A new type RF ESR resonator for pulse techniques was developed. The resonat
or is an LC circuit that consists of a single turn coil (inner diameter, 45
mm) and ceramic capacitors. A two-turn coil-shaped polyethylene tube is lo
cated inside of the loop and an aqueous sodium chloride solution is perfuse
d into the tube at a rate of 6 cm(3)/min. Its resonant frequency is approxi
mately 300 MHz, with a Q of less than 70. Using this resonator, pulsed-long
itudinally detected ESR measurements of a phantom (inner diameter, 20 mm) c
ontaining a triaryl methyl spin probe were performed. The Q value was suffi
ciently low for irradiation over wide frequency band in the pulsed radiowav
e where the pulse width was 200 ns. The apparatus tan handle a sufficient h
igh power (maximum, 100 W) adjusted according to the sample size.