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20Na (1998TI06)

(See Energy Level Diagrams for 20Na)

GENERAL: See Table 20.32 preview 20.32 [General Table] (in PDF or PS) and Table 20.33 preview 20.33 [Table of Energy Levels] (in PDF or PS) here.

μ = 0.3694 ± 0.0002 nm (1975SC20, 1989RA17)

1. 20Na(β+)20Ne Qm = 13.887

20Na decays by positron emission to 20Ne*(1.63) and to a number of other excited states of 20Ne: see Table 20.31 preview 20.31 (in PDF or PS) and reaction 59 in 20Ne. The half-life of 20Na is 447.9 ± 2.3 ms [weighted mean of values quoted in (1978AJ03, 1983CL01, 1989CL02)]; Jπ = 2+: see (1987AJ02). See also (1992KUZO, 1992KUZQ) and (1993BL10; instrumentation). The beta delayed alpha decay of 20Na has been studied by (1989CL02) [see reaction 2]. See also (1993XU06).

2. 12C(10B, nn)20Na Qm = -10.936

Extensive measurements of the decay of 20Na nuclei produced in the 12C(10B, nn) reaction were reported by (1989CL02). Measurements included β+ spectra, β delayed alphas, βνα triple correlation coefficients, branching ratios, 20Ne level energies and the 20Na half-life. Isospin mixing and the weak-vector coupling constant were deduced.

3. 12C(14N, 6He)20Na Qm = -21.576

An 82-MeV 14N beam was used by (1993BAZX) to study 20Na states up to Ex = 4.5 MeV. The cross section for the Ex = 2.646 MeV level was determined and the results suggest that state is not the mirror of the 1+ 3.173 MeV state in 20F as had been proposed. The results are consistent with the suggestion that the 2.646 MeV level is the mirror of the 2.966 MeV Jπ = 3+ state in 20F. See, however, reactions 5 and 8.

4. 19F(p, π-)20Na Qm = -140.611

Angular distributions and analyzing powers have been studied at Ep = 199.6 MeV to 20Na*(0.74, 1.85, 3.01, 4.11) [probably unresolved]: it is suggested that the latter two have J = 6 or 7 (1987CA05).

5. 19Ne(p, γ)20Na Qm = 2.195

The dominant process for the breakout from the HCNO cycle during hot hydrogen burning in stars in considered to be 15O(α, γ)19Ne(p, γ)20Na [see references in the following discussion]. Thus the 19Ne(p, γ)20Na reaction rate at stellar temperatures is of considerable importance. The nuclear levels above the 19Ne(p, γ) threshold are critical for calculation of the reaction rates and have been the object of several experimental studies by the 20Ne(3He, t) reaction (1988LAZY, 1989KU1D, 1989KU15, 1989SMZZ, 1990LA05, 1992SM03, 1995HO1G, 1995HO25, 1995GO16) as well as by 20Ne(p, n)20Na (1989KU15). See reactions 7, 8, 10 and Table 20.35 preview 20.35 (in PDF or PS).

The 20Na state at Ex = 2.646 MeV is presumed to be the strongest (p, γ) resonance and it has been the object of several studies [see refs. mentioned above as well as (1992GO10, 1992KU07, 1990DE34)]. See also (1995MI29). Work by (1993BAZX, 1993BR12, 1993CL09) strongly suggests that the state has Jπ = 3+ (the analog of the 20F 3+ state at Ex = 2.966 MeV) rather than 1+ as had been assumed in earlier work. More recent work described in (1994PA42, 1995HU13, 1995PA1K) determined a 90% confidence-level upper limit of 18 meV for the resonance strength of this level and provides arguments against the Jπ = 3+ assignment.

6. 19Ne(p, p)19Ne

Resonances in 20Na above the proton threshold were studied with radioactive 19Ne beams scattered off polyethelene targets by (1994CO12). Analysis by extended Breit Wigner, R-matrix and K-matrix formalism is described. Results are summarized in Table 20.34 preview 20.34 (in PDF or PS).

7. 20Ne(p, n)20Na Qm = -14.669

Early work on this reaction is described in (1987AJ02). More recently 20Na levels up to Ex = 3.636 MeV were studied at Ep = 35 MeV by (1989KU15). See Table 20.35 preview 20.35 (in PDF or PS).

The 20Ne(p, n) reaction at Ep = 136 MeV was used in measurements of Gamow-Teller strength (1991AN01) and in a study of isovector stretched-state excitation (1992TA04). A Δl = 2 angular distribution measured at Ep = 135 MeV (1995AN18) for the 20Na state at Ex = 2.645 MeV was determined to be consistent with Jπ = 3+.

A review of spin-isospin response in nuclei based on charge exchange reaction data is presented in (1989RA1G). See also (1987EL14). An analysis leading to total Gamow-Teller strength is described in (1988MA53).

8. 20Ne(3He, t)20Na Qm = -13.906

Early work on this reaction is summarized in (1987AJ02). See also (1987EL14). More recent measurements include those at E(3He) = 55.33 MeV (1988KU23, 1989KU15), at E(3He) = 25.5 MeV (1988LAZY, 1990LA05), at E(3He) = 29.7 MeV (1989SMZZ, 1992SM03) and at E(3He) = 33.4 MeV (1990CL06, 1993CL09). Energy levels and spin parity assignments obtained from these experiments are displayed in Table 20.35 preview 20.35 (in PDF or PS). See also (1989AR1H, 1989KU1D). A major concern of this work was the 20Na level at Ex = 2.645 MeV, which is presumed to be the strongest (p, γ) resonance in 19Ne(p, γ) [see reaction 5]. Detailed comparison of data on 20Ne(3He, t)20Na and the analogue reaction 20Ne(t, 3He)20F by (1993BR12) and (1993CL09) has led to the conclusion that the 2.645 MeV state in 20Na is to be identified with the Jπ = 3+ state at Ex = 2.966 MeV in 20F. This conclusion is supported by the work of (1993BAZX) [see however the discussion of reaction 5]. Measurements described in (1995HO1G, 1995HO25) have determined the γ branching ratio for this state to be Γγ/Γ ≈ 0.1. A reanalysis by (1995GO16) of earlier (3He, t) data has resolved conflicting values of excitation energies for levels above the proton threshold.

9. 20Ne(12C, 12B)20Na Qm = -27.256

A study of the response of nuclei to spin-isospin excitation displayed through charge exchange reactions such as 20Ne(12C, 12B)20Na is described in (1988RO17).

10. 20Mg(β+)20Na Qm = 10.726

The 20Mg decay to 20Na has been studied through β-delayed proton and γ-ray measurements. For the earlier work see (1979MO02, 1987AJ02). More recent studies are described in (1992KU07, 1992GO10, 1993PIZZ, 1995PI03). Half-lives measured for this decay are 95 ± 3 ms (1995PI03), 82 ± 4 ms (1992GO10), 114 ± 17 ms (1992KU07), 95+80-50 ms (1979MO02). See Table 20.36 preview 20.36 (in PDF or PS) for β-decay branching ratios and log ft values. A compilation of 20Na levels as observed in beta decay and other experiments is provided in (1995PI03), and serves as the basis for Table 20.33 preview 20.33 (in PDF or PS) here.

11. 27Al(20Ne, 27Mg)20Na Qm = -16.497

The Δ resonance is very strongly excited in this reaction at E(20Ne) = 950 MeV/A (1986BA16).