Z. Phys. A 347, 99-108 (1993) ZEITSCHRIFT FOR PHYSIK A 9 Springer-Verlag 1993 Properties of levels in 22Ne L.D. Olivier*, W.A. Richter, J.A. Stander, J.W. Koen Department of Physics, University of Stellenbosch, Republic of South Africa Received: 27 July 1993/ Revised version: 9 September 1993 Abstract. Levels up to 9.3 MeV excitation in 22Ne were studied with the 19F(c~,p~/) 22Ne reaction at E~ = 12 MeV. Level energies, branching ratios, mean lifetimes, spins and mixing ratios were obtained for a number of levels. Relevant results are compared with many-particle shell- model calculations. PACS: 27.30. +t; 23.20.-g; 21.60.Cs 1. Introduction Although the properties of excited states in 22Ne have been studied extensively, the compilations by Endt [1] and by Endt and Van der Leun [2] show that information on mean lifetimes, level spins and parities and mixing ratios, especially for levels above 6 MeV excitation, is still incomplete. In the present study particle-gamma coincidence mea- surements were carried out on the reaction 19 F (~, p y)22Ne at E~ = 12 MeV and new information on the 22Ne nucleus was obtained. Results on level energies, branching ratios, mean lifetimes, mixing ratios and level spins are discussed in the text. Shell-model calculations for the 22Ne nucleus, including calculations of reduced transition strengths, are presented and compared with experiment in Sect. 7. 2. Level structure and branching ratios 2.1. Experimental procedure The level structure of 22Ne up to 9.32 MeV excitation was studied using the 19F (~, py)22Ne reaction. The incoming alpha particles were accelerated to an energy of 12.0 MeV with the 6 MV Van de Graaff accelerator of the National Accelerator Centre (NAC) at Faure, South Africa. The experimental procedure employing a 3-parameter coin- * This work formed part of the Ph.D. thesis of L.D. Olivier cidence arrangement was similar to those discussed by Buitendag et al. [3]. The target material consisted of a 73 gg/cm 2 layer of natural LiF evaporated onto a 33 ~tg/cm 2 carbon back- ing. Target thickness was determined by weighing on a microbalance and with energy-loss measurements. Pro- tons were detected in a 500 gm Si surface barrier detector placed at an angle of 145 ~ with respect to the direction of the incident beam. The coincident proton spectrum measured in this study is shown in Fig. 1. Gamma rays coincident with protons were detected with two Ge(Li)- detectors positioned at angles of 62.5 ~ and -82.5 ~ to the beam direction. With this geometry gamma rays were observed at angles of 90 ~ and 55 ~ with respect to the average direction of the recoiling residual nuclei to min- imise Doppler shift and angular correlation effects re- spectively. The particle detector was shielded from scat- tered alpha particles with thin aluminium absorbers. The 3-parameter coincidence data was recorded with a mul- tiparameter realtime data acquisition system and stored on magnetic tape. Non-coincident measurements of gamma rays from standard radioactive sources were per- formed in order to extract energy calibrations for gamma ray spectra and to determine the relative efficiencies of the Ge(Li)-detectors. 2.2. Energy levels and branching ratios The energy levels of 22Ne have been studied extensively [4-12]. The present information on the level structure of 22Ne has been summarized by Endt [1 ]. In the present study the level energies of 44 levels up to 9.32 MeV excitation in 22Ne were obtained from the coincident gamma spectra recorded at an angle of 90 ~ with respect to the average direction of the recoil nuclei. The gamma ray peak positions were determined with the computer code PIEKPAS [13]. The results on the level energies obtained in the present study are summarized in Table 1 where it is also compared with the adopted values from literature as summarized by [1]. The coincident