Nuclear Size Depends on probe and relevant physics.

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Presentation transcript:

Nuclear Size Depends on probe and relevant physics. Different experiments give different results  Radius not well defined. Depends on probe and relevant physics. Probes should be close to the order of the size of the nucleus ~ 10-14 m. Visible light?  much larger. 1 MeV ?  = ?? 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  A⅓ Why? In a while …… R = r0 A⅓ with r0 dependent on the method. Matter distribution  charge distribution. [Recently some halo nuclei, e.g. 11Li, found]. What is that? Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

Nuclear Size HW 4 HWc 3 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 3 Compare for A = 4, 40, 120 and 235. 0 = nucleon density near the center. t = “skin” thickness. a = thickness parameter. R = Half-density radius. Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

Nuclear Size R = r0 A⅓ Why? 0 decreases with A? No Yes High-energy e scattering Constant  R  A⅓ Light nuclei? From some experiments….! Charge distribution: r0 = 1.07 fm. a = 0.55 fm. Matter distribution: r0 = 1.25 fm. a = 0.65 fm. R = r0 A⅓ Why? Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

Nuclear Size 40Ca ….. ….. 59Co ….. ….. 115In ….. ….. 197Au ….. ….. HW 5 Nucleus Z/A Charge density 40Ca ….. ….. 59Co ….. ….. 115In ….. ….. 197Au ….. ….. Charge radius ~ nuclear radius, even though heavy nuclei have more neutrons than protons. Explain… Density of ordinary atomic matter ~ 103 kg/m3. Density of nuclear matter ~ 1017 kg/m3. Neutron stars, 3 solar masses, only 10 km across ….. !!! Surface effect? Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

Short range of nuclear force Nuclear Size Three conclusions can be drawn: Inside the nucleus the density is fairly uniform. The transitional surface layer is thin. The central density has a similar value for different nuclei. Liquid Drop Short range of nuclear force Saturation? Get an estimate for nuclear density and thus inter-nucleon distance. Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

Nuclear Size HW 6 How can we get r0 from the graph? 1 Ci Pu-Be Neutron Source Neutron Detector Absorber Beam From Optical Model Dimensions Different targets HW 6 How can we get r0 from the graph? Preferably low  Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

Nuclear Size Quite old!!! Not exactly for Au!!! Alpha particle (+2e) Gold nucleus (+79e) d Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

Nuclear Size Closest approach “d”. E = ECoulomb  d = 2kZe2/E What about the recoil nucleus? HW 7 Show that where mN : mass of the nucleus m : mass of alpha What are the values of d for 10, 20, 30 and 40 MeV  on Au? How does this explain … ? Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

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 8 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: Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).