Theoretical considerations in the selection of neutron sources for total-body neutron activation analysis

Abstract

The factors involved in selecting a neutron source for total-body neutron activation (TBXAA) are the nature of the neutron source, the flux density distribution, the type and positioning of the moderator and the acceptable radiation dose to the subject. Consideration of these factors indicates that 4.5 MeV neutrons have an overall advantage of 2 relative to 14 MeV neutrons in TBXAA. Further, multiple ( U , n) sources in broad beam geometry and simultaneous bilateral exposure have an advantage of 3.6 relative to 14 MeV neutrons from a neutron generator. ( E , n) sources also give ease of operation and high reproducibility.

Concerning the time dependence of the decay rate of 137Cs

“…The irradiator was specifically designed for high reproducibility (Cohn et al, 1973), and comprised an array of fourteen 50 Ci encapsulated 238 Pu/Be sources. In 1976, a second standard set was incorporated to be used on a weekly basis to monitor the reproducibility of the activation and counting systems together (Ellis, 1990).…”

“…This counting system was utilized in conjunction with a broad beam neutron irradiator [28], for the in vivo NAA experiments described in Ellis [9], as mentioned above. The irradiator was specifically designed for high reproducibility [29], and comprised an array of fourteen 50 Ci encapsulated 238 Pu/Be sources. In 1976, a second standard set was incorporated to be used on a weekly basis to monitor the reproducibility of the activation and counting systems together [9].…”

Clinical Measurement of Body Composition Using In Vivo Neutron Activation Analysis

“…There are several ways of generating fast neutrons but the methods utilized are more dependent on locally available technology than on theoretical optimization (but see refs. 45 Table II, together with reported values of precision, accuracy, and radiation dose equivalent used in the determination of total body nitrogen. Finally, from the standpoint of cost alone use of isotopic sources (238Pu-Be or 252Cf ) is undoubtedly the cheapest method and a useful system could be built for a hardware cost of around $50,000 using such sources.…”

Facility optimization to improve activation rate distributions during IVNAA

“…In order to improve the uniformity of depth distribution in the sample, the phantom was surrounded by hydrogenous material in all of this research. In 1973 Cohn et al discussed the selection of neutron sources in total body neutron activation considering articles thitherto published [11]. According to this report, when bilateral irradiation is employed, the most uniform distribution is obtained with moderated 14 MeV neutrons.…”

“…This rather uniform distribution, coupled with the advantage gained through the use of a relatively low energy incident neutron (advantage factor = 2.1 relative to 14 MeV neutrons), renders the use of (α,n) sources attractive for total body neutron activation. An additional benefit accrues from the ease of operation and reproducibility inherent in constant-output radioactive neutron sources [11]. …”