Backward-angle high-resolution inelastic electron scattering on 40, 42, 44, 48Ca and observation of a very strong magnetic dipole ground-state transition in 48Ca

The search for magnetic dipole transitions from the ground state-even Ca isotopes to high lying J^π=1⁺ states by means of low momentum transfer but high resolution inelastic electron scattering is described. The previously detected strongly excited J^π=1⁺ state E_X=10.319 MeV [B(M1)↑=1.12±0.27μ_K²] in ⁴⁰Ca has been confirmed, but - contrary to the expectations of the independent particle shell model - only a fairly weak M1 transition is observed in ${}^{42}\text{Ca [E}{}_{\mathrm{<mtext>X</mtext>}}\text{= 11.235}\text{MeV}\text{, B(}\text{M}\text{1)↑=0.59±0.05 μ}{}^2{}_{\mathrm{<mtext>K</mtext>}}\text{]}$ and none in ⁴⁴Ca between E_{X=8.2?12.2 MeV}. In ⁴⁸Ca, however, a very strong M1 transition [B(M1) ↑ = 4.0 ± 0.3 μ²_K] to a single state at E_X=10.227 MeV has been discovered.     

Generalized neutron particle-hole states in an extended unified model

Negative-parity levels in the doubly even N = 82, Z nuclei, with 3.0 MeV ? E_x? 6.0 MeV are described in an extended unified-model approach, where neutron hole states in the Z = 50, N = 82 closed shell core, (i.e. ) are coupled to the low-lying levels (E_x ? 2.0 MeV) of the odd-neutron N = 83, Z nuclei. This particular configuration space of generalized neutron particle-hole states (GNPH) is particularly suited for describing negative-parity levels obtained in proton inelastic scattering through isobaric analogue resonances (IAR), corresponding to the N = 83, Z low-lying nuclear levels. Level schemes as well as partial decay widths and angular distributions are calculated and compared extensively with the available experimental data. Also spectroscopic factors, as well as wave functions, deduced from the experimental results are studied in detail. Thus in the cases of ¹³⁶Xe, ¹³⁸Ba, ¹⁴⁰Ce, ¹⁴²Nd and ¹⁴⁴Sm, some of the important neutron particle-hole configurations can uniquely be determined in the energy region 3.0 MeV ?E_x ? 6.0 MeV.     

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.     

Measurement of Debye-Waller factors by Raman scattering from inter-term excitons and exciton-multiphonon states in FeF2

We have observed inter-term Raman scattering from ⁵T_2g→⁵E_g Frenkel excitons in antiferromagnetic FeF₂. It differs qualitatively from previously observed intra-term scattering in a sharply reduced zero-phonon cross section and the appearance of relatively strong exciton-phonon scattering. Since the Raman process is fully allowed, it is possible to measure excited state Debye-Waller factors, D, and we find $\text{D(Λ}{}_3{}^{\mathrm{+}}\text{+ Λ}{}_4{}^{\mathrm{+}}\text{,}{}^5\text{E}{}_{\mathrm{g}}\text{) = 0.04}$ and $\text{D(Λ}{}_1{}^{\mathrm{+}}\text{,}{}^5\text{E}{}_{\mathrm{g}}\text{) = 0.03}$.     

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.     

12C(7Li,t)16O and stellar helium fusion

The reaction ¹²C(⁷Li, t)¹⁶O has been studied at $\text{E(}{}^7\text{Li}\text{) = 34}\text{MeV}$ with the LASL tandem accelerator and QDDD magnetic spectrometer. Angular distributions to levels with E_x < 11 MeV have been obtained from 0° to 90°, including 0°. The results have been analyzed with finite-range distorted-wave Born approximation theory. The α-particle spectroscopic factors and reduced widths obtained are compared with those calculated with group theory (SU(3)) and other models. The analysis of data for the 7.1 and 9.6 MeV J^π = 1^? levels, which are of great importance in stellar helium buring, yields a ratio, R, of dimensionless reduced α-widths $\text{θ}{}^2{}_{\mathrm{<mtext>a</mtext>}}\text{(7.1}\text{MeV}\text{)}\text{θ}{}^2{}_{\mathrm{<mtext>a</mtext>}}\text{(9.6}\text{MeV}\text{)}\text{= 0.35b ± 0.13}$. The observed line width of the 9.6 MeV level (Γ_c.m. = 390 ± 60 keV) is less than the accepted value (Γ_c.m. = 510 ± 60 keV) and implies θ²_a(9.6 MeV) ≈ 0.6. These results as well as data for the 6.92 MeV J^π = 2⁺ and 10.35 MeV J^π = 4⁺ “α-cluster” states indicate 0.09 < θ²_a(7.1 MeV) < 0.33 with a mean value θ²_a(7.1 MeV) = 0.14 ± 0.04. The implication for stellar helium burning is discussed.     

Neutron-proton radius differences and isovector deformations from π+ and π− inelastic scattering from 18O

π⁺ and π^? elastic and inelastic scattering from ¹⁸O have been measured at T(π)=164 MeV. Consistent with the results at 230 MeV, it is found that the ratio $\text{σ(π}{}^{\mathrm{?}}\text{)}\text{σ(π}{}^{\mathrm{+}}\text{)}$ for the 2₁⁺ state is 1.86(16), while for the 3₁^? state it is 0.89(6). These results are interpreted as indicating differences in neutron and proton deformations characterizing the 2₁⁺ transition and partial neutron blocking for the 3₁^? transition. Optical model analysis of elastic scattering leads to the conclusion that $\text{〈r}{}_{\mathrm{<mtext>n</mtext>}}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{?〈r}{}_{\mathrm{<mtext>p</mtext>}}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{=0.03(3)}\text{fm}$.     

Spin determination of states with stretched configurations in 16N and 32P via the (d, α) reaction at 52 MeV

The reactions ${}^{12}\text{C}\text{(}\text{d}\text{, α)}{}^{10}\text{B}\text{,}{}^{18}\text{O}\text{(}\text{d}\text{, α)}{}^{16}\text{N and}{}^{34}\text{S}\text{(}\text{d}\text{, α)}{}^{32}\text{P}$ have been investigated at E_d = 52 MeV. Vector analyzing powers as large as $\text{¦iT}{}_{11}\text{¦=0.85}$ are observed. They exhibit patterns characteristic for final spins I = |L?1|, L or L + 1 and provide spin determinations at least for states of unique L-transfer. Local, zero-range DWBA calculations assuming deuteron-cluster pick-up reproduce qualitatively the observed effects. The method has been tested for states of known spin, and then has been applied to determine spins of states with stretched coupling in ¹⁶N: J^π = 3⁺(3.96 MeV), 4^?(6.17 MeV) and in ³²P: J^π = 5⁺(4.75 MeV). There is strong evidence for further 5⁺ states in ³²P at 6.43, 7.96, 8.09 and 8.54 MeV.     

15N(p,po)15N and the levels of 16O for Ex = 14.8–18.6 MeV

Angular distributions of cross section and analyzing power for elastic scattering of protons from ¹⁵N have been measured for E_p = 2.7–7.0 MeV. A phase-shift analysis of the data yields spin-parity assignments and level parameters for seventeen states of ¹⁶O in the excitation energy region 14.8–18.6MeV. Three of the resonances have not previously been identified, among them being a broad J^π = 2^? level at E_p = 6.1 MeV which is almost certainly the analog of the 2^? 1p1h state with configuration ($\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{,}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$) at E_x ∽ 5.0 MeV in ¹⁶N. The broad level previously reported near E_p = 5.0 MeV has been observed and its parameters determined. A resonance analysis of the phase shifts yielded values of E_r, Γ and Γ_p for all of the levels. The J^π assignments are in agreement with previously reported values. For resonances having J = l, the data can usually be fit with a resonant phase shift corresponding to either J = l + 1 or J = l ? 1, in addition to the phase shift for J = l. Which of the two spurious-J solutions occurs seems to depend on whether the partial wave through which the resonant state is formed is $\text{J = l +}\text{1}\text{2}\text{or}\text{J = l ?}\text{1}\text{2}$.     

An experimental investigation of the radiative structure decay K+ → e+υγ

The decay K⁺ → e⁺υγ has been investigated. For the structure-dependent part with positive γ-helicity (SD₊) the branching ratio $\text{Γ(}\text{SD}{}_{\mathrm{+}}\text{)}\text{Γ(}\text{K}{}_{\mathrm{\mu 2}}\text{) = (2.33 ± 0.42) × 10}{}^{\mathrm{?5}}$ is obtained from 51 ± 3 events observed in the kinematical region E_e ? 235 MeV, E_γ > 48 MeV and θ_eγ > 140°. For the corresponding part with negative γ-helicity we obtain an upper limit Γ(SD_?)/Γ(SD₊) < 11 (90% CL) from the sample of electrons with energies 220 MeV ? E_e < 230 MeV and with no γ in the backward direction. This upper limit implies that the ratio of structure-dependent axial vector amplitudes lies outside the region $\text{?1.8 < a}{}_{\mathrm{<mtext>K</mtext>}}\text{υ}{}_{\mathrm{<mtext>K</mtext>}}\text{< ?0.54}$.For the decay $\text{K}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{νν}\text{ν}$ the limit $\text{Γ(}\text{K}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{νν}\text{ν}\text{)/Γ(}\text{K}{}_{\mathrm{e2}}\text{) < 3.8}$ 90% confidence level) was found.     

A determination of the spin of the hypernucleus 12ΛB: (II). A complete analysis

The probability distribution calculated for the decay sequence ${}^{12}{}_{\mathrm{\Lambda }}\text{B(g.s.) →}{}^{12}\text{C}{}^1\text{π}{}^{\mathrm{?}}\text{→ αααπ}{}^{\mathrm{?}}$ passing through the (J^P_N) = (2⁺, 1) intermediate state ¹²C¹ (16.11 MeV) is cast in a symmetrical form and used to calculate the likelihood for $\text{J = 1}\text{relative to}\text{J = 2}\text{for}{}^{12}{}_{\mathrm{\Lambda }}\text{B(g.s.}\text{)}$ on the basis of the 85 examples available for this decay process. This procedure has optimum sensitivity, is free from the uncertainties of the comparisons previously made using only projected angular distributions, and strongly indicates that J^P = 1^? holds for ¹²_ΛB(g.s.). An appendix points out that all the data for the decay sequence passing through the (J^P_N, T) = (1⁺, 0) level of ¹²C¹ is well fitted for J = 1 if the J = 1 → J_n = 1 transition amplitude a_s1 takes a value in the range a_s1/s = 0.08 to 0.09.     

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.     

12C(6Li,d)16O and16O(6Li,d)20Ne at E(6Li) = 42 MeV

Spectra up to 25 MeV excitation in ¹⁶O have been obtained from ¹²C(⁶Li, d) at 42 MeV bombarding energy. Angular distributions have been measured for ten states, including two J^π = 1^? states of astrophysical interest, and appear to be mostly direct α-transfer. In addition, data for ¹⁶(⁶Li, d)²⁰Ne(g.s.) and ²⁰Ne¹(2⁺) have been obtained. Excitation energies and widths have been extracted for states in ¹⁶O, including several states at E_x > 15 MeV. Alpha spectroscopic factors, S_α, and reduced α-widths, γ²_α and θ²_α have been deduced for levels in ¹⁶O and ²⁰Ne and compared with theoretical predictions. The J^π = 1^? levels in ¹⁶O at 7.12 and 9.6 MeV excitation appear to have comparable S_α and γ²_α values, viz. $\text{γ}{}^2{}_{\mathrm{\alpha }}\text{(7.12 MeV)}\text{γ}{}^2{}_{\mathrm{\alpha }}\text{(9.6}\text{MeV}\text{) = 0.6}{}^{\mathrm{+1.7}}{}_{\mathrm{?0.3}}$. Both states have apparent S_α and γ²_α values smaller than that for the J^π = 2⁺ “α-cluster” state at 6.9 MeV however. Furthermore, the observed line shape for the J^α = 1^?, 9.6 MeV level indicates Γ_c.m. = 400 ± 50 keV, which is substantially less than the accepted width for this level Γ_c.m. = 510±60 keV). The possible implications of these results for stellar helium burning calculations are discussed.     

l-type doubling transitions in Δ states of OCS

Molecular beam electric resonance spectroscopy has been used to measure the l-type doubling transitions in carbonyl sulfide. Transitions in J = 4 to J = 20 have been observed for the (02²0) vibrational state and for J = 1 and J = 2 for the (03¹0) state. The data has been analyzed to give the v = 2 energy separation $\text{E}{}_{\mathrm{<mtext>\Delta </mtext>}}{}^0\text{- E}{}_{\mathrm{<mtext>\Sigma </mtext>}}{}^0\text{= ?5.7861(2) + 8.36(1) × 10}{}^{\mathrm{?5}}\text{J(J + 1)}\text{cm}{}^{\mathrm{?1}}$, and the vibrational dependence of q to be 86.52(9)(v₂ + 1) KHz. The dipole moment of the (02²0) vibrational state is 0.6936(3) D.     

Search for 8+ strength in 16O via the 12C(α, α2)12C1(7.66 MeV) reaction

Closely spaced angular distributions have been measured for the ${}^{12}\text{C}\text{(α, α}{}_2\text{)}{}^{12}\text{C}\text{1(7.66}\text{MeV}\text{)}$ reaction between E_α = 17.39 and 20.5 MeV in a search for 8⁺ strength in ¹⁶O. No evidence of 8⁺ strength is found, but evidence is found for a narrow 7^? resonance at 21.52 MeV excitation.     

The hypernucleus 12ΛB and the decay process 12ΛB → π− + 3α

The characteristics of the decay sequences ${}^{12}{}_{\mathrm{\Lambda }}\text{B}\text{→ π}{}^{\mathrm{?}}\text{+}{}^{12}\text{C}{}^1\text{,}{}^{12}\text{C}{}^1\text{→ 3α}$ are discussed for the two sharp levels of ¹²C¹ at excitation energies of 12.7 MeV (J_f = 1⁺, T = 0) and 16.11 MeV (J_f = 2⁺, T = 1), which are observed prominently in this decay process. The transition rates for these processes and the angular correlations in the final four-particle state αααπ^? are discussed quantitatively, using the intermediate coupling model for both the ¹²_ΛB and ¹²C¹ systems, as a function of the ¹²_ΛB spin J. Three distinct tests are proposed, which are sensitive to the spin J for ground-state ¹²_ΛB, and which have been used by the European K^? Collaboration to deduce that J = 1 for ¹²_ΛB. The implications of this conclusion for the ΛN and ΛNN interactions are briefly discussed.     

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.     

Rotational constants of the E O+g state of I2 determined by polarization spectroscopy

The resonant 2-photon E(O⁺_g) ← B(O⁺_g) ← X(O⁺_g) transition of I₂ vapor has been studied by polarization spectroscopy, leading to a rotational analysis of the ν = 0–15 vibrational levels of the E state. The principal constants determined are $\text{B}{}_{\mathrm{e}}\text{= 19.9738(42) × 10}{}^{-3}\text{, α}{}_{\mathrm{e}}\text{= 5.602(84) × 10}{}^{-5}\text{, γ}{}_{\mathrm{e}}\text{= 1.02(41) × 10}{}^{-7}\text{, D}{}^{\mathrm{e}}{}_{\mathrm{J}}\text{= 3.040(74) × 10}{}^{-9}\text{cm}{}^{-1}\text{, and r}{}_{\mathrm{e}}\text{= 3.6470(5)}\text{A}\text{?}$.     

Direct capture in the 24Mg(p, γ)25Al reaction

Excitation functions for the ²⁴Mg(p, γ)²⁵Al capture reaction have been obtained for the beam energy range E_p = 0.2–2.3 MeV. The analysis of these data revealed the presence of the direct capture process to the low-lying states in ²⁵Al at , $\text{945(}\text{3}\text{2}{}^{\mathrm{+}}\text{), 2485(}\text{1}\text{2}{}^{\mathrm{+}}\text{)}\text{and}\text{3062}\text{keV}\text{(}\text{3}\text{2}{}^{\mathrm{?}}\text{)}$. The presence of the weaker direct capture transitions is manifested through interference effects on the tails of the two broad resonances at E_p = 823 and 1623 keV. The deduced spectroscopic factors for these final states in ²⁵Al are compared with the corresponding values from stripping data as well as model calculations. An astrophysical S-factor of S(0) ≈ 30 keV· b for this reaction has been obtained.