POHANG NEUTRON FACILITY BASED ON ELECTRON LINAC G. N. Kim # , R. Machrafi, H. Ahmed, and D. Son Institute of High Energy Physics, Kyungpook National University, Daegu 702-701, Korea Y. S. Lee, H. S. Kang, M. H. Cho, I. S. Ko, and W. Namkung Pohang Accelerator Laboratory, POSTECH, Pohang 790-784, Korea Abstract The Pohang Neutron Facility based on the 100-MeV electron linear accelerator has been constructed as a nuclear data production facility in Korea. It consists of an electron linear accelerator, a water-cooled Ta target with a water moderator, and a time-of-flight path with an 11 m length. As a nuclear data production facility, it has been equipped with a CAMAC data acquisition system consists of a neutron-gamma separation system and a four- position sample changer. A 6 LiZnS(Ag) glass scintillator has been used as a neutron detector at the end of the evacuated flight tube of 11 m long. The data acquisition system has been tested measuring total cross sections by using the neutron time-of-flight method. INTRODUCTION Pulsed neutrons based on an electron linear accelerator (linac) are effective for measuring energy-dependent cross sections with high resolution by using the neutron time-of-flight (TOF) method covering the energy range from thermal to a few tens of MeV neutrons. The Pohang Neutron Facility (PNF) based on a 100-MeV electron linac was proposed in 1997 and constructed at the Pohang Accelerator Laboratory (PAL) on December 1998 [1]. Its main goal is to construct the infrastructure for the nuclear data production in Korea. Since December 1999, a turbo MCS system combined with a circuit based on direct pulse discrimination has been installed and worked in different transmission measurements [2]. As activities at PNF are diversely increasing, the improvement of the data acquisition system is required. Recently, this system has been improved by the addition of a new CAMAC data acquisition system, which consists of a neutron-gamma separation circuit, a four–position sample changer controlled remotely by the CAMAC module and software program for simultaneous accumulation of the neutron TOF spectra from 4 different detectors. To test this system, we have measured the neutron total cross-sections of natural tungsten (W) and titanium (Ti) samples by using the neutron TOF technique. POHANG NEUTRON FACILITY The PNF consists of an electron linac, a water-cooled Ta target, and an 11 m long TOF path. The electron linac consists of standard subsystems: a thermionic RF- gun, an alpha magnet, four quadrupole magnets, two SLAC-type accelerating sections, a quadrupole triplet, and a beam-analyzing magnet. The overall length of the linac is about 15 m. The RF-gun is one cell cavity with a dispenser cathode of 6 mm diameter [3]. The alpha magnet is used to match the longitudinal acceptance from the RF-gun to the first accelerating section. Four quadrupole magnets are used to focus the electron beam in the beam transport line from the thermionic RF-gun to the first accelerating section. The quadrupole triplet installed between the first and the second accelerating sections is used to focus the electron beam during the transport to the experimental beam line at the end of the linac. The characteristics of the electron accelerator are described in elsewhere [4]. A Ta target was designed and constructed for the neutron production by way of Bremsstrahlung under high power electron beams [5]. The Ta target was composed of ten Ta sheets, 49 mm in diameter and 74 mm in total length. There was 1.5 mm water gap between Ta sheets in order to cool the target effectively. The target housing was made of 0.5 mm thick titanium. Since we have to utilize space and infrastructure at PAL, an 11 m long TOF path and a detector room were constructed vertically to the electron linac. The neutron guide tubes were constructed by stainless steel with two different diameters of 15 and 20 cm. The neutron collimation system was mainly composed of H 3 BO 3 , Pb, and Fe which were symmetrically tapered from 10 cm diameter at the beginning, 5 cm in the middle position where the sample was located, and 8 cm diameter at the end of guide tube where the neutron detector was placed. There is 1.8 m thick concrete between the target and the detector room. The details of PNF are described in elsewhere [6]. During the experiment, the electron linac was operated with a repetition rate of 10 Hz, a pulse width of 1.5 µs, and the electron energy of 60 MeV. The peak current in the beam current monitor located at the end of the second accelerator section is above 50 mA, which almost is the same as that in the target. ___________________________________________ # Email: gnkim@knu.ac.kr Proceedings of ICALEPCS2003, Gyeongju, Korea 84