Abstract: A method of nuclear quadrupole resonance testing a sample is disclosed in which the excitation applied to the sample is arranged so that phase and amplitude information may be obtained from the response signal, and in which the signal is resolved into two components. Particularly if a parameter such as radio-frequency field strength varies with position, this may give an indication of the distribution of nuclei in the sample, preferably from the phase of the response signal. Positional information can also be obtained by measuring from two or more reference points. This may be employed in imaging. The phase information may be employed to improve the signal to noise ratio obtainable in other methods where only amplitude information was previously available, for example in distinguishing genuine NQR response signals from spurious signals.

Abstract: A method of NQR testing a sample having at least one NQR property which varies with a given environmental parameter comprises applying excitation to the sample to excite NQR resonance and detecting the NQR response signal. The excitation is such as to excite an NQR response signal which is detectable during the detection step over a predetermined range of the environmental parameter. The invention also relates to a method of, and apparatus for, NQR testing for the presence of selected nuclei (particularly nuclei of integral spin quantum number, such as .sup.14 N) in a sample. It also relates to a method of determining the spatial distribution of temperature within a sample.

Abstract: A method for detecting the presence of a substance in a heterogeneous sample or article (i.e., a contraband substance) in a magnetic field includes establishing a level-crossing condition (B.sub.LC) for the substance to be detected for a set time (t.sub.b), and subsequently measuring nuclear magnetic resonance (NMR) signals to detect some consequence of the level-crossing condition. A saturating signal is applied at the begining of each cyclic test. Apparatus for detecting the presence of predetermined substances is also disclosed.

Abstract: A method of Nuclear Quadrupole Resonance testing includes the steps of applying to a sample in which selected nuclei have an integral spin quantum number a series of at least three pulses of electromagnetic waves at a single radiofrequency to excite quadrupole resonance of the selected nuclei, and detecting responses at a plurality of times when echo response signals are expected to occur.

Abstract: The detection of compounds containing both nuclei of a kind which exhibit nuclear magnetic resonance (nmr) and nuclei of a kind which exhibit nuclear quadrupole resonance (nqr), for example compounds containing both .sup.1 H and .sup.14 N nuclei, is carried out by subjecting a substance suspected of containing such a compound to a magnetic field and repetitively to three parallel activities A,H and B. Activity A comprises two similar rf pulse sequences P.sub.A and P.sub.B at the nmr frequency. Activity H is a temporary change in the value of the magnetic field, which may be a reduction to zero. Activity B is the application of additional rf signals. Activity H and/or activity B are different during each of the respective pulse sequences P.sub.A and P.sub.B. The activity B rf signals are at one or more frequencies selected so that in combination with the activity H in at least one of the pulse sequences the subsequent nmr signal is modified if such a compound is present.