Bulletin Vol. 10 No. 7 Apr–May 1974

particle itself and to its usefulness at a more practical level. The justification for installing a neutron generator comes from a realization of the leading dual rol e which the neutron plays - neutron is one o f the primary units of construction of the atomic nucleus, an d in the form of beams neutron is a unique tool for investigating the structures of atoms, molecules, solids and liquids. Three different kind s of neutron source can be used to provide beams of neutrons. The small and easily obtainable source is a mixture of beryllium with either polonium or radium, which is radioactive. The alpha-particles whic h are emitted from the radioactive element eject neutrons from the beryllium according t o the following nuclear reaction: 4 Be 9 + 2 He 4 → 6 C 12 + 0 n 1 + 5.7 MeV The large and elaborate source is the nuclear reactor, which provides the most intense source of neutrons. Neutrons in the nuclear reactor are produced in the process of nuclear fission, such as when a nucleus captures a bombarding neutron and breaks up into two large pieces together with emission of two or three neutrons: 92 U 235 + 0 n 1 → 92 U 236 The medium and less elaborate source is the electrostatic accelerating machines . The neutron output, which surpasses the simple radioactive sources in intensity, is the result of several nuclear reactions. One of the most useful and convenient nuclear reactions applied in the electrostatic accelerating neutron generato r is the result of bombardment of a tritium target by a beam of deuterons: 1 H 2 + 1 H 3 → 2 He 4 + 0 n 1 + 17.58 MeV It is this type of neutron source that we have in the University. In brief , our neutron generator, Kaman Nuclear's Model A-711, is a miniature sealed tube accelerator which utilizes the above-mentioned nuclear reaction t o produce a high output, greater than 10 11 14.3 MeV neutrons per second, from the ionization of a mixed beam of deuterium and tritium. The accelerating tube is permanently sealed, so that the ionizing gases within it are repeatedly recycled. Thi s recycling, without loss or replacement o f deuterium and tritium, is also the reason fo r the long life and extended high output of neutrons from the target. Since all tritium, which is a radioactive gas, is completely sealed within the accelerating tube, the health hazard normally associated with target changing is effectively eliminated. The nature of the possible research projects using the neutron generator was taken into consideration and the neutron generator room was built with labyrint h geometry. Special consideration had also been given to the design and construction of the radiation shielding in the neutron generator rooms. The shielding materials used are ordinary concrete, paraffin block, iron plate and lead sheet. Due regard had been given to high safety factor in het shielding scheme so that practically no neutrons can be detected in the non-controlled area. The neutron generator rooms and the lay-out of the neutron generator system, which is made up of four separate units, a portable ion accelerator ， a refrigeration-type coolin g unit, a pressurized tank containing the high voltage power supplies, and a control console, are shown schematically in Fig. 1. Also shown in Fig. 1 are the shielding scheme, the counting station, as well as the pneumatic fast transfer system used for transferring samples to-and-from the neutron irradiation station. The special type of neutron generator installed i n the University can be used for both teaching and research in nuclear physics, radio-chemistry, and radio-biology. It is suitable for fast, non-destructive activation analysis i n quality control and production applications in industries . Just recently ， the neutron generator has been installed at radiotherapy centres for clinical uses. Our efforts i n using the neutron generator have been in neutron spectrometry, neutron dosimetry, and neutron activation analysis. We now have an expert, Dr. Esko Karttunen ， who is sent to the University under the sponsorship of the International Atomic Energy Agency for six months' collaborative work i n the neutron generator project. We are hoping that in addition to the teaching and academic research work, we can extend our work in this field; to the service of the community; we are now studying oxygen in steel activation analysis for the Hong Kong steel industry and planning an activation analysis of nitrogen in food products. There are many other projects the neutron generator can be used for and we look forward to its full utilization. — 3 —