Measurements and model calculations of isomeric cross section for (n,a) reaction on 140 Ce isotope around 14 MeV neutrons Iskender Atilla Reyhancan ⇑ Istanbul Technical University, Institute of Energy, Ayazaga Campus, Maslak 34469, Istanbul, Turkey article info Article history: Received 4 July 2011 Received in revised form 29 March 2012 Accepted 4 April 2012 Available online 20 May 2012 Keywords: Neutron cross section Activation technique Gamma-ray spectrometer Statistical model calculation Cerium abstract In this work, cross sections were measured for the 140 Ce(n,a) 137m Ba (T 1/2 = 2.552 min) reaction at neutron energies from 13.57 to 14.83 MeV. The neutrons were produced via the 3 H( 2 H,n) 4 He reaction on a neu- tron generator using a solid Ti–T target. The activation technique was used, and induced gamma activities were measured by a high resolution gamma-ray spectrometer. Corrections were made for the effects of gamma-ray attenuation, random coincidence (pulse pileup), coincidence summing, dead time, neutron flux fluctuations, and low-energy neutrons. The measured cross sections were compared with statistical model (TALYS code) calculation results and the experimental data in the available literature. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Neutron activation cross sections around 14 MeV from deuteron–tritium (D–T) neutrons are utilized for Fast Neutron Activation Analysis (FNAA). Nevertheless, the important applica- tion of the data is for the design of fusion reactor, transmutation, and test of nuclear models used in evaluation of neutron induced reaction cross sections. Generally, for most of the neutron-induced reactions, a lot of cross section data were reported (CINDA, 2010). For some neutron induced reaction cross sections, there is a lack of experimental information in data bases. At the same time, the data are either discrepant or very scarce for some reactions (Pashchenko, 1994, 1995). For such reactions, the poor counting statistics are the main restraint which stems mainly from using the natural isotopic composition of target material (this causes low product nucleus activity fewer target atoms in case of low abundant isotope). Other effects that cause poor counting statistics are the transfer time of irradiated samples from the irradiation position to counting station, the low neutron flux and utilization of a counting system having poor gamma ray efficiency (HpGe detector for its advantage of good resolution). One of the solutions available for the situation is to utilize a Fast Sample Transfer System (FSTS), which allows activation and counting with prede- termined time intervals. The isomeric cross sections for a pair of isomeric states (unsta- ble ground, and metastable states) depend on the energies and spin of the levels of the excited nucleus (Qaim and Mushtaq, 1988). The metastable state of a nucleus can be therefore produced through different nuclear reactions with suitable target nuclei. The isomeric cross sections are difficult to be predicted than those the all reac- tion channels, which are possible through different reaction chan- nels such as (n,p), (n,2n) and (n,a) with 140 Ce selected. Isomeric cross section data are the important factors for testing theoretical nuclear models. Cerium, selected in this work, is an element in the lanthanide series as one of the rare earth elements, and importance for reactor technology and structural material science. Especially, because of low absorption cross section, cerium dioxide is used as a diluent in uranium, plutonium or thorium oxide nuclear fuels. In this work, the cross section measurement with a relatively good accuracy for 140 Ce(n,a) 137m Ba reaction is aimed to make clear the discrepancies between data, which are six times around 14 MeV neutrons in literature (EXFOR, 2011), and the trend of exci- tation function of the reaction by using a statistical model calcula- tion (TALYS). For this reaction, the data were published by the several laboratories (Paul and Clarke, 1953; Wille and Fink, 1960; Bormann et al., 1966; Havlik, 1971; Satoh et al., 1994; Murahira et al., 1995; Kasugai et al., 1997). For this reason, the activation method has been utilized to perform the measurements in the neutron energy range from 13.57 to 14.83 MeV by a SAMES T-400 Neutron Generator in Combination with a Fast Sample Transfer Sys- tem (FSTS) which is described in detail in our previous work (Subas ßı et al., 1996, 1998, 2000). In the neutron energy interval, the cross sections are calculated by TALYS code. 0306-4549/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.anucene.2012.04.009 ⇑ Address: Istanbul Technical University, Department of Physics Engineering, Ayazaga Campus, Maslak 34469, Istanbul, Turkey. Tel.: +90 212 2843214; fax: +90 212 2856386. E-mail address: iareyhancan@itu.edu.tr Annals of Nuclear Energy 47 (2012) 81–84 Contents lists available at SciVerse ScienceDirect Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene