The energy density of isotopes exceeds that of chemical energy storage by six orders of magnitude. Isotopes are used in many commercial applications, and are produced and available at modest prices. The power requirements of many sensors and communications equipment can greatly reduce the power requirements of many devices such as sensors, light sources, and transmitters. Chemical batteries are the mainstay of power for these devices. However, chemical batteries have limited lifetimes. This makes remote use and replacement difficult for applications extending the lifetime use.

The most compelling reason to use isotope power sources for remotely located unattended sensors and communications nodes is the long lifetime power source capability. Isotope batteries provide a continuous flow of energy from decaying isotopes. When isotopes decay, they emit alpha, beta, or gamma particles. The particles’ emitted energy can be converted to electrical energy without intermediate thermalization. Isotopes decay in five possible modes: alpha decay, beta decay, positron emission, electron capture, and isomeric transitions. Combinations of particles are commonly emitted during a given type of decay.

The characteristics desired for unattended sensor are long-life operations and safety. There are several beta emitters that exhibit long life. Long life, in this case, means the lifetime of Infrastructure; ~150 years. Keeping safety first means limiting gamma emission and keeping the amount of radioactive material as low as is reasonably possible, while still providing 100 μW trickle charge output.

Technology issues associated with developing isotope batteries include choices of isotope material, approach to converting energy stored in nucleus to electrical power, and power management. The impact of long-lived power sources can begin to have impact on sensors and network arrays now. The most compelling interest in a radioisotope (RI) power source is the unique niche of long-lived power unmatched in chemical power sources. The potential for nano-sized power sources exists because of the isotope energy density; however, energy conversion in the balance of the system presently accounts for a much larger volume in this type of device.

There are several long-lived isotope candidates; these are low gamma emitters, in addition to having long half-lives. They are not commonly produced for industry, making the cost higher. The cost can be lowered if the commercial use increases; as more material is required, the process can be made efficient.

Sealed radiation sources are one of the important tools available in affecting safety and handling. Sealed Source is a term used to describe radioactive sources that have been designed to prevent spread of radioactive material under normal working conditions.

The most straightforward approach to getting a power source out in the field for trials utilizes components that are commercially available. This completely commercial-off-the- shelf approach represents an inexpensive route to producing and licensing a long-lived power source quickly. The device is not the most efficient, most energy dense, or novel in design. It is simple and straightforward, with the goal of getting this extended lifetime power source into the hands of users. Because of the extended lifetime capability, these types of power sources can have great impact towards persistent sensing, communications signal relay, and unattended remote sensing.

This work was done by Marc Litz of the Army Research Laboratory. ARL-0173


Aerospace & Defense Technology Magazine

This article first appeared in the April, 2015 issue of Aerospace & Defense Technology Magazine.

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