ASNT Radiographic Testing Practice Test 2025 – Comprehensive All-in-One Guide for Exam Success!

The gamma ray intensity at a specific distance from a radioactive source can be calculated using the principles of radiation dosimetry. Cobalt-60 (Co-60) is a commonly used gamma radiation source, and its properties have been well-studied.

For Co-60, the gamma radiation intensity can be expressed in terms of roentgens per hour (R/h) at a distance of 1 foot from the source, based on its activity measured in curies (Ci). The intensity from a 1 Ci source of Co-60 is generally around 15 R/h at a distance of 1 foot.

This value is derived from the known gamma emission characteristics of Co-60, which emits two primary gamma photons with energies of 1.17 MeV and 1.33 MeV. The strength of these emissions, combined with the inverse square law of radiation intensity, contributes to determining the exposure rate.

The intensity resulting from the 1 Ci source captures the average exposure rate, allowing for practical application in the field. Recognizing this standard value is crucial for professionals working with radiation safety and monitoring, as it provides a baseline for the expected exposure rates associated with commonly used radioactive sources like Co-60.