Marginal oscillator type NQR spectrometer with automatic baseline shift suppression

Abstract

The marginal oscillator-detector by means of the frequency modulation for nuclear quadrupole resonance spectrometer causes an incidental output (offset) due to its frequency characteristics. There are two disadvantages resulting from this offset. One is the limitation in performing the high gain amplification of the detected signal, and the other is the shift in the baseline. In order to overcome these difficulties, we constructed the NQR spectrometer with an automatic amplitude control on one side of the excursion of the bi-directional square wave for frequency modulation. This automatic control system enables the high gain amplification and accomplishes the flat baseline over a wide frequency range. Moreover, it is proved that the spectrometer is highly sensitive not only to chlorine and nitrogen compounds (³⁵Cl, ³⁷Cl and¹⁴N) but also to copper(I) compounds (⁶³Cu and ⁶⁵Cu) which show a wide line-width requiring a large modulation amplitude.