Understanding Cobalt Source Exposure in Industrial Radiography

What would be the restricted area on the cold or collimated side of the collimator if a cobalt source of 73 Ci is exposed for 60 minutes with a 14.0 R/Ci factor through a 3 half-value collimator?

• A. 153 ft (46.63 m)
• B. 200 ft (60.96 m)
• C. 253 ft (77.44 m)
• D. 300 ft (91.44 m)

Answer: (C)

To determine the restricted area on the cold or collimated side of the collimator when using a cobalt source of 73 Ci, one must first calculate the exposure rate at a certain distance, and then consider the half-value layers of the collimator. In this situation, the exposure factor is provided as 14.0 R/Ci. First, we calculate the total exposure generated by the cobalt source during the 60 minutes of exposure. This is done by multiplying the activity of the source (73 Ci) by the exposure factor (14.0 R/Ci) and then by the duration (1 hour or 60 minutes): Total exposure = Activity (Ci) × Exposure factor (R/Ci) × Time (hr) Total exposure = 73 Ci × 14.0 R/Ci × 1 hr = 1022 R Next, since the collimator has three half-value layers (HVL), it naturally reduces the exposure rate. Each half-value layer decreases the radiation by half, allowing us to calculate the exposure at an adjusted distance while accounting for the diminished intensity. After passing through three half-value layers, the exposure at the cold side can be calculated to see how far that exposure can reach before

When you think about industrial radiography, there’s plenty of vital knowledge to wrap your head around. One prominent question is how to accurately assess exposure from a cobalt source in a collimated setup. So, let’s unravel this essential aspect of radiation safety, shall we?

Imagine you’re in a radiography lab, hands-on with a cobalt source rated at 73 Curie (Ci). You’re conducting tests and trying to figure out how far the radiation might reach on the cold side of your collimator. You know what’s essential here? Protecting yourself and others from unnecessary exposure while still getting effective results.

First off, the exposure factor we have is a substantial 14.0 R/Ci. This means that for every curie of your source, there’s a generated exposure rate. Calculation time! To determine the total exposure during your 60-minute ordeal, we need a simple formula—multiply the activity of the source by the exposure factor and then by the time duration:

Total exposure = Activity (Ci) × Exposure factor (R/Ci) × Time (hr)

So, in this case:

Total exposure = 73 Ci × 14.0 R/Ci × 1 hr = 1022 R

Whoa, that’s a big number—it’s easy to see why radiation safety is so crucial, right?

Now, let’s consider the collimator you’re using. It has three half-value layers (HVL). You might be thinking, what’s the big deal about half-value layers? Well, each HVL you pass through effectively halves the intensity of radiation. It’s like taking a pizza and cutting it in half—you want fewer slices of that radiation pie.

Let’s break this down:

1. After the first HVL, the exposure drops to 511 R.

2. After the second HVL, it’s down to 255.5 R.

3. After the third HVL, we’re looking at roughly 127.75 R.

Each step reduces potential exposure, keeping those in the vicinity safer. Now, after considerable attenuation through these layers, the exposure level significantly diminishes. However, this asks a crucial question: how far does radiation still reach on the cold side of this system?

To pinpoint the restricted area using our calculated exposure after three HVLs, one would traditionally reference factors and safety zones defined in specific standards. Given this configuration, the corresponding distance we arrive at is approximately 253 feet (77.44 meters).

So, why does it all matter? In safety-sensitive environments like industrial radiography, knowing these details isn’t just helpful; it’s crucial. The more informed you are about exposure rates and safety practices, the safer your work environment becomes.

In conclusion, realizing how to calculate exposure and understand the implications of collimators in radiographic setups is foundational for radiography professionals. Not only does it ensure compliance and safety—but it builds confidence in the materials and methods used. Keep this knowledge handy, and remember, safety first!