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Nuclear and Radiation Physics, BAU, 1 st Semester, 2006-2007 (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 = ???):

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Nuclear and Radiation Physics, BAU, 1 st Semester, 2006-2007 (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 http://www.eas.asu.edu/~holbert/eee460/massdefect.html 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.

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Nuclear and Radiation Physics, BAU, 1 st Semester, 2006-2007 (Saed Dababneh). 3 The Valley of Stability

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Nuclear and Radiation Physics, BAU, 1 st Semester, 2006-2007 (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 ~ 10 -14 m. Visible light? much larger. 1 MeV ? = 1.2 x 10 -12 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?

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Nuclear and Radiation Physics, BAU, 1 st Semester, 2006-2007 (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.

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Nuclear and Radiation Physics, BAU, 1 st Semester, 2006-2007 (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

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Nuclear and Radiation Physics, BAU, 1 st Semester, 2006-2007 (Saed Dababneh). 7 Nuclear Size HW 5 Nucleus Z/ACharge density 40 Ca ….. ….. 59 Co ….. ….. 115 In ….. ….. 197 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?

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Nuclear and Radiation Physics, BAU, 1 st Semester, 2006-2007 (Saed Dababneh). 8 Nuclear Size Neutron Detector 1 Ci Pu-Be Neutron Source Absorber Beam From Optical Model Preferably low Different targets

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Nuclear and Radiation Physics, BAU, 1 st Semester, 2006-2007 (Saed Dababneh). 9 Nuclear Size Alpha particle (+2e) Gold nucleus (+79e) d

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Nuclear and Radiation Physics, BAU, 1 st Semester, 2006-2007 (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?

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Nuclear and Radiation Physics, BAU, 1 st Semester, 2006-2007 (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:

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