The following content has been extracted from NNSA Office of Nonproliferation Research and Engineering
(NA-22) Radiation Detection Technologies Program R&D Portfolio 2003.

Compact Radiation Detector and Global-Positioning-System
Unit in a Cell Phone

Bill Craig
Lawrence Livermore National Laboratory

Detecting illicit radioactive material and mapping the background across a broad area can be performed with a small, high-spectral-resolution detector with a long battery life that operates autonomously. Under National Nuclear Security Administration funding, we developed prototype radiation sensors that meet these requirements. With ongoing Department of Homeland Security funding, we are increasing the performance of these detectors.
New-generation gamma-ray sensors and a global-positioning-system (GPS) module are built into a cell phone. The device uses pixelated cadmium zinc telluride (CdZnTe, often abbreviated CZT) detectors coupled with an ultra-low-power readout with moderate energy resolution. The device requires no cooling and is battery-powered (24 to 48 hours on a single charge).

Because the poorer-quality sections of the CZT crystal are left unconnected, we can use less-expensive, commercial-grade detector materials. The material is literally “sliced and diced” from the ingot, with no material selection or individual detector testing required. This approach dramatically lowers the cost of each detector, which costs less than $350 now and will be less than $100 when the device is mass-produced.
We coupled this compact radiation detector with a cell phone and two-way text messaging and integrated a GPS unit (Figure 1). We currently obtain GPS information with a Trimble Lassen SQ GPS engine and antenna, electronically integrated into our detector package. We expect to incorporate a GPS chipset with massively parallel correlators and assisted GPS capability into future versions.

Detected radiation is “tagged” with detection time and location, and the information is autonomously transferred via a commercial wireless network to a central server using a secure socket layer over a transmission control protocol/Internet protocol (Figure 2). This two-way communication allows near-real-time collection of potentially correlated information and provides the ability to change detection thresholds in field units to address specific threats, reduce false alarms, or respond to other operational considerations. The cell phone display provides a simple user interface for dosimetry and consequence management.

The device reports its health when reporting its data; system maintenance consists of swapping out a malfunctioning unit in much the same way pager or cell phone companies do. The only maintenance requirement is charging the battery periodically. Each device can be used as a programmable radiation alarm, personal dosimeter, search instrument, and analysis tool. A central processing system monitors the data from the network of devices and provides additional sensitivity by tracking below-threshold alerts, correlating measurements from different detectors passing the same location at different times, and iteratively adjusting system thresholds to account for transient events. Such devices are ideally suited for military personnel, Transportation Security Administration screeners, U.S. Customs and Border Protection agents, U.S. Postal Service personnel, public safety personnel, delivery service workers, and even nuclear search teams. `

Figure 1. Compact radiation detector, cell phone, and GPS unit.