National Institute of Standards and Technology (NIST) researchers have released groundbreaking test results demonstrating that a promising class of sensors can be used in high-radiation environments and drive important medical, industrial and research applications.
Photonic sensors transmit information with light instead of electrical currents in wires. They can measure, transmit, and manipulate currents of photons, typically through optical fibers, and are used to measure pressure, temperature, distance, magnetic fields, environmental conditions, and so on.
They are attractive due to their small size and low power consumption and tolerance of environmental variables such as mechanical vibration. However, the general consensus was that high levels of radiation would alter the optical properties of their silicon and lead to false readings.
NIST, a world leader in many areas of photonics research, has launched a program to answer these questions. The test results show that the sensors can be adapted for the measurement of the radiation dose both in industrial applications and in clinical radiotherapy. The results of the first round of testing are reported in NatureWorth Reports .
In particular, the NIST results suggest that the sensors could be used to detect the level of ionizing radiation (with energy high enough to alter the structure) of atoms) when irradiated of food used to destroy microbes and in the sterilization of medical devices ̵
"When we looked at publications on this topic, different laboratories achieved dramatically different results." said project scientist Zeeshan Ahmed, who is part of NIST's photonic dosimetry project and head of NIST's innovative photonic thermometry project. "That was our main motivation for our experiment."
"Another motivation was the growing interest in using photonic sensors that can function accurately in very harsh environments, such as near nuclear reactors, where radiation damage is a major problem." Ahmed said. "In addition, the space industry needs to know how these devices work in high-radiation environments," said project scientist Ronald Tosh. "Will they be damaged or not? What this study shows is that the damage to a particular class of equipment and radiation is negligible."
"We have found that oxide-coated silicon photonics devices can withstand radiation exposure up to 1 million gray," said Ryan Fitzgerald, project manager of Photonic Dosimetry, with the SI unit for absorbed radiation. A gray represents a joule of energy absorbed by one kilogram of mass, and a gray corresponds to 10,000 chest x-rays. That's about what a sensor would get in a nuclear power plant.
"It's the upper limit of what our customers care about calibrations," said Fitzgerald. "It can be expected that the devices will work reliably at industrial or medical radiation levels that are hundreds or thousands of times lower." For example, food irradiation ranges from a few hundred to a few thousand gray, and is typically monitored by its effect on alanine pellets, an amino acid that changes atomic properties when exposed to ionizing radiation.
Determination of Effects The NIST researchers exposed two types of photonic silicon sensors to gamma radiation of radioactive isotope cobalt-60 for hours. In both types of sensors, small variations in their physical properties change the wavelength of the light passing through them. By measuring these changes, the devices can be used as highly sensitive thermometers or strain gauges. This also applies in extreme environments such as space flight or nuclear reactors only if they continue to function properly under ionizing radiation.
"Our results show that these photonic devices are robust even in extreme radiation environments, suggesting that this could be the case is also used to measure radiation over their effects on the physical properties of irradiated devices," said Fitzgerald. "This should be good news for US manufacturing, which wants to serve the large and growing market for the precise delivery of radiation on very small scales, and photonic sensors could then be developed to measure the low-energy electron and X-rays used in the sterilization of medical devices and in the irradiation of food. "
They will also be of great interest to clinical medicine, where physicians want to treat cancer drugs and other diseases with the lowest effective radiation levels, concentrated in the smallest dimensions not to affect healthy tissue, including electron, proton and ion beams. To achieve this goal, radiation sensors with extremely high sensitivity and spatial resolution are required. "We hope to eventually develop chip-scale devices for industrial and medical applications that can detect absorbed dose gradients over distances in the micrometer range, resulting in unprecedented measurement results," said project scientist Nikolai Klimov. One micrometer is one millionth of a meter. A human hair is about 100 microns wide.
The team's findings may have major implications for new medical therapies that use extremely narrow beams of protons or carbon ions, and medical sterilization techniques that use low-energy electron beams. "Our sensors are naturally small and on a chip scale," said Fitzgerald. "Current dosimeters are in the order of millimeters to centimeters, which can lead to erroneous readings for fields that vary over these dimensions."
In the next research phase, the team will test arrays of sensors simultaneously under identical conditions to see if dose variations over small distances can be addressed.
Hall effect magnetic field sensors for high temperatures and harmful radiation environments
Zeeshan Ahmed et al., Evaluation of the Radiation Hardness of Photonic Silicon Sensors, Scientific Reports (2018). DOI: 10.1038 / s41598-018-31286-9