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

2. 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 (
Plenty of information available on the Web

3. Introduction b+: p  n + e+ + n EC: p + e-  n + n ~
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+: p  n + e+ + n
EC: p + e-  n + n
b-: n  p + e- + n ~
a nucleon inside the nucleus is transformed into another

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

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

6. Order of forbiddenness
Classification of b decay transitions
Type of transition
Order of forbiddenness DI
pipf
Allowed
0,+1 +1
Forbidden unique 1 2 3 4 . k2 k3 k4 k5 -1
Forbidden
0, k1

7. Some useful empirical rules
The fifth power beta decay rule:
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) Eb If Ii
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.

8. b decay lifetime
partial half-life of a given b- (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
statistical rate function (phase-space factor): the energy & nuclear structure dependences of the decay transition
contains the nuclear matrix elements

10. N.B. Gove and M. Martin, Nuclear Data Tables 10 (1971) 205
Log ft values
coming from calculations
coming from experiment
Decay Mode
Type
DI (pipf)
log f b-
EC + b+
allowed
0, +1 (+)
1st-forb unique
k2 (-)
N.B. Gove and M. Martin, Nuclear Data Tables 10 (1971) 205

11. Log f ENSDF analysis program LOGFT – both Windows & Linux distribution
LOGFT Web interface at NNDC

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

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 importantw
K~0
j=R
K=7 j1 j2 j
large angular momentum re-orientation
First forbidden  5 < log ft <10
T1/2 =3.8x1010 y 0+ 2+ 4+ 6+ 8+ 7-
log ft =20
log ft =19
K-forbidden decay