(See Energy Level Diagrams for 18O)
Special states: (1978WI1B, 1982BA62, 1982BE1Z, 1982ZH01, 1983BE1W, 1983BR29, 1983LI10, 1983ME12, 1983WA17, 1983KI13, 1984AS07, 1984BA24, 1984BA55, 1984CH1V, 1984GA1T, 1984GE1A, 1984HA14, 1984SA37, 1984ST1E, 1984WI17, 1985BR20, 1985CA1Q, 1985DE24, 1985LE1K, 1985LE1L, 1985MA1Q, 1985MA1R, 1985RO1G, 1985SA29, 1985SO12, 1985SU10, 1985YU1B, 1986AN10, 1986AN07, 1986CA1T, 1986CA27, 1986GU1A, 1986KA1D, 1986YU1B, 1987WA1H, 1987YA03).
Electromagnetic transitions and giant resonances: (1982AL30, 1982BA62, 1982BR24, 1982RI04, 1983BR29, 1983IS1F, 1983KA28, 1983KI13, 1984AS04, 1984AS07, 1984BA55, 1984BR1L, 1984GA1T, 1984HA14, 1984ST02, 1985AL21, 1985DE24, 1985LE1L, 1985SU10, 1985WI17, 1986AN10, 1986CA27, 1986ER1A, 1986HAZY).
Astrophysical questions: (1981WA1Q, 1982BU1A, 1982CA1A, 1982RO1A, 1982WI1B, 1982WO1A, 1983CO1K, 1984BL1J, 1984HA1R, 1984HA1Z, 1984LA1J, 1985HA1Z, 1985HA1R, 1986CO2C, 1986DO1L, 1986LA1C, 1986WI1L, 1987HA1C, 1987HA1D, 1987PR1A, 1987WI11).
Applications: (1982MA1Q, 1982PI1H, 1983AM1A, 1983AM1D, 1983GR1L, 1983KI1D, 1983KU1C, 1983LI1T, 1983TA1P, 1984LE1G, 1984SH2A, 1985WA1R, 1985YO1B, 1985ZA1A, 1986CO2B, 1986DR1E, 1986DU1Q, 1986EN1A, 1986HO1Q, 1986HO1L, 1986NI1C, 1986XU1C).
Complex reactions involving 18O: (1981IC02, 1982MO1K, 1982SA1Q, 1983DE26, 1983EN04, 1983FR17, 1983FR1A, 1983GR10, 1983GR28, 1983LI10, 1983OL1A, 1983SA06, 1983VA23, 1983WI1A, 1984GR08, 1984HI1A, 1984HO23, 1984NA1D, 1985DE60, 1985GAZT, 1985HO05, 1985KAZQ, 1985MA1Q, 1985PO11, 1986AN1F, 1986HA1B, 1986IR01, 1986MA19, 1986ME06, 1986PO06, 1986SA30, 1986SC28, 1986SC29, 1986SO10, 1986VAZZ, 1987LI04, 1987RI03).
Pion capture and reactions (See also reaction 23): (1981SEZR, 1982BI08, 1982LI15, 1982LI1M, 1982LI1N, 1983AM1C, 1983AS01, 1983BE1W, 1983GE12, 1983HO02, 1983JO06, 1983LI08, 1983LI1U, 1983MA16, 1983ME1H, 1983OS1E, 1983RO07, 1983SE16, 1983ZE1C, 1984AL20, 1984AS05, 1984BL17, 1984GR27, 1984HU1C, 1984JO01, 1984KA26, 1984SC09, 1984TR15, 1985AL15, 1985BI01, 1985CA1Q, 1985CH23, 1985GI01, 1985GM01, 1985KE1A, 1985SE08, 1985SE21, 1986BA1C, 1986FO06, 1986GE06, 1986GM01, 1986RO03, 1986SCZX, 1986SI11, 1987TE01).
Ground and 1.98 MeV states of 18O: (1978WI1B, 1982BA62, 1982CA12, 1982LO13, 1983ANZQ, 1983AR1J, 1984ANZW, 1984BA55, 1984FR13, 1984HA14, 1984ST1E, 1984WE04, 1985AN28, 1985BA1A, 1985DE24, 1986CA27, 1986RO03, 1987AB03, 1987SA15).
< r2 > 1/2 = 2.784 ± 0.020 fm: see reaction 22.
Q = -4.2 ± 0.8 e · fm2 [weighted mean of -3.6 ± 0.9 and -5.8 ± 1.5 e · fm2: see (1983GR28); see also (1983AJ01)].
B(E2; 0+ → 2+) = 39.0 ± 1.8 e2 · fm4 [(1979FE06, 1983GR10); see also (1983AJ01)]; = 44.8 ± 1.3 e2 · fm4 (1982NO04); = 47.6 ± 1.0 e2 · fm4 (1982BA06); see also (1987RA01).
For a discussion of the hexadecapole deformation see (1983GR10). See also (1987RA01).
See (1986CU02) for production cross sections of 1.98 MeV γ-rays.
Angular distributions of proton groups have been measured to the states shown in Table 18.5 (in PDF or PS) at E(6Li) = 28 MeV (1986SM01). It is found that when σtot to a particular state in 18O is large in this reaction, it is also large in the 12C(7Li, p) reaction. The relationship between the cross sections in this reaction and in reaction 1 depends on the parity of the final states (1986SM01).
Resonances in the yield of capture γ-rays are observed at Eα = 1.14, 1.79, 2.09, 2.33, 2.44, 2.55 and 2.64 MeV: see Tables 18.6 (in PDF or PS) here and 18.5 (in PDF or PS) in (1978AJ03). Gamma-ray angular distribution and correlation measurements lead to Jπ = 4+, 1-, 1- and 5- for 18O*(7.11, 7.62, 8.04, 8.13), as well as to Jπ assignments for lower states involved in the cascade decay. See also (1982AL30, 1983GA02, 1985GA1J) and (1986HA2D; astrophysics).
Observed anomalies in the scattering [reaction (a)] for Eα = 2 to 8.2 MeV and the resonances in the relative neutron yield [reaction (b)] for Eα = 2.3 to 8.5 MeV are displayed in Table 18.6 (in PDF or PS). See also (1978AJ03) and (1985DE24, 1988UM1A; theor.).
At E(6Li) = 34 MeV angular distributions have been measured for the deuteron groups to many states of 18O (1981CU07) [see also (1983AJ01)] including 18O*(17.6 ± 0.2) (1982CU01). Jπ = 4+, 2+, 2+, (4+) and (4+) are suggested for 18O*(7.86, 8.9, 12.04, 14.6, 17.0) (1981CU07). The 2+, 4+, 6+ and 8+ members of the Kπ = O+2 rotational band based on 18O*(3.62) are 18O*(5.26, 7.12, 11.69, 17.6) (1981CU07, 1982CU01).
Angular correlations have been measured at E(6Li) = 34 MeV; these lead to the assignment of Jπ = 8+ to 18O*(17.6) (1982CU01) and to the assignment of Jπ = 4+, 5-, 6+, 7- and 8+ to sixteen states in 18O with 11.4 < Ex < 23.1 MeV (1983CU03) [see also for assignment of 18O states to bands]. At E(6Li) = 32 MeV (1983AR11) find that the strongest groups are those to (unresolved) structures at Ex = 17.05 and 18.95 MeV [each Γ ≈ 0.35 MeV] dominated by Jπ = 7-. 18O*(11.6, 12.6) with Jπ = (6+, 5-) and 5- are also observed (1983AR11). [See, however, the density of states]. See also (1985KO1B; theor.).
At E(7Li) = 20.4 MeV, triton groups are observed corresponding to a number of states of 18O with Ex < 12.6 MeV. Angular distributions were obtained for some of these, including 18O*(0, 1.98, 7.12, 11.69) with Jπ = 0+, 2+, 4+, 6+. The latter two are the most strongly populated in this reaction: they appear to be part of the ground-state rotational band: see (1972AJ02). See also (1983GA02, 1984RU1A).
Proton groups corresponding to states of 18O are displayed in Table 18.7 (in PDF or PS) (1981CO13). See (1976LA13) for a general discussion of the properties of the states of 18O. Lifetime measurements are reported in Table 18.4 (in PDF or PS) of (1978AJ03). See also reaction 17, (1982AN12, 1985AN17) and (1985BA1A; theor.).
At Eα = 65 MeV, the angular distribution to 18O*(3.55) [Jπ = 4+] has been studied. In addition 18O*(8.04, 9.15, 10.3) are also populated: see (1983AJ01).
At E(10B) = 100 MeV, 18O*(3.55) [first (d5/2)24+ state] is preferentially populated. 18O*(1.98, 5.26, 7.12, 8.0, 8.3, 9.1) are also observed. At E(13C) = 105 MeV the angular distribution to 18O*(3.55) has been measured. See (1983AJ01) and (1983OS07; theor.).
For reaction (a) see (1983AJ01). [The work reported there has not been published.] The scattering amplitude (bound) a = 5.62 ± 0.45 fm, σfree = 3.55 ± 0.25 b. The thermal cross section for reaction (c) is 235 ± 10 mb. See (1983AJ01) for references.
Observed proton groups are displayed in Table 18.8 (in PDF or PS). At Ed = 12 MeV a strong, asymmetric peak is observed corresponding to Ex = 9.0 MeV. On the basis of this work and the measurement of the cross section to a peak at about the same energy observed in the 16O(t, p) reaction, (1985FO11) assign Jπ = 4+ and a (1d5/2) (1d3/2) configuration to 18O*(9.0). Proton-γ coincidence measurements are shown in Table 18.4 (in PDF or PS).
Angular distributions involving 18O*(0, 1.98, 3.55) have been studied at E(12C) = 115 MeV: see (1983AJ01).
The cross sections for the (γ, p), (γ, n), (γ, 2n) and (γ, tot) [tot = total absorption] have been measured with monoenergetic photons to 42 MeV: observed resonances are displayed in Table 18.10 (in PDF or PS). All three of the partial cross sections have substantial strength in the giant resonance region; the (γ, 2n) cross section is a significant fraction of σ(γ, tot) and is even larger than σ(γ, p). Above the GDR the partial cross sections decrease but the integrated σ(γ, tot) between 29 and 42 MeV is about one-third of the value integrated from threshold to 42 MeV. The relative strengths of partial cross sections leads to the T assignments shown in Table 18.10 (in PDF or PS). The T< and T> components of the 18O photo absorption cross section are also derived (1979WO04). Structures in the (γ, α0) cross section are reported at Ex = 18.2, 20.9, 22.1 and 24.2 MeV (1982BA03; Ebrems.). The decay of the GDR to 14C, 15N, 16O, 17N and 17O states has been studied: see (1983AJ01). Less than 20% of the decays of states with 14.5 < Ex < 20 MeV goes via the n0 channel (1987JU07). See (1978AJ03) for the earlier work, (1985SH1P), (1985PY01) and (1983KA28, 1984VA1G, 1985PY01, 1985VA1C; theor.)
The Γγ0 of 18O*(6.20) is 0.18 ± 0.03 eV, assuming Γγ0/Γ = 0.88; Ex = 6202.7 ± 0.8 keV: see (1978AJ03).
The 18O charge radius, < r2 > 1/2 = 2.784 ± 0.020 fm, based on studies of the elastic charge form factors for Ee = 70 to 370 MeV, the resulting determinations of the difference in the 18O and 16O radii, and the rms radius of 16O: see (1983AJ01).
Inelastic scattering has been reported to many states of 18O: see (1983AJ01) and Table 18.11 (in PDF or PS) here (1982NO04, 1983BE36, 1986MA48). See also (1987DE43) and (1986GU05, 1986ST15, 1987MI1E; theor.).
Angular distributions for the scattering to 18O*(0, 1.98, 5.10) have been reported at Eπ± = 29.2 to 230 MeV [see (1983AJ01)] and at 50 MeV (1984TA1A; 18O*(0, 1.98)) at 140, 180 and 220 MeV (1984SE1A; 18O*(1.98)), at 164 MeV (1987CH14; 18O*(0, 1.98, 4.46, 5.10)) and at 180 MeV (1987MO07; 18O*(1.98)). < r2n > 1/2 = 2.81 ± 0.03 fm, < r2n > 1/2 - < r2p > 1/2 = 0.03 ± 0.03 fm: see (1983AJ01). For a discussion of the proton matter distribution in 18O see (1985BA27). For total reaction cross sections at Eπ = 50 and 65 MeV see (1986ME1C; prelim.). At Eπ = 165 MeV, the cross section for reaction (c) is larger for 18O than for 16O while reaction (b) has a lower cross section (1982PI06). For the (π+, 2p), (π+, pn) and (π-, pn) reactions at Eπ = 165 MeV see (1984AL20, 1986AL22). See also the "GENERAL" section here.
At Ep = 24.5 MeV (1974ES02) have studied the angular distributions of the proton groups to 18O*(1.98, 3.55, 3.63, 3.92, 4.46, 5.10, 5.26, 5.53, 7.12): a modified DWBA analysis leads to Jπ = 2+, 4+, 0+, 2+, 1-, 3-, 2+, 2- and 4+ for these states. A coupled-channels calculation suggests β2 = 0.37 ± 0.03, 0.56 ± 0.06 and 0.18 ± 0.04 for 18O*(1.98, 5.10, 7.12). Such calculations also support evidence for a rotational band involving 18O*(0, 1.98, 7.12). The 3- state at 5.10 MeV is stongly excited and collective in nature: B(E3) = 1120 e2 · fm6. For 18O*(1.98, 3.92, 5.26), B(E2) = 45, 8.3 and 24 e2 · fm4 (1974ES02). The 800-MeV data indicates that 18O*(7.12) can be described only if a large hexadecapole deformation is assumed (1982GL08). At Ep = 201 MeV forward angle σ(θ) have been measured to 18O*(8.21, 8.82, 16.40): it is proposed that 18O*(8.82) has Jπ = 1+ and that additional 1+ strength is located in a group centered at Ex ≈ 10.1 MeV as well as in the region Ex = 12.4 to 15 MeV. The 1+; T = 2 state 18O*(18.87), reported in (e, e'), is not observed (1987DJ01).
18O*(1.98) has |g| = 0.287 ± 0.015 [τm = 2.99 ± 0.12 psec]. 18O*(3.55) has |g| = 0.62 ± 0.10 suggesting a mainly (d5/2)2 configuration for this state: see (1983AJ01). See also 19F, (1983CE1A) and (1982KU04, 1982NA13, 1984PH02, 1986DE1G, 1986PE1E; theor.).
Angular distributions are reported with 178.4 MeV antiprotons to 18O*(0, 1.98) (1986BR04, 1986LE13). For atomic effects see (1986KO22). See also (1984PO1A), (1985LI16; theor.) and the "GENERAL" section here.
The elastic scattering has been studied at E(3He) = 11.0 to 41 MeV [see (1972AJ02, 1983AJ01)] and at 14 MeV (1982AB04), at 25 MeV (1982VE13) [the matter radius, < r2 > 1/2m = 2.59 ± 0.12 fm] and at E(3He) = 33 MeV (1983LE03; also Ay; and also to 18O*(1.98)). See also (1985HA11, 1987CO07; theor.).
Angular distributions of many α-groups have been measured in the range Eα = 21 to 40.5 MeV [see (1978AJ03)], at 23.5 MeV (1984SA28; to 18O*(1.98, 3.56 + 3.63, 3.92, 4.45, 5.1 - 5.53)) and at 54.1 MeV (1987AB03; g.s.). The transitions to 18O*(4.46, 5.10) are L = 1 and 3, respectively, fixing Jπ = 1- and 3- for these states. Measurements of α-groups near 180° for Eα = 20.0 to 23.4 MeV confirm assignments of natural parity for 18O*(1.98, 3.55, 3.63, 3.92, 4.46, 5.10, 5.26, 5.34, 6.20, 6.40, 7.12, 7.62, 7.86, 8.22, 8.29, 8.82, 8.96, 9.03, 9.10, 9.36, 9.41, 9.67, 9.72 ± 0.03, 9.88, 10.12, 10.30, 10.40, 11.62, 11.69). [See, however, Table 18.3 (in PDF or PS).] Levels at Ex = 5.38, 8.48 and 8.64 MeV were not observed, and those at 5.53, 6.35 and 6.88 MeV were populated weakly indicating unnatural parity: Jπ = 3+ and 2- respectively for 18O*(5.38, 5.53).
Alpha-gamma correlation measurements involving 18O states below Ex = 6.4 MeV [see Table 18.4 (in PDF or PS)] lead to Jπ = 1- and 3- for 18O*(6.20, 6.40). Other Jπ values agree with previous assignments. The transitions 3.92 → 1.98 and 5.26 → 1.98 are almost pure M1. For τm measurements see Table 18.4 (in PDF or PS) in (1978AJ03). For references see (1983AJ01). See also (1983WI12, 1984BR1P, 1984LA01, 1987AS01; theor.).
Elastic angular distributions have been studied at E(18O) = 32.3 to 57.5 MeV for reaction (a) [as well as at E(18O) = 70, 100 and 140 MeV (1982HE07)] and at E(18O) = 31 MeV for reaction (b). Yields and fusion cross sections are reported by (1982BA49, 1982HE07, 1985BE40, 1985CA01, 1986GA13). See also (1983VO1B). For the earlier work see (1983AJ01). For reaction (c) see (1986STZY).
Angular correlations (reaction (d)) have been studied at E(18O) = 82 MeV. 18O*(7.10, 7.62, 7.86, 8.04, 8.22, 10.30, 11.59, 12.55) are observed: the first seven of these have Jπ = 4+, 1-, 5-, 1-, 2+, 4+, 5- (1984BH01, 1984RA07). In addition 18O*(9.33, 9.65) are also populated [Γ ≈ 0.3 MeV]: a possible interpretation of the data is that these two are 3- states and that there is in addition a very wide (> 1 MeV) 2+ state at ≈ 9.5 MeV (1984RA17). See also (1983CA1N), (1983BI13, 1984HA53) and (1982GI1C, 1982LO13, 1983CI08, 1983MA29, 1984FR1A, 1985CH1R, 1986HA13; theor.).
Angular distributions have been measured at many energies for E(16O) = 24 to 54.5 MeV and E(18O) = 25 to 52 MeV, involving besides 18Og.s., 18O*(1.98, 3.55 + 3.63, 3.92, 4.46, 5.10, 7.12). At E(18O) = 126 MeV 18O*(9.0) is relatively strongly populated. See (1983AJ01). For yields and fusion cross sections, including the effect of 18O*(1.98), see (1985TH03, 1985WU03, 1986GA13, 1986TH01). See also (1983DU13), (1986BA69) and (1983SH04, 1985MA1T, 1986DAZS, 1986VI08, 1987LO01; theor.).
Angular distributions involving 18O*(0, 1.98) are reported at E(17O) = 36 MeV. Angular distributions [reaction (b)] have been studied at E(18O) = 20 to 52 MeV. 18O*(3.55 + 3.63, 4.46, 5.10, 7.12) are also populated; see (1978AJ03, 1983AJ01). See also (1986GA13) and (1982CI1C, 1983DU13).
Elastic angular distributions are reported at E(18O) = 36 to 56 MeV [see (1983AJ01)] and at 351.7 MeV (1984BUZX; also to 18O*(1.98)). See also (1986BL08, 1986GA13), (1983BI13) and (1982LO13, 1983CI08, 1984FR1A, 1985HU04, 1986HOZF; theor.).
Angular distributions have been measured at E(18O) = 62.1 MeV [reaction (a)] for the transitions to 18O*(0, 1.98, 5.10) (1982RE14). For fusion study [reaction (b)] see (1984DE38). See also (1985DE38, 1986OS05, 1986RO12; theor.).
Many states of 18O (Ex < 14.6 MeV) have been populated in this reaction: see Table 18.8 (in PDF or PS) in (1978AJ03). [Comment: Note, however, density of states.] Analyzing powers for the ground-state transition are reported at Epol. d = 12.4 MeV (1983EN02). See also (1983KI13; theor.).
At Ed = 80 MeV angular distributions have been measured for the 6Li groups to the ground state of 18O and to excited states at 1.98, 3.57, 5.10, 6.30, 7.8, 9.4 [± 0.04] MeV (1984OE02) [see also for Srel]. For earlier work see (1983AJ01).