Radiation detector accessories should be calibrated at least annually to ensure accuracy and reliability. However, the specific frequency can depend on several factors, including the type of equipment, manufacturer recommendations, regulatory requirements, and the conditions under which the equipment is used. 
For high-precision applications or environments with high radiation levels, more frequent calibration, such as semi-annually or quarterly, may be necessary. Additionally, if the equipment is subjected to harsh conditions, such as extreme temperatures or mechanical stress, more frequent calibration might be required to maintain accuracy.
Regulatory bodies, such as the International Atomic Energy Agency (IAEA) or national agencies, may have specific guidelines or mandates regarding calibration frequency. It is crucial to adhere to these regulations to ensure compliance and safety.
Furthermore, any time a radiation detector accessory is repaired, modified, or shows signs of drift or inaccuracy, it should be recalibrated immediately. Regular performance checks and inter-comparisons with other calibrated devices can also help determine if recalibration is needed sooner than scheduled.
Ultimately, maintaining a detailed calibration schedule and log, as well as following the manufacturer's guidelines and regulatory requirements, is essential for ensuring the proper functioning of radiation detection equipment.