Nuclear instrumentation

This section is addressed to the person who has not seen or used radiation instruments. Its purpose is to present a general description of the physical appearance and operation of the basic components of a radiation counting system. Every component is treated like a black box, i.e., input and output are discussed without any details about how the output is obtained. Details about the construction and operation of individual units are given in later chapters. 

Detectors are discussed in Chaps. 5 through 7, and the rest of the electronics is discussed in Chap. 10. 

Counting systems are classihed into two types, according to the method of operation  

Pulse-type systems. The output consists of voltage pulses, one pulse per particle detected. 

Current-type systems. The output is an average value, resulting from the detection of many particles. 

Neutror flux at the Wide Range Linear Channel Position 

The main reason to monitor neutron flux in a reactor is that it is proportional to the power density, and this is the variable which we are concerned about. There are mainly five types of neutron detectors, BF3 proportional counters. Boron ( B) lined detectors, fission chambers, He proportional counters, and self powered neutron detectors Two other instruments are widely used to monitor the reactor power, calorimeters, used to monitor power density, and N-16 detectors, used to monitor integral reactor power 

Detectors are usually located in fixed positions about or around the reactor core, and the quantity measured is often the leakage flux, i e, the flux exterior to the core The detector shall be placed in instrument ports that are leak-tight so that they will not be subjected to moisture A purge of inert gas in these ports is also often provided in order to prevent the buildup of corrosive substances Since detectors are located in intense gamma ray fields, which may degrade cable insulation, mineral insulators are preferred such as are provided with integral-lead detectors These cables are procured at the time the detector is ordered, and must be sized for length at that time 

If the detector is sensitive enough, it is recommended to place it as far as possible from the core This will reduce radiation hazard to the detector, and also limit the effect of gamma induced current 

Since the insertion and withdrawn of control rods on top of the core changes the shape of the neutron flux, care must be taken in selecting the right position for the neutron detectors. Periodic calibration and cross checking of neutron detectors is highly recommended. 

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K. Gamo, Nuclear Instruments andMethods in Physics Research B 121, 464—469 (1997). 

For greater details on the techniques of LS counting in general, including the specialized nuclear instrumentation required and sample handling and preparation, see Refs 5, 6 7... 

Figure 8.8 Mean concentration profiles of Zn, Cu and Cd in multilayer acrylic paint, consisting of orange deposited on blue, both on yellow. The arrows define the three paint layer limits as they were evaluated through weighing. After Brissaud [299]. Reprinted from Nuclear Instruments and Methods in Physics Research, B117,1. Brissaud et al., 179-185, Copyright (1996), with permission from Elsevier...

Bohne, W., Rohrich, J. Roschert, G. (1998) Nuclear Instruments and Methods in Physics Research B, 136-138, 633-637. 

Katz, R. and W. Hofmann, Biological Effects of Low Doses of Ionizing Radiations Particle Tracks in Radiobiology, Nuclear Instruments and Methods 203 433-442 (1982). 

SUMMARIZE the operation of typical source, intermediate, and power range nuclear instruments. 

LIST the type of detector used in each of the following nuclear instruments ... 

When discussing nuclear instrumentation, this term refers to the electronic circuitry of the source and intermediate ranges. These ranges utilize logarithms due to the wide range of measured flux and the necessity to measure that flux on a single meter scale. 

Intermediate-range nuclear instrumentation consists of a minimum of two redundant channels. Each of these channels is made up of a boron-lined or boron gas-filled compensated ion chamber and associated signal measuring equipment of which the output is a steady current produced by the neutron flux. 

M. Dowsett and A. Adriaens, Role of SIMS in cultural heritage studies, Nuclear Instruments Methods in Physics Research Section B Beam Interactions with Materials and Atoms, 226, 38 52(2004). 

LTD-10 Proceedings of the 10th International Workshop on Low Temperature Detectors, Genoa, Italy, luly 7-11 2003, Nuclear Instruments and Methods in Physics Research Section A, vol. 520, Issue 1-3, Elsevier (2004)... 

Fleming, S.J. and Swann, C.P. (1986). PIXE spectrometry as an archaeometric tool. Nuclear Instruments and Methods in Physics Research A242 626-631. 

Abraham, M. H., Grime, G. W., Marsh, M. A., and Northover, J. P. (2001). The study of thick corrosion layers on archaeological metals using controlled laser ablation in conjunction with an external beam microprobe. Nuclear Instruments and Methods in Physics Research B 181 688-692. 

Buoso, M. C., Fazinic, S., Haque, A. M. I., el al. (1992). Heavy element distribution profiles in archaeological samples of human tooth enamel and dentin using the proton-induced X-ray-emission technique. Nuclear Instruments and Methods in Physics Research B 68 269-272. 

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