We expect that you are interested in localizing or imaging high-energy sources, such as cobalt-60 with count rates significantly above background levels. You also probably will need to image distributed sources. Not every imager can give a high-quality radiation image for high-energy sources, high count rates, or distributed sources.

When you are measuring sources with count rates significantly above background levels, it is important to note which gamma imagers can handle measurements at the dose rates you expect. Efficiency is not as important for this application, since you will quickly get many counts in the high-dose-rate environment. This is why it is important to always try the imager out via a demonstration in your facility. A demonstration will show you whether or not an imager will be successful at your facility.

If you primarily plan on using a gamma imager for emergency response operations, such as dirty-bomb response, fieldability should be your primary concern. Not all gamma imagers can easily be ready to use in the field. Be sure to confirm you understand the weight, weather resistance, battery life, temperature sensitivity, and startup time of a gamma imager prior to purchase.

In addition, ensure the equipment is easy to use with minimal training. Users should be able to pick up and operate the system easily in the field.

A moving source requires different features of an imager than other emergency-response scenarios. Portability is certainly of even greater importance, since the non-stationary radiation needs to be continually tracked. The moving source could be anything from measuring dirty-bomb plumes to a radiological release at a nuclear power plant. For these types of applications, high imaging efficiency is very necessary since you want to detect as many particles as possible in order to create an accurate image. Due to the dynamic source, you should also look for gamma imagers that have features to handle real-time imaging of a changing environment.

If you are primarily searching for sources in the field or other dynamic environments, your first step is to determine which emission energies you expect to see in your measurements. Not all gamma imagers can accurately image sources at the energies in which you might be interested. If you are looking for low-energy sources, you will want a system with coded aperture or pinhole imaging. Keep in mind that pinhole imaging is less efficient than coded aperture imaging. If you are looking for high-energy sources, Compton imaging is well suited. The various imaging methods have different limitations. For instance, a detector with only coded aperture imaging can image sources as high as 1 MeV, but is not ideal for a search mission because of the limited field of view and challenges with using the same mask at high and low energies. Many other Compton cameras also have a limited field of view, whereas H3D's Compton cameras do not.

If you plan on characterizing and quantifying sources in a controlled environment, we recommend determining which emission energies you expect to see in your measurements, since not all gamma imagers can image over a wide range. Applications such as waste analysis or shipping inspections might require your imager to be capable of quantification in the field. Some gamma imagers even come with extensive post-processing software that allows for in-depth quantification, geometry analysis, and advanced imaging options. Since typical applications in this category are often performed in a stationary, controlled environment, features such as battery life, field of view, and portability aren’t as critical for successful operation, but you may need to evaluate based on your own specific application.

If your team needs to scan a package to render it safe, we recommend a system that can successfully identify sources with a wide range of energies. Characterizing the radiation source is a high priority as well as fieldability. If the imager can’t be transported easily and takes a while to set up, you are potentially putting your team at risk. Angular resolution is important so that the specific distribution of isotopes can be found in the package without disturbing the contents.