Log ft values in Beta Decay

1. Log ft values in Beta Decay Filip G. Kondev kondev@anl.gov 2nd Workshop for DDEP Evaluators, Bucharest, Romania May 12-15,2008

2. Plenty of information available on the Web Some useful references Books • “Week interaction and nuclear beta decay”, H.F. Schopper, 1966 • “Handbook of nuclear spectroscopy”, J. Kantele, 1995 • “Radiation detection and measurements”, G.F. Knoll, 1989 • “Alpha-, Beta- and Gamma-ray Spectroscopy”, Ed. K. Siegbahn, 1965 Journal Articles • W. Bambynek et al., Rev. Mod. Phys. 49 (1977) 77 • N.B. Gove and M.J. Martin, Nuclear Data Tables 10 (1971) 205 • S. Raman and N.B. Gove, Phys. Rev. C7 (1973) 1995 • B. Singh et al., Nuclear Data Sheets 84 (1998 487

3. Beta Decay: universal term for all weak-interaction transitions between two neighboring isobars Takes place is 3 different forms b-, b+ & EC (capture of an atomic electron) ~ b-: n  p + e- + n a nucleon inside the nucleus is transformed into another Introduction b+: p  n + e+ + n EC: p + e-  n + n

4. Classification of b decay transition Lb = n defines the degree of forbiddenness (n) forbidden allowed Iipi Eb Ifpf when the angular momentum conservation requires that Lb=n>0 and/or pipf=-1 when Lb=n=0 and pipf=+1

5. Classification of allowed decay Fermi Gamow-Teller mixed Fermi & Gamow-Teller 0+ 0+ Eb Eb 1+ 0+ 2+ Eb 2+

6. Classification of b decay transitions

7. Some useful empirical rules the speed of a b transition increases approximately in proportion to the fifth power of the total transition energy (if other things are being equal, of course) Ii Eb If • depends on spin and parity changes between the initial and final state • additional hindrance due to nuclear structure effects – isospin, “l-forbidden”, “K-forbidden”, etc. The fifth power beta decay rule:

8. b decay lifetime partial half-life of a givenb-(b+,EC) decay branch (i) g–week interaction coupling constant pe – momentum of the b particle We – total energy of the b particle W0 – maximum energy of the b particle F(Z,We) – Fermi function – distortion of the b particle wave function by the nuclear charge Cn – shape factor Z – atomic number

9. b decay Hindrance Factor contains the nuclear matrix elements statistical rate function (phase-space factor): the energy & nuclear structuredependencesof the decay transition

10. Log ft values coming from experiment coming from calculations N.B. Gove and M. Martin, Nuclear Data Tables 10 (1971) 205

11. Log f • ENSDF analysis program LOGFT – both Windows & Linux distribution http://www.nndc.bnl.gov/nndcscr/ensdf_pgm/analysis/logft/ • LOGFT Web interface at NNDC http://www.nndc.bnl.gov/logft/

12. Log t In = 0.69(10) (net) Out • What we want to know accurately • T1/2, Ig, aT & d

13. Rules for Spin/Parity Assignments ~1000 cases • There are only a few cases where unambiguous assignment can be made • “pandemonium effect” – neutron rich nuclei – log ft is a just lower limit! • needs to know the decay scheme and its properties accurately!

14. Log ft values – latest review ~3900 cases -> gives centroids and widths B. Singh, J.L. Rodriguez, S.S.M. Wong & J.K. Tuli

15. Implications for DDEP evaluations from systematics from calculations from experiment

16. …but be careful, nuclear structure is important j2 First forbidden  5 < log ft <10 j1 j 7- 8+ K=7 6+ large angular momentum re-orientation 4+ w j=R 2+ 0+ K~0 T1/2 =3.8x1010 y log ft =20 log ft =19 K-forbidden decay