The B(E2) for the first 2 state in Zr

A model-independent measurement of the width of the first 2⁺ state (2.186 MeV) of ⁹⁰Zr has been carried out using the resonant scattering of bremsstrahlung and its detection with a Ge(Li) detector. The observed resonance fluorescence yield corresponds to a reduced E2 transition probability B(E2↑) = 608 ± 35 e² · fm⁴. The difference between this value and recent inelastic electron scattering results exceeds the range usually attributed to the model dependence of the latter.     

A measurement of B(E3;0+ → 31−) and some E2 transition probabilities in 132, 134, 136, 138Ba using Coulomb excitation

Reduced transition probabilities, B(E2) and B(E3), have been measured for low-lying 2⁺ and 3^? states in ^{132, 134, 136, 138}Ba using Coulomb excitation by 40 MeV ¹²C ions. The B(E2) values are in general consistent with previous measurements and the B(E3;0⁺ → 3₁^?) values are 0.176 ± 0.022, 0.148 ± 0.018, 0.155 ± 0.018 and 0.133 ± 0.013 e² · b³ for ^{132, 134, 136, 138}Ba respectively. These B(E3) values correspond to about 24 to 17 W.u. and such enhancements suggest that these 3^? states have an essentially collective character which may be attributed to octupole vibrations.     

Isomeric E1 and M1 transitions in 177Ta and in neighbouring odd-A Lu and Ta isotopes

Delayed γ-ray spectra as well as time distributions have been measured applying the r.f.-γ method and the method of delayed γ-γ coincidences. Using the reaction ¹⁷⁵Lu(α, 2n)¹⁷⁷Ta, the half-lives of the levels at 70.6 and 73.6 keV in ¹⁷⁷Ta have been determined as $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 80±10}\text{ns}$ and $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 370±50}\text{ns}$, respectively. In further experiments, upper limits for the lifetimes of the $\text{9}\text{2}{}^{\mathrm{?}}\text{[514]}$ and $\text{5}\text{2}{}^{\mathrm{+}}\text{[402]}$ states in ¹⁷¹Lu and ¹⁷³Lu were estimated. Comparisons of the experimental half-lives to Weisskopf and Nilsson model predictions are performed taking into account pairing correlations. For the calculations, a modified Nilsson Hamiltonian has been used. The hindrance factors obtained are summarized together with those deduced for corresponding transitions in neighbouring odd-proton nuclei. From the experimental results in ¹⁷⁷Ta, conclusions have been drawn on the possible value of the constant k₂ occurring in the magnetic dipole operator.     

The pole peripheral model for (α, 2α) reactions

The peripheral-model approach proposed previously for binary and quasi-binary direct reactions is extended to quasi-elastic (α, 2α) reactions. The calculated angular correlations functions are compared with the experimental ones for (α, 2α) reactions on ⁶Li, ⁹Be and ¹²C and the values of the A → B + α vertex constants are extracted from the analyses. On the whole, the peripheral-model calculations agree with experiment much better than do calculations based on the pure pole knock-out Feynman graph.     

The energy spectra and electromagnetic transitions of odd-a titanium isotopes

The isotopes ^{55, 47, 49, 51}Ti are studied in the framework of the deformed configuration mixing shell model. The calculated spectra and electromagnetic properties agree well with the observed ones. The calculations suggest the existence of an excited $\text{K =}\text{1}\text{2}$ band of states in ^{45, 47, 49}Ti and a $\text{K =}\text{7}\text{2}$ band in ⁵¹Ti. In ⁴⁹Ti this excited $\text{K =}\text{1}\text{2}$ band is more deformed than the “ground state band”. On the basis of the overall agreement between the calculated and experimental spectra and decay properties we suggest the spin assignments $\text{J =}\text{5}\text{2}$, $\text{7}\text{2}$, $\text{9}\text{2}$, $\text{5}\text{2}$ and $\text{7}\text{2}$ to the states in ⁴⁷Ti observed at 2.168, 2.97, 2.408, 2.835 and 3.223 MeV, respectively.     

Cross sections for the (n,n′), (n,p) and (n, 2n) reactions on 107Ag and 109Ag isotopes

The cross sections for (n, n′), (n, p) and (n, 2n) reactions on the target nuclei ¹⁰⁷Ag and ¹⁰⁹Ag were measured by the activation technique in the neutron energy range 13 to 18 MeV. The results are interpreted in terms of the compound nucleus and precompound emission models.     

Distributions of i132 transfer strength in (τ, α)-induced population of odd-a platinum isotopes

The odd-A platinum isotopes ₇₈^{191, 193, 195, 197}pt have been populated by means of the (τ, α) reaction at E_τ = 50 MeV. Spectra covering a range of 4 MeV of excitation energy were obtained. Angular distributions for levels in this excitation range have been deduced. Only a few $\text{13}\text{2}{}^{\mathrm{+}}$ states are strongly populated in each isotope, the actual number being 1, 2, 3, and 2 for A = 191, 193, 195 and 197 respectively. The spacing between these peaks exhibits an interesting variation with neutron number. The data are compared with predictions of current quasiparticle-core coupling models.     

E0/E2 and E2/M1 multipole mixing amplitudes of γ-transitions in 192Pt

Angular correlation measurements of conversion electrons and γ-rays in ¹⁹²Pt following the decay of ¹⁹²Ir (74 d) have been made. In particular, the 296 keV e^?-316 keV γ correlation was measured in order that the electric monopole admixture in the 296 keV transition could be determined. The results of the angular correlation coefficients measured here and the ratio of K-shell to L_III shell conversion electrons measured by others are: ?0.09 < q < +0.26 as +62 < λ < +92 or ?0.29 < q < ?0.06 as ?5 < λ < +45. A possible explanation of the disagreement between two earlier measurements is suggested. The angular correlation coefficients for the measured e^?-γ and γ-γ cascades and the derived multipole mixing ratios are tabulated and compared with other recent measurements and with the predictions of the Kumar-Baranger nuclear model.     

Investigation of the level schemes of 73,75,77As via the (3He,d) reaction

The reactions ^{72, 74, 76}Ge(³He, d) were investigated at E_lab = 23 MeV with a multigap and a Q3D magnetic spectrograph. Some 30 new levels up to $\text{E}{}^1\text{≈ 4}\text{MeV}$ have been found. The level schemes of the odd As isotopes ^{73, 75, 77}As up to $\text{E}{}^1\text{≈ 4}\text{MeV}$ seem to be rather independent of the neutron number. The good agreement of the low-lying level structure with the Coriolis-coupling model including a pairing force was verified and the vacancies of low-lying shell model states were extracted and compared with the simple pairing theory.     

“Exact” shell model calculations in A = 17 and A = 18 nuclei and effective operators in the (2s, 1d) shell

A shell model calculation in an enlarged space spanned by two particles in the (2s, 1d) shell and three-particle-one-hole $\text{2}\text{h}\text{?}\text{ω}$ excitations is performed using the “bare” G-matrix. An effective interaction for the (2s, 1d) shell is generated and its convergence properties are investigated. It is maintained that the series converges reasonably fast in G and that the singleparticle energies used in the calculation are instrumental in this respect. This conclusion is corroborated by the E2 effective charges and B(E2) strengths that we compute for A = 17 and A = 18 nuclei respectively.     

Feeding times in (HI, xnγ) reactions

Feeding times, T_f, for population of the quasi-rotational bands in a number of doubly even nuclei formed in (dHI, xn) reactions have been measured with the recoil-distance Doppler-shift technique. Values of 11±3, 5±2.5, 3±3 and 12_?4^+2.5 ps were obtained for T_f the ^{166, 168, 170}Hf and ¹⁷⁸Os nuclei populated by the ^150,152,154Sm(²⁰Ne,4n) and ¹⁵⁴Sm(²⁸Si,4n) reactions, respectively. In all cases the fraction of slow-feeding component was less than a few percent.     

The Deck model in the reaction dp → d(Nπ)+

A Deck-like model is proposed for the reaction pd → (Nπ)⁺d. The narrow bump Nπ (1150 MeV) is well explained. The different hypothesis and approximations are widely reviewed. In particular other mechanisms which can contribute to the same reaction are calculated and off-shell effects are discussed.     

Cross section and analyzing powers for the reaction pd→3He + γ at intermediate energies

We report the results of measurements of the differential cross section and analyzing power for the reaction pd → γ³He at six energies in the range 200 < E_p < 500 MeV. The cross-section data are in good agreement with the most recent results for the inverse process assuming detailed balance; thus no evidence for time-reversal violation is inferred. In addition, the shapes of the measured angular distributions are in general overall accord with those measured in the photodisintegration reaction. The data are compared with several theoretical calculations showing inclusion of meson-exchange current contributions to be important in reproducing the measured cross section. The analyzing powers measured at E_p = 500 MeV are not yet explained by microscopic models.     

The 16O(γ, po) reaction at intermediate photon energies

The ¹⁶O(γ, p_o) reaction has been investigated between photon energies E_γ = 40 and 105 MeV using a bremsstrahlung beam, full angular distributions being obtained at E_γ = 60, 80 and 100 MeV. While cross-section calculations which introduce a residual interaction of Yukawa form agree well with the data, the need for further work is indicated.     

Fission fragment yield distributions as a function of their excitation energies for 235U(nth, f)

The recent ²³⁵U(n_th, f) data taken at the Grenoble high flux reactor have been reanalysed to determine the fragment mass distributions as a function of their excitation energies $\text{E}{}^1$. The mass distributions for low $\text{E}{}^1$ values show the known fine structures. However, the distributions for $\text{E}{}^1\text{> 30}\text{MeV}$ do not show the fine structure reported by Newson. Beyond $\text{E}{}^1\text{≈ 35}\text{MeV}$, the most probable masses of distributions decrease monotonously as $\text{E}{}^1$ goes up.     

Evidence of E1 excited states in 19F from the (γ, t) reaction2

The ¹⁹F(γ, t)¹⁶O reaction was studied over an energy region of 18 to 23 MeV. Two resonances were observed at 18.8 MeV and 20.1 MeV. The angular distribution of tritons from these resonances indicated that the tritons are emitted predominantly in a p-wave, implying $\text{j}{}^{\mathrm{\pi }}\text{=}\text{1}\text{2}$^?, or $\text{3}\text{2}$^? with T = $\text{1}\text{2}$ for both levels. A comparison with other experiments i the states could be attributed to ¹⁶O+t cluster configurations. In addition, from the measured ratio σ(γ, α)/σ(γ, t) ? 0.01 it is concluded that the formation of ¹⁵N+α cluster states is small in this region of excitation.     

Investigation of 228Th in the (α, α'2n) reaction

The ²³⁰Th(α, α'2n)²²⁸Th reaction at E_α = 56 MeV was used to investigate states of moderately high spin in ²²⁸Th. Conversion electron and e^?-γ coincidence measurements were carried out, where the electrons were detected with an iron-free orange spectrometer. The ground state and low-lying K^π = 0^? rotational bands were observed up to I^π = 14⁺ and 13^?, respectively. The data are interpreted in terms of an ω-expansion for the ground-state rotational band, and an octupole vibrational band distorted by the Coriolis coupling to the K^π ? 1^? excitations for the K^π = 0^? band.     

A study of the 84Kr(α, 2nγ)86Sr reaction

Decay properties of levels of ⁸⁶Sr populated by the 28 MeV ⁸⁴Kr(α, 2nγ) reaction have been studied by in-beam γ-ray spectroscopy. The observation of several new levels with $\text{J ≧ 6}$ allows a detailed comparison of the 2p-2n structures of ⁸⁶Sr with those of neighboring N = 48 nuclei. The results are discussed in terms of the weak-coupling model.