Nuclear Physics

The existence of the nucleus: Rutherford Experiment

Rutherford experiment• http://www.physics.upenn.edu/courses/gladney/phys351/classes/Scatteri

ng/Rutherford_Scattering.html• http://micro.magnet.fsu.edu/electromag/java/rutherford/• http://webphysics.davidson.edu/Applets/pqp_preview/contents/pqp_erra

ta/cd_errata_fixes/section4_7.html• http://www.nat.vu.nl/~pwgroen/sdm/hyper/anim/baan.html

Isotopes and Nuclides

http://en.wikipedia.org/wiki/Isotope_table_(complete)

http://ie.lbl.gov/education/isotopes.htm

Models of the nucleus

Liquid drop model

Alpha particle model

Non-central forceSpectroscopic model

Problem: which potential ??

Decay Law: Half lifeBlue 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

Units Gray [Gy] absorbed dose: energy deposited per unit mass of medium [J/kg]

Sievert [Sv] risk from ionizing radiationrad radiation absorbed doserem roentgen eq. mammal (to gauge bio effects)

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

SafetyAfter low to moderate radiation poisoning [1-6 Gy]

within hours nausea and vomitingdiarrheapossibly headache and fever

With increasing dose cognitive impairmentMortality 5-100%; above 6 Gy > 50%

Primary dangers: (whole body exposure)immunodeficiencydestruction of bone marrowshortage 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 20higher < 20

P > 2 MeV 2

a, fission fragments, heavy nuclei 20