Study of New-Modes of Nuclear Excitation by Means of High-Resolution (p,n) Measurement

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Charge-exchange (p,n) reactions have been proved to be an excellent tool to study new mode s of nuclear excitation , where spin-isospin excitations are observed, for example. The (p,n) reaction has been recently investigated by means of two different proton energies; i.e. (p,n) work at intermediate energy carried out at IUCF (Indiana University Cyclotron Facility), and the other works have been carried out at CYRIC (Cyclotron and Radioisotope Center, Tohoku University) with 35 MeV protons. Due to strong spin-dependent force, the intermediate (p,n) works seem to be much reliable. However, low energy (p,n) reactions may be studied with much better energy resolution. In this project, we have extensively developed the high-resolution measurement by means of the neutron time-of-flight facilities. It should be noted that to achieve a ultimated high-resolution of 100 keV v.s. 30 MeV neutrons a long flight path (44 m) is required. Thus development of the high efficient detector system was also needed.One of the current interests studied by the high-resolution (p,n) measurement is the <0^+> <-!>> <0^-> transition, which carries selectively information on one-pion exchange interaction. We have studied <DELTA> <J^pi> = <0^-> reactions on <^(13)C> , <^(14)N> and <^(15)N> . A shoulder was systematically observed around 50゜ in the angular distributions for the 1/ <2^-> <-!>> 1/ <2^+> and <1^+> <-!>> <1^-> transitions. This shoulder was interpreted as being due to the tensor interaction in the <DELTA> J( <DELTA> L, <DELTA> S) = 0 (1,1) channel. Other topics such as the <0^+> <-!>> <1^+> Gamow-Teller type transition have been extensively studied on s-d shell nuclei. One of the new modes of nuclear excitation, an example for which is <DELTA> J( <DELTA> L, <DELTA> S) = 2(1,1) or 1(1,1), were studied at <E_p> = 41 MeV for heavier nuclei.