units of mass. The energy equivalent of 1 MeV/c2 is 1 MeV.- Atomic Masso In calculations of nuclear energies, you should use more significant figures than usual, and should use the accurate values given in table 30.2 and appendix D.- Binding Energyo The nuclear binding energy is computed by considering the mass difference between the atom and its separate components, Z hydrogen atoms and N neutrons.- Classroom Response Question 2o What is the binding energy per nucleon for 40Ar? Z = 18, mass(u) = 39.962384.o A: 0.369 MeVo B: 8.60 MeVo C: 115 MeVo D: 344 MeVo E. 441 MeV- Forces and energy in the nucleuso The strong nuclear force is the force that keeps the nucleus together.o It is an attractive force between any two nucleons.o It does not act on electrons. o It is a short-range force, acting only over nuclear distances. o Over the range where it acts, it is stronger than the electrostatic force that tries to push two protons apart.- Forces and energy in the nucleuso A nucleus with too many protons will be unstable because the repulsive electrostatic forces will overcome the attractive strong forces.o Because neutrons participate in the strong force but exert no repulsive forces, the neutrons provide the extra “glue” that holds the nucleus together.- Forces and energy in the nucleuso Protons and neutrons have quantized energy levels like electrons.o The proton and neutron energy levels are separated by a million times more energy than the energy separation of electron energy levels.- Low-Z nuclei- Classroom Response Question 3o Match the diagrams below, with the choices, a nuclear ground state, an excited nuclear state, or an impossible nucleus.- Low-Z nucleio12B and 12N could lower their energies if a neutron could turn into a proton or viceversa.- Nuclear Stability- Alpha Decayo When a large nucleus spontaneously decays by breaking into two smaller fragments, one of the fragments is almost always a stable 4He nucleus – an alpha particle (α)o An unstable nucleus that ejects an alpha particle loses two protons and two neutrons, so we write the decay as:o Alpha Decayo The original nucleus X is called the parent nucleus and the decay-product nucleus Y is the daughter nucleus.- Beta Decayo In beta decay, a nucleus decays by emitting an electron.o The neutron changes itself into a proton by emitting an electron. o The electron is ejected from the nucleus but the proton is not. The beta-decay process iso Beta decays occurs only if mX>mY.- Beta Decayo Some nuclei emit a positron. A positron, e+, is identical to an electron except that it has a positive charge. It is the antiparticle of the electron.o To distinguish between two forms of beta decay, we call the emission of an electron beta-minus decay and the emission of a positron beta-plus decay.- Gamma Decayo Gamma decay occurs when a proton or neutron undergoes a quantum jump.- Classroom Response Question 4o Is 238Pu 236U  a possible decay mode?o A: Yeso B: Noo C: It depends on the energy of the alpha particle.- Classroom Response Question 5o What is the daughter nucleus for the following decay?o90Sr ?X + e–o A: 90Yo B: 89Yo C: 90Rbo D: 89Rb- Nuclear Decay and Half-Liveso If you start with N0 unstable nuclei, after an interval of time called the half-life, you will have ½ N0 nuclei remaining.o The half-life t½is the average time required for one-half the nuclei to decay.o The number of nuclei N remaining at time t is - Nuclear Decay and Half-Liveso The figure shows the decay of a sample of radioactive nuclei.o The decay of radioactive nuclei is an exponential decay.o The equation for the number of atoms after a half-life can be written in terms of a time constant τ that is related to the half-life:- Classroom Response Question 6o A sealed box is completely evacuated (perfect vacuum), then 1,000,000 radioactive atoms are added. Their half-life is 2 days. After 4 days have passed, how many atoms are in the box?o A: 1,000,000o B: 500,000o C: 250,000o D: 0- Classroom Response Question 7o Patients with Graves disease have an overactive thyroid gland. A common treatment uses radioactive iodine, which is taken up by the thyroid. The radiationemitted in its decay will damage the tissues of the gland. A single pill is produced with 4.0  1014 atoms of the isotope 131I, which has a half-life of 8.0 days.o How many atoms remain 24 hours after the pill’s creation?- Classroom Response Question 8o Patients with Graves disease have an overactive thyroid gland. A common treatment uses radioactive iodine, which is taken up by the thyroid. The radiationemitted in its decay will damage the tissues of the gland. A single pill is produced with 4.0  1014 atoms of the isotope 131I, which has a half-life of 8.0 days.o Although the iodine in the pill is constantly decaying, it is still usable as long as it contains at least 1.1  1014131I atoms. What is the maximum delay before the pill is no longer usable?- Activityo The activity of a radioactive sample is the number of decays per second. Each decay corresponds to an alpha, beta, or gamma emission.o The activity of a sample N nuclei with a time constant