100 years of nuclear isomers: then and now

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

2. 100 years 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. 100 years 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. 100 years 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. 100 years 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. 100 years 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 importance of spin τm α β γ ground state Carl von Weizsäcker Frederick Soddy τg α β

7. 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, 1932-1960’s (IoP Publishing, Bristol 1998)

8. 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 “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) 044306 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) 013010 Kondev et al., ADNDT 103-104 (2015) 50 A ≥ 150 Dracoulis et al., Rep. Prog. Phys. 79 (2016) 076301 adapted from Walker and Dracoulis, Nature 399 (1999) 35

16. Extreme isomers PRC 2017 PLB 2008 PRC 1992 PRL 2017 PLB 2010 EPJA 2001 long half-life: 180Ta, 9–, 75 keV, >4.5x1016 y high spin: 212Rn, 38+, 12.5 MeV*, 8 ns high energy: 152Er, 13.4 MeV*, 11 ns low energy: 229Th, 3/2+, 8 eV, 7 μs low mass: 12Be, 0+, 2.2 MeV, 230 ns high mass: 270Ds, 10–, 1 MeV, 6 ms 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. Lehnert et al. Phys. Rev. C95 (2107) 044306 180mTa t1/2 > 4.5 x 1016 y Nature’s only naturally occurring isomer Nature’s rarest “stable” isotope 0 Iπ keV J [Belic et al., Phys. Rev. C65 (2002) 035801]

19. 180Ta photoexcitation and decay 10+ 9+ 8+ 7+ Belic et al., Phys. Rev. C65 (2002) 035801 1430 6+ 1220 (γ,γ') 5+ 1010 4+ Kπ = 4+ Kπ = 5+ 3+ isomer >1016 yr 9– 75 180Ta 2+ ground state 8 hr 1+ Kπ = 9– Kπ = 1+ Walker, Dracoulis and Carroll, Phys. Rev. C64 (2001) 061302(R)

20. Prediction of accelerated 93Mo isomer decay in a plasma 93Mo in a plasma based on nuclear excitation by electron capture (NEEC) 7 h 93mMo 30 ms Gosselin et al., Phys. Rev. C70 (2004) 064603; C76 (2007) 044611

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? high-spin isomer n 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 dataa 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 γdecay 1.353(21) MeV Chen et al., Nucl. Phys. A882 (2012) 71

25. 188Pb106 triple-isomer shape coexistence 82 oblate spherical prolate spectroscopy (ANU Canberra) Dracoulis et al. Phys. Rev. C69 (2004) 054318 time-differential perturbed angular distributions (Legnaro) Ionescu-Bujor et al., Phys. Rev. C81 (2010) 024323

26. conversion electrons γ rays T1/2 = 0.71 s 172Dy106Kπ = 8- isomer Watanabe et al., Phys. Lett. B760 (2016) 641 66 RIKEN data: BigRIPS+EURICA_WAS3ABi

27. N = 106, Kπ = 8- isomers: mid-shell → closed shell 0.7 s Z = 66 68 70 72 74 76 78 80 82 Dracoulis, Walker and Kondev, Rep. Prog. Phys. 79 (2016) 076301

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) 044309 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 Xu et al., Phys. Rev. C62 (2000) 014301 oblate collective prolate collective configuration constrained prolate high-K Data for 180Hf: Tandel et al. Phys. Rev. Lett. 101 (2008) 182503

31. summary 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

32. summary 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 1944-2014