Abstract: A highly accurate and precise technique for measurement of the ⁹³Nb(n,n’)^93mNb reaction rate was established for the material surveillance tests,etc.in fast reactors.The self-absorption effect on the measurement of the characteristic X-rays emitted by ^93mNb was decreased by the dissolution and evaporation to dryness of niobium dosimeter.A highly precise count of the number of ⁹³Nb atoms was obtained by measuring the niobium solution concentration using inductively coupled plasma mass spectrometry.X-rays of ^93mNb were measured accurately by means of comparing the X-ray intensity of irradiated niobium solution with that of the solution in which stable ⁹³Nb was added.The difference between both intensities indicates the effect of ¹⁸²Ta,which is generated from an impurity tantalum,and the intensity of X-rays from ^93mNb was evaluated.Measurement error of the ⁹³Nb(n,n’)^93mNb reaction rate was reduced to be less than 4%,which was equivalent to the other reaction rate errors of dosimeters used for Joyo dosimetry.In addition,an advanced technique using Resonance Ionization Mass Spectrometry was proposed for the precise measurement of ^93mNb yield,and ^93mNb will be resonance-ionized selectively by discriminating the hyperfine splitting of the atomic energy levels between ⁹³Nb and ^93mNb at high resolution.

Key words: Isord-10, niobium, reaction rate, material surveillance test, fast reactor, characteristic x-rays, experimental fast reactor joyo, resonance ionization mass spectrometry, hyperfine structure