(See the Energy Level Diagram for 14N)
GENERAL: See also Table 14.5 [Table of Energy Levels] (in PDF or PS).
Theory: See (1955AD1A, 1955OT1B, 1956EL1B, 1956FR1A, 1957BA1H, 1957GR1D, 1957VI1A, 1958FA1A, 1958MA1K, 1958MO17, 1958SK1A, 1959WA16).
Resonances are reported at Eα = 1.51, 1.64, 2.16, 2.26, 2.95, 4.53, 4.85, and 5.36 MeV: see Table 14.6 (in PDF or PS) (1953SH64, 1955SH46, 1956BO61, 1958MA1J, 1959GI47). Angular distributions have been measured at Eα = 1.51 and 2.16 MeV (1955SH46).
Observed resonances in the yields of γ-rays (from 13C*) and of various proton groups are given in Table 14.6 (in PDF or PS). Studies of the angular distributions of protons (1953SH64), γ-ray angular distributions, and (p-γ) correlations (1954ST20) lead to the Jπ assignments given in the table. Angular distributions of the protons at the Eα = 1.51 and 2.16 MeV resonances are identical with those of the neutrons at the same resonances. However, the reduced neutron width at Eα = 1.51 MeV is 5.7 ± 0.5 times the proton width, while at Eα = 2.16 MeV the ratio is near unity. It is suggested that strong isobaric spin mixing must occur for the Eα = 1.51 MeV state: 14N*(12.70) (1955SH46: see also (1957BA1K, 1958MC63)).
Observed resonances are exhibited in Table 14.6 (in PDF or PS) (1953SH64).
Evidence is reported for levels of 14N at 0, 2.0, 3.15, 3.85 and 4.8 MeV (± 0.3 MeV) (1956QU1A). See also (1944PE1A, 1955BR1A) and (1955AJ61).
At Ed = 1.50 MeV, the cross section is less than 1 μb (1955AL16).
Resonances in the yields of protons and neutrons are displayed in Table 14.7 (in PDF or PS): see (1955MA76, 1956BO08, 1956KO26, 1956MC88, 1956VA17, 1957JA37, 1957SA01, 1958MC63). See also (1948BA02, 1949BO67, 1950PH1A, 1957DE22).
Angular distributions of protons for Ed < 1 MeV are reported to be strongly influenced by stripping effects (1956JU1E, 1956KO26, 1956VA17, 1957JU1A); the same influence is seen for Ed > 2 MeV (1956MC88: see 13C). In the region Ed = 0.8 to 1.7 MeV, however, (1957SA01) find no stripping contribution and analyze the observed distributions in terms of 5 resonances: see Table 14.7 (in PDF or PS). Although the Jπ assignments listed are determined in part by choosing γ2n ≈ γ2p, neutron reduced widths seem generally to be nearly a factor of 10 low (1957SA01). A detailed analysis for the region Ed = 2.5 to 3 MeV has been made by (1958MC63). Both stripping and compound nucleus formations are involved. See also (1955AL1D, 1955AL1E).
For Ed = 5 to 30 MeV, the course of the cross section indicates predominance of stripping over compound nucleus effects (1955WI43).
Reported resonances are given in Table 14.7 (in PDF or PS) (1956MC88, 1958MC63). A detailed analysis of the resonances at Ed = 2.502 and 2.735 MeV has been made by (1958MC63). See also (1954CA1C, 1956CA1J) and (1955AJ61).
The cross section rises from ≈ 0.1 mb at Ed = 16 MeV to ≈ 10 mb at 20 MeV. The magnitude of the cross section is indicative of the pick-up character of the reaction (1955WI43).
Proton groups have been observed corresponding to the first five states of 14N. Angular distributions of the various proton groups have been measured for E(3He) = 1.30 to 21 MeV (1957BR18: 1.30 to 2.66 MeV; p0, p1, p2), (1958JO20: 2.0 to 5.0 MeV; p0, p1, p2), (1958SW63: 6.05 MeV; p0, p1, p2, p3+4), and (1958WE1E: 21 MeV). At the lower energies, the distributions show both compound nucleus and direct interaction effects. At the higher energies, the forward peaking increases, and at 6.05 MeV the direct interaction character is well developed.
The de-excitation of the 3.95 MeV state has been studied; the direct ground-state decay is (3.7 ± 0.6)% of the total (1956GO42, 1957BR18); see also (1958MO17) and 13C(p, γ)14N. The angular distribution of the 2.31 MeV γ-rays is spherically symmetric while that of the 1.64 MeV γ-ray (from the 3.95 → 2.31 cascade transition) involves a 22% P2(cosθ) term, consistent with J = 0+ and 1+ for the 2.31 and 3.95 MeV states respectively (1956GO42, 1957BR18). The polarization of the 1.64 MeV γ-ray also indicates that the parity of these two states is the same (1958LI41). Since the Jπ assignments permit M1 transitions for both the ground state and cascade transitions from the 3.95 MeV level, the ground state transition would be expected to dominate by a large factor. However, the M1 matrix element effectively cancels for ΔT = 0, Tz = 0 (1957VI1A, 1958MO17, 1959WA16). The E2 transition is estimated to be 0.9%: the observed value of 3.7% must be ascribed to collective enhancement (1956EL1B, 1957VI1A). See also 14C(β-)14N and 15O.
This reaction has been observed at Eα = 42 MeV. The deuteron angular distribution is similar to the α-particle distribution in the 14N(d, α)12C reaction at Ed = 20 MeV (1958BO71).
Resonances are observed at Ep = 0.45, 0.55, 1.16, 1.25, 1.47, 1.55, 1.75, 2.10, and 3.11 MeV; their parameters are displayed in Table 14.8 (in PDF or PS); see also (1957JA37). The decay schemes of various levels of 14N, as derived from the γ-spectra in this and other reactions are exhibited in Energy Level Diagrams for 14N ((1953CL39, 1953WO41, 1956LE28, 1957BR33, 1957WI27) and D. Hebbard, private communication). At Ep = 114 and 126 keV, the capture cross sections are, respectively, (5.1 ± 2.0) × 10-3 μb and (8.2 ± 2.5) × 10-3 μb (1957LA15). The 0.45 MeV resonance involves both ground state decay and ≈ 4 MeV cascade radiation with about equal radiative widths (D. Hebbard).
The width of the Ep = 0.55 MeV resonance (Ex = 8.06 MeV) indicates s-wave formation (J = 0-, 1-) (1953WO41). The observed isotropy of the radiation supports this assignment (1949DE1A). The level is established as J = 1- from 13C(p, p)13C. (1957BR33) find a 1% anisotropy, indicating a d-wave admixture of ≈ 6%, θ2p(d) = 0.45; see, however, (1959WA04). The γ-width for the ground-state radiation indicates an uninhibited E1 transition, and hence T = 1 for 14N*(8.06) (1953CL39). The relative strength of the T-forbidden transition to 14N*(2.3) is about 2% (1956LE28, 1956PI1B, 1957BR25, 1957WI27), indicating a strong T = 0 admixture in 14N*(8.06). The fact that the 6.23 MeV state, J = (1-); T = 0 (see below) shows a similar contamination, suggests that these two states have a common parentage and contaminate each other (1957WI27): see, however, (1957BR25, 1957BR33, 1959WA04). The strength of the transition 8.06 → 5.69, Γγ ≈ 0.7 eV, suggests E1 radiation and hence J = 0+, 1+, 2+; T = 0 for 14N*(5.69). The further transition 5.69 → 2.3 rules out J = 0+. J = 2+ is excluded by the strength of 8.62 → 5.69, Γγ = 0.7 eV (1956LE28, 1957WI27); see, however, (1957BR33). According to (1959WA04), the transition strength of 8.06 → 5.69 also admits M1, ΔT = 1, and hence J = 1-; T = 0 for 14N*(5.69). The transition 14N*(3.95) → g.s. is 5.5 ± 1.0 % of the cascade, 3.95 → 2.3 (1956LE28, 1956PI1B). See also (1954HI1B, 1956GR17) and 12C(3He, p)14N.
The narrow Ep = 1.16 MeV resonance, 14N* = 8.62 MeV, J = 0+ (from 13C(p, p)13C) shows strong transitions to the ground state and to 14N*(3.95, 5.69): hence T = 1 (1959WA16). The strength of transition to 14N*(6.23) indicates E1 radiation, J = 1-; T = 0 for the 6.23 MeV state (1957WI27). However, the angular correlation in the cascade 8.62 → 6.23 → g.s. favors J = 1+ or 2+ for 14N*(6.23) (1956GO1L, 1956GO39, 1957GA1B, 1957GO30). In this case, the transition strength still requires J = 1; T = 0 for 14N*(6.23). The strong transition 8.62 → 3.95 requires dipole radiation and hence J = 1 for the latter (1959WA04).
The Ep = 1.25 MeV resonance (Ex = 8.71 MeV, J = 0- from 13C(p, p)13C) is established as due to s-waves by its width (1953WO41). Again the large γ-width is consistent with E1 radiation and T = 1 (1953WI1A). The γ-spectrum has been studied by (1957BR33) at Ep = 0.9 and 1.0 MeV, where the main effects should be due to the Ep = 1.25 MeV resonance: see, however, (1957JA37, 1959WA04). The results indicate relatively strong transitions to both the 4.9 and 5.7 MeV levels (see Energy Level Diagrams for 14N) and would appear to exclude the assignments J = 0-, 1- respectively for these levels. An assignment J = 1+ to 14N*(5.10) is suggested. At Ep = 1.4 MeV, (1959WA04) finds no evidence of transitions to the 5.10 MeV state. It is pointed out that some of the reported transitions may derive from the background or from other resonances.
The angular distribution of the ground-state γ-rays at the Ep = 1.75 MeV resonance (14N*(9.17)) indicates J = 1+, 2+ or 2-; the relatively large γ-width, 13.3 eV, suggests an uninhibited E1 transition, J = 2-; T = 1 (1951DA1A, 1951DA1B, 1953WO41, 1956MA87). However, the polarization is consistent with M1 or E2 but not E1 (1958ST33); see also (1959WA16). The total width is < 400 eV (1956MA87), < 150 eV (1958PA1D), 75 ± 50 eV (1958BO71). The resonant energy is 1746.9 ± 0.8 (1956MA87), 1747.6 ± 0.9 keV (1958BO76). If the transition 9.17 → 6.44 is dipole (ωΓγ = 1.3 eV), and if J(9.17) is 2, the angular distribution requires J(6.44) = 3 (1953WO41) and T = 0 (1959WA16). See also (1958ME77).
From elastic scattering work (see 13C(p, p)13C), the Ep = 1.47 MeV resonance, 14N* = 8.90 MeV, has J = 2-, with 3- and 1- possible. The resonance at Ep = 2.11 MeV, 14N* = 9.50 MeV has J = 3-, with 2- and 1- possible. A study of the gamma decay scheme and angular distributions confirms the assignments J = 2- (T = 1) and J = 3-; T = 1 for these two levels. For the latter, the channel spin mixture is (56 ± 14)%Jc = 0. Levels at 14N* = 5.83 and 5.10 MeV are J = 3(-) and J = 2. The mean lives for these two levels, determined by Doppler shift, are 0.5 < τ < 6.5 × 10-13 sec, and τ > 3 × 10-13 sec, respectively. The 7.02 MeV level probably has J = 2, while the 6.44 MeV level has J = 2, 3 or 4. Shell-model assignments and the correlation with the levels of 14C are discussed in some detail (1959WA04). See also (1956WI1G).
At the Ep = 3.11 MeV resonance (Ex = 10.43 MeV), the angular distribution of ground-state γ-rays is 1 - (0.40 ± 0.02)P2(cosθ), indicating J = 2-, formed by d-waves with channel spin mixture σ(Jc = 0)/σ(Jc = 1) = 3/2, followed by E1 radiation, or J = 2+, f-wave formation, Jc = 1, M1 radiation. The relatively large gamma width, 17 eV, suggests E1 radiation and T = 1 (1957WI30). According to (1959WA16), however, the assignment J = 2+ (p or f) is equally satisfactory. The integrated cross section is 0.033 MeV-mb, in good agreement with the corresponding value for 14N(γ, p)13C (1957WI30).
The elastic scattering has been studied for Ep = 0.15 to 0.75 MeV by (1957HE1C), for Ep = 0.45 to 1.60 MeV by (1954MI05) and for Ep = 1.5 to 3.4 MeV by (1957ZI09, 1958ZI17): see Table 14.8 (in PDF or PS). Assignments and level parameters for Ep < 2 MeV are based in part on a qualitative analysis of the elastic scattering and in part on 13C(p, γ)14N (1952SE01, 1953WO41, 1954MI05). Near the 0.55 MeV resonance, the cross sections of (1957HE1C) are about 10% lower than those of (1954MI05). A close fit to the theory is obtained from Ep = 0.12 to 0.65 MeV when the energy variation of Γ and E0 are taken into account (1957HE1C: see also (1956CH1E)). Above Ep = 2 MeV, the non-resonant background requires s, p and d waves. At the 9.51 MeV level, the channel spin mixture σ(1)/σ(0) = 2/3 corresponds to (5/2, 1/2) in j-j coupling (1957ZI09, 1958ZI17): compare 14N*(10.43) in 13C(p, γ).
The yield of γ-rays in reaction (b) has been measured for Ep = 3.6 to 5.0 MeV: the 3.1 MeV γ-yield shows broad resonances at Ep = 3.80, 4.1, and 4.14 MeV, while the 3.7 MeV γ-yield shows one strong resonance at Ep = 4.52 MeV (14N*(11.1, 11.36, 11.39, 11.7)) (1957BA29, 1957CO1G).
Observed resonances are exhibited in Table 14.9 (in PDF or PS) (1950AD1A, 1951BL1A, 1953BA1C, 1957BA29). Absolute cross sections have been determined from threshold to 5 MeV by (1958MA1F, 1959GI47). The behavior at threshold appears to reflect the effect of a bound level, possibly that at Ep = 3.11 MeV. See also (1958BL55).
Observed neutron groups are exhibited in Table 14.10 (in PDF or PS) (1952BR1C, 1953BE1D, 1955BI1B, 1955GR1D). At Ed = 0.86 MeV the third excited state shows a strong, l = 0 stripping pattern (1955GR1D: see also (1955BI1B)). In the range Ed = 0.4 to 4.2 MeV, a single strong neutron threshold occurs at Ed = 0.422 ± 0.005 MeV (14N*(5.685 ± 0.007)). The outgoing neutrons are likely to be p-wave, and the incident deuterons s-wave (because of their low energy): the results are consistent with J = 1+ (1955MA76); see, however, (1959WA04). Observed γ-rays attributed to transitions in 14N are shown in Table 14.11 (in PDF or PS) (1952TH24, 1955BE62, 1955MA36, 1958RA13). A study of the angular correlation of internal pairs indicates that the transition 14N*(5.69) → g.s. is M1 or E2; of the two transitions (4.91 → g.s.) and (5.10 → g.s.), one is E1 and the other is E2 or M1 (1958CH1A). See also (1958GO81). See also (1955AU1A, 1956EL1B; theor.).
Neutron thresholds have been observed at Ep = 671.5 ± 0.5 and 3149.6 ± 1.1 keV, corresponding to the ground state of 14N and to an excited state at 2.3119 ± 0.0012 MeV (1956SA06). See also 15N.
The cross section for neutron production, reactions (a) and (c), exhibits a maximum at Eγ = 22.5 MeV, Γ = 3.2 MeV, σ = 15.3 mb (1954FE16: see also (1951JO1B, 1957LI1A)). Below this maximum, there are less intense peaks in the cross section of reaction (a) at (≈ 10.8), ≈ 11.5, and ≈ 12.7 MeV. The latter two have widths of ≈ 0.3 and ≈ 1 MeV, respectively (1955CH1B). At Eγ(max) = 23 MeV, proton + recoil energies (reaction (b)) of 0.51, 1.63, and 2.92 MeV are observed, corresponding to the 8.06, 9.18, and 10.43 MeV levels of 14N. Integrated cross sections of 0.6, 0.8, and 1.2 MeV-mb respectively, are found, in good agreement with those obtained from the inverse reaction 13C(p, γ)14N (1956WR22). In a resonance absorption experiment, using γ-radiation from 13C(p, γ)14N at Ep = 1.76 MeV, ((1957HA1K) and private communication) find for the 9.17 MeV level of 14N, Γ = 0.07 ± 0.02 keV, σres ≈ 6 b, (2J + 1)Γγ ≈ 48 eV. For the 8.06 MeV level, (1956GR17, 1958GR97) finds Γγ = 10.5 ± 6 eV (compare 13C(p, γ)14N).
At Eγ(max) = 70 MeV, reaction (d) appears to proceed via a level at 8.2 MeV in 10B (which then decays by proton emission) (1956LI05). See also (1950HO80, 1954BI04, 1955RA1E, 1955SA1F, 1955TI1A, 1956GO1G, 1956JO1C, BE57A, 1958CO1F, 1958JO1C, 1958RH1A) and (1955AJ61).
Elastic scattering of 14 MeV neutrons has been studied by (1952CO41, 1954SM97, 1956BU95). At En = 3.95 MeV, a 2.30 ± 0.05 MeV γ-ray is observed (1956DA23). See also 15N.
At En = 14 MeV, deuteron groups are observed leading to 13C*(0, 3.7). The reduced width of 14N(0) for separation into p + 13C(0) is θ2p0 = 0.025; for separation into p + 13C*(3.7), θ2p2 = 0.06. The ratio is consistent with 14N(0) = 3S1 but not with pure 3D1. On the other hand, the value of θ2p0, when suitably corrected, is consistent with a large amount of D character for 14N(0). Upper limits for decomposition into 13C*(3.09) or 13C*(3.86) are θ2p1 < 0.003 and θ2p3 < 0.03 (1957CA07): see also 14N(p, d)13N.
Angular distributions measurements for ground-state deuterons at Ep = 18 MeV indicate ln = 1. The peak cross section (18°, c.m.) is 5.0 ± 0.6 mb/sr, yielding a reduced width θ2 = 0.021 for 14N(0). With appropriate correction, the reduced width is in qualitative agreement with that calculated form the independent-particle model and the result suggests that the 14N ground state is largely D. Upper limits of 0.1 to 0.4 mb/sr are quoted for the transition to the first excited state of 13N and are taken to indicate admixtures of p8s2 or p8sd in 14N of a few per cent or less (1954ST1D, 1956ST1D). See also 14N(n, d)13C.
Elastic proton scattering has been studied at Ep = 9.5 MeV (1954FR38, 1957GI14), Ep = 9.8 MeV (1957HI56), 19.4 MeV (1956VA1B, 1957VA1B) and 20 MeV (1955CH1A). Analysis in terms of the optical model is not entirely satisfactory (1956BU95, 1957HI56). Elastic deuteron scattering has been studied at Ed = 8 MeV by (1952GI01).
Observed inelastic proton and deuteron groups are shown in Table 14.12 (in PDF or PS) (1952AR29, 1953BO70, 1956BU16). At Ep = 9.5 MeV, the p1 group (to the 2.3 MeV first excited state) is surprisingly weak: < 1/6 of p2 (1954FR38). At Ep = 6.98 MeV, θ = 90°, the ratio of the intensities of the p1 and p2 groups to the p0 (elastic group) is 5 and 10 %, respectively. For deuterons, the ratio for the d2 group is 10%, while an upper limit of about 0.5% is set for the d1 group corresponding to the T = 1, 2.31 MeV state, as expected from the T selection rule (1953BO70). Angular distributions of the p0 and p2 groups have been studied at Ep = 9.5 MeV (1954FR38). See also (1956BA1G; theor.). At Ep = 96 and 185 MeV, inelastic groups with Q = -9.2, -17, and -21.5 MeV are reported (1958TY46: see also (1956ST30)). See also (1958MA1B, 1958TY49). Inelastic scattering of deuterons is also reported at Ed = 9 MeV by (1956GR37): the d2, d3 and d4 groups are observed.
For Ep = 3.9 to 4.9 MeV, the 2.3 MeV γ-radiation is isotropic, confirming the J = 0 assignment to the first excited state (1956BA34). The Doppler shift is very nearly the maximum possible, indicating a half-life less than 3.5 × 10-13 sec (1955SH84), < 2 × 10-13 sec (1955TH1A). See also 15O.
At Eα = 21.5 MeV, inelastic alpha groups are reported to 14N states at 3.95 ± 0.04, 5.12 ± 0.07, 5.79 ± 0.07, 6.47 ± 0.09, 7.02 ± 0.06, 7.94 ± 0.07, 8.45 ± 0.07 and 10.05 ± 0.07 MeV. Except for the 7.94 MeV level, which has recently been observed in 13C(p, γ)14N, the last three have not been reported in other reactions. The absence of the Q = -2.3 and Q = -8.06 MeV groups is consistent with their T = 1 assignment (1956MI17: see also (1956WA29)). At Eα = 31.5 MeV, the upper limit for the α1 group, corresponding to 14N*(2.3), T = 1, is 6% of the α2 group (1956WA29).
The decay proceeds almost entirely to the Jπ = 0+; T = 1 state of 14N at 2.3 MeV: see 14O.
At Ep = 18.6 MeV, the transitions to the ground and first excited states of 14N have been observed. The angular distributions of both groups are fitted by ln = 1 pickup curves. The peak cross section for the ground state is about 7 times greater than that for the 2.31 MeV state (1957BE49, 1957SH1B). See also (1956FR1A; theor.).
Alpha-particle groups leading to 14N levels at 0, 3.95, 5.01, and 5.70 MeV are reported by (1951AS1A); 0, 3.98 ± 0.04, 5.06 ± 0.05 MeV by (1951BU1A); 0, 3.9, and ≳ 5 MeV by (1953FR23); 0, 3.949 MeV by (1955BR1B). The group leading to 14N*(2.3), T = 1, is ordinarily not observed; however, careful studies in the range Ed = 5.5 to 7.5 MeV (1956BR36) and Ed = 6.8 to 8.9 MeV (1958DA16) show a weak α1-group whose intensity shows marked resonance effects. The observed intensity is consistent with the expected isobaric spin impurity of the 16O, 18F*, and 14N* states involved (1956BR36): see 18F. Angular distributions of α-groups have been measured at Ed = 7.0 MeV (1956BR36; α0, α1, α2), 6.8 and 8.9 MeV (1958DA16; α0, α2) and at 19 MeV (1953FR23; α0). See also (1957EL1D; theor.) and (1953SP1A, 1956GR37).