Q & A about Passive Detection™ Technology

What makes the RDU-18 detector unique?

The RDU-18 is unique for three main reasons:

Passive Detection™ technology makes it simple, reliable, and robust to environmental variation, while providing good sensitivity and low probability of false alarms.
It is designed to differentiate between levels of radiation in a simple system of 4 levels. These 4 levels are related to the regulations for radiation exposure that apply to the public. Personnel training required to understand these levels, and responses to them, is therefore greatly simplified.

Alert Level	Threshold
Minimum Detectable Level	Indicates the presence of unusual radiation above the statistical(1x10^-6) false alarm threshold for local background.
LOW >1 mR/hr	Low Radiation Hazard. Long term exposure, on the order of days, will exceed regulatory limits for the public.
MODERATE >10 mR/hr	Moderate Radiation Hazard. Short-term exposure, on the order of hours, will exceed regulatory limits for the public.
HIGH >100 mR/hr	High Radiation Hazard. Immediate action required to protect public safety.

The output of the sensor is designed to be interfaced to communications equipment or automated alarms systems. This allows transmission of the sensor data to a central decision support system or computer-aided dispatch system for processing. The data can be collected without making additional work for the first responders. Sensors can also be deployed, unattended, in facilities and in public places.

How do you prevent false alarms?

The Passive Detection™ technology provides three mechanisms to prevent false alarms:

The sensor continuously monitors its internal circuitry for proper operation. If the monitors determine that the sensor is not working properly all outputs are disabled. The sensor health LED on the ADU-4 Alert Display Unit goes dark in this condition, indicating that the sensor should be checked.
The sensor continuously measures background radiation levels, and the alarm thresholds are referenced to this background level. This accommodates the significant variation of background radiation between different locales.
A statistical filter is used to determine if the measured radiation level is above the alarm threshold with a false alarm probability of less than 1 x 10^-6. Radioactive decay is very erratic. This statistical filter tests the randomness of detector events and determines when it is sufficiently unusual to meet the 1 x 10^-6 test.

How much radioactive material can the RDU-18 detect? What is the range of the detector?

The RDU-18 can detect 5 µCi of ¹³⁷Cs placed ~1 foot from the detector. This is a very small amount of material. The amount that can be detected is a function of the quantity and distance. To estimate the amount necessary to trigger the alarm multiply 5 µCi by the square of the ratio of distances.

That is: quantity [ in Ci ] = 5 x 10^-6 * ( distance / 1 ft. )²
or:

Distance [Feet]	Quantity [µCi]
2	20
5	125
10	500

For reference:

1 Curie of:
Radionuclide	Mass [gm]
Cobalt 60	0.001
Radium 226	1
Uranium 238	635,600

Why put the radiation detectors on vehicles?

Our vision is to have radiation detectors widely deployed in public places to monitor and assure the public safety. Detectors can be placed under traffic lights, on lamp posts, in storage facilities, scrap yards, and just about any populated place. Of course, a broad deployment like this will take time and money to implement, so prioritization is important. We believe that the most effective first deployment is on police vehicles, for many reasons.

Police vehicles are constantly patrolling our communities, and they are immediately called to the scene of emerging events. Additionally, police vehicles are equipped with communications equipment and GPS location sensors; everything necessary for collecting and integrating radiation (and other sensor) data for analysis and response. This approach also provides a means for collecting sensor data without adding any responsibility to the police officer's already long list.

Similarly, fire apparatus and aid vehicles provide a suitable platform for sensor deployment. Postal delivery vehicles, that pass just about every road in America every day, would be a high priority for sensor deployment.

What is gamma radiation?

Gamma radiation is an ionizing radiation in the form of electromagnetic energy (no rest mass, no charge) similar in many respects to visible light (but far more energetic). Due to its high energy, lack of charge or rest mass, gamma rays can travel thousands of feet in air and can easily pass through the human body or even radiation detectors. Gamma rays are produced by fission products (from power reactors or nuclear explosions) and many naturally occurring radioactive materials. People are exposed to small amounts of gamma radiation during our normal lives, from materials in the environment and from within our own bodies.

Some radioactive materials also emit alpha or beta particles.

An alpha particle is ionizing radiation that consists of two protons and two neutrons. The neutrons and protons give the alpha particle a relatively large mass as compared to other ionizing radiation particles. Because of this large size, the alpha particle has a relatively low speed and low penetrating distance (one or two inches in air). The particle tends to travel in a straight line, causing a large number of ionizations in a small area. Alpha particles are easily absorbed by a thin sheet of paper or the body’s outer layer of skin.

A beta particle is a high-speed ionizing radiation particle that is usually negatively charged. The charge of a beta particle is equal to that of an electron (positive or negative), and its mass is equal to about 1/1800th of that of a proton or neutron. Due to this relatively low mass and charge, the beta particle can travel through about 10 feet of air and can penetrate very thin layers of some materials. However, clothing will stop most beta particles.

Can the detector help prevent terrorist attacks?

Yes, we believe that deploying radiation detectors in large numbers will help uncover nuclear terror conspiracies, and identify accidents or losses involving common nuclear materials, especially when deployed on police and fire vehicles. Due to the nature of gamma radiation (it doesn't interact with matter very much) it makes sense to deploy sensors more widely to increase the likelihood that radiation will be detected. Not just at ports and border crossings, but everywhere.

Is the detector directional?

Fundamentally, no, but placement of the detector on the surface of an absorbing material (like a concrete wall or steel vehicle) will reduce its sensitivity in the directions blocked by the absorber. Choose the placement of the detector to favor the direction of interest, and closest to the expected source.

For police vehicles we recommend mounting the sensor on the right side of the front bumper to place it as close as possible to vehicles during traffic stops.

For fire apparatus and aid vehicles we recommend mounting on the underside of the front bumper or frame to place the sensor nearest the ground where material would be accumulating following a bomb blast or fire.

What maintenance of the detector is required?

At common background levels, the sensor will operate for years without requiring maintenance.

Why hook the sensors to automated systems?

Our first responders have enough to worry about during a routine day. By connecting the sensors to the communication system, and collecting the data in a central system, the first responder is relieved of the effort required to monitor and analyze the sensor data. Better still, having collected data from widely deployed sensors, more sophisticated analysis of spacial and temporal patterns can be applied. When suspicious patterns of sensor data are identified an investigation can be initiated to discover the cause. In the event of an emerging attack or accident the data can be analyzed to decide what operational response is appropriate given the circumstance. In these scenarios automation improves responsiveness and decreases workload in the operations center.

We worry about a "Dirty Bomb", but what about our more common operations fighting fires or responding to accidents? How does the detector help?

Fire fighters need to know if radioactive materials are involved in a fire, accident, or bomb incident. Lacking other information, fire fighters will assume that radiation is present when responding to a bomb attack. Fighting a fire involving radiation is much more difficult due to the additional protective equipment and procedures required to assure safety. If the threat of radiation is eliminated, as in most fires, firefighters can "take the gloves off", so to speak, and wage a more effective battle.

Our ports are being outfitted with radiation detection portals, so why do we need detectors anywhere else?

There are large quantities of nuclear material already within the United States. Spent reactor fuel is stored at nuclear sites, waste is transported to storage areas, and radioactive materials are used for non-destructive testing and cancer treatments. New materials are produced for the medical industry and shipped around the country to hospitals. Because this material is so radioactive, and decays rapidly, it is often transported by air so that it can be hot enough for certain procedures.

Thus, the opportunity for accidents and incidents involving nuclear material is large even if no additional material enters the country. The Passive Detection™ concept focuses on environmental surveillance to identify problems earlier, and situational awareness to protect our first responders and the public.

What is the difference between a Geiger Counter and a Passive Detection™ unit?

A Geiger Counter is a survey meter used to measure the amount of radiation in a particular location. The Geiger Counter displays a continuous reading of dose rate on a dial, meter, or digital output. An operator must analyze and interpret the dose rate, and the situation that produced the reading, to decide how to respond.

The Passive Detection™ Radiation Sensor provides a simplified indication of the radiation level that is based on regulations for radiation exposure to the public. These radiation alarm levels indicate how quickly people in the area may accumulate a dose that exceeds the limits for public exposure. This measure is more directly useful to guide the actions of the responders and incident commanders.

Which is better, a scintillation detector or a Geiger tube?

Each have their strengths and weaknesses.
Scintillation detectors can be very sensitive because of their higher density (the radiation is more likely to be absorbed and detected). They can also resolve the relative energies of the radiation being detected. On the negative side, Scintillation crystals are expensive, and the overall complexity of the sensor is greater. Instruments that take advantage of the energy resolution of Scintillation detectors cost $X0,000.

Geiger-Mueller (GM) tubes are simple and robust, readily available, and low cost. The overall complexity of the sensor is much less than for scintillation detectors. On the negative side, GM tubes are not as sensitive (they are filled with gases under a vacuum), and do not provide information about the energy of the radiation.

For the Passive Detection™ concept the Geiger tube wins out: it provides a level of sensitivity consistent with our design for differentiating the regulatory limits for public exposure, and can be implemented in a simple and robust sensor design.

What are other potential applications?

Our vision for Passive Detection™ technology is to deploy sensor throughout the community to protect our first responders and the public. Police and fire vehicles are our highest priority for this effort, but there are many other potential uses:

Nuclear Power Industry

The RDU-18 can be used as an area monitor in nuclear facilities and power plants.

Safety Monitor for Non Destructive Testing Radioactive Sources

The RDU-18 can be placed in vehicles and storage areas that contain radioactive sources to assure that the containers are properly closed and secure.

Scrap Yards and Recycling Centers

The RDU-18 can be used in scrap and recycling centers to detect radioactive materials that may be present among materials being collected.

Rental Storage Facilities

An RDU-18 sensor can be installed in each storage unit to detect when radioactive materials are being stored or collected.

Medical Facilities

An RDU-18 can monitor an area to assure that radioactive tracers are properly stored and secured.

What kind of battery does it need? How is it powered?

The RDU-18 and ADU-4 are designed to operate on vehicle power, or 9-15 Volts DC from an alarm system or wall transformer in stand-alone applications.

How often does the unit need to be replaced?

The unit should be tested annually with a 5 µCi check source. If the unit fails to alert with the check source at 8-10 inches from tube it should be replaced. In normal conditions, at common background levels, the sensor should last for many years.

Protected by US Patent #7,327,270. Other patents pending.