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.

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