Method and apparatus for detecting ionizing radiation
A method for detecting ionizing radiation with the aid of a scintillation counter and a photomultiplier using an inorganic solid-matter scintillator that incorporates at least one decay time component greater than 100 ns and measures the photons emitted by the scintillator with a fast single-photon counter. The single-photon counter is composed of a fast photomultiplier with high internal amplification, a stabilized high-voltage supply and a fast amplifier/discriminator with standard pulse output. With this arrangement, the measurement of all types of radiation, like alpha, beta, gamma and X radiation, can be performed, with low manufacturing costs for the detector, a high degree of sensitivity especially with regard to low beta energies, only small sensitivity changes over a large temperature range of −20 to +50 degrees C., and good long-term stability.
1. A method for simultaneously detecting ionizing radiation of different types, comprising:
exposing a single solid matter scintillator that incorporates at least one decay time component greater than 100 ns to the radiation; and
measuring photons emitted by the scintillator with a single-photon counter that includes a photomultiplier connected to receive photons from the scintillator and a single-photon amplifier connected to convert output pulses from the photomultiplier into single-photon pulses, wherein said step of measuring comprises:
in a first channel, performing a burst recognition by opening a gate circuit for a certain time period TG in response to a first single-photon pulse from the single photon amplifier, and generating an output signal as a measure for an ionizing event as soon as a certain number N of additional pulses from the single photon amplifier is registered by the single-photon counter during the time period TG; and
in a second channel in parallel with the first channel, performing an independent measurement of alpha radiation to which the scintillator is exposed by:
pulse shaping of the output pulses from the photomultiplier; and
when an alpha particle is detected in the second channel, preventing the start of a burst recognition for a pre-definable veto time.
2. The method according to claim 1 , wherein the duration of TG is between 1 and 20 μs.
3. The method according to claim 1 , further comprising, in order to discriminate or select a certain type of ionizing radiation with a single measurement, setting values of N and TG that are characteristic for a selected type of the radiation.
4. The method according to claim 1 , wherein the veto time is between 1 and 10 ms.
5. The method according to claim 1 , further comprising, for classification of the output pulses of the photomultiplier as alpha particles, setting a first amplitude threshold (Dl) in the second channel.
6. The method according to claim 5 , further comprising setting a second amplitude threshold (D 2 ) greater than the first amplitude threshold (DI) at the beginning of counting in the second channel so that blocking of the burst recognition takes place prior to activation of the second channel.
7. The method according to claim 1 , wherein the scintillator comprises ZnS(Ag).