1. 100 years of nuclear isomers:
then and now
• early years
• extreme cases
• applications
• recent observations
Phil Walker
University of Surrey, UK

2. τm τg 100 years “We can have isotopes with identity
Isomer prediction: Soddy, Nature 99 (1917) 433
“We can have isotopes with identity
of atomic weight, as well as of chemical
character, which are different in their
stability and mode of breaking up.”
isomeric state τm
α β γ
ground state
Frederick Soddy τg
α β

3. τm τg 100 years “We can have isotopes with identity
Isomer prediction: Soddy, Nature 99 (1917) 433
“We can have isotopes with identity
of atomic weight, as well as of chemical
character, which are different in their
stability and mode of breaking up.”
234Pa, 1.2 min
6.7 h
Hahn, Ber. Deutsch. Chem. Ges.
B54 (1921) 1131
isomeric state τm
α β γ
ground state
Frederick Soddy τg
α β

4. τm τg 100 years “We can have isotopes with identity
Isomer prediction: Soddy, Nature 99 (1917) 433
“We can have isotopes with identity
of atomic weight, as well as of chemical
character, which are different in their
stability and mode of breaking up.”
234Pa, 1.2 min
6.7 h
Hahn, Ber. Deutsch. Chem. Ges.
B54 (1921) 1131
isomeric state τm
α β γ
Gamov, Phys. Rev. 45 (1934) 728
ground state
Frederick Soddy τg
α β

5. τm τg 100 years “We can have isotopes with identity
Isomer prediction: Soddy, Nature 99 (1917) 433
“We can have isotopes with identity
of atomic weight, as well as of chemical
character, which are different in their
stability and mode of breaking up.”
234Pa, 1.2 min
6.7 h
Hahn, Ber. Deutsch. Chem. Ges.
B54 (1921) 1131
isomeric state τm
α β γ
Gamov, Phys. Rev. 45 (1934) 728
1935: “excessive numbers
of half-lives”
ground state
Frederick Soddy τg
n bombardments of indium:
Szilard and Chalmers
Nature 135 (1935) 98
α β
n bombardments of bromine
Kurtchatov et al., Comptes
Rendus 200 (1935) 1201

6. τm τg 100 years “We can have isotopes with identity
Isomer prediction: Soddy, Nature 99 (1917) 433
“We can have isotopes with identity
of atomic weight, as well as of chemical
character, which are different in their
stability and mode of breaking up.”
explanation:
von Weizsäcker,
Naturwissenshaften
24 (1936) 813
spin doctor at age 24
isomeric state τm
importance of
spin
α β γ
ground state
Carl von Weizsäcker
Frederick Soddy τg
α β

7. Von Weizäcker, in a theoretical textbook published [earlier] in
Weart, 1983*:
Von Weizäcker, in a theoretical textbook published [earlier] in
1936, declared that isomers “in fact do not seem to occur”.
* S.R. Weart in “Discovery of nuclear fission”, contribution to “Otto Hahn and the
Rise of Nuclear Physics”, W.R. Shea (Ed.), D. Reidel Publishing Company, 1983
(University of Western Ontario Series in Philosophy of Science, Vol. 22)
See also: M. Mladjenović, The Defining Years of Nuclear Physics, ’s
(IoP Publishing, Bristol 1998)

8. 80Br Bethe (Rev. Mod. Phys. 9 (1937) 69)
“The best established case … is a radioactive nucleus formed in
bromine by capture of slow neutrons”
80Br
Bethe (Elementary Nuclear
Theory, Wiley, 1947, p.13):
“In* was the first observed [isomer]”
Kurtchatov et al., Comptes Rendus 200 (1935) 1201
Amaldi et al., Ricerca Scientifica 61 (1935) 581
Grinberg, Sov. Phys. Usp. 23 (1980) 848

9. isomer and fission timeline
1917: Soddy predicts existence of isomers
1921: Hahn’s discovery: UZ, UX2 (234m,gPa, 1.2 min, 6.7 h)
1932: Chadwick discovers neutrons
1935: isomers observed in indium and bromine
1936: von Weizsäcker explains isomers as spin traps
1938: Hahn identifies barium from neutrons on uranium
1939: Meitner and Frisch explain Hahn’s discovery: fission
“The whole ‘fission’ process can thus be
described in an essentially classical way ...”
“… it might not be necessary to assume
nuclear isomerism”.
Meitner and Frisch,
Nature, Feb 1939
Otto Hahn
discoverer of
isomers and fission
Lise Meitner
“mother of
nuclear structure”

10. isomer comments isomers nowadays: T1/2 > 1 ns (?)
“The prevalence of isomerism towards the end of a shell … is easily understood …
These are the regions where levels with very different spins are adjacent.”
Goeppert-Mayer, Phys. Rev. 75 (1949) 1969
“Isomeric states are distinguished from ordinary excited states of nuclei
by the fact that they have lifetimes measurable with present techniques”
Goldhaber and Sunyar in: Siegbahn, “Beta and Gamma-ray Spectroscopy”
(North Holland, Amsterdam, 1955) p.453
isomers nowadays: T1/2 > 1 ns (?)
The possibility to separate isomers in time and/or space, from the other products
of nuclear reactions, gives them an experimental status akin to ground states,
except that isomers can also decay by γ-ray (and conversion electron) emission.

11. 240,242,244Cm fission isomers T1/2 = 10±3 ps 240Cm
Sletten et al., Phys. Lett. B60 (1976) 153

12. Nuclear isomers: energy traps
excited state half-lives ranging from nanoseconds to years
Walker and Dracoulis, Nature 399 (1999) 35

13. Shape isomers – e.g. fission isomers
242Am, 14 ms (first, as well as longest lived)
Polikanov et al., JETP (Sov. Phys.) 42 (1962) 164
Spin isomers: first examples: 234Pa, 115In, 80Br
longest lived: 180Ta, 9-, > 4.5x1016 y
Lehnert et al. Phys. Rev. C95 (2017)
K isomers: 180Hf, 5.5 h [190Os, 10 min] first examples
Burson et al., Phys. Rev. 83 (1951) 62 [Chu, Phys. Rev. 79 (1950) 582]
theory: Alaga et al., Mat. Fys. Medd. Dan. Vid. Selsk. 29 (1955) No. 9*
longest lived: 178Hf, 16+, 31 y, Helmer and Reich, Nucl. Phys. A211 (1973) 1
* degree of K-forbiddenness, ν = ΔK - L

14. > 10 ns
energy
MeV
Jain et al., Nucl. Data Sheets 128 (2015) 1

15. nuclear chart with >1 MeV isomers
recent isomer reviews:
high-K
Walker & Xu: Phys. Scr. 91 (2016)
Kondev et al., ADNDT (2015) 50
A ≥ 150
Dracoulis et al., Rep. Prog. Phys. 79 (2016)
adapted from Walker and Dracoulis, Nature 399 (1999) 35

16. Extreme isomers decay rates vary over at least 32 orders of magnitude
long half-life: Ta, 9–, 75 keV, >4.5x1016 y
high spin: Rn, 38+, 12.5 MeV*, 8 ns
high energy: Er, MeV*, 11 ns
low energy: Th, 3/2+, 8 eV, μs
low mass: Be, 0+, MeV, 230 ns
high mass: Ds, 10–, 1 MeV, ms
PRC 2017
PLB 2008
PRC 1992
PRL 2017
PLB 2010
EPJA 2001
decay rates vary over at least 32 orders of magnitude
* unbound to both p and n emission

17. 99mTc: an isomer in the clinic
99mTc 6 hours
1/2-
2 keV
7/2+
α = 1010
141 keV
α = 0.1
9/2+
99gTc
200,000 years

18. 180mTa Iπ keV t1/2 > 4.5 x 1016 y Lehnert et al. Phys. Rev. C95
(2107)
180mTa
t1/2 > 4.5 x 1016 y
Nature’s only naturally
occurring isomer
Nature’s rarest
“stable” isotope
Iπ keV J
[Belic et al.,
Phys. Rev. C65
(2002) ]

19. 180Ta 180Ta photoexcitation and decay 10+ 9+ 8+ 7+
Belic et al., Phys. Rev. C65 (2002)
1430 6+
1220
(γ,γ') 5+
1010 4+
Kπ = 4+
Kπ = 5+ 3+
isomer
>1016 yr 9–
180Ta 75 2+
ground state
8 hr 1+
Kπ = 9–
Kπ = 1+
Walker, Dracoulis and Carroll, Phys. Rev. C64 (2001) (R)

20. Prediction of accelerated 93Mo isomer decay in a plasma
based on nuclear excitation by electron capture (NEEC)
7 h
93Mo in a plasma
93mMo
30 ms
Gosselin et al., Phys. Rev. C70 (2004) ; C76 (2007)

21. 53mCo proton decay (1.56 MeV protons)
first example of proton radioactivity
247 ms p
1.5% β+
240 ms
Jackson et al., Phys. Lett. B33 (1970) 281

22. neutron radioactivity
unique to isomers? n
high-spin isomer
threshold
A – 1 + n gs A β
candidate 19/2- isomer predicted in 129Pd
Yuan et al., Phys. Lett. B762 (2016) 237

23. recent isomer data a variety of examples

24. 213Bi: new isomer in the Experimental Storage Ring at GSI
238U fragmentation
● first observation of this isomer
● single ion with γ decay
Schottky mass spectrometry
Nushell calculation (E. Simpson):
25/2ˉ isomer at 1.38 MeV
γ decay
1.353(21) MeV
Chen et al., Nucl. Phys. A882 (2012) 71

25. 188Pb106 triple-isomer shape coexistence82
oblate spherical prolate
spectroscopy (ANU Canberra)
Dracoulis et al. Phys. Rev. C69 (2004)
time-differential perturbed angular distributions (Legnaro)
Ionescu-Bujor et al., Phys. Rev. C81 (2010)

26. 172Dy106 Kπ = 8- isomer γ rays conversion electrons T1/2 = 0.71 s 66
Watanabe et al.,
Phys. Lett. B760 (2016) 641 66
RIKEN data: BigRIPS+EURICA_WAS3ABi

27. mid-shell → closed shell
N = 106, Kπ = 8- isomers:
mid-shell → closed shell
0.7 s
Z =
Dracoulis, Walker and Kondev, Rep. Prog. Phys. 79 (2016)

28. 177Hf: on-line low-temperature nuclear orientation at ISOLDE
Kπ = 37/2-
μ = 7.33(9) μN
=> gR = 0.21(4) gR
Muto et al.,
Phys. Rev. C89 (2014)
Np - Nn
Stone et al., Phys. Lett. B726 (2103) 675

29. Hf charge radii and moments from laser resonance fluorescence
Boos et al.,
Phys. Rev. Lett.
72 (1994) 2689
Z = 72 (hafnium) gs
4-s isomer
(4 s)
(31 y)
Jyväskylä IGISOL
Bissell et al., Phys. Lett. B645 (2007) 330

30. TRS calculations for n-rich hafnium isotopes
n-rich Hf: E vs I
182Hf
186Hf
oblate collective
Xu et al., Phys. Rev. C62 (2000)
prolate
collective
configuration constrained
prolate high-K
Data for 180Hf: Tandel et al. Phys. Rev. Lett. 101 (2008)

31. summary 100 years of nuclear isomers: 10 ps → 1016 y 8 eV → 13 MeV
decay modes: α, β, γ, fission, proton
(but not yet neutron decay)
shape isomers
spin isomers
K isomers
→ single-ion sensitivity
→ moments, radii
→ competition from oblate collective rotation
access to excited states in exotic nuclei

32. summary and special thanks to George Dracoulis
100 years of nuclear isomers: 10 ps → 1016 y
8 eV → 13 MeV
I = 0 → 38 ħ
decay modes: α, β, γ, fission, proton
(but not yet neutron decay)
shape isomers
spin isomers
K isomers
→ single-ion sensitivity
→ moments, radii
→ competition from oblate collective rotation
access to excited states in exotic nuclei
and special thanks to George Dracoulis