231 Th decay; t1/2 = 25.52 h (t = 36.82 h).

  1. 231Th [b (+ g)] 231Pa   (~ 100%)
  2. 231Th [a (+ g)] 227Ra   ( 10-8%;   t1/2 ~ 30 My)

Decay no. 2 is expected (with 4.2 MeV decay energy); the small predicted branching ratio means that it has not been observed.

g + c.e.(a) b
E(b) I(c) (c) Ic.e. E(b) I(c)
189.0 1.4 10-6 1.6 10-7 142.0 0.0012
170.0 5.3 10-7 7.4 10-8 "  
163.0 6.8 10-5 3.6 10-4 "  
146.0 1.4 10-5 7.6 10-5 "  
145.0 2.6 10-6 6.3 10-6 "  
136.0 3.4 10-5 2.9 10-4 "  
63.9 1.0 10-5 3.6 10-4 "  
184.0 1.4 10-5 1.7 10-6 206.0 0.0056
125.0 2.5 10-5 7.4 10-6 "  
106.0 3.1 10-6 3.4 10-7 "  
99.3 5.3 10-5 3.3 10-4 "  
82.1 1.8 10-4 0.0015 "  
81.2 3.9 10-4 0.0039 "  
102.0 1.8 10-4 2.1 10-5 287.0 0.0053
93.0 2.0 10-5 3.0 10-6 "  
18.1 1.1 10-5 0.0088 "  
42.9 2.6 10-5 3.0 10-5 288.0 0.016
17.2 1.0 10-4 0.019 "  
84.2 0.0029 0.0073 305.0 0.015
25.6 0.0064 0.029 "  
58.6 2.1 10-4 0.034 58.6 1.5 10-4
      390.0 9.7 10-6

Notes:                                                                     

  1. c.e.: conversion electrons
  2. Energies in keV
  3. Intensities per `parent' decay of natural U (i.e. 0.956 238U, 0.044 235U)
  4. Data from compilations and amendments in Nuclear Data Sheets to Vol. 64 (1991);
    6 b-decays and 2 other levels  (and 27 associated gs) with yields < 0.1% omitted - full details here
  5. g and conversion electron intensities are totals from given level; part may be associated with different (lower energy) primaries
  6. 231Th and 227Ra entries in KAERI nuclide chart