GB1177261A - System for Studying Electron Nuclear Double Resonance - Google Patents

Abstract

1,177,261. Gyromagnetic resonance spectrometers. INSTITUT POLUPROVODNIKOV AKADEMII NAUK UKRAINSKOI SSR. March 21, 1967, No. 13205/67. Heading G1N. Apparatus for studying electron-nuclear double resonance (ENDOR) comprises an electron spin resonance spectrometer having a sample cavity 9 and an automatic frequency control system for locking the micro-wave frequency of the spectrometer to the sample cavity or to a reference cavity 18 and a radio frequency push-pull oscillator 45 having an LC tank circuit of variable resonance frequency for producing an r.f. pumping field for saturating nuclear transitions in the sample to produce an ENDOR signal. The frequency of oscillation of the oscillator 45 is changed in discrete steps by switching the tank circuit inductance, continuous variation is frequency being effected by smoothly varying the capacitance of the tank circuit. As shown in Fig.1, a micro-wave oscillator 1 is connected via isolators 2, 7, directional couplers 3, 4, 5 and a calibrating attenuator 6 to a double- T bridge 8 one arm of which is connected via an adjustable coupling 10 to the sample cavity and another arm of which is connected via an impedance transformer 12 to a matched load 11. The imbalance signal from the bridge due to absorption of energy by the sample is converted to a first intermediate frequency in a mixer 14 fed with a signal derived from a single side-band modulator 17 connected to the oscillator 1 via coupler 5 and to an h.f. crystal controlled oscillator 27. After amplification, the resulting signal is converted in mixer 32 to a second intermediate frequency, by mixing with a signal from a local oscillator 34, and is fed via an amplitude detector 35 to an oscilloscope (not shown) and to a phase detector 36 provided with a reference signal derived from the oscillator 1 via coupler 4 and mixers 24 and 33. The output from the phase detector 36 is fed to a pen recorder 40 via a phase sensitive detector 39 fed with a reference signal from a low frequency oscillator 41 which is used for modulating the polarizing field or pulse modulating the r.f. pumping field as set by switch 42. The frequency of the r.f. pumping field is measured by a device 46 to provide frequency markers for the pen recorder 40. The polarizing field at the sample is generated by an electromagnet 44, regulated by unit 47 and the strength of the field is measured by an N.M.R. probe 49 and indicated at 48. In use, for measuring stationary ENDOR of samples with short relaxation times (#) switch 20 is set (as shown) so that the frequency of the oscillator 1 is locked to the sample cavity 9, the polarizing field is not modulated and the r.f.o. 45 is pulsed at a frequency ½ 1/# and the absorption signal is recorded. For measuring non- stationary ENDOR of samples with long relaxation times switch 20 is set so that the frequency of the oscillator 1 is locked to the reference cavity 18, the polarizing field is modulated by 1.f.o. 41, the r.f.o. 45 is operated continuously and the dispersion signal is recorded.