
^{18}F (1995TI07)(See Energy Level Diagrams for ^{18}F) GENERAL: See 3 [Electromagnetic Transitions in A = 1819] (in PDF or PS), 18.23 [General Table] (in PDF or PS), 18.24 [Table of Energy Levels] (in PDF or PS) and 18.25 [Radiative decays in ^{18}F] (in PDF or PS).
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 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 fixes J^{π} = 1^{+} for ^{18}F_{g.s.}. The ratio ε_{K}/β^{+} = 0.030 ± 0.002: see (1978AJ03, 1987AJ02). See also (1989SA1P, 1989KA1S). The influence of meson exchange currents of the second kind is discussed in (1988SA12) and in (1989SA1H) which also considers the effects of neutrino mass. Chargedcurrent (ν_{e}, e^{}) reactions on ^{18}O and the predicted effects on a proposed neutrino elastic scattering measurement of the Weinberg angle is discussed in (1988HA22).
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)]. More recently, measurements of cross sections at E(^{6}Li) = 210 MeV are reported in (1988NA02). Vector analyzing power measurements have been made at E(^{6}Li) = 150 MeV (1987TA21, 1988TA08) and at E(^{6}Li) = 30 MeV (1994RE01). For elastic scattering and at E(^{6}Li) = 30 MeV (1988VAZY, 1989VA04) for inelastic scattering to ^{12}C*(4.43). Neutron yields from ^{6}Li + ^{12}C at E(^{6}Li) = 40 MeV have been measured by (1987SC11). 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 of 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 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) show 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. Analyzing power measurements are reported for many deuteron and α groups and for elastically scattered ^{6}Li ions at E(^{6}Li) = 20 MeV. VAP measurements for elastic scattering are also reported at E_{d} = 9.0 and 19.2 MeV (1983RU09) and at 150 MeV (1986KA1C, 1986TA1B). For fusion studies see (1982DE30, 1987PA12). For references to earlier work and for additional comments see (1978AJ03, 1983AJ01, 1987AJ02), ^{12}C in (1985AJ01), ^{14}N in (1986AJ01), and ^{16}O in (1986AJ04, 1993TI07).
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).
For ^{18}F*(4.85) [5^{}; T = 0] τ_{m} = 5.2 ± 0.9 ps. 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 18.25 (in PDF or PS) and 18.26 (in PDF or PS).
The nonresonant Sfactor for this reaction is S ≈ 0.7 MeV · b: see (1978AJ03). A number of resonances have been observed for E_{α} < 3 MeV: see 18.27 (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 18.29 (in PDF or PS), 18.30 (in PDF or PS), 18.31 (in PDF or PS)] have led to the determination of branching ratios, mixing ratios and widths ( 18.25 (in PDF or PS)), lifetimes ( 18.26 (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. A recent measurement reported in (1989BO01) determines a value E_{x} = 5672.57 ± 0.32 keV for the first ^{18}F level above the proton threshold. This level is important for calculating the rate of ^{17}O destruction during hydrogen burning in stars. 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 (1987AJ02), and see the tables of reaction rates (1988CA26) and the reviews of (1989KA24, (1989WH1B, 1989TH1C).
Observed resonances are displayed in 18.27 (in PDF or PS). See also ^{17}O in (1986AJ04, 1993TI07).
Observed anomalies in the elastic scattering [reaction (a)] are exhibited in 18.27 (in PDF or PS). Resonances in the α_{1} isospinforbidden yield are displayed in 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 [ 18.16 (in PDF or PS) of (1978AJ03)]. The agreement 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} leads to a relative suppression of 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 conserve 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 also (1987AJ02), and see (1987BU27, 1989BE1R, 1990WE14, 1991LE33).
Angular distributions have been measured for the deuteron groups to ^{18}F*(5.34 [4^{+}], 6.56 [5^{+}], 9.58, 11.2, 14.1) at E(^{6}Li) = 36 MeV. 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 strongly 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, 1987AJ02) for the earlier work.
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*(20.10) [(1983WA05): see for (2J + 1)Γ_{3He}Γ_{γ} values]. It is suggested that structures decaying by γ_{0} have J^{π} = 2^{} (and possibly T = 1) (1983WA05). For analyzing power measurements at E(^{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 J^{π} = 5^{+} state, although the group is unresolved] and to ^{18}F*(7.15, 9.45) [J^{π} = (7^{}) and (6^{})]. No single state is strongly preferentially populated in reaction (b). 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 displayed in 18.28 (in PDF or PS). See also ^{17}O in (1986AJ04, 1993TI07) and ^{17}F in (1986AJ04, 1993TI07), (1987AJ02), and see (1992LA08) for applications.
The yields and polarized observables of elastically scattered deuterons 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_{d} = 20.5 MeV (1984FR14; TAP), 56 MeV (1986MA32, VAP, TAP) and 200, 400 and 700 MeV (1987NG01; VAP, TAP). An analysis for E_{d} = 400 MeV in terms of the folding model is discussed in (1987GR16). Virtual breakup effects in (d, d) elastic scattering have been studied (1988IS02). For references to earlier work see (1987AJ02), and see the ^{16}O sections of (1986AJ04, 1993TI07).
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 18.28 (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 isospinmixed 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 18.14 (in PDF or PS) in (1978AJ03).] Polarized beam measurements are reported for E_{d} = 6.8 to 16 MeV: see (1978AJ03, 1983AJ01).
Vector and tensor polarized beam measurements are reported for the transitions to ^{12}C*(0, 4.4) at E_{d} = 18 and 22 MeV (1987TA07; VAP, TAP) and 51.7 MeV (1986YA12; VAP; also to ^{12}C*(14.1)).
Recent measurement of neutron yields for E_{x} = 20 MeV are discussed in (1993DR03, 1993DR04). Applications are discussed in (1987BO16, 1990BA1S). For earlier work see (1983AJ01, 1987AJ02).
Excitation energies derived from measurements of γrays are displayed in 18.29 (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 18.25 (in PDF or PS) and 18.26 (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, 1988BI07), (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, 1987AJ02) and ^{19}Ne. A discussion of nuclear tests of fundamental interactions is presented in (1989MC1C). For recent work on the use of this reaction for oxygen analysis, see (1991BA62, 1992CO08). For applications related to ^{18}F production see (1991GU05, 1991SU17).
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. The use of this reaction in ^{18}F production is discussed in (1991GU05).
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 ± 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). Alphagamma angular correlations are consistent with J^{π} = 5^{}, and T = 0 (1982FR15). See also (1986GL02) and (1986IC01).
See (1983AJ01).
Gammaray measurements lead to the very accurate E_{x} determinations for ^{18}F states below 6.2 MeV: see 18.30 (in PDF or PS). Observed resonances are displayed in 18.31 (in PDF or PS); branching ratios, radiative widths and multipole mixing ratios are shown in 18.25 (in PDF or PS); and τ_{m} in 18.26 (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 MeV) have J^{π} = 1^{+}, 1^{}, 1^{} and 2^{}. The 1^{} states have mixed isospin. For astrophysical work, see the thermonuclear reaction rate tables in (1985CA41) and the analytical expression presented in (1988CA26). See also (1978AJ03, 1983AJ01, 1987AJ02).
Observed resonances are displayed in 18.31 (in PDF or PS). Analyzing power measurements are reported at E_{p} = 135 MeV (1983PUZZ; n_{0}). For astrophysicsrelated work see the thermonuclear reaction rate tables of (1985CA41) and the analytical expressions of (1988CA26).
The elastic scattering has been studied for E_{p} = 0.5 to 13 MeV [see (1978AJ03, 1983AJ01)]: observed anomalies are displayed in 18.31 (in PDF or PS). Analyzing powers have been measured at E_{p} = 89.7 MeV (1985VO12).
Analyzing powers have been reported at E_{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 18.31 (in PDF or PS). The Rmatrix fit of (1979KI13), obtained using 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 for (p, α) reaction for a wide range of stellar temperatures (1979KI13). See also (1987AJ02, 1987AS05). Measurements (1989BO01; see ^{14}N(α, γ)^{18}F reaction) of the first level (J^{π} = 1^{}) of ^{18}F above the proton threshold determined E_{x} = 5672.57 ± 0.32 keV. This result and a new value for the proton width of this level deduced from ^{17}O(^{3}He, d)^{18}F measurements (1989LA19) lead to substantial changes in the stellar reaction rate for ^{17}O(p, α)^{14}N. [See discussion in (1989LA19).] A direct search for the E_{x} = 70 keV resonance (E_{p} = 5672.57 ± 0.32 keV) was carried out and an upper limit for the resonance strength (ωγ ≤ 8 × 10^{10} eV) was reported in (1992BE21).
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). Proton widhts of states near the proton threshold were measured by (1989LA19). See also (1987ER05).
Measurements and DWBA analysis of differential cross sections at E_{α} = 65 MeV are reported in (1992YA08). Measured level energies and spectroscopic information are included in 18.32 (in PDF or PS).
See (1983AJ01).
See (1983AS01, 1984AS05, 1989LE1L).
(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 MeV) 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). Multipole decomposition of data from measurements at E_{p} = 494 MeV is reported in (1994ME07). See also (1978AJ03, 1987AJ02). More recently the (p, n) reaction as a probe of beta decay strength is discussed in (1987GO1V, 1987TA13, 1988MA53). See also (1989RA1G). Studies of stretched state excitation are described in (1986AN1E) and measurement of spin observables at E_{p} = 135 MeV are discussed in (1989WAZZ, 1990WAZT). Total cross sections for ^{18}O production from ^{18}O(p, n) were measured by (1990WA10). See (1988HI1F, 1991GU05) for related applications.
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. A_{y} measurements for t_{0} have been reported at E(^{3}He) = 33 MeV. See (1983AJ01) for references.
The reaction was studied at E(^{6}Li) = 156 MeV by (1990MO13). Evaluated cross sections for GamowTeller transitions at 0° and strengths for analogous beta decays were compared.
The halflife of ^{18}Ne is 1672 ± 8 ms [see ^{18}Ne]. The decay is to ^{18}F*(0, 1.04, 1.08, 1.70 MeV): see 18.33 (in PDF or PS). and reaction 1 under ^{18}Ne.
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 MeV): see (1983AJ01). Cross sections for the (γ, n_{0}) photoneutron reaction were measured between 48° and 139° for E_{γ} = 15  25 MeV by (1989KU10). The E1 absorption strength was deduced.
Cross sections have been measured at E_{n} = 18, 21, 23, 25, and 27 MeV (1991HA17).
Angular distributions have been reported to many states of ^{18}F with E_{x} ≤ 6 MeV: see 18.20 (in PDF or PS) in (1983AJ01). See also (1987AJ02). Spectroscopic factors derived from measurements of E_{p} = 18.6 MeV are discussed in (1987VA28). See also (1989VAZM).
See (1972AJ02, 1978AJ03), and see (1989VAZM) for cross section measurements and deduced level energies and spectroscopic factors. A recent measurement of total cross sections at E_{d} = 5  12 MeV (1993AB18) detected eight resonances with widths Γ ≈ 200  400 keV.
See (1978AJ03, 1987VA1I, 1988GOZB), and see (1989VAZM) for cross section measurements and deduced level energies and spectroscopic factors.
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 MeV): T = 1. Measurements of the TAP for E_{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 MeV). See (1972AJ02, 1978AJ03, 1983AJ01) for references and for other results and (1987HI1B) for applications. Use of this reaction for ^{18}F production is discussed in (1991GU05).
See (1987GOZX).
The ^{18}F yield from protons on ^{23}Na at E_{p} = 20  67.5 MeV was measured (1992LA25) and cross sections were deduced.
See (1984NE1A).
Cross sections have been measured for E(^{16}O) = 13.6 GeV/nucleon by (1993CU05).
