Level structure of 49V deduced from 50Cr(t, α) and 48Ti(3He, d) reactions

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Text of Level structure of 49V deduced from 50Cr(t, α) and 48Ti(3He, d) reactions

  • 1 ~ Nuclear Physics A106 (1968) 577--590; (~) North-Holland Publishiny Co., Amsterdam

    Not to be reproduced by photoprint or microfilm without written permission from the publisher

    LEVEL STRUCTURE OF 49V

    DEDUCED FROM SCr(t, ~) AND 4STi(3He, d) REACT IONS

    D. BACHNER *, R. SANTO, H. H. DUHM Tt and R. BOCK Max-Planck-lnstitut fiir Kernphysik, Heidelberg, Germany

    and S. HINDS tit

    A WRE Aldermaston, En#land

    Received 31 August 1967

    Abstract: The level scheme of 49V has been investigated using the ~Cr(t, c0 and 48Ti(~He, d) reactions. Angular distributions have been measured and spectroscopic factors have been extracted by

    DWBA analysis. The data indicate particle-hole and configuration mixing in the proton states involved. The excitation of states of the (f~_)3 configuration is discussed in connection with pos- sible target excitation processes.

    E [ NUCLEAR REACTIONS sCr(t,~), 48Ti(3He, d), E t = 13 MeV, E3He ~ 18 MeV; measured

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  • 4V LEVEL STRUCTURE 579

    The level scheme of 49V was investigated theoretically by Bayman, McCullen and Zamick 7) on the basis of a pure f model. By coupling the three protons, states with spin 7- , ~-, ~- , ~-, ~L- and '2 --s-- are expected from this model, the ~- state being the ground state. Only the 2 z - member of this sextuplet can be excited by a first-order stripping or pick-up process. The cross sections of the a2- and ~- states may give an estimate for the amount of mixing of these (f)3 configurations with p~ and f~ single- particle strength. Since the Nilsson-Coriolis coupling model, where orbits 12 and 13 especially are highly mixed, can describe the order of the low-lying levels properly 8), one expects some p~ and f~ strength within these levels. The excitation of the high- spin states, however, would point to a different type of reaction mechanism as target-excitation processes or compound-nucleus reactions.

    2. Experimental procedure

    The (t, ~) experiment was performed with the Aldermaston Tandem using a triton beam of 13 MeV. The ~-groups were analysed by a broad-range multi-angle spectrograph with an energy resolution of about 20 keV. The (3He, d) data were taken at the Heidelberg Tandem using a broad-range single-gap spectrograph. Self- supporting targets of high enrichment were used in the case of 4STi, whereas the 50Cr targets were prepared by evaporation onto a thin carbon backing.

    Energy spectra for the SCr(t, ~)49V and 4STi(3He, d)49V reactions are shown in fig. 1. For the (t, ~) reaction, angular distributions have been measured between 5 and 102.5 in 7.5 steps. Due to the high triton background, however, no use could be made of the 5 and 12.5 spectra. For the 48Ti(aHe, d) reaction, spectra were only taken for seven angles between 5 and 30 , which, in most cases, was sufficient to fix the/-value by means of the DWBA analysis. Absolute cross sections were deter- mined for 48Ti by adjusting the measured elastic 3He cross section at 6 MeV to the Rutherford cross section.

    3. Analysis

    DWBA analyses of the (t, ~) and (3He, d) angular distributions have been perform- ed with the code JUL IEt . The optical parameters used are listed in table 1. The

    TABLE 1

    Optical-model parameters used in the DWBA calculations leading to the angular distribbtions of figs. 2 and 3

    V W r r e a r' a' Wd VB.o. Ref. (MeV) (MeV) (fro) (fm) (fm) (fm) (fm) (MeV) (MeV)

    t 144 20 1.36 1.25 0.678 1.45 0.841 5 9) 183.7 26.6 1.4 1.4 0.564 12)

    SHe 165 20.2 1.14 1.3 0.723 1.6 0.81 5 11) d (85.7) 1.15 1.3 0.81 1.44 0.61 66.4 10)

    t We thank Dr. Drisko for making available the JULIE code.

  • 580 D. BACHNER et al.

    triton potential was derived from an optical parameter set found by Hafele et al. 9) i an analysis of elastic triton scattering from 52Cr at 15 MeV. For the deuterons th parameters of Siemssen and Mayer-B6ricke ~ 0) were used with an energy-depender real potential. The resulting DWBA curves are shown in figs. 2 and 3 together wit the experimental data. The stronger (3He, d) distributions allow/-assignments wit

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  • ~gV LEVEL STRUCTURE 581

    and proton-hole states, respectively. From the comparison of the (aHe, d) and (t, ~) transition strengths for ! = 0, l -- 2, one obtains, of course, an estimate for the s-, d-hole admixtures contained in the +8Ti ground state, and comparing the l -- 1 and l = 3 transition strengths in both reactions one obtains, similarly, the f+ and p+ particle admixtures in the 50Cr ground state.

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    Fig. 2(b). See caption to fig. 2(a).

    4. D iscuss ion

    The spectroscopic factors l!sted in table 2 were obtained for the (3He, d) data by the DWBA analysis 13) with a normalization constant of N = 4.42. Since absolute cross sections have not been determined for the (t, ~) data and the normalization constant is not well known, the spectroscopic factors for the (t, cQ reaction were normalized to the expected s{ strength: Czss~ = 2.0. This normalization is probably

  • 582 D. BACHNER et aL

    only slightly too high for 'Cr, since in a recent 'Cr(aHe, d) experiment t4), th~ 2.23 MeV l = 0 state, which is presumably the ld~ hole state, was only weakl,. excited. We obtain from the ~STi(aHe, d) reaction a value of about 10 % 2s hol, admixture within the proton configuration of the 48Ti ground state. Unfortunately thi value is associated with a large error since it results from unfolding the peak a

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    1.65 MeV by a superposition of DWBA curves with 1 = 0 and l = i. We attribu the l = 1 distribution to a level at 1.67 MeV.

    The main d~ hole strength in 49V is found to be concentrated in the level at 0.7~ MeV. This is in fair agreement with an excitation energy of about 1 MeV predict~ for the d~ hole state by the formula of Bansal and French ts). In addition to t~ strong transition, a number of l = 2 transitions are observed with appreciable cro

  • 49V LEVEL STRUCTURE 583

    section up to an excit