Building on basic radiation detection, this unit introduces energy-sensitive detection and temporal correlation. You will move beyond simply counting pulses to analyzing the energy spectrum of gamma rays and determining the specific energies of various radioactive transitions.
While a G.M. counter is an "event counter," a Scintillation Detector (typically Sodium Iodide doped with Thallium) provides a pulse height proportional to the energy of the incident photon.
These circuits are used to detect events that occur simultaneously (or within a very short time window). This is essential for studying decay schemes where multiple particles are emitted sequentially.
Coincidence: Outputs a pulse only if two detectors record an event at the same time. Used to map correlated gamma emissions.
Anti-Coincidence: Outputs a pulse only if one detector records an event and the other does not. Used to reduce background cosmic ray noise.
Alpha particles have a very high ionizing power but a very short range in matter. In this lab, a Spark Counter or a specialized air-filled chamber is used to find where the alpha particles stop.
As the distance between the source and the detector window increases, the count rate remains constant until the Mean Range is reached, at which point it drops sharply to zero.
Feather Analysis is an empirical method to determine the maximum energy (Emax) of a beta-ray emitter.
Since beta particles have a continuous energy spectrum, their absorption curve is not a simple exponential. By comparing the absorption of an unknown source with that of a standard source (like Bi-210), the range Rp in Aluminum can be found, which then gives Emax via the Feather relation.
Tip: In Alpha range experiments, ensure the source and detector are in a dust-free environment. Dust particles can act as thick absorbers, significantly shortening the measured range.