A technique for the detection of weak nuclear resonance interactions in solids is carried out by a pulsed method which obtains nuclear double resonance. The resonance of the unknown species to be detected does not require a Boltzmann population difference in spin orientation, but must have a sufficient dipole-dipole interaction with a second spin species. At resonance, a single 180° pulse reorients the unknown spins at the time of the 180° pulse in the 90°-180° pulse sequence necessary to obtain the observed spin-echo signal of the second species. A reduction of the spin-echo signal signifies double resonance due to changes in local dipolar fields, coupled to the observed spins, which scrambles their precessional phases. Nuclear quadrupole coupling interactions of K, Cs, and Rb isotopes are measured in the chlorates of these ions, where the ${\mathrm{Cl}}^{35}$ nucleus provides the observed nuclear quadrupole echo. An analysis is presented for the case of low concentration of unknown spin species. Double quantum transitions and special properties of nuclear quadrupole spectra are observed.

• Received 2 November 1959

DOI:https://doi.org/10.1103/PhysRev.118.414