Development of the Lund AMS Facility for the Detection of 59Ni – with Applications in the Nuclear Industry

Sammanfattning: Accelerator mass spectrometry (AMS) is a highly sensitive method for counting atoms and it is used for detecting very low concentrations of both radionuclides and stable isotopes in small samples. The two major advantages of the AMS method are that the required amount of sample material is very small, but also that the efficiency is rather high, it takes less than an hour to analyse a sample. The sample mass can be reduced at least a thousand fold compared to the amount necessary when using the decay counting techniques. 59Ni is an important radioisotope in nuclear waste management. 59Ni is produced by neutron activation in the stainless steel close to the core of a nuclear reactor. The main area of interest for determining the activity concentration of 59Ni is the classification of construction material in a nuclear power plant, in order to be able to define how exchanged parts are to be stored. In this thesis a method to detect the medium-heavy nuclide 59Ni using a small tandem accelerator (< 3 MV) is presented. This thesis consists of two parts. In the first part the technical developments made to make it possible to run nickel through the accelerator system are described. In the second part a description of the work to develop the method of measuring 59Ni is presented. This includes the optimisation of the detection technique where the ions are slowed down in a suitable target producing characteristic projectile X-rays. These X-rays are then counted with an X-ray detector, which makes it possible to identify the bombarding ions by atomic number. In this way interfering isobars are suppressed. Two methods to chemically reduce the amount of cobalt, i.e. the disturbing isobar 59Co, in the sample material, are described. Determination and improvements of the detection limit for 59Ni has been made. Finally some results of measurements of samples provided by the nuclear industry are presented. The technique developed to measure 59Ni is now used on a routine basis.