1. Nuclear Spectroscopy: From Natural Radioactivity to Studies of the Most Exotic Isotopes.
Prof. Paddy Regan
Department of Physics
University of Surrey, Guildford,
&
Radioactivity Group,
National Physical Laboratory,
Teddington

2. Outline of talk Elements, Isotopes and Isotones
Alpha, beta and gamma decay
Primordial radionuclides…..why so long ?
Internal structures, gamma rays and shells.
How big is the nuclear chart ?
What could this tell us about nucleosynthesis?

4. Darmstadtium
Copernicium
Roentgenium 4

5. •ATOMS ~ 10-10 m •NUCLEI ~ 10-14 m •NUCLEONS-10-15 m •QUARKS ~?
The Microscopic World…
•ATOMS ~ m
•NUCLEI ~ m
•NUCLEONS m
•QUARKS ~?

7. Nuclear Isotopes
Mass Spectrograph (Francis Aston 1919)
Atoms of a given element are ionized.
The charged ions go into a velocity selector
which has orthogonal electric (E) and magnetic
fields (B) set to exert equal and opposite forces
on ions of a particular velocity → (v/B) = cont.
The magnet then separates the ions according
to mass since the bending radius is
r = (A/Q) x (v/B) Q = charge of ion &
A is the mass of the isotope
Not all atoms of the same chemical element have the same mass (A)
Frederick Soddy (1911) gave the name isotopes.
(iso = same ; topos = place).
0.4%
Results for natural terrestrial krypton
Krypton, Z=36
N =

8. Nuclear chart 8

9. Atomic Masses and Nuclear Binding Energies
M(Z,A) = mass of neutral atom of element Z and isotope A
The binding energy is the
energy needed to take a nucleus of Z protons and N neutrons apart into A separate nucleons
M(Z,A) m ( 11H ) + Nmn - Bnuclear
energy
Mass of Z protons
+ Z electrons + N
neutrons (N=A-Z)
= binding energy
(nuclear + atomic)
Mass of neutral atom
 MeV
 eV

10. increasing Z →
increasing Z →
A=125, odd-A
even-Z, odd-N
or odd-Z, even N
A=128, even-A
even-Z, even-N
or odd-Z, odd- N
increasing binding energy = smaller mass
125Sn,
Z=50,
N=75
125Xe,
Z=54,
N=71
ISOBARS have different combinations of protons (Z) and neutrons (N) but same total nucleon number, A → A = N + Z.
(Beta) decays occur along ISOBARIC CHAINS to reach the most energetically favoured Z,N combination. This is the ‘stable’ isobar.
This (usually) gives the stable element for this isobaric chain A=125, stable isobar is 125Te (Z=52, N=73); Even-A usually have 2 long-lived.

11. A=137 Mass Parabola Mass (atomic mass units) 137Xe83 137Ba81 137Cs82
Nucleus can
be left in an
excited
configuration.
Excess energy
released by
Gamma-ray
emission.
b - decay: 2 types:
1) Neutron-rich nuclei (fission frags)
n → p + b- + n
2) Neutron-deficient nuclei (18F PET)
p → n + b+ + n

12. Some current nuclear physics questions
286 combinations of protons and neutrons are either stable or have decay half-lives of more than 500 million years.
What are the limits of nuclear existence…i.e. how many different nuclear species can exist?
N/Z ratio changes for stable nuclei from ~1:1 for light nuclei (e.g., 16O, 40Ca) to ~1.5 for 208Pb (126/82 ~ 1.5)
How does nuclear structure change when the N/Z ratio differs from stable nuclear matter?

13. Accelerator facility at GSI-Darmstadt
The Accelerators:
UNILAC (injector) E=11.4 MeV/n
SIS 18Tm corr. U 1 GeV/n
Beam Currents:
238U pps
some medium mass nuclei pps
(A~130)
FRS provides secondary radioactive ion beams:
fragmentation or fission of primary beams
high secondary beam energies: 100 – 700 MeV/u
fully stripped ions

14. An Efficient Way to Make Exotic Nuclei: Projectile Fragmentation Reaction Process
Ablation
Formation of an exotic compound nucleus
Reaction products travelling at Relativistic Energies
Abrasion
Beam at Relativistic Energy ~0.5-1 GeV/A
Target Nucleus
FIREBALL

15. Dream of every student to press a button and level scheme pop out

18. A few physics examples….

19. b+ decay/ec
b- decay

21. How are the heavy elements made ?
Is it via the Rapid Neutron Capture (R-) Process ?
205Au126
T1/2 = 10.4 s
K-electrons
L-electrons
202Pt
Many of the nuclei which lie on the r-process
predicted path have yet to be studied.
Do these radioactive nuclei act as we expect ?

22. SN1987a before and after !!

24. A (big!) problem, can’t reproduce the observed elemental abundances.
We can ‘fix’ the result by changing the shell structure (i.e. changing
the magic numbers)….but is this scientifically valid ?
N=82
N=126
Need to look at N=82 and 126 ‘exotic’ nuclei in detail….

25. Even-Even Nuclei Excited states spin/parities depend
Excitation energy
(keV)
Ground state (Ex=0)
config has Ip=0+ ; 2+ 0+
~2 D =
‘pair
gap’
Excited states spin/parities depend
on the nucleon configurations.
i.e., which specific orbits the
protons and neutrons occupy.
Result is a complex energy
‘level scheme’.
First excited state in (most)
even-N AND even-Z has Ip=2+

26. 2+ 0+ Excitation energy (keV) Ground state Configuration.
Spin/parity Ip=0+ ;
Ex = 0 keV
PHR, Physics World, Nov. 2011, p37

27. Is there evidence for a N=82 shell quenching ?
r-process abundances
exp.
pronounced shell gap
shell structure quenched
mass number A
Certainly all of you have seen this figure before. It shows the solar r-process abundances with the characteristic two peaks around mass 130 and 195 which are closely related to the N=82 respectively N=126 shell gaps. These gaps determine the properties of the waiting-point nuclei in the r-process path shown here as red squares and therefore the dynamics of the nucleosynthesis of elements above iron.
Already in the nineties it has been shown that the assumption of a N=82 shell quenching leads to a considerable improvement in the global abundance fit in r-process calculations, namely the filling of the troughs around A=120 and shown here in blue compared to the non-quenched calculation in green. However ...
Assumption of a N=82 shell quenching leads to a considerable
improvement in the global abundance fit in r-process calculations !

29. Search for the 8+ (g9/2)-2 seniority isomer in 130Cd
(structure should look lots like 98Cd…apart from size?)
two proton holes in the g9/2 orbit
g9/2
Since an 8+ seniority isomer based on two proton holes in the g9/2 orbit is expected to exist in 130Cd in complete analogy to the one known in 98Cd we decided to try to obtain independent experimental information about 130Cd using isomer spectroscopy within RISING.
M. Górska et al., Phys. Rev. Lett. 79 (1997)

30. Evidence for nuclear shell structure…
Evidence for nuclear shell structure….. energy of 1st excited state in even-even nuclei….E(2+).

31. Facility for Anti-Proton and Ion Research (FAIR)
To be constructed at the
current GSI site, near Darmstadt, Germany
Will bring currently ‘theoretical nuclear species’
into experimental reach for the first time.

32. Summary Radionuclides (e.g. 235U, 238U, 232Th, 40K) are everywhere.
Radioactive decays arise from energy conservation and other (quantum) conservation laws.
Characteristic gamma ray energies tell us structural info.
The limits for proton-richness in nuclei has been reached.
Neutron-rich nuclei are harder to make at the extremes, but we are starting to be able to reach r-process radionuclides.
Does the nuclear shell model remain valid for nuclei with ‘diffuse neutron skins’ ?
FAIR will increase dramatically our reach of nuclear species for experimental study