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.     

A study of the 35Cl(p, γ)36Ar reaction and the energy levels of 36Ar

Proton energies and strengths of (p,γ) and (p, p₁) resonances of the ³⁵Cl + p reaction were determined for E_p = 0.4?3.0 MeV and 1.9?3.0 MeV, respectively. The γ-decay of 84 resonances was studied with a 40 cm³ Ge(Li) detector. The branching ratios and excitation energies of 38 bound levels were determined. A new bound level was observed at E_x = 8472.0 ± 1.0 keV. Doppler-shift attenuation experiments yielded lifetimes of 20 bound levels. Spins and/or parities for bound levels and resonances were derived on the basis of observed transition strengths.     

Étude des états excités du noyau 34Cl: (I). Courbe d'excitation de la réaction 33S(p, γ)34Cl, énergies,rapports d'embranchement et vies moyennes des niveaux du 34Cl

Resonance energies and strengths are reported for forty-five ³³S(p, γ)³⁴Cl resonances in the range E_p = 1.0–2.0 MeV. Analysis of the γ-ray spectra by means of two Ge(Li) detectors leads to precise excitation energies of bound states and branching ratios of resonant levels and bound states. New bound levels are found. The reaction Q-value is 5140.3 ± 1.5 keV. Mean lives (or limits) of twelve bound states of ³⁴Cl have been obtained from DSA measurements at seven of the studied ³³S(p, γ)³⁴Cl resonances.     

6Li-α scattering below 3 MeV

Angular distributions for ⁶Li-α scattering at six α-particle energies between 1.39 and 2.98 MeV (lab) along with the excitation functions for two narrow resonances have been measured. A phaseshift analysis of the off-resonance angular distributions was made for l ≦ 3 with the higher phases fixed at values calculated for d-exchange. The l ≦ 3 phase-shifts are compared with those calculated for d-exchange and known wide resonances.     

Energy levels in 93Mo populated by the 93Nb(p,nγ) reaction

Energy levels of ⁹³Mo have been investigated by means of the ⁹³Nb(p, nγ)⁹³Mo reaction. The excitation functions of the level de-excitation γ-rays were measured with a Ge(Li) detector under proton bombardment in the energy range 3.0 to 5.0 Me V. A detailed γ-ray decay scheme which includes 69 levels and 123 γ-ray lines was constructed from the threshold energies for 64 γ-rays and the γ-ray excitation functions around five isobaric analogue resonances in the ⁹³Nb(p, nγ) reaction. Spin-parity values for 59 levels and favourable values for 8 levels were assigned from the analysis of relative neutron yields via the isobaric analogue resonances of the parent odd-odd nucleus ⁹⁴Nb. The results of the present experiment are compared with shell-model calculations.     

Intermediate resonance of inelastic 12C + 12C scattering

The intermediate resonances observed in the inelastic ¹²C + ¹²C cross sections to the single and mutual 2₁⁺(4.43 MeV) excitations and the single 3₁^? (9.64 MeV) excitation are studied by the coupled-channel method with the use of the coupling interaction derived by the folding procedure between ¹²C and ¹²C. It is shown that the model is successful in reproducing the gross structures of the inelastic cross sections and especially the correlated resonance energies of the inelastic channels. The inelastic resonances are shown to be due to the molecular resonances in an adiabatic potential between two ¹²C, which reproduces correctly the coupled channel resonances.     

An accurate measurement of the 7Li(d,p)8Li excitation function from Ed = 0.6 MeV to 2.0 MeV

The excitation function for the ⁷Li(d, p)⁸Li reaction was determined at incident deuteron energies ranging from 0.613 to 1.948 MeV by measuring delayed α-particles. This excitation function revealed resonances at 0.773 ± 0.010 MeV and 1.025 ± 0.010 MeV with cross sections of 181 ± 8 mb and 168 ± 7 mb, respectively. No resonance was observed in the region of 1.4 MeV.     

Spin and parity assignments for 35Cl levels from the 31P(α, p)34S reaction

³⁵Cl states at excitation energies between 9.9 and 11.8 MeV have been identified through sharp resonances in the ³¹P(α, p_o)³⁴S excitation functions at 25°, 105° and 155° for E_α = 3.25–5.50 MeV. Forty-eight on-resonance angular distributions, normalized to an absolute cross section scale, have been subjected to single-level and two-level analyses resulting in spin and parity assignments for each resonance. Approximately half the resonances were of the pure single-state type, having unique angular distribution shapes. Data from 12 resonances of an earlier experiment ¹) were analyzed with the same theory, extending the diagnostics down to a ³⁵Cl excitation energy of 9.1 MeV. A set of optical potentials consistent in all four reactions that this experimental program encompasses has been incorporated in the present analysis. Validity of the optical potential is demonstrated for α-particles elastically scattered by ³¹P.     

Shell-model calculation with Hartree-Fock condition

Giant resonances and spectroscopic factors of ¹⁶O are studied in the framework of the shell model with (0 + 2)ħω model space. It is found that the Hartree-Fock condition is crucial in order to obtain reasonable excitation energies of giant resonances in ¹⁶O. The calculated spectroscopic factors in ¹⁵N are quenched only by 10% due to the coupling to 1p-2h states. The spectroscopic factor of the s-state in ¹¹B is also discussed.     

20Ne(p,p0)20Ne and states of 21Na

Cross-section and analyzing power angular distributions have been measured for ²⁰Ne(p, p)²⁰Ne and ²⁰Ne(p, p₁)²⁰Ne¹(1.63 MeV) for proton energies between 3.7 and 7.9 MeV. The measurements were made in 25 keV intervals between 3.7 and 4.4 MeV, and in 10 keV intervals over most of the region between 4.4 and 7.9 MeV. A phase-shift analysis of the elastic-scattering data has yielded resonance parameters for thirty-three levels in ²¹Na in the excitation energy region 6.0–9.9 MeV. Some of the strong even-parity resonances can be understood within the framework of the Nilsson model or the shell model. These resonances are also predicted by a macroscopic coupled-channels calculation involving rotational excitation of the 2⁺ and 4⁺ states of ²⁰Ne.     

Theory of molecular collective excitation in the scattering of identical nuclei

The excitation of nuclear molecules, formed in the scattering of ¹²C on ¹²C, is treated by the collective two-center model (CTCM). The model is referred to a rotating coordinate system and describes the continuous transition from the collective states of the separated nuclei to the states of the compound system. The diagonalization of the interaction between the nuclei leads to a splitting of the excitation energies as function of parity and angular momentum projection. The theory is applied for the explanation of the molecular resonances observed in the ¹²C-¹²C scattering.     

Large-angle elastic scattering of α-particles from 20Ne and 22Ne

Resonances observed in the 177° (lab) excitation function of α-particles scattered elastically from ²⁰Ne are investigated in terms of a single Regge pole. The position of the pole in the complex angular momentum plane is determined from angular distributions measured at incident α-particle energies of 25.8 and 27.0 MeV, at which energy values prominent maxima were observed in the excitation function and the pole contribution to these angular distributions is therefore expected to be a maximum. The complete trajectory of the pole over the energy region investigated (24.6 to 31.7 MeV) is obtained by means of extrapolation. The pole trajectory across the surface absorption region of the target nucleus clearly shows the reason for the occurrence of only three large resonances in this energy region, the remaining resonances being attenuated considerably. An angular distribution obtained for ²²Ne(α, α)²²Ne at an incident energy of 27.0 MeV also indicates the presence of the Regge pole found for ²⁰Ne at the same energy, even though its strength is severely reduced due to the isotopic dependence effect.     

Resonances and fluctuations in the 16O + 15N and 12C + 19F collisions

The search and study of quasi-molecular resonances in the ³¹P composite system populated via two entrance channels are performed with two different experimental techniques. The ¹⁶O + ¹⁵N reaction products have been studied by the γ-ray detection method at cm. energies ranging from 15.5 MeV to 36.1 MeV. Binary channels of the ¹⁶O + ¹⁵N and ¹²C + ¹⁹F collisions have been studied by using the kinematical coincidence method at 26 incident energies ranging from E_c.m. = 20.6MeV to 33.5MeV for the first system, and at energies corresponding to the same excitation energies of the composite system for the second system. The ¹⁶O + ¹⁵N reaction exhibits two prominent gross structures in the large angle elastic scattering excitation function correlated with the resonant structures observed in inelastic channel γ-ray yield measurements. Spin assignments were tentatively made for the two resonances. On the contrary, no such structures can be clearly established in the ¹²C + ¹⁹F system where only indications of non-correlated structures in various channels have been observed.     

High energy structures in heavy ion collisions: A multi-phonon description

Energy spectra of fragments from the³⁶Ar+²⁰⁸Pb reaction at 11 MeV/n exhibit structures at high excitation energies. These structures are interpreted in terms of target multi-phonon excitations built from giant resonances. The importance of such processes for the kinetic energy dissipation in heavy ion collisions is emphasized.     

The study of the (α, α′ f) reaction at 120 MeV on 232Th and 238U: (II). Fission barrier properties deduced from fission probabilities and angular distributions

The fission probabilities and angular distributions of the fission fragments for the (α, α'f) reaction on ²³²Th and ²³⁸U at a bombarding energy of 120 MeV have been measured from about 4 to 14 MeV excitation energy. Evidence for sub-barrier resonances has been found, the negativeparity ones occurring at the same excitation energy where photofission resonances have been observed. The data are analyzed with the two-humped barrier model. For ²³⁸U the data are reasonably well fitted with barriers similar to those known from the literature. For ²³²Th though, the outer barrier parameters are quite different: the height E_B = 6.6 MeV and the width (khω)_B = 1.2 MeV. Also for ²³²Th, introducing an additional mass symmetric and axially asymmetric outer barrier, as was previously found necessary for ²³⁸U, does not result in a good fit to the data at higher excitation energies.     

Resonances in the isomeric and prompt fission probabilities of240Pu

The prompt and isomeric fission probabilities of²⁴⁰Pu have been studied using the²³⁹Pu(d,p) reaction. A number of resonances are observed in the subbarrier population of the 4 ns fission isomer for excitation energies between 4.0 and 6.2 MeV. Apart from a structure at 4.3 MeV, they do not coincide with transmission resonances found in prompt fission. Calculations with an extended doorway state model which simultaneously reproduce the measured delayed and prompt fission probabilities yield revised fission barrier parameters as well as spectroscopic information on fission and gamma widths of highly excited states in the second minimum.     

Evidence of an isoscalar E3 giant resonance in 16O

Differential cross sections and analyzing powers for the inelastic scattering of polarized protons from ¹⁶O leading to the 2^? state at 8.88 MeV excitation have been measured at incident energies of 31.7, 33.8, 35.8, 36.8 and 39.9 MeV. These data have been analyzed using a distorted wave theory in which the effects of virtual excitation of E1, E2 and E3 giant resonances as doorway states are included explicitly. This analysis shows that the strong energy variation in the data between 30 and 40 MeV may be predominantly due to a new isoscalar E3 resonance with the contributions from the E1 and E2 resonances corroborating earlier findings.     

Excitation energies and intensities of λπ=0−, 2− charge exchange modes in spherical nuclei

Theβ ^?, (n→p) and (p→n), transition strengths and excitation energies for first forbidden resonances with λ^π=0^? and 2^? in spherical nuclei are calculated in the framework of the linear response theory. The results show that the intensities associated with these modes are strongly fragmented, particularly, for the λ^π=2^? states.     

Alpha chain states in 4N-nuclei

We review the experimental evidence for alpha chain states in 4N-nuclei. Bloch-Brink cranked cluster model calculations suggest that such states should exist in all light A=4N nuclei. Recently a strong resonance has been observed in the¹²C(¹²C,¹²C(O ₂ ⁺ ))¹²C(O ₂ ⁺ ) reaction at 33 MeV which has been taken as evidence of a 6-α chain state in²⁴Mg. The angular distributions show strong peaks at 90° due to the simultaneous excitation of several nearly degenerate resonances with a range of L-values. We review our analysis of these data and present the results of calculations for the widths of resonances in hyperdeformed nuclei. We demonstrate that such resonances may have relatively narrow widths despite their high excitation energies. We surmise that the 33 MeV resonance in¹²C+¹²C scattering has a chain state structure.     

Energy distribution of the <Emphasis Type="Italic">E</Emphasis>1-transition strengths in the <Superscript>46</Superscript>Ti nucleus

The structure of levels of the ⁴⁶Ti nucleus is studied by means of the nonselective reaction ⁴⁵Sc(p, γ) at proton energies ranging between 1.2 and 3.1 MeV. Spin-parity assignments for ⁴⁶Ti states of excitation energies up to 5.5 MeV are obtained by using the method of averaged resonances. Radiative strength functions for E1 transitions populating these states are determined. The resulting data are compared with predictions of various models.