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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 u MeV/c 2 kg

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nuclear mass
Nuclear Mass
  • Unified atomic mass unit u based on 12C.
  • Replaced both physical and chemical amu based on 16O and natural oxygen, respectively (Find conversion factors).
  • 1 u = M(12C)/12 = ……… kg = …………… MeV/c2.
  • Rest masses
  • u MeV/c2 kg
  • electron ………… …………… ………
  • proton ………… …………… ………
  • neutron ………… …………… ………
  • 12C 12 …………… ………
  • Avogadro’s number ….. !!
  • Mass  Stability. E = mc2.Tendency towards lower energy  Radioactivity.
  • Neutron heavier than proton  “Free” neutron decays (T½ = ???):

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

nuclear mass1
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 < ZmH + Nmn.

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

the valley of stability
The Valley of Stability

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

nuclear size
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  A⅓Why? In a while ……
  • R = r0 A⅓with 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, 1st Semester, 2006-2007 (Saed Dababneh).

nuclear size1
Nuclear Size

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?

0 = nucleon density near the center.

t = “skin” thickness.

a = thickness parameter.

R = Half-density radius.

HWc 2

Compare for A = 4, 40, 120 and 235.

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

nuclear size2
Nuclear Size

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

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

nuclear size3
Nuclear Size

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
  • ~ 3 ×1017 kg/m3.
  • Neutron stars, 3 solar masses, only 10 km across ….. !!!
  • Surface effect?

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

nuclear size4
Nuclear Size

1 Ci Pu-Be Neutron Source

Neutron

Detector

Absorber

Beam

From Optical Model

Different

targets

Preferably low 

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

nuclear size5
Nuclear Size

Alpha particle (+2e)

Gold nucleus (+79e)

d

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

nuclear size6
Nuclear Size
  • Closest approach “d”.
  • E = ECoulomb d = 2kZe2/E
  • What about the recoil nucleus?
  • HW 6Show that
  • where mN : 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, 1st Semester, 2006-2007 (Saed Dababneh).

nuclear shape
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:

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

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