The United States never has experienced a dirty bomb incident, but the potential remains and fear of one is never far from the collective fire department consciousness. First responders soon may have a more practical way of detecting radioactive material in the field. Scientists at the Brookhaven National Laboratory have devised ways to improve the performance of radiation detectors, such as those used by first responders to locate and identify radioactive material.

The improved sensors can be used at room temperature, which makes them not only easier to use but also makes them more cost effective than existing detectors. Existing detectors are built to be operated at extremely cold temperatures using expensive liquid nitrogen. The Brookhaven version also can detect the X-rays and gamma rays emitted by radiological sources such as dirty bombs and other illicit materials more accurately.

Radiation detectors work by detecting electrons and vacancies or “holes” left by liberated electrons when ionizing radiation or high-energy particles strike the detector crystal. When the free electrons and holes flow toward electrodes (an anode and a cathode) at either end of the detector, they generate a signal that can be measured and recorded.

According to the researchers, in an ideal detector all of the electrons and holes created by the ionization process would arrive at the electrodes. But in reality, holes travel a very short distance before getting trapped by defects in the crystal. Also, because the electrostatic field inside the detector causes some of the electrons to drift, not all of them arrive at the anode. These losses lead to a subsequent inaccuracy in radiation measurements.

The Brookhaven designed sensors improve on this situation by combining methods to shield the detector and focus the electrons toward the anode. In addition, the electrodes at each end of the detector give information about how many electrons/holes get trapped. This “correction factor” can then be used to reconstruct the number of electrons/holes originally created by incident gamma rays or high-energy particles.

“Together, these techniques enhance the energy resolution and efficiency of these detectors,” said Brookhaven physicist Aleksey Bolotnikov, one of the inventors.

In practical terms it means that the improved devices will be able to detect more minute quantities of radiation more quickly or from greater distances, better identify the source of the radiation, and distinguish illicit sources of concern from common naturally occurring radioactive materials, Bolotnikov said.