Fujiwara, Noboru

Fukunaga, Kiyoji

Kakigi, Shigeru

Nakamura-Yokota, Hitoshi

Ohsawa, Takao

Okihana, Akira

Sekioka, Tuguhisa

Tanaka, Seiji

Kyoto University Research Information Repository

Title Excited States of ⁴He Investigated via the ⁴He(α, αp)3HReactio n at 119 MeVAuthor(s)Kakigi, Shigeru; Fukunaga, Kiyoji; Ohsawa, Takao; Tanaka,Seiji; Okihana, Akira; Nakamura-Yokota, Hitoshi; Sekioka,Tuguhisa; Fujiwara, NoboruCitationBulletin of the Institute for Chemical Research, KyotoUniversity (1981), 59(1): 9-14Issue Date1981-02-28URL http://hdl.handle.net/2433/76924RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversityBull. Inst. Chem. Res., Kyoto Univ., Vol. 59, No. 1, 1981           Excited States of  4He Investigated        via the 4He(a, ap)3H Reaction at 119 MeV   Shigeru KAKIGI*, Kiyoji FUKUNAGA*, Takao OHSAWA**, Seiji TANAKA***,   Akira OKIHANA* * * *, Hitoshi NAKAMURA-YOKOTAt, Tuguhisa SEKIOKAtt, and                         Noboru FuJIWARAttt                               Received December 4, 1980     Kinematically complete experiments were made for the 4He(a, ap)3H reaction at 119 MeV. Angular correlations were fitted with the Legendre polynomials and the cross sections integrated over the dacay angle were obtained as a function of the excitation energy. Peaks were observed at the excitation energies of 25.5, 27.5, 28.6, 29.5, 31.3 and 34.2 MeV. The results for the first five peaks seem to confirm the previous results for the 4He(a, ad)2H reaction.    KEY WORDS: 4He(a, ap) 4He excited states Angular correlations/                          1. INTRODUCTION    Excited states of 4He have been observed in the 4He(a, a')4He* and 4He(a, ad)2H reactions at 119 McV.1 In single energy spectra of a-particles are observed broad bumps extending from 25 MeV to 40 MeV of excitation energy and in a-d coinci-dence spectra are observed peaks at the excitation energies as EeR=25.5, 27.8, 29.7, 31.7 and 35.3 MeV. For the last three states, the spins and parities are assigned as J=2+, 2+(1-) and 2+, respectively. The results previously reported for the T=0 states above the d+d threshold are as follows; the 25.5-MeV (0k, 1-), 28.5—MeV 1-and 31.7—MeV states by Haase et a1.2> and the 25.5—MeV 0+ and 27.5—MeV 1- states by Fukunaga et a1.3) The 31—MeV 1- and 33-MeV 2+ states also have been re-ported.4) There are some discrepancies in the excitation energy and the spin and parity of these results. Then it is worthwhile to further investigate the T=0 states of 4He through the p+t decay channel in addition to the d+d decay channel.    In the present experiment, T=0 states were selectively excited in the 4He(a, a') 4He* inelastic sacttering at 119 MeV and the scattered a-particles were measured in coincidence with the protons decaying from the excited states.   * lrI1 m, #1i7ca~ : Nuclear Science Research Facility, Institute for Chemical Research, Kyoto     University, Kyoto. ** : Laboratory of Nuclear Reaction, Institute for Chemical Research, Kyoto University,     Kyoto. *** FEIi I j : Hosoda Juutaku, Santanda 1-12-10, Amagasaki. **** j : Kyoto University of Education, Kyoto. t tAE6 : Faculty of Science, Tokyo Institute of Technology, Tokyo. tt P /J~ : Himeji Institute of Technology, Himeji. ttt ffig; : Faculty of Science, Nara Women's University, Nara. ( 9 )                           S.  KAKIGI,  K. FUKUNAGA; T. OHSAWA etal.                    2. EXPERIMENTAL PROCEDURE   By a 119 MeV a-particle beam of the AVF cyclotron at the Research Center for Nuclear Physics (RCNP) of Osaka University was bombarded a target of 4He gas at pressure of 2 atm filled in a gas cell with windows of 10 Atm Havar foil.    Alpha-particles and protons from the reactions were detected in coincidence by two dE-E telescopes. For each coincidence event, parameters 4E„, Ea, 4Ep, Ep and Tap (TAC) were obtained through an ordinary electronic system and were stored on a magnetic tape through the RCNP RAWDATA PROCESSOR-PDP 11 system. The arrangement of detectors and the block diagram of the electronic system are described in Ref. 1. Off-line analyses of the parameters were performed with the FACOM M-160AD system at the institute for Chemical Research of Kyoto University. The analyses comprised random coincidence subtraction, particle iden-tification and reduction of two-dimentional E„ Ep spectra.                     3. RESULTS AND DISCUSSIONS   In the E„ Ep spectra, yields were localized along the kinematical locus of three-body process. The yields were projected onto the E° axis. Figure 1 shows the energy spectra for the 4He(a, ap)3H reaction measured at four angle pairs of (Ca, Op) = (25°, 35°), (25°, 45°), (25°, 55°) and (25°, 65°) in the laboratory system. Each point was obtained by smoothing counts over adjacent channels considering the energy resolution of about 1.4 MeV corresponded to about two channels. Error bars represent statistical uncertainty. The edges appearing at the highest energies E ex ( MeV )               35 30 25 20 I 1 III II II 0.5_ BP= 65° a, -               - 0.5— 55° "a •••.+{+•...4 4.i4           0.545°++44+{{                              4++44{+               0.5 _35°40{0404                     -.ee4{++44++++44+4{~~~              0-I••.•I.I1I 1~         506070 Ed( MeV)            Fig. 1. Coincidence nergy spectrafor the 4He(a, ap)3H reaction. The                   a-particle angle was fixed at 0a=25° and theprotonangle was                    varied as Op= 35°, 45°, 55° and 65° in the laboratorysystem.                            ( 10 )             Excited  States of 4He Investigated via the 4He(a, ap)3H Reaction of a-particles are due to the kinematical limit. Near the edges, part of yields were lost because, there, the energy of protons coincident with a-particles became lower than the minimum value for the detected proton energy. Accordingly angular cor-relations were measured for the excitation energies above 23 MeV. 36.0/i.(a)__...„ \/+  i0.3-\,~~.-/~.33.5l'               l~T31.5   60.2•\,33.011/T\\\1;'T\1.0 i11ll/7,1030.5  tl\~~1i\\ 32.5T~~-   -1.g0. -:\_..34'5\+-4,/lTi 2, 32.0      0  i i i I i i i , 7 I ii i i , I I i  -60 0 60 -600 60-60 0 60                                 01,`"' (deg )     29.4- _  Nu_rj `i27.2/l~i25.0 -  .T~}l'T   E 28.9~`A'/1 ".~/24.4  02 -\i......4~TT- u. "1~T1          1T~T_~~~¢=a`25.5+ .-,23.3`\   0  i1 1i--. I0 , 1 1 ,       -600 60-6600 60 -60 0 60                              epm(deg )   Fig. 2. Angular correlations for the 4He(a, a')4He*(p)3H reaction at 0e=25°. Full circles re-         present experimental points and full lines the Legendre polynomialsfitwith kmax=4 and          dashed lines the one with kmax=2. The angular correlationsare designated with the          corresponding excitation energies for 4He* and are shown by shifted upward successively          by a factor 0.075.                            ( 11 )                           S. KAKIGI, K. FUKUNAGA, T.  OHSAWA et al... As seen in Fig. 1, in the energy spectra are observed no sharp peaks but broad bumps extending up to about 35 MeV of the excitation energy and at higher ex-citations the cross sections decrease to nearly zero. Then angular correlations are analysed for each excitation energy. The differential cross sections in the laboratory system (d5a/dEp,d12Q,df2p)Iab are transformed to the ones in the 4He* recoil center-of-mass system (d5a/dEQ,d22,,,d2p)r°m. In Fig. 2 they are plotted with full circles as a function of the proton decay angle Fpm, where the direction 8=O0 is defined as the direction of the recoil momentum of 4He* in the laboratory system.    The scattering angle of a-particles in the center-of-mass system varies from Oa=58.1° for EeX=23.3 MeV to Oa=67.7° for EeX=36.0 MeV corresponding to the angle in the laboratory system Oab=25°. The angular range for protons in the recoil center-of-mass system varies from —43.7°<Om<32.7°for EeX=23.3 MeV to —49.5°<Bp m<3.0°for EeX=36.0 MeV corresponding to 25°<Op b<65    The angular correlations are fitted with the Legendre polynomials as (d5c)r°m = E AkPk(cos(Op m—Ooem)) , where the summation is taken over even values of k and the symmetry angle 60°m is searched for as well. The purposes of the fit are (1) to obtain the cross section integrated over the decay angle, which is equal to the coefficient Ao multiplied by a factor 47r and (2) to obtain the maximum value of k characterizing the shape of angular correlation. The fits were performed for only two cases kmax=2 and 4. This seems to be reasonable because the excitation energies are not far from the p+t threshold and then the lowest two or three values of the decay angular mo-     2 —(a)                    N                                          1                T,11                           if + 0 11 1 I 1 1 I I I i iI 2 —(b) TTT} - H¢}T+ +++, + 0 Ili i i i I I I i i I i i  35 3025 Eex (MeV)           Fig. 3. Coefficients Aa of the Legendre polynomials, multiplied by a factor 4ir. The upper part (a) corresponds to the fit with kmax=4 and                  lower part (b) to the fit with kmax=2.                           ( 12 )              Excited States  of  'He Investigated via the 4He(a, ap)3H Reaction          Table L Excitation energies of 4He*, values of kmaxobtained in the Legendre                  polynomials fit for the angular correlationsand spinsand parities                  assigned previously.            PresentResultPrevious Result') 'He (a, ap)3H'He (a, ad)2H Eex(MeV)kmaxEex(MeV) J'    25.525.5       27.54 or 227.8       28.62     29.5429.7 2+       31.34 or 231.7 2+ or 1       34.24                        35.3 2+ mentum 1 can contribute to the reaction.    The results of the fits are shown in Figs. 2 and 3, and Table I. In Fig. 2 the curves fitted with kmax=4 are represented by the solid lines and the curves fitted with kmax=2 by the dashed lines. These two groups of the fitted curves give similar good-ness of fit for most of the excitation energies, except that for Eex=23.3, 29.4 and 29.9 MeV, the curves fitted with kmax=4 are favored compared with the ones fitted with kmax=2• In Fig. 3 are plotted the coefficient Ao multiplied by a factor 4'v against the excitation energy. The upper part (a) of the figure corresponds to the fit with kmax=4 and the lower part (b) to the one with ka ax=2. It should be noted that there remains an ambiguity in the analysis of the angular correlations owing to the measured angular ranges smaller than 90°, as mentioned above. In fact, for each angular correlation are obtained two solutions which give the same distribu-tions with the symmetry angles shifted by 90° from each other and also with the different coefficients A0. The points in Fig. 3 are obtained by averaging these two values of the coefficient. In Fig. 3(a) are observed peaks at EeX=25.5, 27.5, 29.5, 31.3 and 34.2 MeV and in Fig. 3(b) two bumps in the energy ranges from 27 MeV to 29 MeV and from 31 MeV to 32 MeV. The high energy part of the first bump in Fig. 3(b) corresponds to the peak at Eex=27.5 MeV in Fig. 3(a) and the low energy part, its center being at Eex=28.6 MeV, to a minimum in Fig. 3(a). The second bump in Fig. 3(b) corresponds to the peak at Eex=31.3 MeV in Fig. 3(a). Un-certainty in the assignment of the peak position is of ±0.3 MeV. The excitation energies corresponding to the observed peaks and bumps are listed in Table I to-gether with the values of kmax obtained in the Legendre polynomials fit. Among the listed excitation energies, four values, that is, EeX=25.5, 27.5, 29.5 and 31.3 MeV agree with the corresponding values previously reported within the uncertainty.    The peak at Eex=29.5 MeV in Fig. 3(a) nearly corresponds to a minimum between two bumps in Fig. 3(b) and two angulr correlations near Eex=29.5 MeV are fitted uniquely with kmax=4, the fit with kmax=2 giving a poor goodness of fit, as seen in Fig. 2. Therefore, the present experiment confirms the 29.7-MeV 2+ state observed in the 4He (a, ad)2H reaction. For the peak at Eex=31.3 MeV in Fig. 3(a), the corresponding bump is observed in Fig. 3(b) and the angular cor-                          (13)                           S. KAKIGI, K. FUKUNAGA, T. OHSAWA  et at. relations near EeX=31.3 MeV are well fitted with both kmaX=4 and 2. Then for the 31.7—MeV 2+ or 1- state observed in the 4He(a, ad)2H reaction, the spin remains not decided between the two alternatives also in the present experiment. The peak at EeX=34.2 MeV in Fig. 3(a) is thought not to correspond to the 35.3—MeV 2+ state previously reported, because a difference in excitation energy of about 1 MeV is out of the uncertainty. Moreover, no peak is observed at the corresponding energy in Fig. 3(b), though the angular correlations near EeX=34.2 MeV are fitted with both kmax=4 and 2. Then it seems improbable to conclude the peak at EeX=34.2 MeV from the present data. On the other hand, there is no indication of the 35.3— MeV 2+ state.    The peak at EeX=27.5 MeV (kmaX=4 or 2) can correspond to the 27.5—MeV 1-state reported by Fukunaga et a1.3> if kmaX=2 is taken. The bump at EeX=28.6 MeV (kmaX=2) observed in Fig. 3(b) seems to correspond to the 28.5—MeV 1- state reported by Haase et al.2) The 25.5—MeV state is weakly excited in the 4He(a, ap)3H reaction at 119 MeV.                       ACKNOWLEDGMENTS    The authors would like to express their thanks to Professor H. Ogata for the valuable suggestions and discussions for the methods of data taking. The authors also thank the staff and the cyclotron crew of the Research Center for Nuclear Phy-sics of Osaka University for their kind help during the experiments. Off-line data analyses were made with the FACOM M-160AD system at the Institute for Chemi-cal Research of Kyoto University.                             REFERENCES (1) S. Kakigi, K. Fukunaga, T. Ohsawa, S. Tanaka, A. Okihana, H. Nakamura-Yokota, T. Sekioka,      and N. Fujiwara, J. Phys. Soc. Japan, 48, 1797 (1980). (2) E. L. Haase, W. N. Wang, and M. A. Fawzi, Nucl. Phys., A172, 81 (1971); E. K. Lin, R. Hagel-     berg, and E. L. Haase, Nucl. Phys., A179, 65 (1972). (3) K. Fukunaga, T. Ohsawa, N. Fujiwara, S. Tanaka, A.  Okihana, and T. Yanabu, J. Phys. Soc.     Japan, 44, 1413 (1978). (4) S. Fiaman and W. E. Meyerhof, Nucl. Phys., A206, 1 (1973).                            ( 14 )

Excited States of ⁴He Investigated via the ⁴He(α, αp)3H Reactio n at 119 MeV

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Excited States of ⁴He Investigated via the ⁴He(α, αp)3H Reactio n at 119 MeV

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