(See Energy Level Diagrams for 20F)
Electromagnetic transitions: (1976MC1G).
Astrophysical questions: (1978WO1E).
Ground state of 20F: (1976MC1G).
Q = 0.070 (13) b (1978LEZA).
At E(13C) = 27.9 MeV angular distributions are reported by (1980BO21: d0, d1+2+3+4).
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) (1978LE19).
The 20F states observed in this reaction at E(7Li) = 16 MeV are displayed in Table 20.7 (in PDF or PS). The cross sections for forming states of known Jπ are proportional to 2Jf + 1 with slopes which are different for the even- and the odd-parity states. Extrapolation of these relationships to states of unknown Jπ leads to the assignments shown in Table 20.6 (in PDF or PS) (1977FO11).
Angular distributions have been measured at E(7Li) = 24 MeV for the 3He groups corresponding to the states shown in Table 20.7 (in PDF or PS). It is suggested that the states at Ex = 4.20, 4.52, 4.58 and 5.41 MeV have high spin and (sd)4 configurations (1978FO14).
Vector analyzing power measurements [reaction (b)] have been carried out at Ed-bar = 10 MeV (1979ST21; p0, p2, p3, p4) and at 14 MeV: see (1978AJ03). See also (1981NE1B; theor.). See also 19O. For reaction (a) see 19F.
VAP measurements are reported at Ed-bar = 52 MeV for reaction (a) (1981MA14: to 17N*(0, 1.37, 1.85, 2.53, 5.51, 6.99) and (b) (1982MA25: to 16N*(0, 0.30, 3.36, 3.96, 4.32, 6.17). TAP measurements are reported to reaction (b) at Ed-bar = 8.5 to 11.3 MeV (1978BA43). For excitation functions see (1972AJ02). See also 16N, 17N in (1982AJ01) and (1979SE04).
The thermal capture cross section is 9.8 ± 0.7 mb (1974SH1E). A number of resonances have been observed: see Table 20.8 (in PDF or PS). See also (1981MUZQ). The primary γ-rays resulting from capture at thermal energies (20F*(6.60); Jπ = 0+, 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 20.9 (in PDF or PS) here. It appears that the thermal capture [20F*(6.60)] is dominated by two intense transitions (probably 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). 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 two states have approximately normal strengths (1967BE36, 1974KE18). The strongest transitions from the 27 keV resonance appear to be M1. On the basis of the Jπ of the final states involved in the decay of the 44 keV resonance J = 3 or 4, assuming dipole transitions (1974KE18). Branching ratios for other 20F states involved in this reaction are shown in Table 20.4 (in PDF or PS).
The differential cross section at 92° for production of the 96 keV γ-ray has been studied by (1976MO13: En = 4.0 to 18.6 MeV): the cross section increases sharply at En = 6 MeV and then gradually decreases beyond En = 12 MeV. Cross sections have also been measured for En = 12.6 to 21 MeV: see (1972AJ02) and the summary in (1976GAYV). See also (1978SM1E, 1979BR08, 1979HA60).
Cross sections at 5.3 and 10.4 MeV above threshold are reported by (1979MA39).
States of 20F observed in this reaction are displayed in Table 20.14 (in PDF or PS). Angular distributions have been measured at Ed = 0.6 to 16 MeV [see (1978AJ03)] and at 12 MeV (1977MO16). See (1978AJ03) for a discussion of the earlier work. See also (1980HU1D, 1980HU1J).
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 (1979TR1B, 1982RI1B).
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 20.15 (in PDF or PS). The spectroscopic factors of analog states are consistent to within 20% for states excited by a single l-transfer (1974MI13).
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 errors ± 0.1 MeV)] (1964CE05, 1969HA38).
Angular distributions have been obtained at Ed = 10 MeV to all 20F states with Ex < 4.4 MeV: they are generally featureless. Observed states of 20F are displayed in Table 20.16 (in PDF or PS). See also (1978AJ03).