Nanosecond Fluorescence Apparatus with a Spontaneously Fissioning Excitation Source

We report the development of a versatile apparatus for the precise measurement of fluorescent lifetimes. Based on the pulse sampling method, the device utilizes a unique excitation source—a few microcuries of the spontaneously fissioning nuclide 252Cf. A stochastic analysis of distortion effects demonstrates that the random risetimes and amplitudes of the excitation pulses cause negligible distortion in comparison to that produced by convolution with the photomultiplier tube's impulse response function. Experimental results for the nitrogen second positive group (SPG) and the first negative group (FNG) were in excellent agreement with values reported by others. Simultaneous observation of the processes N2(C3Πu)→ lim k1N2(B3Πg)+hν, and N2(C3Πu)+N2(X1Σg+)→ lim k2products,gave τ=1/k1=40.5±1.3 nsec and k2/k1=1.75±0.06×10−2 Torr−1.