1. Lecture 4 ½
The end of the SEMF
9 Nov 2005, Lecture 4

2. 4.1 Overview 4.2 Shortcomings of the SEMF magic numbers for N and Z
spin & parity of nuclei unexplained
magnetic moments of nuclei
value of nuclear density
values of the SEMF coefficients
9 Nov 2005, Lecture 4

3. 4.2 Shortcomings of the SEMF
9 Nov 2005, Lecture 4

4. 4.2 Shortcomings of the SEMF (magic numbers in Ebind/A)
SEMF does not apply for A<20
There are deviations from SEMF for A>20
(2,2)
2*(2,2)
= Be(4,4)
Ea-a=94keV
(6,6)
(8,8)
(10,10)
(N,Z)
9 Nov 2005, Lecture 4

5. N Z
Neutron Magic
Numbers
4.2 Shortcomings of the SEMF (magic numbers in numbers of stable isotopes and isotones)
Proton
Magic
Numbers
Magic Proton Numbers (stable isotopes)
Magic Neutron Numbers (stable isotones)
9 Nov 2005, Lecture 4

6. 4.2 Shortcomings of the SEMF (magic numbers in separation energies)
Neutron separation energies
saw tooth from pairing term
step down when N goes across magic number at 82
Ba Neutron separation energy in MeV
9 Nov 2005, Lecture 4

7. 4.2 Shortcomings of the SEMF (abundances of elements in the solar system)
Z=50
N=82
Z=82
N=126
iron mountain
Complex plot due to dynamics of creation, see lecture on nucleosynthesis
no A=5 or 8
9 Nov 2005, Lecture 4

8. 4.2 Shortcomings of the SEMF (other evidence for magic numbers)
Nuclei with N=magic have abnormally small n-capture cross sections (they don’t like n’s)
First excitation energy
Close to magic numbers nuclei can have “long lived” excited states (tg>O(10-6 s) called “isomers”. One speaks of “islands of isomerism” [Don’t make holydays there!]
208Pb
9 Nov 2005, Lecture 4

9. 4.2 Shortcomings of the SEMF (others)
spin & parity of nuclei do not fit into a drop model
magnetic moments of nuclei are incompatible with drops
value of nuclear density is unpredicted
values of the SEMF coefficients except Coulomb and Asymmetry are completely empirical
9 Nov 2005, Lecture 4

10. End of Lecture 4
9 Nov 2005, Lecture 4