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Log ft values in Beta Decay. Filip G. Kondev kondev@anl.gov. 2 nd Workshop for DDEP Evaluators, Bucharest, Romania May 12-15,2008. Plenty of information available on the Web . Some useful references. Books “ Week interaction and nuclear beta decay”, H.F. Schopper, 1966

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log ft values in beta decay

Log ft values in Beta Decay

Filip G. Kondev

kondev@anl.gov

2nd Workshop for DDEP Evaluators, Bucharest, Romania

May 12-15,2008

some useful references

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
introduction

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

slide4

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

slide5

Classification of allowed decay

Fermi

Gamow-Teller

mixed Fermi & Gamow-Teller

0+

0+

Eb

Eb

1+

0+

2+

Eb

2+

slide7

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:

slide8

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

slide9

b decay Hindrance Factor

contains the nuclear matrix elements

statistical rate function (phase-space factor): the energy & nuclear structuredependencesof the decay transition

slide10

Log ft values

coming from experiment

coming from calculations

N.B. Gove and M. Martin, Nuclear Data Tables 10 (1971) 205

slide11

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/

slide12

Log t

In

= 0.69(10)

(net)

Out

  • What we want to know accurately
      • T1/2, Ig, aT & d
slide13

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!
slide14

Log ft values – latest review

~3900 cases -> gives centroids and widths

B. Singh, J.L. Rodriguez, S.S.M. Wong & J.K. Tuli

slide15

Implications for DDEP evaluations

from systematics

from calculations

from experiment

slide16

…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