
^{20}F (1987AJ02)(See Energy Level Diagrams for ^{20}F) GENERAL: See (1983AJ01) and Table 20.2 [Table of Energy Levels] (in PDF or PS). Model calculations:(1978WI1B, 1982HA43, 1983BR29, 1984FO16, 1984RA13, 1986CA27, 1986COZZ, 1986VO05, 1986WA1R, 1987HA08, 1987IA1B). Complex reactions involving ^{20}F:(1983BE02, 1983DE26, 1983WI1A, 1984GR08, 1984HO23, 1984KO25, 1985BE40, 1985HA1N, 1985PO11, 1986GA1I, 1986HA1B, 1986ME06, 1986PO06, 1987RI03, 1987RO10). Hypernuclei:(1984AS1D). Other topics:(1978WI1B, 1983AR1J, 1983BR29, 1985AN28, 1986AN07, 1986VO05, 1987HA08). Ground state of ^{20}F:(1978WI1B, 1983ANZQ, 1983AR1J, 1984KO25, 1986CA27).
Q = 0.070 (13) b (1978LEZA)
The halflife of ^{20}F is 11.00 ± 0.02 sec: see (1978AJ03). ^{20}F decays principally to ^{20}Ne*(1.63): see ^{20}Ne, reaction 33. See also (1984KO25, 1985HE08).
For excitation curves involving ^{20}F*(0, 1.82 + 1.84 + 1.97 + 2.04 + 2.19) see (1982HU06, 1983JA09). At E(^{9}Be) = 12 to 27 MeV angular distributions are reported for p_{0} and p_{1+2+3+4}: see (1983AJ01).
For fusion cross sections see (1982DE30). See also ^{13}C in (1986AJ01) and (1983AJ01).
See (1983AJ01).
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 ^{20}F*(1.97, 0.82) [J^{π} = (3^{}), 4^{+}]: this is consistent with J^{π} = (4^{}) for ^{20}F*(2.968).
Tables 20.5 (in PDF or PS) here and 20.5 (in PDF or PS) (1983AJ01) display ^{20}F states reported in this reaction.
For reported states see Table 20.6 (in PDF or PS) in (1983AJ01).
See (1983AJ01) for a listing of the polarization measurements. For VAP measurements at E_{pol. d} = 52 MeV (reaction (e)), see (1982MA25). See also ^{19}O and ^{19}F here, and ^{16}N and ^{17}N in (1986AJ04). See also (1986SE1B).
Proton groups have been observed to states of ^{20}F with E_{x} < 4.1 MeV: see Table 20.8 (in PDF or PS) in (1978AJ03). Angular distributions, γray polarization data and branching ratios lead to the J^{π} values shown in that table. A state at E_{x} = 6519 ± 3 keV is also populated. It decays principally (> 90%) to ^{20}F*(1.06) [J^{π} = 1^{+}]: the γrays are isotropic. ^{20}F*(6.52) is the 0^{+}; T = 2 analog of the ground state of ^{20}O: see (1978AJ03).
At E_{α} = 64.4 MeV angular distributions have been reported to ^{20}F*(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 E_{x} ≈ 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 γrays resulting from capture at thermal energies (^{20}F*(6.60); J^{π} = 1^{+}) and at E_{n} = 27, 44 and 49 keV (^{20}F*(6.63, 6.643, 6.647); J^{π} = 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 [^{20}F*(6.60)] is dominated by two intense transitions (E1) to ^{20}F*(5.94, 6.02) [thus J^{π} = 1^{}, 2^{}]. If the groundstate 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 ^{20}F*(6.63, 6.64, 6.65) [J^{π} = 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 J^{π} of the final states involved in the decay of the 44 keV resonance J = 3 or 4, assuming dipole transitions. Branching ratios for other ^{20}F 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 ^{20}F states involved in cascade and in primary γtransitions (1983HU12). For the earlier references see (1978AJ03). See also (1984VO1H) and (1986KR16; theor.).
The scattering amplitude (bound) a = 5.654 ± 0.010 fm, σ_{free} = 3.641 ± 0.010 b (1979KO26). The difference in the boundstate scattering lengths, b^{+}  b^{} = 0.019 ± 0.002 (1979GL12). The total cross section has been measured for E_{n} = 0.5 to 29.1 MeV: see (1978AJ03). Observed resonances are displayed in Table 20.9 (in PDF or PS). Observed resonances in the excitation functions involving ^{19}F*(0.11, 1.5(u)) are displayed in Table 20.10 (in PDF or PS). For reaction (c) see (1983CSZX). See also (1986BAYL) and (1986SA40; theor.).
Reported resonances are shown in Table 20.11 (in PDF or PS).
States of ^{20}F observed in this reaction are displayed in Table 20.12 (in PDF or PS). See (1978AJ03) for a discussion of the earlier work. See also (1983JI04).
The decay is to ^{20}F*(1.06, 3.49), J^{π} = 1^{+}: see ^{20}O. The E_{x} of ^{20}F*(1.06) is 1056.848 ± 0.004 keV. The β branch to ^{20}F*(3.17) (1^{+}) is < 0.012%, log f_{0}t > 5.1 (1987AL06). [See also for general discussion of the lowlying states of ^{20}F].
The branching ratio to ^{20}F*(1.06) [J^{π} = 1^{+}] is compared to the analogous M1 decay width ^{20}Ne*(11.24) [J^{π} = 1^{+}] → ^{20}Ne_{g.s.}. The M1 amplitude contains (47 ± 16)% spinflip, in agreement with shellmodel calculations. The population of ^{20}F*(0, 1.31, 1.84) [J^{π} = 2^{+}, 2^{}, 2^{}] is also reported (1981MA04). See also (1986BA16) and (1983KN05; theor.).
The ^{20}F states observed at E_{d} = 26 MeV in this reaction and analog [T = 1] states observed in ^{20}Ne 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 ltransfer.
At E_{p} = 43.7 to 45.0 MeV analog states have been studied in ^{20}F and ^{20}Ne [the latter via ^{22}Ne(p, t)^{20}Ne]. Angular distributions for the ^{3}He ions and the tritons corresponding to the first T = 2 states (J^{π} = 0^{+}) [^{20}Ne*(16.722 ± 0.025) and ^{20}F*(6.513 ± 0.033)] have been compared. There is indication also for the excitation of the 2^{+}; T = 2 states [at E_{x} = 8.05 MeV in ^{20}F and at 18.5 MeV in ^{20}Ne (estimated ± 0.1 MeV)]: see (1978AJ03).
Angular distributions have been obtained at E_{d} = 10 MeV to ^{20}F states with E_{x} < 4.4 MeV: they are generally featureless. Observed states are displayed in Table 20.17 (in PDF or PS) of (1978AJ03).
The Δ resonance is very strongly excited in the reaction at E(^{20}Ne) = 950 MeV/A (1986BA16).
For lifetime measurements of some ^{20}F states see Table 20.4 (in PDF or PS).
