Nuclear Physics

The existence of the nucleus: Rutherford Experiment

Rutherford experiment http://www.physics.upenn.edu/courses/gladney/phys351/classes/Scattering/Rutherford_Scattering.html http://micro.magnet.fsu.edu/electromag/java/rutherford/ http://webphysics.davidson.edu/Applets/pqp_preview/contents/pqp_errata/cd_errata_fixes/section4_7.html http://www.nat.vu.nl/~pwgroen/sdm/hyper/anim/baan.html

Empirical findings of properties of nuclei

Isotopes and Nuclides http://en.wikipedia.org/wiki/Isotope_table_(complete) http://ie.lbl.gov/education/isotopes.htm

Stability diagram nuclei

Binding energy per nucleon

Complexity ~ nuclear is thy name

Models of the nucleus Liquid drop model

Alpha particle model

Non-central force Spectroscopic model Problem: which potential ??

Decay Law: Half life Blue Stable elements;   Green   Radioactive elements with very long-lived isotopes. Their half-live of over four million years confers them very small, if not negligible radioactivities;      Yellow Radioactive elements that may present low health hazards. Their most stable isotopes have half-lives between 800 and 34.000 years. Because of this, they usually have some commercial applications;       Orange Radioactive elements that are known to pose high safety risks. Their most stable isotopes have half-lifes between one day and 103 years. Their radioactivities confers them little potential for commercial uses;       Red Highly radioactive elements. Their most stable isotopes have half-lifes between one day and several minutes. They pose severe health risks. Few of them receive uses outside basic research;      Purple  Extremely radioactive elements. Very little is known about these elements due to their extreme instability and radioactivity.

. Penetration Depth The energy of radiation is typically measured in MeV, mega electronvolt: If a beam of photons with intensity I0 traverses a layer of material of thickness x, the intensity emerging from the layer is where m is called the linear absorption coefficient. It is related to the cross section s for photon absorption by where NA is Avogadro’s constant and r is the density of the material.

Radioactivity a, b, g decay

Natural clocks:

137Cs , 60Co – case studies in the advanced lab

Fusion and Fission

Fast breeder

The search for artificial elements

Radioactivity and Health The number of radioactive nuclei of an isotope varies in radioactive decay according to where N is the number of nuclei at t=0, N0 the remaining number at t, and l is the decay constant. T1/2 is the half-life, the time from t=0 when half the original nuclei remain. a, b, g decay Units Gray [Gy] absorbed dose: energy deposited per unit mass of medium [J/kg] Sievert [Sv] risk from ionizing radiation rad radiation absorbed dose rem roentgen eq. mammal (to gauge bio effects)

Safety After low to moderate radiation poisoning [1-6 Gy] within hours nausea and vomiting diarrhea possibly headache and fever With increasing dose cognitive impairment Mortality 5-100%; above 6 Gy > 50% Primary dangers: (whole body exposure) immunodeficiency destruction of bone marrow shortage of white blood cells

Weighting factors WR for equivalent dose: how dangerous are types of radiation? Radiation Energy wR x-ray, g-ray, e-, e+, m 1 n < 10 keV 5 < 100 keV 10 < 2 MeV 20 higher < 20 P > 2 MeV 2 a, fission fragments, heavy nuclei 20