18C

β--Decay Evaluated Data



Measurements
1988DUZT: 18C(β-n); measured β-delayed xn emission, associated multiplicity, x = 0-4.
1988MU08: 18C; measured T1/2, neutron emission probabilities.
1989LE16: 18C; measured T1/2, delayed n emission probabilities.
1989MUZU: 18C(β-n); measured T1/2, β-delayed neutron emission probabilities.
1991PR03: 18C; measured Eγ, Iγ, T1/2, βγ-coin. 18N deduced levels, β-branching.
1991RE02: 18C; measured T1/2, neutron emission probability, upper limits. Tof isochronous spectrometer, ion-neutron delayed coincidence.
1993REZX: 18C(β-n); measured β-delayed neutron average energies.
1994RE1R: 18C(β-n); measured delayed n intensity, T1/2.
1995SC03: 18C(β-n); measured β-decay curves, neutron spectra; deduced T1/2, log ft. 18N levels deduced branching ratios.
2009IWZZ: 18C(β-); measured Eγ, Iγ, θ(γ); deduced 2+-state half-life, B(E2) using recoil shadow method.
Measured half-life for 18C(β-)18N

Recommended value (July, 2015): 92 ± 2 ms  
Summary Table of Uncertainty Analysis:          Table 18C preview (PDF)  
Measured values: 92 ± 2 ms   (1995SC03)
95 ± 10 ms (1991PR03)
92.9 ± 5.3 ms   (1994RE1R: see also 94 ± 27 ms in (1991RE02) and 92 ± 5 ms in the
unpublished private communications of (2008REZZ)/(1995REZZ).)
78+20-15 ms (1989LE16)
66+25-18 ms (1988MU08, 1987MU1J)
Other Reviews: 92 ± 2 ms   (2015BI05)

Previous Measurements

 

Decay to 18N*
(MeV)
Branching Ratio (%) a log ft Pn (%)
(1991PR03) (1991PR03) b (1987MU1J) ≈ 25
0.115       (1988MU08)    25 ± 4.5
0.587 ≤ 1 ≥ 6.36 ≥ 6.4 (1989LE16)   50 ± 10
1.735 9 ± 7 5.18 ± 0.78 5.2 ± 0.4 (1991PR03) 19 ± 5
2.614 72 ± 10 4.11 ± 0.22 4.08 ± 0.08 (1991RE02) 43.3 ± 6.5
  (1995SC03)    21.4 ± 4.4 c
a) (1991PR03), calculated with the hypothesis that there is no direct β-feeding of the 0.115 MeV level. The total probability of β decay to gamma emitting states plus to the ground state is Pγ = (81 ± 5)%. The β-delayed neutron probability is Pn = 1 - Pγ.
b) log ft's were recalculated by evaluators (1995TI07) and are slightly different from those in (1991PR03) due to use of level energies from Table 18.4 in (1995TI07) and Q-values from (1993AU05).
c) See the following table.

Experimental results for the β-delayed neutron decay of 18C (1995SC03)

Elabn (MeV) Ecmn + Sn a (MeV) Branching Ratio (%) log ft b
0.88 ± 0.02    3.65 ± 0.02 c 13.1 ± 1.3   4.55 ± 0.05
   1.55 ± 0.02 d 4.47 ± 0.02 3.65 ± 0.41 4.92 ± 0.06
1.91 ± 0.02 4.85 ± 0.02 0.87 ± 0.16 5.44 ± 0.09
2.47 ± 0.02 5.44 ± 0.02 0.76 ± 0.13 5.31 ± 0.09
2.78 ± 0.02 5.77 ± 0.02 0.96 ± 0.14 5.11 ± 0.07
3.25 ± 0.03 6.27 ± 0.03 1.24 ± 0.15 4.82 ± 0.06
4.59 ± 0.04 7.68 ± 0.04 0.86 ± 0.12 4.39 ± 0.06
Total Branching Ratio (%) e 21.4 ± 4.4    
a) For details see text in (1995SC03).
b) Assuming neutron decay to the ground state of 17N; for neutron transitions to excited states in 17N, the log ft values represent an upper limit.
c) The large branching ratio suggests a transition to the first excited state of 17N leading to an excitation energy of 5.13 MeV; for details see discussion in Section 4.2 in (1995SC03).
d) Γ = 180 + 40 keV. An unresolved doublet with En = 1.51 and 1.65 MeV cannot be excluded. This assumption would lead to excitation energies of 4.42 and 4.57 MeV and to branching ratios of 1.8% and 1.3%.
e) The errors of the total efficiency (10%), the background subtraction (15%), and the number of observed fl-decays (10%) have been added after summing.

Assignment of γ-rays observed in 18C(β-)18N (1991PR03)

18N transitions (keV) I (relative) a Branching Ratio (%) b
Eγ Ei → Ef
  114.9 ± 0.2 115 → 0     32 ± 1 100
  471.7 ± 0.2 587 → 115 15 ± 2 100 ± 16
1734.8 ± 0.4 1735 → 0       25 ± 5 33 ± 8
1619.9 ± 0.3 1735 → 115   25 ± 5 38 ± 9
1147.8 ± 0.4 1735 → 587   17 ± 5   29 ± 10
2614.2 ± 0.4 2614 → 0       100 ± 11 49 ± 8
2499.3 ± 0.4 2614 → 115   41 ± 9 22 ± 6
2025.3 ± 0.8 2614 → 587     7 ± 5   3 ± 2
  879.7 ± 0.2 2614 → 1735 44 ± 4 26 ± 6
1374.0 ± 1.0 β-delayed neutron emission 24 ± 5  
1849.9 ± 0.4 β-delayed neutron emission 11 ± 5  
a) The intensities have been normalized to 100 for the 2614 keV line.
b) The branching ratios are normalized to get 100% flux out of a level, taking into account corrections for summning effects.


18N(β-)18O Evaluated Data

18F(β+)18O Evaluated Data

18Ne(β+)18F Evaluated Data

A = 18 Beta-Decays Diagram

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Last modified: 19 September 2018