Safety_Series_025_1968 - gnssn - International Atomic Energy ...

This publication is no longer validPlease see http://www.ns-iaea.org/standards/Pocket electrometers and pocket ionization chambers normallyused for gamma rays can also serve as personnel monitors for betaradiation of energy greater than 0. 5 MeV. There are availabletypes of pocket electrometer and ionization chamber, with sufficientlythin walls of light material, capable of detecting beta radiation ofenergies as low as 0. 1 MeV.4. 1. 1. 1, 3. Measurement of neutron radiation. Although neutronsare not directly ionizing particles, they do produce nuclear reactionsin the matter through which they pass and the reactions in turn maygive rise to ionizing radiation capable of detection by the methodspreviously described. These nuclear reactions may also lead to theformation of induced radioisotopes, the radiation from which canlikewise be measured. It is thus possible to detect neutrons eitherduring or after irradiation.For the detection of neutrons during irradiation, monitoringapparatus of the types described above can be used, equipped withcertain accessories. Among these are cadmium scrieens able tocapture thermal neutrons and subsequently emit measurable' gammaradiation. Likewise, incorporation of b oron -10 in the detectorsmakes it possible to measure the alpha particles by the nuclearreactions between the neutrons and the boron.Highly energetic neutron radiation can be detected by photometricmethods using nuclear plates on which the number of tracksleft by recoil protons formed in a hydrogenated medium can be observedthrough a microscope.When the nuclear reactions induce radioactive substances, itis possible to determine the degree of neutron irradiation subsequently.One method consists in using in the detector, or gettingthe worker to carry on his person, certain metals which are rapidlyactivated by neutron radiation (e. g. indium, gold). In this way detectorswith several thresholds for neutrons of different energiescan be obtained. They can measure the neutron flux values for eachenergy range.In special circumstances it is even possible to use the humanbody as a monitor, since the sodium and phosphorus it contains areactivated by neutrons into the radioactive form s sodium -24 andphosphorus-32. By gamma spectrometry the amount of sodium-24contained in the whole body, the blood or the urine can then be determined.Similarly, the amount of phosphorus-32 contained in theblood or urine can be determined by beta radiochemical methods.85