Nuclear and Radiation Physics, BAU, 1 st Semester, (Saed Dababneh). 1 Nuclear Mass Unified atomic mass unit u based on 12 C. Replaced both physical and chemical amu based on 16 O and natural oxygen, respectively (Find conversion factors). 1 u = M( 12 C)/12 = ……… kg = …………… MeV/c 2. Rest masses uMeV/c 2 kg electron ………… …………… ……… proton ………… …………… ……… neutron ………… …………… ……… 12 C12 …………… ……… Avogadros number ….. !! Mass Stability. E = mc 2. Tendency towards lower energy Radioactivity. Neutron heavier than proton Free neutron decays (T ½ = ???):

Nuclear and Radiation Physics, BAU, 1 st Semester, (Saed Dababneh). 2 Nuclear Mass Nuclear masses measured to high accuracy: mass spectrograph. energy measurement in nuclear reactions. Mass decrement = difference between actual mass and mass number: Δ = m – A Negative Δ mass into energy. Binding Energy? Stability? Fission? Fusion? More later …….. Usually atomic masses are tabulated. Mass of the atom < Zm H + Nm n.

Nuclear and Radiation Physics, BAU, 1 st Semester, (Saed Dababneh). 3 The Valley of Stability

Nuclear and Radiation Physics, BAU, 1 st Semester, (Saed Dababneh). 4 Nuclear Size Different experiments give different results Radius not well defined. Depends on probe and relevant physics. Probes should be of the same order of the size of the nucleus ~ m. Visible light? much larger. 1 MeV ? = 1.2 x m. But interacts with orbital electrons. Suitable probes: p, n,, e, X.Charge distribution. Mass distribution. All experiments agree qualitatively and somehow quantitatively. Project …. R A Why? In a while …… R = r 0 A with r 0 dependent on the method. Matter distribution charge distribution. [Recently some halo nuclei, e.g. 11 Li, found]. What is that?

Nuclear and Radiation Physics, BAU, 1 st Semester, (Saed Dababneh). 5 Nuclear Size 0 = nucleon density near the center. t = skin thickness. a = thickness parameter. R = Half-density radius. HW 4 Experiments show that t = (2.4 ± 0.3) fm for all nuclei t / R A -1/3 Is surface effect the same for all nuclei? HWc 2 Compare for A = 4, 40, 120 and 235.

Nuclear and Radiation Physics, BAU, 1 st Semester, (Saed Dababneh). 6 Nuclear Size High-energy e scattering Light nuclei? Constant R A From some experiments….! Charge distribution: r 0 = 1.07 fm. a = 0.55 fm. Matter distribution: r 0 = 1.25 fm. a = 0.65 fm. R = r 0 A 0 decreases with A? YesNo

Nuclear and Radiation Physics, BAU, 1 st Semester, (Saed Dababneh). 7 Nuclear Size HW 5 Nucleus Z/ACharge density 40 Ca ….. ….. 59 Co ….. … In ….. … Au ….. ….. Charge radius nuclear radius, even though heavy nuclei have more neutrons than protons. Explain… Density of ordinary atomic matter ~ 10 3 kg/m 3. Density of nuclear matter ~ 3 ×10 17 kg/m 3. Neutron stars, 3 solar masses, only 10 km across ….. !!! Surface effect?

Nuclear and Radiation Physics, BAU, 1 st Semester, (Saed Dababneh). 8 Nuclear Size Neutron Detector 1 Ci Pu-Be Neutron Source Absorber Beam From Optical Model Preferably low Different targets

Nuclear and Radiation Physics, BAU, 1 st Semester, (Saed Dababneh). 9 Nuclear Size Alpha particle (+2e) Gold nucleus (+79e) d

Nuclear and Radiation Physics, BAU, 1 st Semester, (Saed Dababneh). 10 Nuclear Size Closest approach d. E = E Coulomb d = 2kZe 2 /E What about the recoil nucleus? HW 6 HW 6 Show that where m N : mass of the nucleus m : mass of alpha What are the values of d for 10, 20, and 30 MeV on Au?

Nuclear and Radiation Physics, BAU, 1 st Semester, (Saed Dababneh). 11 Nuclear Shape Crude Nucleons in the nucleus are confined to an approximately spherically symmetric structure Nuclear radius. Deformations…! Consequences….!! Is there a sharp spherical wall…???!!! HW 7 if it is assumed that the charge is uniformly spherically distributed in a nucleus, show that the electric potential energy of a proton is given by: