Patent GB-1359083-A (GB)
Title: Method of recording spin resonance spectra and a device suited for the purpose
IPC: G01N24/00
Filed: 1972-03-24
Abstract: 1359083 Spin resonance spectrometers SPECTROSPIN A G 24 March 1972 [9 June 1971] 13946/72 Heading G1N In a spin resonance spectrometer in which a sample is excited by a sequence of R. F. pulses 34, Fig. 2, to produce interferograms which are stored and averaged and the resonance frequencies computed by Fourier Analysis, certain resonance lines A are selectively excited (e.g. to inhibit spin coupling, to saturate a strong line covering a weak line, or for "tickling") by an additional sequence of R. F. pulses 31 whose carrier and pulse repetition frequencies are selected so that only such frequencies 32 of its frequency spectrum 32, 33 which coincide at least approximately with the certain lines A fall within the resonance spectrum f 4  to be recorded, and the interferograms are received for storage in the intervals between the additional pulses 31. In the spectrometer shown in Fig. 1, a first R. F. generator 1 and R. F. gate 2 generate a sequence of R. F. pulses 34 of carrier frequency t 1  and pulse repetition frequency 1/T 1  for exciting all the spins of a sample reached through cable 5. A second R. F. generator 21 and R.F. gate 22 generate an additional sequence of R. F. pulses 31 at a carrier frequency f 2  equal to the Larmor frequency of a certain line A. Other R. F. generators 121 and gates 122 may be provided for exciting other lines. Signals from the sample pass through a gated preamplifier 6, mixer 7, I. F. amplifier 8, phase detector 9 and low pass filter 10, resulting in a chopped A. F. interferogram. A gate 18 removes transients from the edges of the pulses which are sampled and stored in a mean value converter 11 connected to a Fourier transformer 12. A local oscillator 13 supplies mixer 7 and a mixer 14 which also receives f 1  from R. F. generator 1 to supply I. F. to the phase detector 9. The R. F. gates 22, 122 are controlled by pulses (a), Fig. 3, (not shown), from a pulse generator 16 which also supplies clock pulses (d) in the intervals between pulses (a) to the preamplifier 6 and R. F. gate 17 and supplies pulses (f) whose leading edges are delayed with respect to pulses (d) to gate 18. The stepping rate in the store of the mean value converter may be equal to, or any integral multiple of, or any integral fraction of, 1/T 2  . As shown, a frequency divider 19 supplies pulses at half the frequency of pulses (a) to control the addressing in the store of the mean value converter. The last stage of the store sends a pulse via pulse former 20 to the R. F. gate 2. The pulse repetition rate of the additional sequence of R. F. pulses is determined by a variable frequency oscillator 61 controlled by a voltage source 62. Periodic or stochastic variations in pulse sequences. The control voltage from source 62 may vary periodically whereby the additional sequence of pulses can excite two lines spaced from the carrier frequency f 2  by the modulation frequency. Several modulation frequencies may be used. Alternatively, the control voltage may fluctuate stochastically between given values, giving continuous frequency bands, symmetrical with respect to the carrier frequency f 2 , in the spectrum of the additional sequence. The phase of the carrier frequency f 2  may change stochastically from pulse to pulse.