(a) By referring to a reference on NAA or by using an Internet search engineto find the

Chapter 32, Problem 32-20

(choose chapter or problem)

(a) By referring to a reference on NAA or by using an Internet search engineto find the information, describe in some detail the instrumental and radIOchemicaldifferences between prompt gamma-ray neutron activation anddelayed gamma-ray neutron activation.(b) What are the types of elements for which prompt gamma-ray activationanalysis is most applicable?(c) Why is delayed gamma-ray emission most often used in NAA?(d) Why is NAA considered to bc a very selective and sensitive method?(e) A crvstal of potassium fluoride is to be studied via NAA. The followingtabl~ summarizes the behavior of all naturally occurring isotopes in thecrystal.19F,2oNe. 39K. "K, and 42Ca are stable, and we will assume that 40Kis alsostable because it has a half-life of 1.3 x 109 years. What sort of irradiationand detection sequcnce would you use if you wanted to base your analysison fluorine?What sort of irradiation and detection sequence would you use if youwanted to base the analysis on potassium?Refer to part (e) and calculate the activity due to 2F and 42Kin a 58-mg(l.O-millimole) sample of pure potassium fluoride that has been irradiatedfor 60 s. The thermal neutron cross sections for "F and 41K are 0.0090 X10-24cm 2and 1.1 X 10-24cm 2,respectively. Assume a flux density of 1.0 x1013 neutrons cm-' S-I.Find a method in the literature that describes the use of NAA for determiningselenium in freshwater ecosystems. Describe the method in detail. Includethe neutron source, the irradiation time, and the calculations used.Give the advantages and disadvantages of the method over other inltlytiealtechniques.

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