Which device can be used to determine a shutter timer error?

The ionization chamber is the correct choice for determining a shutter timer error due to its sensitivity and ability to measure radiation dose accurately. This type of device operates by collecting ion pairs created when radiation interacts with air within the chamber. When a shutter is not functioning correctly, the output from the ionization chamber will reflect an incorrect exposure, allowing for the detection of timing errors.

In contrast, other devices listed serve different functions. A Geiger counter, for instance, is primarily used for detecting and measuring ionizing radiation but does not provide the precise dose measurements required to analyze shutter timing errors. Film dosimeters measure exposure by recording the intensity of radiation on film but lack the necessary accuracy for timer-related discrepancies. Similarly, thermoluminescent dosimeters are effective in measuring cumulative radiation exposure; however, they do not provide real-time feedback to determine timing errors. Their readout requires processing and is generally not suitable for immediate assessment of timing malfunctions.