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Spectroscopic study of Np(V) oxidation to Np(VI) in 3 mol/dm$$^{3}$$ nitric acid at elevated temperatures

3mol/dm$$^{3}$$の加熱硝酸中におけるNp(V)のNp(VI)への酸化の分光学的研究

伴 康俊; 袴塚 保之; 筒井 菜緒; ト部 峻一; 萩谷 弘通; 松村 達郎

Ban, Yasutoshi; Hakamatsuka, Yasuyuki; Tsutsui, Nao; Urabe, Shunichi; Hagiya, Hiromichi; Matsumura, Tatsuro

加熱した3mol/dm$$^{3}$$硝酸中におけるNpの吸光スペクトルを光路長1cmのウォータージャケット付き分光セルで測定し、Np(VI)のモル吸光係数($$varepsilon$$$$_{T}$$)を種々の温度で求めた。$$varepsilon$$$$_{T}$$は温度の上昇と共に減少し、$$varepsilon$$$$_{T}$$の温度依存性を表す式として$$varepsilon$$$$_{T}$$=-0.14${it T}$+85.5 (${it T}$は温度)を得た。加熱した3mol/dm$$^{3}$$硝酸中におけるNp(V)のNp(VI)への酸化を上述の分光セルで観察し、Np(V)の酸化はNp(V)の濃度に対する疑一次反応として進行することを示した。さらに、336-362KにおけるNp(V)の酸化反応速度式として-d[Np(V)]$$_{t}$$/dt=2.2$$times$$10$$^{7}$$exp[-65$$times$$10$$^{3}$$/(${it RT}$)][Np(V)]$$_{t}$$ (${it R}$及び[Np(V)]$$_{t}$$は気体定数及び時間${it t}$における[Np(V)]の濃度)を導出した。

Optical absorption spectra of Np in 3 mol/dm$$^{3}$$ nitric acid at elevated temperatures were measured using an optical glass cell with a water jacket having a light path of 1 cm, and molar extinction coefficients of Np(VI), $$varepsilon$$$$_{T}$$, were obtained at various temperature. The values of $$varepsilon$$$$_{T}$$ was found to decrease with increasing the temperature, and could be described by the equation $$varepsilon$$$$_{T}$$ = -0.14${it T}$+85.5, where ${it T}$ is the temperature. Oxidation of Np(V) to Np(VI) in 3 mol/dm$$^{3}$$ nitric acid at elevated temperatures was observed using the optical glass cell. Oxidation of Np(V) proceeded as pseudo-first order with respect to Np(V) concentration. The rate equation in the temperature range of 336-362 K was obtained as follows: -d[Np(V)]$$_{t}$$/dt = 2.2$$times$$10$$^{7}$$ exp[-65$$times$$10$$^{3}$$/(${it RT}$)][Np(V)]$$_{t}$$, where ${it R}$ and [Np(V)]$$_{t}$$ indicate the gas constant and Np(V) concentration at time ${it t}$, respectively.

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