Energy levels of 24Na from the 23Na(d,pγ)24Na reaction

Excited states in ²⁴Na have been investigated by means of the ²³Na(d, pγ)²⁴Na reaction at incident deuteron energies of 2.5 and 2.8 MeV. Excitation energies and γ-ray decay for levels up to 4.2 MeV have been determined from proton-gamma coincidence spectra obtained with a surface barrier detector and a Ge(Li) detector on-line with a computer. Two new levels at 3944 ± 2 and 4195 ± 3 keV excitation energies are reported.     

Lifetimes and branching ratios of excited states of 24Na

The decay of ²⁴Na levels below 4.3 MeV excitation was studied by means of the ²³Na(d, pγ)²⁴Na reaction at E_d = 2.45 MeV. Gamma-ray spectra were measured at three angles, in coincidence with proton groups detected around 180°. Excitation energies, branching ratios and Doppler shifts were determined. Mean lives were obtained for the levels at 1341 keV (62±15 fs), and 1846 keV (200±50 fs). The 1347 keV level has τ >3 ps. For other levels above 1 MeV upper limits of ≈ 60 fs are set. In some cases spin restrictions follow. In particular J = 2 is assigned to the 1341 keV level.     

The brute-force polarization of 23Na and the 23Na(n, γ)24Na reaction

A Na target has been polarized by brute force to 22% and the γ-radiation produced by polarized thermal neutron capture has been investigated. The J^π = 2⁺ channel spin contribution has been determined model-independently and unambiguously for 22 primary transitions. The average J^π = 2⁺ channel contribution is 5.8(5)%. The data resulted in one spin assignment and two spin restrictions. The energies and lifetimes of positive-parity levels as well as branching ratios and the magnetic moment of the ground state are in agreement with a shell-model calculation in the complete sd shell.     

Formation of 24Na in “fission-like” reactions

Formation of ²⁴Na in reactions induced by protons of energy 40–85 MeV on ⁴⁰Ca, ⁴⁵Sc, ⁴⁸Ti, and naturally occurring V was measured. Evidence is presented that ²⁴Na is formed in a binary break-up reaction. The results are compared with transition state (fission) calculations.     

The lowest five levels of 25Na: Lifetime,spin and transition strength measurements

Particle-gamma angular correlations and lifetime measurements (delayed coincidences and DSAM) have been performed in the ²⁶Mg(t, α)²⁵Na reaction. The results for J^π (and τ_m) are $\text{3}\text{2}{}^{\mathrm{+}}\text{or}\text{5}\text{2}{}^{\mathrm{+}}\text{(7.4±0.4}\text{ns}\text{),}\text{1}\text{2}{}^{\mathrm{+}}\text{(2.3}{}_{\mathrm{?0.8}}{}^{\mathrm{+2.0}}\text{ps}\text{),}\text{3}\text{2}{}^{\mathrm{+}}\text{(<25}\text{fs}\text{),}\text{7}\text{2}{}^{\mathrm{+}}\text{(200±140}\text{fs}\text{)}\text{and}\text{3}\text{2}\text{or}\text{7}\text{2}$ for the levels at 90, 1069, 2202, 2417 and 2788 keV respectively. Branching and mixing ratios have been measured, and strengths of the transitions calculated. Evidence for configuration mixing is given. The results are compared with shell-model calculations.     

The reaction 23Na(n, γ)24Na studied with unpolarized and polarized thermal neutrons

The γ-radiation produced by thermal neutron capture in a natural Na sample has been investigated. Of the 158 γ-rays ascribed to the ²³Na(n, γ)²⁴Na reaction, 143 have been placed in a ²⁴Na decay scheme accounting for 100(2) % of the total primary strength. The reaction Q-value amounts to 6959.42 ± 0.08 keV. The data resulted in spin assignments for four and spin restrictions for six levels.The circular polarization of 14 γ-rays from the capture of polarized neutrons has been measured. The contribution of the J^π = 2⁺ channel in thermal capture was determined to be below 5 %.     

Energy levels in 23Na from the 19F(α, n)22Na reaction

The 0° differential cross sections for the production of four neutron groups, populating the ground state and the four lowest excited states of the residual ²²Na nucleus were measured. For incident α-energies of up to 4.7 MeV more than sixty resonances, corresponding to levels in ²³Na were seen; most of them had not been reported previously. Angular distributions were measured at eight α-energies. The excitation curve for the ¹⁹F(α, P₁γ)²²Ne reaction was also obtained and eighteen additional levels were identified in ²³Na.     

The reaction 26Mg(d, τ)25Na and the structure of 25Na

The nuclear structure of the nucleus ²⁵Na has been studied with the (d, τ) proton pick-up reaction on ²⁶Mg at a bombarding energy of 29 MeV with an energy resolution of 25 to 30 keV FWHM. Excited states in ²⁵Na have been measured up to excitation energies of 8 MeV. The experimental angular distributions show good agreement with the predictions from the standard distorted-wave Born-approximation theory (code DWUCK; non-local and finite range). However, the agreement is improved considerably if the procedure of Kunz, Rost and Johnson is applied which accounts approximately for strong couplings to inelastic channels in the initial and final (strongly deformed) nuclei. The influence of this treatment on the evaluation of spectroscopic factors has been investigated and was found to be particularly pronounced for l = 0 transitions. The measured spectroscopic factors are compared to those from other experimental work and from shell-model and Nilsson-model calculations.     

The 24Mg(α, α')24Mg reaction; statistical analysis

The ²⁴Mg(α, α')²⁴Mg reaction to the 1.37 MeV state has been studied over an α-energy range of 9.625–13.825 MeV, in ≈40 keV steps, and over a 25°–160° angular interval. These cross sections have been analysed in terms of statistical theory and a number of deviations from its predictions are found. These deviations point to the importance of non-statistical processes, such as intermediate structure, to the α-scattering. The average compound nuclear width o₁ 62±7 keV is found for ²⁸Si over the 18–22 MeV excitation.     

Gamma-ray transitions from the lowest f = 2 states of 24Na and 28Al

Using a DWBA code which exactly includes finite-range and recoil effects, calculations are shown for ¹²C(¹⁶O, ¹²O)¹⁶O, ⁴⁰Ca(¹⁶O, ¹²C)⁴⁴Ti and ⁴⁰Ca(⁶Li, d)⁴⁴Ti which seem to be in quantitative agreement with the assumption that these reactions proceed via the simple one-step transfer of an α-particle.     

Electromagnetic decay of fragmented analogue states in 45Sc

The ⁴⁴Ca(p, γ) reaction was studied for 45 resonances for E_p = 1.6?2.2 MeV. The overall proton energy resolution was 300–350 eV; the γ-rays were detected with both NaI(T1) and Ge(Li) detectors. Partial and total γ-ray widths were measured for each of the fine structure states of the $\text{3}\text{2}{}^{\mathrm{?}}$ and $\text{1}\text{2}{}^{\mathrm{?}}$ analogue states at E_p = 1.65 and 2.04 MeV, respectively. The data are examined for correlations between the partial widths (Γ_p, Γ_p′, Γ_γi, Γ_γ^total) in different channels. The γ-ray intensities are compared with (τ, d) spectroscopic factors.     

Nuclear excitation by electron transition in 189Os

A precise experiment on nuclear excitation by electron transition (NEET) was first performed on ¹⁸⁹Os. An osmium film was bombarded with electrons of 72–100 keV to measure the absolute values of the cross section for osmium isomer (^189mOs) production. The threshold energy for this process is 74 keV, and the cross section is, e.g., 1.1 nb at 100 keV. The NEET probability derived from the measured excitation function is (1.7 ± 0.2) × 10^?7     

The 22Ne(d,n) 23Na reaction

Absolute differential cross sections are determined for 32 states from the ²²Ne(d, n) ²³Na reaction by the neutron time-of-flight method. A gaseous ²²Ne target was bombarded with 5.5 MeV deuterons and angular distributions taken from 0° to 160°. In addition yield curves were taken at a fixed angle of 10° in 0.5 MeV steps from 2.5 to 5.5 MeV. The analysis of both types of data used computer programs for DWBA and compound-nucleus calculations. With two exceptions and three additions the l_p values determined in the present experiment agree with those of a recent (τ, d) experiment on the same target nucleus. The two previous (τ, d) experiments show considerable differences in proton transfer strengths to various states. The present experiment agrees well with the one which showed generally lower strengths for individual states, and hence with an assumption of greater spreading of the single-particle strength. The implications of those results on the Nilsson-model scheme for ²³Na are discussed.     

Analyzing powers of the continuum spectra: 65 MeV polarized protons on 12C, 28Si, 45Sc, 58Ni, 93Nb, 165Ho, 166Er and 209Bi

Analyzing powers of the continuum spectra were measured for 65 MeV protons from ¹²C, ²⁸Si, ⁴⁵Sc, ⁵⁸Ni, ⁹³Nb, ¹⁶⁵Ho, ¹⁶⁶Er, ${}^{209}\text{Bi}\text{(}\text{p}\text{,}\text{p\#}\text{prime;}\text{X}\text{)}$ and ($\text{p}$, dX) reactions and from ⁹³Nb, ²⁰⁹Bi($\text{p}$, αX) reactions. The analyzing powers of the continuum spectra were found to be small at forward angles where the pre-equilibrium process is important. However they do not show a systematic tendency. This feature indicates the importance of the spin-dependent interaction as well as nuclear structure effects. On the other hand, the analyzing powers were very large and positive at backward angles where the shape of the energy spectra resembles that of an evaporation spectrum. The maximum values of the analyzing power in the backward hemisphere depend on the target mass for the A < 45 mass region and they are as large as 15%, 20% and 35% for ${}^{93}\text{Nb}\text{(}\text{p}\text{,}\text{p}\text{′}\text{X}\text{)}$, ($\text{p}$, dX), ($\text{p}$, αX) reactions at E_X = 20 MeV, respectively. These large values are mainly due to the entrance channel effect. There is no appreciable even-odd mass effect on the analyzing power for medium-mass nuclei. These features were unexpected from the conventional pre-equilibrium reaction models.     

Electromagnetic transition probabilities between the low-lying states of 203Tl, 205Tl and 209Bi

A high-accuracy investigation of absolute γ-ray yields and angular distributions after Coulomb excitation of ²⁰³Tl, ²⁰⁵Tl and ²⁰⁹Bi allowed the determination of B(E2) and B(M1) values in these nuclei. Some of the data obtained are compared with direct lifetime measurements and internal conversion data. The influence of deorientation effects on our results is discussed. A comparison is made between the experimental transition matrix elements and shell-model and core-coupling-model calculations. The “l-forbidden” M1 transitions, which are caused by core-polarization effects, have strengths of ≈ 10^?3 W.u. In ²⁰⁹Bi the strength of the $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{→}\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$. E2 transition is equivalent to a surprisingly large proton polarization charge of (2.8 ± 0.2)e.     

Lifetimes of levels in 25Na and 26, 27Mg excited via the 26Mg bombardment of 3H

Lifetimes have been measured for nine levels in ²⁵Na, the first two excited states of ²⁷Mg, and the First excited state of ²⁶Mg by bombarding a Ti³H target with 40 MeV ²⁶Mg ions. Mean lifetimes were determined by fitting the Doppler-broadened γ-ray lineshapes with lineshapes calculated using experimentally-measured stopping powers. The ²⁵Na results are compared to predictions of recent shell-model calculations.     

Spectroscopy of the continuum states of 24Mg using the 20Ne(α, α′) and 23Na(p, α) reactions

We have measured excitation functions for the ²⁰Ne(α, α′)²⁰Ne and ²³Na(p, α)²⁰Ne reactions in the energy ranges corresponding to, respectively, 17.85-21.67 and 19.35-20.65 MeV of excitation in ²⁴Mg, that is in the region of the sub-Coulomb resonances in ²⁴Mg observed in the ${}^{12}\text{C}\text{+}{}^{12}\text{C}$ reactions. By using statistical analysis techniques we have determined the energies of possible quasibound states in ²⁴Mg responsible for the deviations from the average trends in the above excitation functions and compared them to the energies of known sub-Coulomb resonances in ²⁴Mg. The comparison speaks in favour of interpreting the simple structures associated with the resonances as alpha-like configurations in the ²⁴Mg continuum.     

The 59Co (d, 3He)58Fe reaction and 58Fe levels in the particle-vibration coupling model

The ⁵⁹Co(d, ³He)⁵⁸Fe reaction at a deuteron energy of 33.3 MeV was used to populate proton hole states in ⁵⁸Fe. Angular distributions were measured for the states up to 6 MeV excitation. From DWBA analysis, l-values and spectroscopic factors were extracted. The particle-vibration coupling model was used to interpret the positive-parity states observed in the present experiment as well as the related properties of ⁵⁸Fe established so far. The model calculation has reproduced rather well the level properties of ⁵⁸Fe.     

Study of the 91Zr(d, 3He)90Y reaction

The ⁹¹Zr(d, ³He) reaction was studied at a deuteron energy of 28 MeV. Angular distributions were measured from 13° to 47°; l_p values were extracted for the prominent lines of ⁹⁰Y. The l_p values and transition strengths were determined by DWBA analysis. The angular distributions for the $\text{(π}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)(ν}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)}$ doublet (g.s. and 0.20 MeV state) exhibit the characteristic l = 1 shape. States at 1.42, 1.57, 1.64 and 1.81 MeV were also populated strongly in the (d, ³He) reaction; the 1.42, 1.57 and 1.81 MeV levels contain l= 1 transition strength and are most likely members of the $\text{(π}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{)(ν}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)}$ multiplet. The 2.03 MeV state has a characteristic l = 3 angular distribution and is suggested to be the only member of the $\text{(π}\text{f}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{)(ν}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)}$ sextet to be unambiguously observed in this study, most probably the 5^? or 4^? member. The members of the $\text{(π}\text{g}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)(ν}\text{d}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}$ sextet were populated weakly (less than 100 μb/sr) in this reaction.