
^{18}F (1987AJ02)(See Energy Level Diagrams for ^{18}F) GENERAL: See (1983AJ01) and Table 18.13 [Table of Energy Levels] (in PDF or PS). Shell model: (1978WI1B, 1982ZH01, 1983BR29, 1983KI13, 1984MI1H, 1984MI17, 1985LE1K, 1986YU1B). Cluster, collective and deformed models: (1983ME12, 1984QU1A, 1985BA1A, 1987ER05). Special states: (1978WI1B, 1982ZH01, 1983BI1C, 1983BR29, 1983ME12, 1983KI13, 1984AD1E, 1984HA14, 1984HO1H, 1984MI1H, 1984MI17, 1985AD1A, 1985HA18, 1985LE1K, 1985MI10, 1985SO12, 1985YU1B, 1986AN07, 1986CA27, 1986HA1E, 1986HA1Q, 1986SI1K, 1986TO1D, 1986WI1P, 1986YU1B, 1987ER05). Electromagnetic transitions: (1982RI04, 1983BR29, 1983KI13, 1984BI10, 1984HA14, 1984MI1H, 1984QU1A, 1985AD1A, 1986CA27, 1986SI1K, 1987ER05, 1987KI03). Astrophysical questions: (1982WI1B). Applications: (1982HI1H, 1982YA1C, 1984HI1D, 1984NI1C, 1985HU02, 1986HI1B, 1987HI1B). Complex reactions involving ^{18}F: (1983DE26, 1983JA05, 1983OL1A, 1983WI1A, 1984GR08, 1984HI1A, 1984HO23, 1985BE40, 1985CU1C, 1985DR07, 1985GR1K, 1985PO11, 1986AV07, 1986BA3G, 1986GR1A, 1986HA1B, 1986HO27, 1986PO06, 1986SC28, 1986SC29, 1986VA23, 1987RI03, 1987RO10). Pion capture and reactions (See also reaction 32.): (1982LI15, 1983HO02, 1986GE06, 1986NA1K). Hypernuclei: (1984AS1D). Other topics: (1978WI1B, 1983AD1B, 1983AG1C, 1983AR1J, 1983BI1C, 1983BR29, 1983SH32, 1984BI10, 1984HO1H, 1984MI1H, 1985AD1A, 1985AN28, 1985MI10, 1985YU1B, 1986LA29, 1986NA1K, 1986TO1D, 1987KI03). Ground and 1.12 MeV states of ^{18}F: (1978WI1B, 1983ANZQ, 1983AR1J, 1984HA14, 1985AN28, 1985HA18, 1986CA27).
Q_{1.12} = 0.13 ± 0.03 b [see (1983AJ01)].
The positron decay is entirely to the ground state of ^{18}O [J^{π} = 0^{+}, T = 1]; the halflife is 109.77 ± 0.05 min [see Table 18.11 (in PDF or PS) in (1972AJ02)]; log ft= 3.554. The fact that the β^{+} transition to ^{18}O_{g.s.} is allowed indicates J^{π} = 1^{+} for ^{18}F_{g.s.}. The ratio ε_{K}/β^{+} = 0.030 ± 0.002: see (1978AJ03). See also (1985BR29), (1982KA1C; applications), (1985AR1A, 1985KL1A, 1986HE1C, 1987GOZX; astrophyics) and (1983CA03; theor.) [see for discussions of weak magnetism form factor and of search for heavy neutrinos].
See (1986CU02) for production cross sections of 0.94 MeV γrays.
Cross sections for these and other charged particle channels have been measured for E(^{6}Li) = 1.9 to 36 MeV [see (1978AJ03, 1983AJ01)]. The cross section for the isospinforbidden α_{1} group [to ^{14}N*(2.31), 0^{+}, T = 1] is 1 to 2% of the cross section to the allowed α_{0} and α_{2} groups for E(^{6}Li) = 3.2 to 6 MeV while for 9 to 14 MeV it varies from 0.4 to 1.8%. At 20 MeV, the α_{1} yield is 0.02% of the allowed yield. Structures are reported at E(^{6}Li) = 11.0 and 13.0 MeV in the α_{0} yield, at 11.5 and (13.0) MeV in the α_{1} yield and at ≈ 11.7 and 12.8 MeV in the α_{2} yield. A resonance is also reported in the α_{1} yield at E(^{6}Li) = 4.2 MeV: E_{x} = 15.99 ± 0.02 MeV, Γ_{c.m.} = 290 ± 30 keV, J^{π} = 2^{+} (onelevel BW fit). It is suggested that this resonance is due to 2^{+} states with T = 0 and T = 1 which are unresolved. Cross sections for populating ^{16}O*(8.87, 10.36, 11.08, 11.10) are reported by (1981GL02). The excitation functions for the ^{6}Li ions to ^{12}C*(0, 4.43) shows a single isolated structure at E(^{6}Li) = 22.8 MeV, in the range 20  36 MeV, with Γ ≈ 0.8 MeV. It is unlikely to be due to an isolated state in ^{18}F. At E(pol. ^{6}Li) = 20 MeV analyzing power measurements are reported for many deuteron and α groups and for elastically scattered ^{6}Li ions. VAP measurements for elastic scattering are also reported at E_{pol. d} = 9.0 and 19.2 MeV (1983RU09) and at 150 MeV (1986TA1B, 1986KA1C). For fusion studies see (1982DE30, 1987PA12). For references to earlier work and for additional comments see (1978AJ03, 1983AJ01). See also (1980KR1F), (1984MU1D; theor.) and ^{12}C in (1985AJ01), ^{14}N in (1986AJ01) and ^{16}O in (1986AJ04).
Angular distributions are reported at E(^{9}Be) = 12 to 27 MeV to ^{18}F_{g.s.} and to the unresolved states at 1 MeV: see (1983AJ01). For excitation functions see (1982HU06, 1983JA09).
τ_{m} = 5.2 ± 0.9 psec for ^{18}F*(4.85) [5^{}; T = 0]. The E1 strength is (3.4 ± 0.6) × 10^{6} W.u. for the transition to ^{18}F*(1.12) [5^{+}; T = 0] and the E2 strength is 14.8 ± 2.6 W.u. for that to ^{18}F*(3.79) [3^{}; 0]. The latter strength, which is that of a highly collective transition, corresponds to a quadrupole moment Q_{0} = 395 ± 35 mb and suggests that ^{18}F*(4.85) is the 5^{} state of a (strongly decoupled) K^{π} = 1^{} band 1982KO24). See also Tables 18.14 (in PDF or PS) and 18.15(in PDF or PS).
The nonresonant Sfactor for this reaction, S ≈ 0.7 MeV · b: see (1978AJ03). A number of resonances have been observed for E_{α} < 3 MeV: see Table 18.16 (in PDF or PS). Studies of these, principally by the Toronto and Queen's groups [see references in (1978AJ03, 1983AJ01)] in conjunction with work on ^{14}N(α, α), ^{16}O(^{3}He, p), ^{17}O(p, γ) and ^{17}O(p, α) [see Tables 18.18 (in PDF or PS), 18.19 (in PDF or PS), 18.20 (in PDF or PS)] have led to the determination of branching ratios, mixing ratios and widths (Table 18.14 (in PDF or PS)), lifetimes (Table 18.15 (in PDF or PS)) and the E_{x}, J^{π} and K^{π} assignments for ^{18}F states with E_{x} < 6.9 MeV. The reader is referred to the series of papers by the Toronto group for the most complete and definitive arguments on the parameters of the lowlying states of ^{18}F. No evidence is seen for the excitation of the (forbidden) state at E_{x} = 4.753 MeV [J^{π} = 0^{+}; T = 1] (1981LE1A, 1983LE08). See also (1985GO27; applications) and (1982BA1D, 1985AR1A, 1985KL1A, 1985MA1A, 1986HE1C, 1981LE1A, 1987GOZX; astrophysics).
Observed resonances are displayed in Table 18.16 (in PDF or PS). See also ^{17}O in (1986AJ04).
Observed anomalies in the elastic scattering [reaction (a)] are exhibited in Table 18.16 (in PDF or PS). Resonances in the α_{1} isospinforbidden yield are displayed in Table 18.14 (in PDF or PS) of (1978AJ03). In the α_{1} study, carried out for E_{α} = 7.6 → 16.9 MeV, a partialwave analysis involving a method of removing ambiguities and parametrizing Smatrix elements gives the level parameters of 151 isospin mixed, naturalparity states in ^{18}F with 10.4 < E_{x} < 17.5 MeV. Many of these states have also been reported in the ^{16}O(d, α_{1}) reaction [Table 18.16 (in PDF or PS) of (1978AJ03)]. The argeement is best for lowlying 2^{+} or 4^{+} states, and is quite good for 3^{} and 5^{} states, while for highJ states the greater centrifugal barrier for ^{16}O + d at the same E_{x} relatively suppresses highJ states in the ^{16}O + d work. A study of the energy dependence of averaged intensities of the partial waves shows some indication that the lower partial waves reconserve isospin as E_{x} increases. The total cross sections for formation of ^{10}B and ^{6}Li have been studied for E_{α} = 21 to 42 MeV [see (1978AJ03)], as has the cross section for production of 1.64 and 2.31 MeV γrays from threshold to E_{α} = 26 MeV [(1985DY05): see for astrophysical implications.] See also (1984RE14, 1986CO11) and (1986ALZZ; theor.).
At E(^{6}Li) = 36 MeV angular distributions have been measured for the deuteron groups to ^{18}F*(5.34 [4^{+}], 6.56 [5^{+}], 9.58, 11.2, 14.1). Angular correlations lead to J^{π} = 6^{+} and 8^{+} for ^{18}F*(9.58, 14.1) and the data are consistent with J^{π} = 7^{+} for ^{18}F*(11.2) (1983ET02). For the earlier work see (1978AJ03).
At E(^{7}Li) = 36 MeV the K^{π} = 1^{+} band appears to be selectively populated. States at E_{x}=9.58 ± 0.02, 11.22 ± 0.03 and 14.18 ± 0.04 MeV are stongly populated. It is suggested that the first two are the 6^{+} and 7^{+} members of that band: see reaction 8. [Angular distributions are reported for ^{18}F*(1.70, 2.10, 2.52, 3.36, 4.40, 5.30, 6.57, 9.58, 11.22, 14.18).] See (1978AJ03) for the earlier work, and (1986NE1A; E(^{14}N) = 150 MeV). See also (1986CO11; theor.).
These reactions have been studied at E(^{11}B) = 115 MeV and E(^{13}C) = 105 MeV. Differential cross sections at three angles are reported for the transitions to ^{18}F*(9.58, 10.57 ± 0.07, 11.2) in reaction (a) and to ^{18}F*(5.30, 6.57, 9.58, 10.60 ± 0.08, 11.2) in reaction (b). In addition to these states ^{18}F*(14.18) is strongly excited in both reactions, and transitions to ^{18}F*(15.79 ± 0.10, 18.62 ± 0.12) are also reported: see (1983AJ01).
Excitation functions have been measured for E(^{3}He) = 2.5 to 16 MeV for the γ_{0} and γ_{1} → 4 yields. Resonances are observed corresponding to E_{x} = (19.00 ± 0.15) [γ_{1} → 4], 20.1 ± 0.2 [γ_{0}, γ_{1} → 4], 22.7 ± 0.2 [γ_{0}, γ_{1} → 4] and (24.1 ± 0.2) MeV [γ_{1} → 4], with Γ_{c.m.} = 0.5 ± 0.15, 1.6 ± 0.1, 1.2 ± 0.1 and 1.4 ± 0.3 MeV, respectively. The γ_{0} yield is dominated by ^{18}F*(20.1) (1983WA05) [see for (2J + 1)Γ_{3He}Γ_{γ} values]. It is suggested that the structures decaying by γ_{0} have J^{π} = 2^{} (and possibly T = 1) (1983WA05). For analyzing power measurements at E(pol. ^{3}He) = 33 MeV see (1986DR03).
At E(^{6}Li) = 30 MeV preferential excitation of oddparity states of ^{18}F below E_{x} = 5 MeV is reported. Angular distributions of the tritons to ^{18}F*(0, 0.94, 2.10, 4.40) [J^{π} = 1^{+}, 3^{+}, 2^{}, 4^{}] are all strongly forward peaked: see (1978AJ03).
These reactions have been studied with E(^{11}B) = E(^{12}C) = 115 MeV. Reaction (a) is dominated by the transitions to ^{18}F*(1.12) [presumably the J^{π} = 5^{+} state, although the group is unresolved] and to ^{18}F*(7.15, 9.45) [J^{π} = (7^{}) and (6^{})]. In reaction (b) no single state is strongly preferentially populated. Differential cross sections for ^{18}F*(4.40, 6.10, 7.15, 9.45) [J^{π} = 4^{}, (5^{}), (7^{}), (6^{})], are fitted by FRDWBA: see (1983AJ01).
The capture cross section rises from 0.1 μb at E_{d} = 0.4 MeV to 25 μb at 3.5 MeV: Γ_{γ} over this range is ≈ 2 eV: see (1972AJ02).
Excitation functions and polarization studies have been carried out to E_{d} = 17 MeV [see (1978AJ03, 1983AJ01)] and at E_{d} ≈ 5.6 to 8.3 MeV (1985GR1B; p_{0}, p_{3}, p_{4}). Structures attributed to states in ^{18}F are displyed in Table 18.17 (in PDF or PS). See also ^{17}O and ^{17}F in (1986AJ04), (1985JOZZ, 1986SE1B) and (1983DA31; applications).
The yield of elastically scattered deuterons and elastic polarization measurements have been reported for E_{d} = 0.65 to 56 MeV: see (1978AJ03, 1983AJ01). More recent measurements are those by (1985GR1B) [excitation functions for E_{d} ≈ 5.6 to 8.3 MeV] and the polarization studies at E_{pol. d} = 20.5 MeV (1984FR14; TAP), 56 MeV (1986MA32; VAP, TAP) and 200, 400 and 700 MeV (1987NG01; VAP, TAP). See also (1982AO06, 1983AO03, 1986NG1B, 1986YA1R, 1987MA09; theor.) and ^{16}O in (1986AJ04).
The yields of various groups of αparticles have been measured for E_{d} ≤ 20 MeV: see (1978AJ03, 1983AJ01). The yield curves have been fitted in terms of a large number of states in ^{18}F: see Tables 18.17 (in PDF or PS) here, and 18.16 (in PDF or PS) in (1978AJ03). A detailed study by (1973JO13) of the isospinforbidden α_{1} yield, analyzed by Smatrix theory, identifies a large number of isospin mixed states in ^{18}F, possibly as many as 138 with 9.2 < E_{x} < 19.4 MeV. The reaction mechanism appears to be almost entirely compound nuclear. The isospin impurity, averaged over 1 MeV intervals, is 3  10% for the above E_{x} range. The average coherence width increases from ≈ 100 keV at E_{x} = 14 MeV to ≈ 500 keV at E_{x} = 20 MeV. The level densities appear to be consistent with predictions of the Fermigas model (1973JO13). See also (1985JOZZ). [For mixed isospin states observed in ^{14}N(α, α_{1}) see Table 18.14 (in PDF or PS) in (1978AJ03).] Polarization measurements are reported for E_{d} = 6.8 to 16 MeV: see (1978AJ03, 1983AJ01).
Polarization measurements for the transitions to ^{12}C*(0, 4.4) are reported at E_{pol. d} = 18 and 22 MeV (1987TA07; VAP, TAP) and 51.7 MeV (1986YA12; VAP; also to ^{12}C*(14.1)).
See (1987BO16; applied) and (1983AJ01).
Excitation energies derived from measurements of γrays are displayed in Table 18.18 (in PDF or PS) together with lassignments obtained from distortedwave analyses, and J^{π}; T and K^{π} assignments from branching ratios, radiative widths, linear polarization, γray angular distributions and τ_{m} measurements [see also Tables 18.14 (in PDF or PS) and 18.15 (in PDF or PS)]. Studies of this reaction, together with the work on ^{14}N(α, γ) and ^{17}O(p, γ), have defined the lowlying states of ^{18}F. The gfactor of ^{18}F*(0.94) [J^{π} = 3^{+}] is +(0.56 ± 0.05): see (1983AJ01). The circular polarization of the 1.08 MeV → g.s. γray, P_{γ} = (10 ± 18) × 10^{4} (1982AH07), (2.7 ± 5.7) × 10^{4} (1985BI03), (1.6 ± 5.6) × 10^{4} (1985EV03), (1.7 ± 5.8) × 10^{4} (1987PA07). The weak pionnucleon coupling constant deduced from the weighted average of all recent P_{γ} measurements [(1.2 ± 3.9) × 10^{4}] is (0.3^{+1.0}_{0.3}) × 10^{7}. Together with PNC matrix elements in other experiments this suggests that the isovector weak NN interaction may be strongly suppressed compared with the isoscalar weak NN interaction (1985EV03, 1987PA07). For a measurement of the ICC of the 0.94, 1.02, 1.04 and 1.08 MeV γrays see (1986KR04). See also (1978AJ03, 1983AJ01), (1984BE1A; applications), (1987ER05; theor.) and ^{19}Ne.
Angular distributions of the deuteron groups to ^{18}F*(1.12) [J^{π} = 5^{+}] have been studied at E_{α} = 28.0 to 33.6 MeV: see (1983AJ01). At E_{α} = 65.3 MeV a number of angular distributions are reported to ^{18}F states with E_{x} ≤ 11.4 MeV: ^{18}F*(9.49, 10.54) are suggested to have J^{π} = 6^{} and 7^{+} respectively (1986KA36). See, however, reactions 9 and 10.
Angular distributions have been measured at E(^{6}Li) = 5.5 to 34 MeV [see (1983AJ01)] and at E(^{6}Li) = 48 MeV (1984CO05; α_{0}, α_{1}, α_{4}). (1982FR15) report the excitation of a state at E_{x} = 4848.3 ± 0.5 keV which decays (35 ± 4)% to ^{18}F*(3.79) [E_{γ} = 1056.8 ± 0.4 keV] and (65 ± 4)% to ^{18}F*(1.12). Alphaγ angular correlations are consistent with J^{π} = 5^{}, and T = 0 (1982FR05). See also (1986BGL02) and (1986IC01; theor.).
See (1983AJ01).
Gammaray measurements lead to the very accurate E_{x} determinations for ^{18}F states below 6.2 MeV: see Table 18.19 (in PDF or PS). Observed resonances are displayed in Table 18.20 (in PDF or PS); branching ratios, radiative widths and multipole mixing ratios are shown in Table 18.14 (in PDF or PS); and τ_{m} in Table 18.15 (in PDF or PS). The direct capture cross section has been studied for E_{p} = 0.3 to 1.9 MeV: ^{18}F*(5.603, 5.605, 5.668, 5.786) have J^{π} = 1^{+}, 1^{}, 1^{} and 2^{}. The 1^{} states have mixed isospin. For astrophysical considerations see (1978AJ03, 1983AJ01) and (1982RO1A).
Observed resonances are displayed in Table 18.20 (in PDF or PS). Analyzing power measurements are reported at E_{pol. p} = 135 MeV (1983PUZZ; n_{0}).
The elastic scattering has been studied for E_{p} = 0.5 to 13 MeV [see (1978AJ03, 1983AJ01)]: observed anomalies are displayed in Table 18.20 (in PDF or PS). Analyzing powers have been measured at E_{pol. p} = 89.7 MeV (1985VO12; p_{0}).
Analyzing powers have been reported at E_{pol. p} = 89.7 MeV for the triton groups to a number of ^{15}O states (1985VO12).
The yield of α_{0} shows a number of resonances for E_{p} = 0.49 to 3.0 MeV: see Table 18.20 (in PDF or PS). The Rmatrix fit of (1979KI13), obtained from data from E_{p} = 400 to 1400 keV, confirms the earlier result [see, e.g., (reaction 31 in (1978AJ03))] that a significant quantity of ^{17}O is burned up in the (p, γ) rather than in the (p, α) reaction for a wide range of stellar temperatures (1979KI13). See also (1982RO1A, 1987RO25) and (1986BA89; theor.).
At E(^{3}He) = 15 MeV DWBA analysis of angular distributions of deuteron groups corresponding to states of ^{18}F with E_{x} < 5 MeV have led to J^{π} values and spectroscopic information: see (1972AJ02). See also (1987ER05; theor.).
See (1983AJ01).
(1983AN05) have studied the distribution of GamowTeller (GT) strength. At E_{p} = 135 MeV angular distributions have been studied to the 0^{+} state at 1.04 MeV and to the 1^{+} states ^{18}F*(0, 1.70, 3.72, 4.36, 6.26) as well as to possible 1^{+}; T = 1 groups at E_{x} = 9.9 10.9 and 11.9 MeV. 82% of the observed strength lies in the ground state group and 5.5% in the (T = 1) states. The observed GT strength is ≈ 2/3 of that expected from the simple sum rule (1983AN05). See also (1985TAZY), (1985WA24), (1986MA1P, 1987HI1B; applied) and the earlier work in (1978AJ03).
At E(^{3}He) = 16 MeV, the triton spectrum is dominated by strong groups to ^{18}F*(0, 0.94) and to the 0^{+} and 2^{+}, T = 1 states ^{18}F*(1.04, 3.06). Angular distributions have been studied to these and many other states at this energy and at E(^{3}He) = 17.3 MeV. At E(pol. ^{3}He) = 33 MeV A_{y} measurements for t_{0} have been reported. See (1983AJ01) for references.
See (1978AJ03).
The halflife of ^{18}Ne is 1672 ± 8 msec [see ^{18}Ne]. The decay is to ^{18}F*(0, 1.04, 1.08, 1.70): see Table 18.21 (in PDF or PS).
Cross sections have been reported to 30 MeV for the transitions to ^{18}F*(0.94, 1.04, 1.08, 3.06, 3.13, 4.75): see (1983AJ01).
Angular distributions have been reported to many states of ^{18}F with E_{x} ≲ 6 MeV: see Table 18.20 (in PDF or PS) in (1983AJ01). See also (1986VAZV [E_{p} = 18.6 MeV; d_{0}, d_{2}]), (1983BEYY) and (1981CL05, 1983KI13; theor.).
See (1978AJ03).
See (1978AJ03).
At E_{d} = 11 MeV αgroups are observed to many states of ^{18}F with E_{x} < 7 MeV. Weak or absent (each ≤ 0.3% of the total yield at 30°) are the groups corresponding to ^{18}F*(1.04, 3.06, 4.66, 4.74, 4.96): T = 1. Measurements of the TAP for E_{pol. d} = 10.25 to 12.0 MeV leads to assignments of 2^{}, 1^{+}, 0^{+}, 1^{}, 1^{+}, 3^{+}, 3^{+} to ^{18}F*(4.23, 4.36, 4.75, 4.86, 5.603, 6.16, 6.48). See (1972AJ02, 1978AJ03, 1983AJ01) for references and for other results and (1987HI1B; applications).
See (1987GOZX).
See (1984NE1A). 