(See Energy Level Diagrams for 20F)
Model calculations: (1959BR1E, 1963KU19, 1964MO1E, 1965DE1H, 1965DE1M, 1966CH1G, 1966PI1B, 1967BO09, 1967GU05, 1967GU1D, 1968AR02, 1968CO11, 1968GU1E, 1968HA17, 1968HA1P, 1969HO32, 1970AN27, 1970BA66, 1971AR25, 1971JO01, 1971WI01).
Excitation functions have been measured for Ed = 0.9 to 2.0 MeV (1960AM03; α0, α1, α2, α3), 0.5 to 3.0 MeV (1957BO04; α) and 9.6 to 11.5 MeV (1970BO08; α4, α5, α6, α7+8, α16, α17). At the lower energies a number of sharp structures are reported: see (1957BO04, 1960AM03). At the higher energies, there is no substantial resonant structure with widths less than a few hundred keV (1970BO08).
The lifetime of 20F*(0.82), τm = 79 ± 6 psec and J = 2, 4. The 167-keV γ-ray from this state to 20F*(0.63) is observed to have a multipole mixing ratio near zero for both of the above J values. The results are consistent with 20F*(0.82) having Jπ = 4+ and being the third member of the ground state rotational band (1971PR10).
Proton groups have been observed to states of 20F with Ex < 4.1 MeV (1970RO06): see Table 20.7 (in PDF or PS). Directional correlation and branching ratio measurements [see Table 20.6 (in PDF or PS)] lead to the Jπ assignments shown in Table 20.7 (in PDF or PS) (1970QU04). See also (1967BI01, 1967QU01). Angular distributions of the protons corresponding to 20F*(1.06, 3.49) are very similar at E(3He) = 18 MeV: both show an L = 0 + 2 pattern, and therefore both are Jπ = 1+ states. This implies that 20F*(3.53) which is only weakly excited has Jπ = 0+: see the discussion in (1971FO14) and in reaction 19 [see also (1971BE19)]. See also (1969BA1Z).
The thermal capture cross section is 9.8 ± 0.7 mb (1963GL01: see (1964ST25)). At En = 30 keV it is reported to be 4.5 ± 1.0 mb (1963MA60). A number of resonances have been observed for En ≤ 1.65 MeV: see Table 20.8 (in PDF or PS) (1959GA08). The primary γ-rays resulting from capture at thermal energies (20F*(6.60); Jπ = 0+, 1+) and at En = 27 and 48 keV (20F*(6.63, 6.65); Jπ = 2- and 1-, respectively) have been studied by several groups: see Table 20.9 (in PDF or PS) (1965BI03, 1967BE36, 1967VA08, 1968BL1C, 1968SP01, 1969HA04). See also (1962BI1C, 1963NA08). There is some disagreement between the results of the various groups but it appears that the decay of 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, 6.65) [Jπ = 2- and 1-, respectively] 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 (1965BI03, 1967BE36). Branching ratios for other 20F states involved in this reaction are shown in Table 20.6 (in PDF or PS) (1967BE36, 1968BL1C, 1968SP01, 1969HA04).
Table 20.10 (in PDF or PS) displays excitation energies for 20F states involved in cascade and in primary γ-transitions (1968SP01, 1969HA04). (1968BL1C) suggest 4+ for 20F*(0.83) since neither 20F*(6.60) nor 20F*(6.02) [Jπ = 0+, 1+, and Jπ = 1-, respectively] decays to it and 3+ for 20F*(0.66) since the 6.60 MeV state decays to it and 20F*(6.02) does not. See also (1958GR01, 1961WA03, 1963GI1D) and (1964ST25).
The total cross section has been measured for En = 1 to 300 keV (1964HI04), 0.2 to 2.2 MeV (1964EL02), 0.45 to 1.20 MeV (1966CA14), 2.5 to 15 MeV (1971FO1P, 1971FO24), 2.61 to 2.83 MeV (1965SO1A), 3.35 to 5.07 MeV (1960TS02), 7 to 14 MeV (1957PE1B), 13.70 to 14.60 MeV (1968HU17), 14.5 MeV (1970AN1F), and 17.7 to 29.1 MeV (1960PE25). See also (1966GA1K, 1969AN1E). For earlier measurements see (1959AJ76). Observed resonances in the total cross section are shown in Table 20.11 (in PDF or PS) (1958WI36, 1960TS02, 1964HI04, 1964ST25, 1966CA14). The level density may be appreciably greater than that shown in Table 20.11 (in PDF or PS): see (1964HI04) and (1964EL02).
Angular distributions and polarization measurements have been carried out over the range En = 0.2 to 2.2 MeV (1964EL02). The results have been interpreted in terms of doorway states: see (1967AF01, 1967MO1M, 1968LE1P). Angular distributions have also been measured at En = 14.1 MeV (1970CL03) and for En = 0.66 to 2.92 MeV (1958WI36). See also (1970GA1A). Polarization measurements are reported by (1962OT01) at En = 3.5 MeV. See also (1959MA1C, 1965WY1B, 1966EL1C, 1967EL1F) and (1964ME1B, 1967FE1F, 1971BU02, 1971GI05; theor.).
The excitation function for 0.110, 0.197, 1.24 and 1.37 MeV γ-rays has been measured from threshold to 2.2 MeV by (1955FR1B). See also (1966VE1B, 1971BE1G). Resonances are reported at En = (100), 270, 420, (500), 780, 830, 880 and 950 keV, corresponding to the excitation of 20F states at Ex = (6.70), 6.86, 7.00, (7.08), 7.34, 7.39, 7.44 and 7.50 MeV (1955FR1B). See also (1966VE1B). The cross section for excitation of 19F*(2.78) has been studied for En = 3 to 3.6 MeV. The very slow rise for the first 300 keV above threshold is consistent with the large spin difference between 19F*(2.78) and the ground state [Jπ = 9/2+ for the former, 1/2+ for the latter]. See also (1970CL03) and (1964ST25).
Cross sections have been measured from En = 10 to 37 MeV (1961BR1A), 12.4 to 20.9 MeV (1965PI03), 12.6 to 19.6 MeV (1965BO42), 12.7 to 19.4 MeV (1967ME22), 13.5 to 15.0 MeV (1967BO24), 13.6 to 14.6 MeV (1968VO1B), 13.9 to 14.8 MeV (1964ST1F), 14.1 MeV (1962CE1B), 14.2 MeV (1965NA1C), 14.4 MeV (1961RA06, 1963RA1A) and at 14.7 MeV (1967PA27). See (1959AJ76) for earlier reports. See also (1960MC05, 1961WI1C, 1963PI1B, 1964HE18, 1965GO1C, 1967CS02), (1964ST25, 1966JE1B) and (1969CH1N; theor.).
Cross sections have been measured for En = 12.6 to 19.6 MeV (1965BO42), 14.4 - 14.8 MeV (1962KA37, 1966MI14, 1966PR14, 1967CS03, 1967PA27, 1968RE07) and for En = 18.2 to 21.0 MeV (1965PI03). See also (1959AJ76), (1961DA16, 1963PI1B), (1960BU1C, 1963LE1D, 1964ST25, 1966JE1B, 1971CU1B, 1971PR09) and 19O.
Observed resonances are shown in Table 20.12 (in PDF or PS) (1955MB01, 1960SM03, 1961DA16): see graph in (1964ST25). Excitation functions are reported from threshold to En = 6 MeV (1960SM03), En = 8.2 MeV (1961DA16) and for En = 14.2 to 21.0 MeV (1965PI03). See also (1959AJ76), (1962KA37, 1963PI1B, 1966BH05, 1966KN02, 1968RE07, 1969BR1F), (1960BU1C, 1963CH20, 1966JE1B), (1964GA1A; theor.) and 16N in (1971AJ02).
Measurements of proton spectra and γ-rays have led to the identification of a number of states of 20F: see Table 20.13 (in PDF or PS) (1969HE20, 1969HO20, 1970RO06). Angular distributions have been studied at Ed = 0.6 MeV (1970SC14), 0.8 to 2.5 MeV (1964EL01), 1.32 to 2.03 MeV (1959ON26), 1.35 to 2.00 MeV (1969BA2M), 1.5 MeV (1964LO1A), 2 MeV (1963RO21, 1968BI09), 2.6 to 4.0 MeV (1970ZA02), 3 MeV (1971LA1F, 1972LA1N), 8.9 MeV (1956EL1A, 1971RO06), 9 and 13 MeV (1966SC09) and 16 MeV (1970FO1J). See also (1959AJ76).
Branching ratio and angular correlation measurements, together with lifetime determinations [see Table 20.14 (in PDF or PS)] permit a unique choice of Jπ in many cases, from among the Jπ values stemming from direct interaction analyses of angular distributions [see Table 20.13 (in PDF or PS)]. These Jπ values are displayed in Table 20.6 (in PDF or PS) (1969HE20, 1969HO20, 1970HO05, 1970RO06). See also (1964CH21, 1965NE07).
(1970QU1A), using polarized deuterons, have looked at the protons corresponding to 20F*(0.66, 2.04). These two states are found to be populated by a j = 5/2 neutron transfer. This result, togther with (p-γ) correlation data, provides a unique Jπ = 3+ assignment for 20F*(0.66) and is in agreement with 2+ for 20F*(2.04). Transitions to 20F*(2.19, 2.97) appear to be admixed j = 3/2, 5/2 transfer implying J = 2 for both these states (1970QU1A). See also (1972HA2H). Comparison of the results of this reaction and of the 18O(3He, p)20F and 22Ne(d, α)20F reactions leads to assignments of Jπ = 1+ and 0+ for 20F*(3.49, 3.53) (1971FO14).
At Ep = 43.7 to 45.0 MeV, analog states have been studied in 20F and 20Ne [the latter via 22Ne(p, t)20Ne]. The experimental cross-section ratio, R, for the transitions to 20Ne*(10.28) and 20F(0) [2+; T = 1] is 2.00 ± 0.20; R for the transitions to 20Ne*(12.25 ± 0.03) and 20F*(1.82) [(3-); T = 1] is 1.40 ± 0.15 (1969HA19). 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 also 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 (estomated errors ± 0.1 MeV)] (1964CE05, 1969HA38). See also (1970OL1B).
At Ed = 10 MeV, α-particle groups are observed to a number of states below Ex = 6.0 MeV. 20F*(1.82) was more strongly excited than 20F*(1.84) (1970FO1H). The angular distributions (at Ed = 10 MeV) of the α-particles corresponding to 20F*(3.49, 3.53) have been measured. 20F*(3.49) is strongly populated and the angular distribution shows direct interaction features while 20F*(3.53) is weakly populated and the angular distribution is roughly symmetric about 90°. These results are consistent with the assignments Jπ = 1+ and 0+ for 20F*(3.49, 3.53), respectively (1971FO14): see reactions 8 and 19. See also (1966LA14).