The study of the (α, α'f) reaction at 120 MeV on 232Th and 238U: (I). Fission probabilities and angular distributions in the region of the giant quadrupole resonances

The fission decay channel of ²³²Th and ²³⁸U has been investigated, using the (α, α'f) reaction at 120 MeV bombarding energy. The angular distributions of the fission fragments and the fission probabilities up to around 15 MeV excitation have been measured. No evidence for the fission decay of the giant quadrupole resonance has been found, although for ²³⁸U, a weakly excited structure is seen in the (α, α'f) spectrum at about 9.5 MeV excitation at backward angles with respect to the recoil axis. This effect is similar to what has been found in a (⁶Li, ⁶Li'f) experiment reported recently. The over-all feature of the fission probability for excitation energies above the fission barrier are well reproduced by statistical calculations.     

Excitation of strontium atom in electron–atom collisions

The excitation of ³D levels of strontium atom by slow monoenergetic electrons has been studied experimentally. Thirty six excitation cross-sections were measured at 30-eV electron energy. Optical excitation functions for most of the transitions were recorded in the 0–200-eV electron-energy range. The excitation cross-section as a function of the principal quantum number has been found to correspond to a power law for all ³D series.     

Fusion of light exotic nuclei at near-barrier energies: Effect of inelastic excitation

The effect of inelastic excitation of exotic light projectiles (proton-as well as neutron-rich)¹⁷F and¹¹Be on fusion with heavy target has been studied at near-barrier energies. The calculations have been performed in the coupled channels approach where, in addition to the normal coupling of the ground state of the projectile to the continuum, inelastic excitation of the projectile to the bound excited state and its coupling to the continuum have also been taken into consideration. The inclusion of these additional couplings has been found to have significant effect on the fusion excitation function of neutron-rich¹¹Be on²⁰⁸Pb whereas the effect has been observed to be nominal for the case of proton-rich¹⁷F on the same target. The pronounced effect of the channel coupling on the fusion process in the case of¹¹Be is attributed to its well-developed halo structure.     

Study of 94Mo through the (n,n′γ) reaction

The ⁹⁴Mo(n, n′γ) reaction has been studied in the neutron energy range 1.5–4.0 MeV. Neutron inelastic scattering cross sections for levels up to an excitation energy of 2.6 MeV have been measured from 1.5 to 3.0 MeV. The results have been analyzed with the optical-statistical and coupled-channels theories. The 1.74 MeV level has been observed and has been assigned to be 0⁺. The branching ratios for the γ-rays deexciting the levels below the 3.5 MeV excitation have also been obtained.     

A study of electron impact excitation of molecular oxygen at a scattering angle of 180°

Excitation of molecular oxygen by electron impact has been observed at the backward scattering angle of 180°. For these studies a new solenoid system with a conical geometry has been designed to implement the angle-changing technique. Energy loss spectra have been measured to deduce differential cross-sections for vibrational excitation of the X³Σ_g⁻ ground state and excitation of the a¹Δ_g state at 180°. Excitation of the b¹Σ_g⁺ state has not been observed at 180° in agreement with the theoretically predicted selection rule Σ⁻←↦Σ⁺ at that angle.     

Spectroscopy of 41Sc by resonant scattering of protons: Observation of an intermediate structure

Excitation functions of elastic and inelastic scattering of protons on ⁴⁰Ca have been measured for incident proton energies between 4.8 and 8.2 MeV. Spin and parity assignments and partial width determinations of ⁴¹Sc states between 5.8 and 8.7 MeV excitation energy have been made on the basis of quantitative analyses of the data for the different inelastic channels. Intermediate structure has been identified in the excitation function for the inelastic scattering to the 3^? (3.73 MeV) state in ⁴⁰Ca. This has been interpreted as being due to the presence of a state in ⁴¹Sc which consists primarily of the core nucleus ⁴⁰Ca in its 3^? state with a 2p particle weakly coupled to it.     

Role of single particle transfer in heavy ion fusion

Fusion excitation functions in heavy ion collision have been calculated taking into account the effect of random transfer of single particles in a classical dynamical model. The model has been applied to fusion of ¹⁶O+²⁷Al and ⁴⁰Ar +¹⁰⁹Ag. The transfer does not affect the low energy fusion excitation function but the effect of transfer is appreciable for high energies.     

Coulomb-nuclear interference for inelastic deuteron scattering

The interference between Coulomb excitation and nuclear excitation has been observed for ^{54, 56}Fe, ⁶⁰Ni, ¹¹⁴Cd, ¹⁵²Sm, and ¹⁹²Os by measuring excitation functions of elastic and inelastic deuteron scattering at back angles. The interference is strongly constructive, indicating a predominantly imaginary nuclear form factor. DWBA calculations using the collective model, although predicting constructive interference, are unable to predict the magnitude of the observed effect.     

Shape isomer excitation by mu-minus atomic capture?

The possibility of excitation of the ²³⁸U shape-isomer by the atomic cascade of a negative muon has been investigated by a search for back-decay γ-rays. No candidates for such γ-rays have been found with yields greater than 1% per stopping muon, indicating that the probability of the isomer excitation by muons is less than 3%. The lifetime of a μ^? bound to ²³⁸U has been determined from capture γ-rays to be 79.1 ± 0.5 ns, which also set the upper limit of this probability to 7–15%.     

E1 polarization in coulomb excitation of 7Li

Coulomb excitation of the 0.478 MeV $\text{J}{}^{\mathrm{\pi }}\text{=}\text{1}\text{2}{}^{\mathrm{?}}$ state of ⁷Li has been studied by a partiele-γ coincidence technique. From the dependence of the excitation probabilities on bombarding energy and scattering angle a sizeable interference contribution from E1 excitation of continuum states has been determined. General expressions for the size of the E1 polarization effect in Coulomb excitation are given and the observed magnitudes in ^6,7Li are compared with schematic model calculations.     

Radiative capture of protons by the deformed nuclide232Th

The excitation function for the radiative capture²³²Th(p, γ)²³³Pa has been determined in the proton energy range 7 to 20 MeV by an activation method. The results are compared with a compound nucleus model prediction and earlier experimental data for another deformed nuclide¹⁷⁶Yb. As in previous cases an enhancement over the CN-model prediction is observed and the excitation of the giant dipole resonance via the direct-semidirect reaction process is a likely explanation. Supplementary measurements of the²³²Th (p, f) excitation function in the proton energy range 11–20 MeV have been performed.     

Highly selective multistep ionization of atoms by laser radiation

The possibility of dramatic selectivity increase during the stepwise ionization of atoms due to selective excitation at every step has been examined. Evaluations have been made to estimate the selectivity of excitation and ionization by laser radiation of some atoms, their isotopic shifts of absorption lines being observed at several excitation steps, for instance those of U, Yb, Gd. During three-step ionization of Yb atoms in atomic beam one may obtain an excitation selectivity equal to 4.4 × 10¹⁶ cm².     

Optical properties of Eu:CsGd2F7 downconversion phosphor

Luminescence spectra and excitation spectra in 150-420 nm spectral region have been recorded at room temperature for polycrystalline sample of (0.5%)Eu³⁺:CsGd₂F₇. The relatively intense emission has been observed from ⁵D₃, ⁵D₂ and ⁵D₁ levels. Emission and excitation spectra prove that the excitation energy is efficiently transferred from the ⁶G_J and ⁶I_J levels of Gd³⁺ ions to Eu³⁺ ions. The visible quantum cutting via downconversion has been detected, with efficiency of the cross-relaxation step of ∼50%.     

Fluorescence of Mn2+ in CaCO3

The fluorescence of Mn²⁺ ion as impurity in CaCO₃ has been investigated. Emission bands from the ⁴D(E_g), ⁴D(T_2g) and ⁴G(T_1g) levels have been observed. The analysis of excitation and emission spectra has allowed to obtain the values of field strength (Dq) for the excited energy levels of Mn²⁺ in CaCO₃ lattice. The temperature dependence of excitation and emission spectra yield an activation energy for thermal quenching of luminescence very close to theoretical calculation. The behaviour of luminescence lifetime with temperature has also been obtained.     

Interference effects in the strong isospin dependence of the polarization asymmetry in 12C(p,p′)12C11+ transitions

The strong isospin-dependence observed in the polarization asymmetry data for the ¹²C(p,p′)¹²C¹ 1⁺ transitions has been successfully interpreted as a result of interference effects between one-step and two-step (pdp′) excitation mechanisms, in addition to the interference between the central and tensor terms in the one-step excitation process.     

On the interference between Coulomb and nuclear excitation in the inelastic scattering of Li ions

Angular distributions have been measured for inelastic and elastic scattering of ⁶Li ions on ⁵⁸Ni and ¹²⁰Sn. Strong interference between Coulomb and nuclear excitation in inelastic scattering has been observed.     

Intensitätsmessung von Röntgen- und Kerngammastrahlung an einigen schweren Myonenatomen

Absolute intensities of the 5–4 muonic X-ray transition in muonic W, Os, and Bi, and relative intensities of other X-ray transitions have been measured and compared with cascade calculations. The excitation of several levels in W, Os, Ir, Tl, and Bi nuclei resulting from the muonic cascade process has been observed and absolute excitation probabilities have been determined. For the first 2⁺ level of¹⁸⁸Os and the first 3/2⁺-levels of^203,205Tl the excitation probabilities are larger than calculated. The results are discussed.     

Cross sections for the excitation of the 41 S-, 41 D- and 31 P-levels of helium excited by fast He+-ions

An experimental study has been made of the excitation of the 4¹ S-, 4¹ D- and 3¹-P-levels of helium by fast He⁺-ions in the energy range of 80 to 1100 keV. Absolute cross sections have been obtained by normalization on proton-impact results. A pronounced broad maximum has been found in the three excitation functions. The results are compared with proton-impact results of equal velocities.     

Coulomb excitation of the Kπ=16+ rotational band in 178Hf

A heavy-ion multiple Coulomb excitation experiment on a very exotic target containing microweight quantities of ¹⁷⁸Hf in the K^πn = 16⁺ isomeric state has been performed at 4.77 MeV/u ²⁰⁸Pb beam energy. The first excited I^π = 17⁺ state has been observed at an excitation energy of 357.4 ± 0.3 keV with respect to the isomeric state. The intrinsic electric quadrupole moment of Q ₀ = 8.2 ± 1.1 b has been derived from the experimental data within the rigid rotor model.     

Evidence for shape deformations of fragments in deep inelastic collisions

The number and energy spectra of neutrons evaporated by the heavy and light fragments in deep inelastic collisions have been obtained for the system 240 MeV⁴⁰Ar +¹⁹⁷Au. They indicate that at the scission point the deformation energy is a large part of the total excitation energy espe cially for the light fragment. In the last two years, neutron emission has been studied in deep inelastic reactions^1?6. All the results are similar: the incident energy which is lost during the process is transformed into excitation energy of the final fragments and is shared between the two products proportionnally to their masses. This means that the nuclear temperature was uniform in the composite system. The excitation energy equilibration time is really very short since equilibration is achieved after reaction times as small as 10^?22 s^2,6. Moreover, no preequilibrium emission (direct neutrons-) has been observed.