Authors: Balraj Singh, Jagdish K. Tuli, and Edgardo Browne |  Citation: Nucl. Data Sheets 185, 560 (2022) |  Cutoff date: 31-Aug-2022 

 Full ENSDF file | Adopted Levels (PDF version) 

Q(β-)=3864 keV 14S(n)= 5478 keV 10S(p)= 7380 keV SYQ(α)= 2230 keV SY
Reference: 2021WA16

General Comments:

1985Hi02: 231Fr produced and identified in 238U(p,X),E=600 MeV reaction. Measured γ- and x-ray spectra, T1/2.

2001Fr05: 231Fr was produced by spallation of 1 GeV proton beam on uranium targets. The activity was mass-separated at CERN ISOLDE on-line separator, deposited on a magnetic tape, and then radiations were counted at two stations.

2014Bu06: 231Fr produced in 1.4-GeV proton bombardment of UCx target using HRS mass separator, ISCOOL gas-filled segmented linear Paul trap, and RILIS at ISOLDE-CERN facility. Measured hyperfine spectra, magnetic dipole moments and rms charge radii by Collinear Resonance Ionization Spectroscopy (CRIS)

Measured atomic masses: 2014Kr09, 2012Ch19 (also 2008ChZI thesis)

Theoretical nuclear structure calculations: consult NSR database ( for two primary references, also listed in ’document records’ in this dataset, which can be accessed through on-line ENSDF database at

Q-value: Estimated uncertainties (2021Wa16): 200 keV for S(p), 300 keV for Q(α)

Q-value: S(2n)=9730 9, S(2p)=17390 400 (syst) (2021Wa16)

Jπ(level) T1/2(level)
  0.0 (1/2+) 17.6 s 6 
% β- = 100

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Additional Level Data and Comments:

  0.0(1/2+) 17.6 s 6 
% β- = 100
μ=+1.56 2 (2014Bu06)
Isotope shift δν(231Fr,221Fr)=-22.14 GHz 10 (2014Bu06).

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