Sc Reaction Research Articles

High-spin precursors of the Jpi=19-/2isomer in43Sc

Three high-spin precursors of the 19-/2 isomeric level at 3.12 MeV in 43Sc have been studied using the 29Si(16O,pn)43Sc reaction at beam energies of 40 and 42 MeV. The decay scheme was established with the aid of gamma - gamma coincidence experiments. These previously unreported levels have excitation energies of 5517, 6429 and 7355 keV with probable spins and parities of 19+/2, 23+/2 and 25+/2 respectively. The mean lifetimes of these levels have been found to be <90 fs for the 5517 keV level, 23.5+or-2.2 ps for the 6429 keV level and 600+or-160 fs for the 7355 keV level. Definite spin and parity assignments of 11-/2 and 15-/2 have also been made for the 1830 keV and 2987 keV levels respectively. The data are compared with the results of a simple shell-model calculation.

The 48Ca( 3He, t) 48Sc reaction at 66 and 70 MeV : Reaction mechanism and Gamow-Teller strength

The 48Ca( 3He, t) 48Sc reaction has been studied at E 3 He = 66 MeV and 70 MeV. Angular distributions are given from θ = 8° to 35°. The 0 +–7 + multiplet in 48Sc is strongly excited at these energies and the spectra are further characterized by some broad structures on a continuous background. Broad peaks at E ex = 7.8, 10.6 and 13.3 MeV have an angular distribution similar to the low-lying 1 + state. The broad peaks are interpreted as envelopes of groups of 1 + states carrying a significant part of the Gamow-Teller strength. The strength distribution is consistent with a shell-model calculation. The reaction mechanism has been examined at 66 MeV. The cross section is calculated for the 0 +–7 + multiplet in 48Sc as a coherent sum of one-step and two-step processes. The two-step contribution is calculated in a full finite-range 2nd-order DWBA. The result is similar contributions from ( 3He, α, t) and ( 3He, d, t). The calculations account reasonably well for the data with the exception of the transition to 0 +, IAS.

On positive-parity states of45Sc,47Sc and49Sc

The 46,48,50Ti(d,3He)45,47,49Sc reactions have been investigated at an incident energy of 52 MeV. Angular distributions have been measured and spectroscopic factors have been deduced by means of a DWBA analysis. Positive-parity states have been found up to about 9 MeV excitation energy, revealing about 70% of the 1d5/2 proton-hole strength. The 2s1/2, 1d3/2 and 1d5/2 strength distributions are compared with predictions from phonon-hole coupling calculations.

Population of [formula omitted] states in the [formula omitted] reaction

Angular distributions have been measured for the 41 Ca(α, p) 44 Sc reaction at a bombarding energy of 25 MeV. The emerging protons have been analysed with a magnetic spectrograph and recorded in photographic emulsions. Angular distributions for the 40 Ca(α, p) 43 Sc reaction have been measured with Si(Li) detectors both for normalisation of the 41 Ca(α, p) 44 Sc cross sections and to test the optical potential used in the DWBA description of the ( α, p) reaction. Only positive parity states are observed below 1.6 MeV of excitation energy. The spectroscopic factors for these states have been calculated in a semi-microscopic model employing the f 4 7 2 model wave functions of McCullen, Bayman and Zamick. Also the spectator description is discussed at some length.

Cross section and stellar reaction rates for the 42Ca(p, γ) reaction

The cross section for the 42 Ca(p, γ) 43 Sc reaction has been measured over the lab energy range from 0.7 to 5.5 MeV using a positron spectrometer to measure the annihilation radiation from the decay of 3.9 h 43 Sc. Stellar reaction rates N A 〈 σv 〉 have been calculated from the experimental cross section curve for a series of three temperatures of interest for explosive oxygen and silicon burning in stars. The calculated rates are compared with the theoretical predictions of Woosley et al. and found to be in agreement within the experimental errors and the quoted validity of the theoretical calculation

Effects of nonorthogonality corrections in two-step processes in ( τ, t) reactions

A coupled-reaction-channel (CRC) calculation is made of the 48Ca(τ, t) 48Sc reaction leading to the lowest 0 +–7 + states of the [f 7 2 −1f 7 2 ] configuration taking into account both one-step charge exchange and two-step τ-α-t and τ-d-t processes. Particular attention is focused on effects arising from the non-orthogonality between different channel wave functions. It is shown that these effects play an essential role in obtaining a consistent explanation of the experimental data for the reaction.

A Study of the 42Ca(p,?)43Sc Reaction

The 42Ca(p, y)43SC reaction has been studied below 2�75 MeV proton bombarding energy. Approximately 100 resonances have been identified and located in the range Ep = 2�00-2�75 MeV. Nine resonances at Ep = 1045, 1201, 1299, 1319, 2038, 2471, 2523, 2643 and 2714 keV for the 42Ca(p, y)43SC reaction were investigated with either a 54 or a 120 cm3 Ge(Li) detector. Single spectra were obtained at each of these resonances, and these were used to derive consistent y ray decay schemes and accurate level energies for the resonant and bound levels of 43Sc. Fifty-two bound levels up to an excitation energy of 4�47 MeV were observed, out of which seventeen new levels have been identified at 2�114,2� 796,2' 846,2' 860,2' 875,3 '160,3' 331,3' 374,3 '463,3;504,3' 645, 3'734,3'757,3'860,4'007,4'038 and 4�430 MeV. In addition, new results or results differing from earlier reports have been obtained for the decay properties of levels below 4�47 MeV in 43SC? The strengths of the nine resonances were measured relative to the reported strength at Ep = 2038 keV. The resonance at Ep = 2643 keV was shown for the first time to populate levels of spin&gt; 7/2 via the proton capture reaction. A strong M1 (analogue to anti-analogue) transition from the resonance level to the level at 1� 931 MeV (9/2+) was observed. From measurements of y ray angular distributions, the following spin and parity assignments were made: 9/2+ at 7'514, 7/2+ at 4'371, &gt;7/2 at 4'038 and 7/2 at 3�808 MeV. The resonance level at 7�514 MeV has possibly aT = 3/2 character. The low-lying excited states in 43SC are in reasonable agreement with the theoretical predictions of Johnstone (1968).

Investigation of direct and two-step mechanism in the 48Ca( 6Li, 6He) 48 Sc reaction

The mechanism of the ( 6Li, 6He) reaction is investigated including the direct charge exchange and two types of two-step reactions, namely the pickup-stripping ( 6Li, 7Li) ( 7Li, 6He) and the stripping-pickup ( 6Li, 5He) ( 5He, 6He) processes. In this way we are able to provide a consistent description for the 48Ca( 6Li, 6He) 48 Sc reaction for all states in the [ν f 7 2 −1, π f 7 2 ] J + multiplet with a unique force strength of V σσττ = V Tens, ττ = 10 MeV. The importance of recoil effects, post-prior ambiguities and of non-orthogonality corrections is studied.

Lifetime and g-factor measurements in44Sc

The lifetimes of the 235 keV, 2− state and 350 keV, 4+ state in44Sc have been measured via the44Ca(p, n)44Sc reaction with a pulsed proton beam. The time integral perturbed angular distribution technique with an external field was used to measure the precession angles of the 2− and 4+ states populated by the30Si(16O,pnγ)44Sc reaction. The following values for the mean-lives andg-factors were obtained: τ(2−)=8.83(33) ns, g(2−)=0.30(13) and τ(4+)=4.52(27)ns, g(4+)=0.90(12). The results for the 2− state support a rotational description of the negative parity states in44Sc. The magnetic moment of the 4+ state is compared to shell model predictions.

Split analogue of the 2.02 MeV state of 47Ca

The elastic scattering of protons by 46Ca has been measured at seven angles for E p = 1.82−1.90 MeV. Thirteen resonances are observed and interpreted as components of the split analogue of the 47Ca first excited state. The resonance parameters are extracted and the proton width of the IAS is determined. The partial reduced widths are fitted to the Robson one-level formula and the pertinent parameters are deduced. In addition, γ-rays from the 46Ca(p, γ) 47Sc reaction were detected; the decay scheme and Γ γ are deduced. The summed M1 strength for the IAS is 1.0 W.u. Hindrance of the M1 decay is explained as resulting from the polarization due to the spin-isospin interaction, which is especially strong for the analogue-to-antianalogue transitions.

Nuclear structure of 47Sc : (I). Gamma-ray correlations and lifetime measurements

Levels of 47Sc below an excitation energy of 2.7 MeV have been investigated through the 44Ca(α, pγ) 47Sc reaction. Gamma-ray spectra in coincidence with protons were recorded with a Ge(Li) detector positioned at several angles and at α-energies of 10.15 and 11.00 MeV. Level positions, lifetimes, decay modes and spin values were deduced from these measurements. This study was supplemented by a γ-γ coincidence measurement. The electromagnetic properties for the negative parity states are compared with intermediate coupling predictions. A classification of the positive parity states into several rotational bands is proposed.

Étude des niveaux d'énergie de 47Sc au moyen de la réaction 45Sc(t, p) 47Sc

The energy levels of 47Sc are investigated through the 45Sc(t, p) 47Sc reaction using 11.8 MeV incident tritons and a multigap magnetic spectrograph with nuclear emulsions to analyse the resulting protons. Seventy states are excited in 47Sc up to 6.9 MeV. The data are analysed using the distorted wave Born approximation and values of the orbital angular momentum L of the transferred neutron pair are derived for 28 levels. Good agreement with previous results is generally obtained, new states in 47Sc are detected and more precise information on the spins of some levels in 47Sc are deduced. The results are compared with shell model calculations. Strong L = 0 and mixed L = 0 + 2 transitions to 47Sc levels other than the ground state are detected, and qualitative explanations for them are presented.

The43Ca(3He, d) reaction and the parity of the 425 keV state of44Sc

The Harwell multi-angle magnetic spectrograph and tandem accelerator have been used to study the 425 keV state of 44Sc populated in the 43Ca(3He, d)44Sc reaction. Comparison of the measured angular distribution of the deuteron group populating the 425 keV state with predictions based on the distorted wave Born approximation suggests that population of the state proceeds by l=2 proton transfer. The consequent assignment of negative parity to the 425 keV state removes an inconsistency which has existed within earlier particle transfer reaction studies of this state.

The ( 6Li, 6He) spin-isospin-flip reaction

A formulation of the ( 6Li, 6He) spin-isospin-flip scattering problem is presented. The method is applicable to quasielastic collisions between 6Li described in pure LS coupling scheme and any target nucleus which can be described in a shell model or an adiabatic deformed-nucleus model picture. The effective interaction responsible for the ( 6Li, 6He) reaction involves an integration of the ( σ 1 · σ 2) ( ρ 1 · ρ 2) compo nent of the central part and the ( τ 1· τ 2) tensor part of the nucleon-nucleon interaction over the internal wave function of the projectile. The 48Ca( 6Li, 6He) 48Sc reaction populating the ( πf 7 2 νf 7 2 −1 ) multiplet in 48Sc is analysed. It that the tensor force makes some contribution to the transitions to high spin states.

The [formula omitted]-induced three-nucleon transfer reaction on [formula omitted

Analog (fp) 3 states preferentially excited in the 40 Ca( 6 Li,t) 43 Ti and the 40 Ca( 6 Li, τ) 43 Sc reactions have been identified in the mass 43 mirror nuclei. A simple zero-range DWBA calculation made with a cluster form factor gives good agreement with the measured angular distributions, but spectroscopic strengths deduced for mirror levels do not agree. The 3p-0h states are excited with a rather uniform cross section not strongly correlated with spins.

Spin-parity determination from neutron threshold measurements and the second excited state of44Sc

The « counter ratio method »,i.e. the ratio between slow-and fast-neutron yields has been used in the44Ca(p, n)44Sc reaction to assign spin and parities to some44Sc levels. The method is presented as an useful tool for spin-parity assignments in the case of odd-odd nuclei formed through (p, n) reactions. The48Ti(p, n)48V reaction is discussed as an example. The44Ca(p, n)44Sc reaction has been investigated by using the proton beam of the Van de Graaff accelerator of the Laboratori Nazionali di Legnaro. The results are consistent with the following spinparity assignments to44Sc levels: ground state (2+), 68 keV state (1−), 146 keV (0−), 667 keV (1+). Of special interest is the 0− assignment to the second excited state at 146 keV.

Study of the 48Ca( 6Li, 6He) 48Sc reaction at 34 MeV

Angular distributions have been measured in the range from 5° to 50° for the 48Ca( 6Li, 6He) 48Sc reaction at E( 6Li) = 34 MeV in a magnetic spectrograph. A rather clean spectrum of 6He particles was obtained by using a sonic spark counter as the position defining device together with three proportional counters in an anticoincidence set-up. A microscopic description of the reaction has been used to predict absolute cross sections for the unnatural parity states of the ( f 7 2 ) 2 multiplet. A calculation of the configuration mixing shows that the cross section to especially the 1 + state is strongly dependent on such a mixing. A number of states with excitation energies above 2.5 MeV are excited with cross sections similar to the low lying states. Comparison with DWBA calculations puts limits on the spins of the final states.

A Study of Excited States in 44Sc by means of the 41K(α,nγ)44Sc Reaction

The 41K(α,nγ)44Sc reaction has been studied at 10, 12 and 14 MeV incident energy. By use of single spectra, γγ-coincidence measurements and yield functions, the decay modes of several excited states have been obtained and spins have been assigned. On theoretical grounds a K = 0- band has been proposed in 44Sc. In the present work the following members of this band are suggested: 68 keV (1-), 235 keV (2-), 425 keV (3-), 532 keV (3-), 631 keV (4-). Two possible candidates for the 5- state are discussed.

Spin-Parity Assignments of the 49Sc Levels from the Gamma-Decay of the 3/2- Isobaric Analogue State In 49Sc

Gamma ray spectra and the angular distributions for the 1975 keV resonance, which is the strongest of the seven resonances associated with the 49 Ca ground state analogue in the 48 Ca( p , γ) reaction, have been measured with Ge(Li) detector. Gamma-gamma coincidence spectra have also been measured to confirm the decay scheme. To identify the transitions between the low-lying states, gamma rays from the 48 Ca( d , n γ) 49 Sc reaction have been measured at E d =3.0 MeV. Spins and parities of some of the levels in 49 Sc as well as the tentative gamma decay scheme have been determined from these data with the aids of previous reaction data.

Calculations of the excitation functions and isomer ratios of the 41K(α, n)44Sc reaction in the equilibrium and pre-equilibrium statistical models

Abstract Angular-momentum effects are incorporated in the pre-equilibrium statistical model using Williams' spin-dependent level density as a function of the particle and hole numbers. Excitation functions and isomer ratios for the 41 K(α, n) 44 Sc reaction are analyzed both in the equilibrium and pre-equilibrium models in the energy range 8 to 40 MeV. Conventional pairing-energy corrections are introduced and their influence on the pre-equilibrium decay is investigated. The results are compared with published experimental data. The best fit was obtained for almost-pure pre-equilibrium decay with the initial excited-particle-plus-hole number n o = 5 when pairing corrections were taken into account. No success was achieved in fitting the decrease of the isomer ratios at high energies, which is probably caused by the contribution from direct processes.