The γ-decay of the g92 analogue state in 59Cu

An investigation of the γ-decay of the $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ analogue state in ⁵⁹Cu has been performed using the ⁵⁸Ni(p, γ)⁵⁹Cu reaction. The (p, γ) excitation function has been taken in the range E_p = 3450–3650 keV. The decay schemes of the (p, γ) resonances at E_p = 3483, 3532 and 3547 keV, measured with Ge(Li) detectors, lead to eight new levels in ⁵⁹Cu with excitation energies between 1.8 and 4.7 MeV and to spin assignments of several states. The spins of the first two resonances are found to be ($\text{1}\text{2}$, $\text{3}\text{2}$) and ($\text{5}\text{2}$). The spin of the E_p = 3547 keV resonan is, from angular distributions, uniquely determined to be $\text{J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{+}}$ and this state is found to be the unfragmented analogue state of the $\text{E}{}^1\text{= 3.062}\text{MeV}$, $\text{J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{+}}$ parent state in ⁵⁹Ni. The measured complete decay scheme of this resonance shows that its isovector M1 decay is in disagreement with all existing theoretical predictions.     

Gamma-spectroscopic investigations on 67Ge

By γ-γ coincidence measurements following the ⁵⁷Fe(¹²C, 2nγ) reaction at E_12C = 40 MeV several new states above 1.5 MeV excitation energy in ⁶⁷Ge have been established. Spin and parity assignments on the basis of the angular distribution, linear polarization and γ-ray yield function indicate very similar structures in ^{67, 69}Ge. The positive-parity states can be followed up to the $\text{17}\text{2}{}^{\mathrm{+}}$ state at E_x = 3.07 MeV followed by a sequence of negative-parity high-spin states at nearly the same excitation energy relative to the $\text{9}\text{2}{}^{\mathrm{+}}$ single-particle state as in the neighbouring nucleus ⁶⁹Ge where these states were found to have strong single-particle admixtures. A reinvestigation of the spin of the E_x = 2.75 MeV level in ⁶⁹Ge resulting in a change of its spin from $\text{15}\text{2}{}^{\mathrm{+}}\text{to}\text{17}\text{2}{}^{\mathrm{+}}$ and for all spins above, removed the discrepancy concerning the spin assignments of corresponding levels in ^{67, 69}Ge. The excitation pattern of the Ge isotopes with 34 ≦ N ≦ 39 clearly indicate same structures probably due to the strong competition between collective and single-particle excitations along the whole chain similar to the results for the Zn isotopes.     

Das Niveauschema von 47V aus dem γ-zerfall von Analogresonanzen

A high-accuracy investigation of the level scheme of ⁴⁷V has been performed using the ⁴⁶Ti(p, γ)⁴⁷V reaction. The γ-decay schemes of the strong (p, γ) resonances at E_p = 1546, 1549, 1565 and 1572 keV lead to 17 new energy levels in ⁴⁷V with excitation energies between 2.7 and 5.1 MeV. From the (p,γ) angular distributions mixing ratios of the primary γ-transitions and J^π values of the resonances and of many states populated in the γ-decay have been determined. The total width of the E_p = 1549, 1565 and 1572 keV resonances for γ-decay are found to be Γ_γ = 0.12, 0.15 and 0.03 eV, respectively. The Q-value of the ⁴⁶Ti(p,γ)⁴⁷V reaction is found to be 5168.6 keV. The two resonances at E_p = 1549 and 1565 keV, which have $\text{J}{}^{\mathrm{\pi }}\text{=}\text{3}\text{2}{}^{\mathrm{?}}$, are interpreted as fine structure components of the analogue state of the $\text{E}{}^1\text{= 2.545}\text{MeV}\text{J}{}^{\mathrm{\pi }}\text{=}\text{3}\text{2}{}^{\mathrm{?}}$ level in ⁴⁷Ti while the ($\text{7}\text{2}$) resonance at E_p = 1546 keV might correspond to the $\text{E}{}^1\text{= 2.615}\text{MeV}\text{7}\text{2}{}^{\mathrm{?}}$ parent state in ⁴⁷Ti. The analogue-antianalogue M1 transition strength of the split $\text{3}\text{2}{}^{\mathrm{?}}$ analogue state is 0.01 single-particle units and fits well into our systematics of IAS → AIAS transitions in fp-shell nuclei.     

The reaction 36S(p,γ)37Cl: (I). Excitation energies and γ-ray branchings of bound states deduced from resonances in the range Ep = 500–2000 keV

Yield curves of the reaction ³⁶S(p, γ)³⁷Cl have been measured over the range E_p = 500–2000 keV with a highly enriched (81%) ³⁶S target. Proton energies, with a precision of typically 0.3 keV, and strengths are presented for the nearly 200 observed resonances. Several previously reported resonances, among which the well-known $\text{J}{}^{\mathrm{\pi }}\text{=}\text{7}\text{2}{}^{\mathrm{?}}\text{, E}{}_{\mathrm{p}}\text{= 1887}\text{keV}$ analogue resonance, are proven to be multiplets.At 75 selected resonances in the ranges E_p = 500–1200 and 1800–2000 keV the decay schemes have been studied. These measurements also provide rather detailed information on the γ-ray branching ratios of more than 50 bound states of which the majority has not been observed previously. Precision excitation energies have been determined; for the levels with E_x < 5 MeV the median uncertainty amounts to 30 ppm. The reaction Q-value is Q = 8386.34 ± 0.23 keV.These precision data invalidate several previous spin and parity assignments to low-lying bound states of ³⁷Cl. They also provide a basis for the lifetime measurements and spin and parity assignments to be discussed in the following paper.     

Proton induced resonances on 21Ne

Excitation curves for the ${}^{21}\text{Ne}\text{(}\text{p}\text{, γ)}{}^{22}\text{Na}\text{,}{}^{21}\text{Ne}\text{(}\text{p, p}\text{′γ)}{}^{21}\text{Ne and}{}^{21}\text{Ne}\text{(}\text{p, p}\text{)}{}^{21}\text{Ne}$ reactions have been obtained for E_p = 0.4–1.6 MeV. Neon gas enriched to 92 % in ²¹Ne was recirculated in a differentially pumped gas target system. The fifteen previously reported (p, γ) resonances were established and nineteen new (p, γ) resonances found. Anomalies in the elastic scattering yield were observed for fourteen resonances. The reported state at E_x = 7278 ± 7 keV in ²²Na was resolved into a doublet separated by 1 keV. All unbound states in ²²Na, observed previously in other reactions, have been confirmed as resonance states in the energy range covered, with the exception of the E_x = 7942 ± 7 keV state. The new E_p = 663, 694, 1235, 1432 and 1543 keV resonances correspond to new unbound states in ²²Na. Excitation energies, γ-ray decay schemes, resonance widths and strengths as well as limits on J^π assignments are reported for all the resonances. From the Coulomb excitation of the E_x = 350 keV, first excited state in ²¹Ne a value of B(E2) = 0.014 ± 0.002 e² · b² is deduced. The astrophysical as well as the nuclear structure implications of the present results are discussed.     

High-spin states in 40K investigated with the 26MG + 16O reaction

Yrast levels in ⁴⁰K and ⁴⁰Ar have been investigated with the ²⁶Mg(¹⁶O, pnγ)⁴⁰K and ²⁶Mg(¹⁶O, 2pγ)⁴⁰Ar reactions at a beam energy of 34 MeV. Gamma-ray angular distribution and γ-γ coincidence measurements have been performed with a high-resolution large volume Ge(Li)-NaI(Tl) Compton-suppression spectrometer. Gamma-ray linear polarizations have been measured with a three-crystal Ge(Li) Compton polarimeter. The ⁴⁰K decay scheme involves new high-spin levels at E_tx = 4365.6±0.3, 4875.6±0.4 and 6227.0±0.5 keV with lifetime limits of < 1, < 1 and < 2ps, respectively. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{= 5}{}^{\mathrm{?}}\text{, 6}{}^{\mathrm{+}}\text{, 8}{}^{\mathrm{+}}\text{, 9}{}^{\mathrm{+}}\text{and}\text{(8, 10)}{}^{\mathrm{?}}$ to the ⁴⁰K levels at E_x = 0.89, 2.88, 4.37, 4.88 and 6.23 and of $\text{J}{}^{\mathrm{\pi }}\text{= 4}{}^{\mathrm{+}}\text{and}\text{6}{}^{\mathrm{+}}\text{to the}{}^{40}\text{Ar}$ levels at E_x = 2.89 and 3.46 MeV, respectively, have been obtained. Branching ratios and multipole mixing ratios are reported.     

High-spin yrast levels of 38Ar

High-spin states of ³⁸Ar have been studied with the ³⁵Cl(α, pγ)³⁸Ar reaction at E_α = 18 MeV and with the ²⁴Mg(¹⁶O, 2pγ)³⁸Ar reaction at $\text{E(}{}^{16}\text{O}\text{) = 38}\text{and}\text{45}\text{MeV}$. The ³⁸Ar level scheme is obtained with the former reaction from a proton-γ coincidence measurement. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization experiments have been performed with a Ge(Li)-Na(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{= 7}{}^{\mathrm{?}}\text{, 7}{}^{\mathrm{+}}\text{, 8}{}^{\mathrm{+}}\text{, 7}{}^{\mathrm{?}}\text{, 9}{}^{\mathrm{?}}\text{and}\text{11}{}^{\mathrm{?}}$to the ³⁸Ar levels at E_x = 7.51, 8.08, 8.57, 8.97, 10.17 and 11.61 MeV, respectively, are obtained. The 8.57 MeV, 8⁺ level has a mean life below 0.8 ps. Excitation energies, branching ratios, multipole mixing ratios and transition strengths are reported. The experimental results are compared with shell-model calculations.     

High-spin states of 39K and 42Ca

High-spin states of ³⁹K and ⁴²Ca have been investigated with the ²⁸Si(¹⁶O, αpγ)³⁹K and ²⁸Si(¹⁶O, 2pγ)⁴²Ca reactions at a beam energy of 45 MeV. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization measurements were performed with a Ge(Li)-NaI(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. High-spin states of ³⁹K at E_x = 7.14,7.78and8.03 and of ⁴²Ca at E_x = 7.75MeV are established. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{=}\text{11}\text{2}{}^{\mathrm{?}}\text{,}\text{13}\text{2}{}^{\mathrm{?}}\text{,}\text{15}\text{2}{}^{\mathrm{+}}\text{,}\text{15}\text{2}{}^{\mathrm{?}}\text{,}\text{17}\text{2}{}^{\mathrm{+}}\text{and}\text{19}\text{2}{}^{\mathrm{?}}$ to the ³⁹K levels at E_x = 5.35, 5.72, 6.48, 7.14, 7.78 and 8.03 MeV and of 6^?, 7^?, 8^?, 9^? and(8, 10)^? to the ⁴²Ca levels at E_x = 5.49, 6.15, 6.41, 6.55 and 7.37 MeV, respectively, have been obtained. Further spin-parity restrictions, lifetime limits, excitation energies, branching ratios and multipole mixing ratios are reported. Discrepancies with previous J^π assignments are discussed in detail.     

Spin-parity assignments to high-spin states of 41K and 41Ca

Yrast states of ⁴¹K and ⁴¹Ca have been investigated with the ²⁶Mg(¹⁸O, p2nγ)⁴¹K and ²⁶Mg(¹⁸O, 3nγ)⁴¹Ca reactions at a beam energy of 34 MeV. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization measurements were performed with a Ge(Li)-NaI(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{=}\text{7}\text{2}{}^{\mathrm{+}}$, $\text{11}\text{2}{}^{\mathrm{+}}$, $\text{11}\text{2}{}^{\mathrm{?}}$, $\text{13}\text{2}{}^{\mathrm{+}}$, $\text{15}\text{2}{}^{\mathrm{?}}$ and $\text{19}\text{2}{}^{\mathrm{?}}$ to the ⁴¹K levels at E_x = 1.68, 2.53, 2.76, 2.77, 4.27 and 4.98 MeV and of $\text{9}\text{2}{}^{\mathrm{+}}\text{,}\text{11}\text{2}{}^{\mathrm{+}}\text{and}\text{15}\text{2}{}^{\mathrm{+}}$to the ⁴¹Ca levels at E_x = 3.20, 3.37 and 3.83 MeV, respectively, have been obtained. Excitation energies, branching ratios, multipole mixing ratios and transition strengths are reported. The main features of the ⁴¹K and ⁴¹Ca level and decay schemes are reproduced in a 2p-1h and 3p-2h shell-model calculation.     

Spectroscopy of states in 33S by means of neutron-gamma angular correlation measurements

Levels of ³³S for E_x < 5 MeV have been studied with the ³⁰Si(α, nγ)³³S reaction at bombarding energies of E_α = 7.5 and 10.2 MeV. Neutron-gamma angular correlation experiments lead to three unambiguous spin and parity assignments: $\text{J}{}^{\mathrm{\pi }}\text{(3.83) =}\text{5}\text{2}{}^{\mathrm{+}}\text{, J}{}^{\mathrm{\pi }}\text{(4.048) =}\text{9}\text{2}{}^{\mathrm{+}}\text{and}\text{J}{}^{\mathrm{\pi }}\text{(4.09) =}\text{7}\text{2}{}^{\mathrm{+}}$. The measured branching and mixing ratios yield transition strengths for dipole and quadrupole transitions.     

The second 132+ state in 19F

A cryogenically pumped gas target has been used to study resonances in the ¹⁵N(α, γ)¹⁹F reaction for E_α = 5.1 to 8.6 Mev. Gamma-ray intensity and angular distribution measurements for a resonance at E_α = 8.105 Mev, corresponding to a state at 10.411 MeV in ¹⁹F, restrict the spin and parity of the state to $\text{11}\text{2}{}^{\mathrm{+}}$ or $\text{13}\text{2}{}^{\mathrm{+}}$. Comparison with shell model calculations indicate that the state is a strong candidate for the second $\text{13}\text{2}{}^{\mathrm{+}}$ (2s, 1d)³ level in ¹⁹F.     

A study of the low-lying levels in 61Ni

Electromagnetic decay properties for seventeen states in ⁶¹Ni have been examined by means of the ⁵⁸Fe(α,nγ)⁶¹Ni reaction with E_α = 8 MeV and the ⁶⁰Ni(d, pγ)⁶¹Ni reaction at E_d = 6 MeV. Mean lifetimes were obtained with the Doppler-shift attenuation method. Spins, parities, and mixing ratios were determined from angular correlation studies and linear polarization measurements. The combined results permit new J^π assignments of $\text{7}\text{2}{}^{\mathrm{?}}\text{,}\text{5}\text{2}{}^{\mathrm{?}}\text{,}\text{7}\text{2}{}^{\mathrm{?}}\text{,}\text{and}\text{9}\text{2}{}^{\mathrm{+}}$ for the levels at 1016, 1611, 2020 and 2123 keV, respectively. Experimental results, including transition strengths, are compared to shell model predictions.     

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.     

In-beam γ-ray studies of complex band structures and of isomeric states in 152, 153Dy nuclei

The high-spin level structures of ¹⁵²Dy and ¹⁵³Dy were studied experimentally with ^{154, 155}Gd(α xnγ) in-beam reactions, and for ¹⁵²Dy also with ${}^{\mathrm{144,\; 146}}\text{Nd}\text{(}{}^{12}\text{C, x}\text{n}\text{γ)}$ reactions. The experiments included measurements of singles γ-ray and conversion-electron spectra, γ-ray angular distributions and E_γ-t and E_γ-E_γ-t coincidences. A multiplicity filter set-up was used to study the feeding and decay of isomeric states in ¹⁵²Dy. In ¹⁵²Dy about twenty so far unknown levels were found, including two high-spin isomeric states with $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{≈ 60}\text{and}\text{≈ 13}\text{ns}$ at excitation energies E_x ≈ 5.04 and 6.08 MeV, respectively. These states are compared with recent calculations on yrast traps. The level scheme of ¹⁵³Dy contains 28 levels up to E_x = 4.1 MeV and $\text{J}{}^{\mathrm{\pi }}\text{= (}\text{37}\text{2}{}^{\mathrm{+}}\text{)}$. Band structures in both nuclei are discussed in comparison with other N = 86 and N = 87 isotones.     

Evidence for assignment of 14.0 MeV state in 11B from 10B(n,n)10B

The differential cross section and polarization for neutrons scattered from ¹⁰B have been measured at E_n = 2.63 MeV (E_x = 13.85 MeV). The results of this experiment and other available neutron scattering data in the range 1 < E_n < 4 MeV are interpreted through a single-level R-matrix calculation over the region 12 < E_x < 15 MeV. Based on this analysis the most probable J^π assignment for the 14.0 MeV level in ¹¹B is $\text{11}\text{2}{}^{\mathrm{+}}$. The anomaly near E_x = 13.1 MeV can only be explained in terms of two overlapping levels having assignments of ($\text{5}\text{2}$, $\text{7}\text{2}$)^? and ($\text{3}\text{2}$, $\text{5}\text{2}$, $\text{7}\text{2}$)⁺.     

Alpha-decay widths in 20Ne

The α-decay of several unbound levels in ²⁰Ne has been studied by ¹⁶O(α, α) elastic and inelastic scattering. A narrow resonance, Γ_c.m. = 13±4 eV, with J^π = 5^? was found at $\text{E}{}_{\mathrm{<mtext>x</mtext>}}\text{(}{}^{20}\text{Ne}\text{) = 8.451±0.005}\text{MeV}$ and is associated with the lowest K = 2^? quasirotational band. Several new, narrow resonances were found between E_x = 16.0?18.4 MeV. Reduced α-decay widths have been obtained for the lowest K = 0⁺, 2^? and 0^?bands. For states described predominantly by the (8, 2) representation of SU(3) we note a reduction of the reduced widths with increasing spin. Reduced widths of positive parity bands are reviewed.     

High spin states in 57Co

High spin states of ⁵⁷Co have been studied via prompt γ-ray spectroscopy in the reactions ⁴⁸Ti(¹²C, p2n) and ⁵⁴Fe(α, p) at 26–48 MeV and 12–24 MeV, respectively. The energies and decay modes of these levels were determined from the analysis of γ-ray singles and γ-γ coincidence spectra, excitation functions, angular distributions and correlations. The relevant lifetimes were measured by the Doppler-shift attenuation method. The new levels established in this work are at 4037, 4814 and 5918 keV with the most probable J^π assignment of $\text{15}\text{2}{}^{\mathrm{?}}$, if $\text{17}\text{2}{}^{\mathrm{?}}$ and $\text{19}\text{2}{}^{\mathrm{?}}$, respectively. The previously known level at 2524 keV was assigned to have $\text{J}{}^{\mathrm{\pi }}\text{=}\text{13}\text{2}{}^{\mathrm{?}}$. These together with the known $\text{9}\text{2}{}^{\mathrm{?}}$(1224 keV) and $\text{11}\text{2}{}^{\mathrm{?}}$(1690 keV) levels constitute the yrast states of ⁵⁷Co. The measured lifetimes of the above six levels are (in order of increasing energies) 0.085±0.030, 0.32±0.10, 0.16±0.06, 0.10_?0.07^+0.06, 1.5_?0.5⁴ and 0.17_?0.07^+0.08 ps, respectively. Comparisons with some theoretical calculations are presented.     

Study of particle and γ decays of the Ex = 12.00 MeV 63+ level in 24Mg

Direct coincidence observation of α- and γ-decays of the E_x = 12.0 MeV level populated in the ${}^{12}\text{C}\text{(}{}^{16}\text{O}\text{, α)}{}^{24}\text{Mg}$ reaction has been used to show that both 6⁺ and 3^? levels exist near this excitation energy. Comparison of the present work with previous radiative capture studies permits the conclusion that the 6₃⁺ level in ²⁴Mg decays primarily by γ-emission, in agreement with recent shell-model calculations using an (sd)⁸ basis. Absolute E2 and M1 strengths deduced from the data are not, however, in good quantitative agreement with the predictions of the shell model.     

Alpha capture to the giant dipole resonances of 42Ca, 44Ca and 52Cr

Differential cross sections for the ${}^{38}\text{Ar}\text{(α, γ}{}_0\text{)}{}^{42}\text{Ca}\text{,}{}^{40}\text{Ar}\text{(α, γ}{}_{\mathrm{0,\; 1}}\text{)}{}^{44}\text{Ca and}{}^{48}\text{Ti}\text{(α, γ}{}_{\mathrm{0,\; 1}}\text{)}{}^{52}\text{Cr}$ reactions were measured at 90° to the beam direction in 50 or 100 keV steps over the bombarding energy ranges 6.0–15.0 MeV, 5.5–11.1 MeV and 6.0–12.0 MeV respectively. Gamma-ray angular distributions were measured at forty bombarding energies. These show that the (α, γ₀) reaction proceeds through 1^? levels and to a lesser extent 2⁺ levels, whereas the (α, γ₁) reaction most probably proceeds through 1^? and 3^? levels. It is deduced that 〈Γ〉/〈D〉 ≦ 1 for the ⁴⁰Ar(α, γ)⁴⁴Ca. reaction whereas the fine structure observed in the ⁴⁸Ti(α, γ)⁵²Cr reaction is probably due to fluctuations. From a comparison with other data it is shown that the (α, γ) reaction is most probably statistical in nature. Using Hauser-Feshbach theory it is deduced that the ³⁶Ar(α, γ)⁴⁰Ca. reaction is inhibited by isospin selection rules and an estimate is made of isospin mixing in the ⁴⁰Ca giant dipole resonance. The ${}^{38}\text{Ar}\text{(α, γ)}{}^2{}^{42}\text{Ca and}{}^{40}\text{Ar}\text{(α, γ)}{}^{44}\text{Ca}$ data are considered with respect to theories of isosopin splitting of the giant dipole resonance.