Nuclear Event Detector Detailed Information

Why is a Nuclear Event Detector required? 

The short pulse of ionizing radiation produced by a nuclear weapon presents a major threat to military electronics. This radiation is normally in the form of x-rays or gamma rays, which generate excess electron-hole pairs within all semiconductor devices. These excess electron-hole pairs result in a transient leakage current, called photocurrent, across reverse biased junctions. The transient photocurrents can cause devices to upset or to be permanently damaged. Circumvention encompasses all of the design features required to prevent this upset or permanent damage from ionizing radiation pulses. Using circumvention, the upset-hardening requirements for the majority of the system have been reduced or eliminated, thus minimizing the impact of nuclear hardening on the overall system. Consequently, circumvention allows designers to utilize components that inherently do not meet the hardening requirements. thus providing a cost-effective means of achieving the required nuclear hardness for the prompt ionizing radiation environment. 

The heart of any circumvention system is the nuclear event detector. It is the nuclear event detector that senses the ionizing radiation and quickly triggers the protection circuitry. The nuclear event detector also remembers that an event has been detected, so that the system can use that knowledge to improve both the speed and accuracy of the recovery procedures. 

Radiation Hardness – A Key Aspect of the Maxwell Technologies' NED 

In addition to the nuclear event detector's high speed and flexible design characteristics, it has been designed with nuclear hardness as the primary objective. The circuit operates with the severe parameter degradation that the internal semiconductors will experience from the neutron and total ionizing dose environments. To prevent damage due to excessive photocurrents all semiconductors are current limited with resistors. The NED is available with guaranteed or designed-in hardness. 

Guaranteed performance is achieved by manufacturing devices from large qualified manufacturing lots of semiconductor components. Manufacturing lots are qualified by performing radiation characterization of sample NEDs from the material lots. The dose rate detection level of each NED is tested with pulsed ionizing radiation. A certification report is provided for each device documenting the NED trip and no-trip levels and the delay time of the NED output signal. 

Designed-in performance is achieved by manufacturing devices using the same design and manufacturing processes used for the NEDs provided with guaranteed performance. No lot qualification is performed and only 10% of the production devices are tested with pulsed ionizing radiation. Certification reports documenting the NED trip and no-trip levels and the delay time of the NED output signal are provided for the 10% sample of devices.

Unique Features of the Maxwell Technologies' NED Product Line 

Maxwell’s Nuclear Event Detector products provide designers with the following unique features not available elsewhere in the market:

• +5V single supply operation. Other detectors require significantly higher detector bias voltage to provide predictable and reliable detection characteristics. The NED provides a very critical function with the simplicity of a logic device.
• Very low detection levels. Maxwell’s NED is capable of reliably detecting ionizing dose rates as low as 1E5 rads(Si)/sec. This is an order of magnitude lower than most detector designs today. The NED is capable of protecting state-of-the-art integrated circuits.
• Wide range of adjustable detection levels. Maxwell’s NED is capable of detection levels over two orders of magnitude. Adjustment is a simple as changing one external resistor. Designers can use one device type in many systems to provide different levels of hardness.
• 100% Built-in-test. Maxwell’s NED is the only detector available with the ability to test 100% of the device. Complete testing, including the detector, is achieved by irradiating the detector with light to simulate ionizing radiation. The NED provides users the ability to clarify this critical function during operation.