When harnessed, radioactivity has proven itself to be an unparalleled tool for the exploration of the world around us. The functioning of living bodies and of our environment can all be examined with tremendous accuracy by radiation detection methods.
These methods are constantly improving, allowing us to produce equipment sensitive enough to detect the decay of an individual nucleus. The reasons that allow us to detect such an unimaginably small event are twofold.
Firstly, the radiation that is emitted by a decaying nucleus is capable of ‘electrifying’ many of the atoms it passes. Alpha and beta particles are capable, owing to their electrical charge, of direct “ionisation”, while the neutral gamma rays can collide and put in motion charged particles, thus achieving an indirect ionisation. The hundreds of thousands of atoms that are electrified (ionised) as a result of the decaying nucleus serve as an excellent amplifier of the event.
The effects of this primary ionisation are then further amplified by electronics with high gain values, creating a signal large enough to be detected.
A third important amplifying factor is the tremendous quantity of atoms present in a given sample of matter. In 18 grams of water – less than a mouthful – there are over 600 million billion billion molecules (the exact figure, 6.02 x 1023, is known as Avogadro’s number). The sheer size of the sample means that even with a comparatively low proportion of radioactive atoms, the actual number present will be extremely large. The counting rate of the detector, which is directly related to the number of disintegrations per second, will remain high enough to be measurable.