Pulse Height Analysis (PHA): 

It is a nuclear technique used for distinguishing one γ radiation from the other by means of proportionality between the radiation energy and the pulse size. It is used to generate a detailed spectrum and, thus, to resolve a complex mixture of x or γ rays. A single channel pulse height analyzer utilizes an electronic gate, typically 0.1 V wide, which only accepts pulses between the preset upper and lower limits. It is a commonly used device with the scintillation detector. The gate scans through the range of pulse height and feeds the signal to the number of pulses falling within the gate. If the sample has several radionuclides of different energies then such a spectrum should be recorded with a multi-channels analyzer (MCA) having 512 to 1024 channels connected to a scintillation detector.  The MCA receives the voltage pulses, examines them simultaneously by using a large number of channel or gates, classifies each pulse according to its pulse height and stores all the pulses of equal height in the same memory location (channel).