A pressure-regulating large-area windowless airflow proportional counter is provided, which includes a chamber, a metal tray, a side cover, a gas cylinder, and a voltage input and signal output terminal. The chamber has a side opening. A large-area source is placed on the metal tray and the metal tray is moved into or out of the chamber via the side opening. The side cover is fixed to the side opening by an O-ring via a locking device to form an airtight structure. The gas cylinder is used to supply a dedicated gas into the chamber. The voltage-input/signal-output terminal is used to supply voltage to an anode wire net. The free electrons generated by the large-area source due to the free phenomenon are collected by the anode wire net, and outputted to a voltage signal processing module through the voltage-input/signal-output terminal for analysis of pulse height or pulse count.

A pressure-regulating large-area windowless airflow proportional counter is provided, which includes a chamber, a metal tray, a side cover, a gas cylinder, and a voltage input and signal output terminal. The chamber has a side opening. A large-area source is placed on the metal tray and the metal tray is moved into or out of the chamber via the side opening. The side cover is fixed to the side opening by an O-ring via a locking device to form an airtight structure. The gas cylinder is used to supply a dedicated gas into the chamber. The voltage-input/signal-output terminal is used to supply voltage to an anode wire net. The free electrons generated by the large-area source due to the free phenomenon are collected by the anode wire net, and outputted to a voltage signal processing module through the voltage-input/signal-output terminal for analysis of pulse height or pulse count.

An apparatus for measuring ionizing radiation includes a detector having a cathode, an anode, a counting gas between the cathode and the anode for generating gas ionization by ionizing radiation, a voltage source for applying a voltage between the cathode and the anode, and a current measuring device for measuring a detector current between the cathode and the anode. The detector current is generated in the counting gas by the ionizing radiation. The apparatus further includes a setting device, wherein the setting device is configured for independently setting the apparatus into different operating modes depending on the measured detector current, and/or wherein the setting device is configured for independently setting the apparatus into different measurement ranges depending on the measured detector current.

A radiometric measuring device has a counting tube having an anode and a cathode, and is configured to determine a measurement variable depending on properties of ionizing radiation that impinges on the counting tube. In a first measurement mode, a constant first voltage is set between anode and cathode such that the counting tube operates as a proportional counting tube, and the measurement variable is determined depending on a current flowing between anode and cathode. In a second measurement mode, the current flowing between anode and cathode is controlled to a current setpoint value, wherein the voltage between anode and cathode serves as a manipulated variable of the current control, and the measurement variable is determined depending on the voltage between anode and cathode. In a third measurement mode, a constant second voltage is set between anode and cathode such that the counting tube operates as an ionization chamber, and the measurement variable is determined depending on the current flowing between anode and cathode. Either the first, second, or third measurement mode is activated depending on the current flowing between anode and cathode and/or depending on the voltage between anode and cathode.