Beta emitting radionuclides are normally measured by a gas ionization detector or liquid scintillation counting (LSC). In LSC the scintillation takes place in a solution, the cocktails contain two basic components, the solvent and the scintillator(s). This allows close contact between the isotope atoms and the scintillator what becomes an advantage in measuring low-energy electron emitters due to the absence of attenuation. Once the solvent must act as an efficient collector of energy, and it must conduct that energy to the scintillator molecules instead of dissipating the energy by some other mechanism (National Diagnostics, 2004). Liquid scintillation cocktails absorb the energy emitted by radioisotopes and re-emit it as flashes of light. A в particle, passing through a scintillation cocktail, leaves a trail of energized solvent molecules. These excited solvent molecules transfer their energy to scintillator molecules, which give off light. With LSC the short path length of soft в emissions is not an obstacle to detection. LSC can thus be used for the measurement of both high and low energy emitters.

A pulse height spectrum is a representation of the average kinetic energy associated with the decay of a particular isotope. When an isotope decays it liberates an electron or beta particle and a neutrino that have the energy associated shared between the two particles. As a result of that the resulting beta particles have a continuous distribution of energies from 0 to maximum decay energy (Emax). The amount of light energy given off is proportional to the amount of energy associated with the beta particle. Therefore, the beta decay shows a continuous energy distribution and beta particle spectrometry becomes an analytical thecnique in which it is difficult to identify individual contributions in the spectrum beta. The determination of various beta emitters such as 3H, 14C, 63Ni, 55Fe, 90Sr requires chemical separation of the individual radionuclides from the matrix and from the other radionuclides before couting.

The isotope 63Ni is an artificial radionuclide. It is a pure в emitter with a half-life of 100 years. The maximum energy of the emitted в-radiation is 67 keV. No у radiation is observed. Except 59Ni with a half-life of 7.6 x 104 years all nickel radionuclides have very short half — lifes. They range between 18 seconds and 54.6 hours. Therefore they don’t disturb a measurement of 63Ni. Besides, LSC has a high couting efficiency for 63Ni, about 70%., i. e., the ratio cpm/dpm, counts per minute to disintegration per minute expressed as a percentage, in other words, the percentage of emission events that produce a detectable pulse of photons, making the technique widely used for the determination of 63Ni.