Beta decays of 44V and 52Co

We have studied the prevously unknown β⁺ decay branches from ^44,44mV and ⁵²Co to particle-bound states in ⁴⁴Ti and ⁵²Fe, respectively. These intense branches populate a few states in the daughters from an excitation energy of about 1 MeV up to the isobaric analogue states at about 6 MeV. We have measured the first precise energy values for the latter states as well as the β-branching ratios to all states in this excitation energy region. We have calculated the β⁺ decay of ^44,44mV in the full fp shell model space as well as in a truncated space. Renormalized transition operators are constructed for the truncated space and tested against experimental data in ⁴⁴V and ⁵²Co. In general there is good agreement between theory and experiment for the half-lives, level energies and beta branches, but not all the states found are reproduced by the calculations.     

Measurement and hybrid-model analysis of proton-induced reactions with V,Fe and Co

On target elements V, Fe and Co (natural isotopic composition) proton-induced reactions were investigated in the energy region from 12 to 45 MeV using the stacked-foil technique. The product nuclides observed were ⁴⁸Cr, ⁴⁹Cr, ⁵¹Cr, ⁴⁸V, ^{46m + g}Sc, ⁴⁷Sc and ⁴⁸Sc from V, ⁵⁵Co, ⁵⁶Co, ⁵⁷Co, ^{58m + g}Co, ⁵²Fe, ^{52m + g}Mn, ⁵⁴Mn, ⁵¹Cr and ⁴⁸V from Fe, and ⁵⁶Ni, ⁵⁷Ni, ⁵⁶Co, ⁵⁷Co, ^{58m + g}Co, ⁵⁴Mn and ⁵⁶Mn from Co. The comprehensive set of excitation functions extending and improving earlier studies is compared with calculations considering equilibrium as well as preequilibrium reactions according to the hybrid model of Blann. The overall agreement between experiment and theory is good. Certain discrepancies, however, indicate the necessity to revise the hybrid model with respect to the emission of complex particles.     

Investigation of giant-dipole-resonance decay in the (<Emphasis Type="Italic">γ, n</Emphasis>) reactions on <Superscript>52</Superscript>Cr and <Superscript>51</Superscript>V nuclei

The cross sections for the emission of fast neutrons (? _n > 3.7 MeV) in the reactions ⁵²Cr(γ, n)⁵¹Cr and ⁵¹V(γ, n)⁵⁰V at incident-photon energies in the range between 16.0 and 25.8 MeV were studied. The neutron energy spectra were measured at the bremsstrahlung-photon endpoint energies of 18.5, 21.0, and 23.0 MeV for the ⁵²Cr and ⁵¹V nuclei and at the bremsstrahlung-photon energy of 25.5 MeV for the ⁵¹V nucleus. Special features of giant-dipole-resonance decay that are associated with the existence of a structure in photoneutron cross sections and spectra are discussed.     

Complete and incomplete fusion studies in7Li and16O induced reactions on51V by measurement of excitation functions and recoil ranges

Excitation function and mean projected recoil ranges of nuclei produced in the⁷Li and¹⁶O induced reactions on⁵¹V target were measured by conventional stacked foil and thick-target thick-recoil-catcher technique for bombarding energiesE ≤ 50.0 MeV for⁷Li ions andE ≃ 60.0-96.0 MeV for the¹⁶O ions. The measured recoil ranges are converted to momentum transfer. The momentum transfer information was used to get clues about some aspects of the interaction such as complete and incomplete fusion reaction mechanism which correspond to full and reduced momentum transfer respectively. The measured excitation functions are compared with the calculation based on the statistical model which describes only equilibrium decay of the compound nucleus using the CASCADE code. The comparison of the CASCADE code with the measured excitation functions for the residue radioisotopes⁵¹Cr and⁵⁴Mn for the⁷Li +⁵¹V system indicates the reaction mechanisms is complete fusion of⁷Li with the target nucleus⁵¹V. Similarly the comparison of the CASCADE code with the measured excitation functions of the residue radioisotopes for the system¹⁶O +⁵¹ V indicates that the four reaction mechanisms (i) complete fusion of¹⁶O, (ii) incomplete fusion of¹²C, (iii) incomplete fusion of⁸Be and (iv) incomplete fusion of⁴He respectively with the target might be contributing to reaction cross sections.     

Gammaübergänge und Energieniveaus im49V aus der Reaktion48Ti(p, γ)49V

Deexcitation gamma rays of⁴⁹V from the⁴⁸Ti (p, γ)⁴⁹V reaction have been investigated at the resonancesE _p=1007, 1209, 1362 and 1374 keV corresponding to excited states in⁴⁹V at 7742, 7940, 8090, 8102 keV. A 4 cm²× 0.35 cm lithium-drifted germanium detector was used. The target was TiO₂ enriched in⁴⁸Ti to 99.4%. 71 gamma transitions have been observed. A level scheme of⁴⁹V is proposed involving 8 new levels in the energy range from 0 to 5.2 MeV excitation energy.     

Complete spectroscopy of51,52V via the50,51V(n, γ) reactions

The gamma-ray spectra emitted after thermal neutron capture in highly enriched⁵⁰V and^natV targets have been studied using in-pile targets at the ILL high flux reactor and pair and germanium detectors. The neutron binding energies in⁵¹V and⁵²V were determined to beB _n (⁵¹V)=11051.11(17) keV andB _n (⁵²V)=7311.22(26) keV. The thermal neutron capture cross-section in⁵⁰V was measured to be 21 _–2 ⁺⁴ b. From 724 lines attributed to⁵¹V, 330 transitions, comprising 90% of the-ray flux, were placed into the level scheme. Fifty-nine primary dipole transitions from the 11/2⁺ or 13/2⁺ capture states in⁵¹V were established from which the E1 strength distribution was deduced. The energy scaling of these primary transitions was found to follow the E1-giant dipole resonance dominance. Many new levels were established; a number of states proposed in previous (d,p) and (n,) work were confirmed from their primary population and decaying secondary radiations. The density of levels in the high spin (9/2I15/2) region was parametrized with the Fermi gas model. The spin distributions of⁵¹V were analyzed and a spin cut-off parameter =2.8 (3) was deduced. — A nearly complete level scheme of⁵²V up to 3.5 MeV excitation and similar results concerning the level density and the primary -ray spectrum were obtained in the⁵¹V (n, )⁵²V study.Supported by Deutsches BMFT under contract 06GÖ141     

Incomplete fusion reactions: Analysis of excitation functions and recoil range distributions in 16O + 51V

Incomplete fusion reactions were investigated by measuring the excitation functions of nine evaporation residues in ¹⁶O + ⁵¹V reaction in the beam energy 4-6 MeV/amu, using the well-known recoil catcher technique and gamma-ray spectrometry. The experimental data were compared with that obtained from Monte Carlo simulation calculations using the PACE2 code. The results indicate the presence of incomplete fusion process in the production of two alpha emission products. This was further confirmed by the measurement of recoil range distribution of these isotopes at 96 MeV beam energy. Calculations of the average angular momentum associated with these products revealed the peripheral nature of these ICF reactions. Received: 20 June 2001 / Accepted: 11 September 2001     

Excitation energy division in 51V + 197Au collisions at and near the barrier

Mass- and charge-yield distributions for 19 < Z < 84 were determined radiochemically for the binary collision products of ⁵¹V + ¹⁹⁷Au collisions at a bombarding energy corresponding exactly to the Bass-model barrier, E _cm = B, and at E _cm = B + 25 MeV. The average excitation energies as a function of Z are determined by comparing the centroids of the experimental, secondary mass distributions for given values of Z with the calculated primary centroids from minimization of the potential energy of the di-nuclear system, i.e. from the missing masses. At the barrier, in striking contrast to a thermal equilibrium, we find an extreme donor-acceptor asymmetry in the excitation-energy division reminiscent of the “sawtooth” phenomenon in low-energy nuclear fission. Here, the excitation energy sharing is apparently dominated by shape fluctuations at scission. At the slightly higher bombarding energy, E _cm = B + 25 MeV, we observe a rapid change toward equipartition of the excitation energy indicating that, here, the excitation energy division due to shape fluctuations is already covered up by the dissipative exchange of nucleons. Also, the balance of integral cross sections for fusion fission, deep-inelastic scattering, and quasi fission is investigated and is shown to contain important information about the dynamical evolution of the ⁵¹V + ¹⁹⁷Au system after having passed the entrance channel barrier.     

Neutron emission spectra and angular distributions at 25.7 MeV neutron bombarding energies

Inelastic scattering of 25.7 MeV neutrons to unresolved final states with excitation energies up to ~13 MeV were measured for monoisotopic samples of ⁵¹V,⁵⁶Fe, ⁶⁵Cu, ⁹³Nb and ²⁰⁹Bi. Time-of-flight spectra were taken at several angles between 25° and 145° using the beam swinger spectrometer. Double differential cross sections, angle-integrated spectra and energy-binned angular distributions are compared with the predictions of pre-equilibrium theory.     

Search for M1 strength in 51V and the difference in 51V(e,e′) and 51V(p,p′) spectra

Following the studies of the distribution of M1 strength in the even-even N = 28 isotones ⁴⁸Ca, ⁵⁰Ti, ⁵²Cr and ⁵⁴Fe by inelastic electron scattering, the result of a search for M1 transitions in the odd-even N = 28 nucleus ⁵¹V is reported. No strong M1 excitation has been detected, in contrast to a recent (p, p') experiment. There is no immediate explanation for this discrepancy. Shell-model calculations indicate that a part of it might be accounted for by an interference between the spin and orbital term of the electromagnetic transition operator in the (e, e') experiment.     

Isomerenverhältnis für die Reaktion51V(α,3n)52g,mMn

The isomeric cross-section ratio has been measured for the reaction⁵¹V(α, 3n)^{52 g,m}Mn between 32 and 51 MeV. The experimental results are compared with statistical-model calculations. In these calculations two models for the gamma cascade have been used: the simple dipole cascade model ofVandenbosch andHuizenga, and alternatively the model ofPönitz which includes quadrupole transitions. With the latter model agreement between theory and experiment could be achieved.     

Total (p,n) reaction cross section study on51V over the incident energy range 1·56 to 5·53 MeV

The total (p, n) reaction cross section for⁵¹V has been measured as a function of proton energy in the energy range 1·56 to 5·53 MeV with thick and thin targets. The fluctuations in the fine resolution excitation functions were analysed, to extract 〈Γ〉, the coherence width. The thick target excitation function suitably averaged over appropriate energy intervals has been compared with the optical model, Hauser-Feshbach and Hauser-Feshbach-Moldauer calculations. The strong isobaric analog resonance atE _p ～ 2·340 has been shape analysed to extract the proton width Γ _p , the spreading withW and the spectroscopic factor.     

Derp 3/2-Analogzustand in51V

In an investigation ofT=7/2 analogue states in⁵¹V the⁵⁰Ti(p, γ) excitation curve has been measured for proton bombarding energies 1280–1480 keV and 2340–2660 keV. From the (p, γ) resonances 29 new virtual levels in the region of 9316–9510 keV excitation energy in⁵¹V were determined. The strong resonance atE _p=1 371 keV has been identified as the isobaric analogue state of the⁵¹Ti ground state by determining spin and parity of this resonance to be 3/2^?. There is no evidence for a strong analogue resonance in⁵¹V corresponding to the 1.16 MeV _{p 1/2} state in⁵¹Ti. The γ-decay of the _{p 3/2} analogue state has been studied by measuring branching ratios and angular distributions of primary γ-transitions with a Ge(Li) detector.M1E2 mixing ratios have been determined for these transitions. The total width of the resonance for γ-decay is found to be Γ_γ=1.6±0.4 eV. New bound levels in⁵¹V have been introduced at 3576, 4651 and 4661 keV excitation energy. TheJ ^π values of the 3085, 4770, and 4863 keV states are determined to be 5/2^?, 5/2^?, 3/2^?, respectively. The analogue-antianalogueM1 transition strength is found to be considerably reduced compared to the situation ins-d shell nuclei.     

The new element 111

In an experiment carried out to identify element 110, we have observed an-decay chain, that can be unambiguously assigned to²⁶⁹110. In a scries of preexperiments the excitation functions of the fusion reactions⁵⁰Ti +²⁰⁸Pb²⁵⁸104^* and⁵⁸Fe +²⁰⁸Pb²⁶⁶108^* were measured with high precision in order to get the optimum projectile energies for the production of these heavy elements. The cross-section maxima of the 1n evaporation channels were observed at excitation energies of 15.6 MeV and 13.4 MeV, respectively. These data result in an optimum excitation energy of 12.3 MeV of the compound nucleus for the production of²⁶⁹110 in the reaction⁶²Ni +²⁰⁸Pb²⁶⁹110 + 1n. In irradiations at the corresponding beam energy of 311 MeV we have observed a decay chain of 4 subsequent a decays. This can be assigned to the isotope with the mass number 269 of the element 110 on the basis of delayed - coincidences. The accurately measured decay data of the daughter isotopes of the elements 108 to 102, obtained in the previous experiments, were used. The isotope²⁶⁹110 decays with a hair-life of (270 _-120 ⁺¹³⁰⁰ ) s by emission of (11.132±0.020) MeV alpha particles. The production cross-section is (3.3 _-2.7 ^+6.2 ) pb.     

The influence of the spectroscopic deformation of Li-isotopes on their interaction with51V

The energy dependence of the total reaction cross sectionσ ^r and its tensor analyzing powerT ₂₀ ^r was measured for the⁷Li?⁵¹V interaction in the energy rangeE _Li=10–20 MeV using two different experimental methods. Reaction residues were observed directly by their characteristicγ-emission, and the elastic scattering of⁷Li from⁵¹V was investigated. Additionally, the elastic scattering of⁶Li from⁵¹V was measured at 9.8, 12 and 14 MeV. The tensor analyzing power data can be interpreted as being caused by the spectroscopic mass deformation of the Li-ions. The energy dependence of σr andT ₂₀ ^r above the Coulomb barrier can be described in terms of the classical sharp-cutoff model.     

The structure of 32S I. Spectroscopy of highly-excited states

Assignments of I, π, T are made to 30 levels in ³²S between 7.35 and 11.76 MeV excitation energy, making the spectroscopy of the T= 0 states rather complete up to 10 MeV and that of the T = 1 states up to 12 MeV. A reassessment of existing data in the light of the new results clarifies the spectrum of I ^π = 1⁺, T = 1 states up to 15 MeV excitation energy. High-spin states (I = 52 - 7) below 10 MeV excitation energy have been investigated by n t γ angular-correlation measurements with the ²⁹Si(α, nγ) reaction at E _α 14.4 MeV. Five g-wave resonances of the ³¹P(p, γ) reaction, leading to the formation of I _π + 4⁺, 5⁺ states in ³²S, have been identified between 10 and 12 MeV excitation energy. The spectrum of T = 1 states between 10.7 and 12 MeV, has been investigated by measurements of γ-ray angular distributions on resonances of the ³¹P(p, γ) reaction and by measurements of resonance strengths. Several ³²S levels between 7.35 and 8.75 MeV excitation energy were studied as final states in resonance decays. Finally a search was performed for I ^π = 0⁺ resonances of the ²⁸Si(α, γ) reaction.     

A new sequence of high-spin states built on the 17/2+ isomer in85Kr

High-spin states in⁸⁵Kr have been studied via in-beam spectroscopy by bombarding a⁸²Se target with 32 MeV⁷Li ions. Since⁸⁵Kr is only formed with a small relative cross section proton-— coincidence techniques have been applied to enhance the rays of⁸⁵Kr, even with respect to those of⁸⁶Kr, in the measurements. A new sequence of high-spin states with excitation energies up to 4.8 MeV and tentative spins up to (23/2) has been established on top of the 17/2⁺ s isomer. A tentative assignment of the configurationvg ₉ ^2/–1 (g _9/2 p ₃ ^2/–1 orf ₅ ^2/–1 ) to the new levels is proposed.Supported by Deutsche Forschungsgemeinschaft     

Photospallation of51V at intermediate energies

The yields of⁵¹V(, xpyn) reactions have been measured at maximum bremsstrahlung energies from 75 to 800 MeV. Mean cross sections have been deduced, compared to Monte-Carlo calculations and analysed with a semiempirical Rudstam formula. Total isobaric mean cross sections and anN/Z dispersion curve in the mass regionA = 42–48 have been obtained. The results are in agreement with cascade-evaporation theory and with earlier data obtained with photons and protons.     

Study of Ar from S(He, n)Ar and S(He, nγ)Ar

The ⁵⁰ti(τ, p)⁵²V reaction has been studied at 15 MeV incident energy using a multiangle spectrograph. Seventy-seven transitions up to 8.84 MeV in excitation have been identified, and many of the corresponding proton angular distributions measured. The distribution shapes together with DWBA calculations allow the assignment of a number of new spin and parity values. The results of the present work are compared with other data on ⁵²V. The isobaric spin (τ, p) intensity relations are applied to $\text{T = 3}\text{and}\text{T = 4}\text{states with}\text{J}{}^{\mathrm{\pi }}\text{= 0}{}^{\mathrm{+}}\text{in}{}^{52}\text{V}$, and it is found that the T = 3 levels take up only 18 % of the expected anti-analog strength.