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How do radiation detectors measure alpha particles?

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detector output connected to a measuring circuit — radiation measurement Figure 1: (A) A simple equivalent circuit for the development of a voltage pulse at the output of a detector. R represents the resistance and C the capacitance of the circuit; V(t) is the time (t)-dependent voltage produced. (B) A representative current pulse due to the interaction of a single quantum in the detector. The total charge Q is obtained by integrating the area of the current, i(t), over the collection time, t_c. (C) The resulting voltage pulse that is developed across the circuit of (A) for the case of a long circuit time constant. The amplitude (V_max) of the pulse is equal to the charge Q divided by the capacitance C.

Radiation detectors measure alpha particles—which are positively charged, weakly penetrating particles—using several types of active detection technology. Because alpha particles have a short range, detectors often require specific design features to allow the particles to enter the active volume.123

Gas-Filled Detectors

Geiger-Müller counters are commonly used to detect alpha radiation. Because alpha particles are weakly penetrating, these tubes are often fitted with a thin entrance window that allows the particles to reach the fill gas. When an alpha particle enters the gas, it creates ion pairs, triggering a discharge that produces an electrical pulse. While these detectors are excellent for indicating the presence of radiation, they do not provide energy information.1

Scintillation Detectors

Scintillation detectors measure alpha particles by converting the energy deposited by the particle into light.4
* Process: As an alpha particle stops in a scintillator material, it creates excited atomic or molecular states that emit visible or ultraviolet light.4
* Conversion: This light is collected and converted into an electrical pulse by a photomultiplier tube or photodiode.4

Historically, early researchers like Ernest Rutherford manually counted these scintillation flashes using a zinc sulfide screen and a microscope.4