(See Energy Level Diagrams for 20F)
Q = 0.070 (13) b (1978LEZA)
The upper of the two states at 2.97 MeV has an excitation energy of 2968 ± 1.5 keV and γ branching ratios of (61 ± 4) and (39 ± 4)%, respectively, to 20F*(1.97, 0.82) [Jπ = (3-), 4+]: this is consistent with Jπ = (4-) for 20F*(2.968).
See (1983AJ01) for a listing of the polarization measurements. For VAP measurements at Epol. d = 52 MeV (reaction (e)), see (1982MA25). See also 19O and 19F here, and 16N and 17N in (1986AJ04). See also (1986SE1B).
Proton groups have been observed to states of 20F with Ex < 4.1 MeV: see Table 20.8 (in PDF or PS) in (1978AJ03). Angular distributions, γ-ray polarization data and branching ratios lead to the Jπ values shown in that table. A state at Ex = 6519 ± 3 keV is also populated. It decays principally (> 90%) to 20F*(1.06) [Jπ = 1+]: the γ-rays are isotropic. 20F*(6.52) is the 0+; T = 2 analog of the ground state of 20O: see (1978AJ03).
At Eα = 64.4 MeV angular distributions have been reported to 20F*(0, 0.66, 0.82, 1.06, 1.82, 2.20, 2.97, 4.24, 4.54, 5.07, 5.44, 5.80, 6.67, 7.29, 7.75, 8.34, 8.75, 9.00, 9.24, 9.78, 10.01, 10.51, 10.85, 11.56, 12.32, 12.72): L assignments are made [the groups above Ex ≈ 2.9 MeV are probably unresolved] (1986KA36).
The thermal capture cross section is 9.8 ± 0.7 mb. A number of resonances have been observed: see Table 20.6 (in PDF or PS). The primary γ-rays resulting from capture at thermal energies (20F*(6.60); Jπ = 1+) and at En = 27, 44 and 49 keV (20F*(6.63, 6.643, 6.647); Jπ = 2-, (3, 4) and 1-) have been studied by several groups: see (1972AJ02) and Table 20.7 (in PDF or PS) here. It appears that the thermal capture [20F*(6.60)] is dominated by two intense transitions (E1) to 20F*(5.94, 6.02) [thus Jπ = 1-, 2-]. If the ground-state transition is mainly M1, these two E1 transitions are (in terms of W.u.) about 150 times stronger than the M1 transition (1968SP01). See also (1983HU12). It appears also that at 20F*(6.63, 6.64, 6.65) [Jπ = 2-, (3, 4) and 1-] the E1 transitions to the ground state are very weak, even though other E1 transitions in the decay of these three states have approximately normal strengths. The strongest transitions from the 27 keV resonance appear to be M1. On the basis of Jπ of the final states involved in the decay of the 44 keV resonance J = 3 or 4, assuming dipole transitions. Branching ratios for other 20F states involved in this reaction are shown in Table 20.3 (in PDF or PS).
Table 20.8 (in PDF or PS) displays excitation energies for 20F states involved in cascade and in primary γ-transitions (1983HU12). For the earlier references see (1978AJ03). See also (1984VO1H) and (1986KR16; theor.).
The scattering amplitude (bound) a = 5.654 ± 0.010 fm, σfree = 3.641 ± 0.010 b (1979KO26). The difference in the bound-state scattering lengths, b+ - b- = -0.019 ± 0.002 (1979GL12). The total cross section has been measured for En = 0.5 to 29.1 MeV: see (1978AJ03). Observed resonances are displayed in Table 20.9 (in PDF or PS).
The decay is to 20F*(1.06, 3.49), Jπ = 1+: see 20O. The Ex of 20F*(1.06) is 1056.848 ± 0.004 keV. The β branch to 20F*(3.17) (1+) is < 0.012%, log f0t > 5.1 (1987AL06). [See also for general discussion of the low-lying states of 20F].
The branching ratio to 20F*(1.06) [Jπ = 1+] is compared to the analogous M1 decay width 20Ne*(11.24) [Jπ = 1+] → 20Neg.s.. The M1 amplitude contains (47 ± 16)% spin-flip, in agreement with shell-model calculations. The population of 20F*(0, 1.31, 1.84) [Jπ = 2+, 2-, 2-] is also reported (1981MA04). See also (1986BA16) and (1983KN05; theor.).
The 20F states observed at Ed = 26 MeV in this reaction and analog [T = 1] states observed in 20Ne in the (d, t) reaction are displayed in Table 20.16 (in PDF or PS) of (1978AJ03). The spectroscopic factors of analog states are consistent to within 20% for states excited by a single l-transfer.
At Ep = 43.7 to 45.0 MeV analog states have been studied in 20F and 20Ne [the latter via 22Ne(p, t)20Ne]. Angular distributions for the 3He ions and the tritons corresponding to the first T = 2 states (Jπ = 0+) [20Ne*(16.722 ± 0.025) and 20F*(6.513 ± 0.033)] have been compared. There is indication also for the excitation of the 2+; T = 2 states [at Ex = 8.05 MeV in 20F and at 18.5 MeV in 20Ne (estimated ± 0.1 MeV)]: see (1978AJ03).
The Δ resonance is very strongly excited in the reaction at E(20Ne) = 950 MeV/A (1986BA16).
For lifetime measurements of some 20F states see Table 20.4 (in PDF or PS).