Ultra-small Light Beacons Detect Ultra-light Particles

Detectors used for particle astrophysics may soon become more sensitive thanks to quantum dots--ultra-small light beacons with specialized optical properties. Researchers at the Massachusetts Institute of Technology are testing the properties of quantum dots to extend this technology to next-generation neutrino detectors used to study the lightest particles in the universe.

Improved neutrino detectors will enable researchers to understand the properties of these ultralight particles. However, a detector coated with quantum dots is currently too expensive to construct. As quantum dots expand their applications in biology and medicine the cost is expected to come down. This project will further research on the first compact, neutrino detector.

Quantum dots are semiconducting nanocrystals with optical and electrical properties that are closely related to their physical size. In optical applications, the size of the dot determines the color of the light emitted. Smaller dots absorb and re-emit higher energy or bluer light, while larger dots absorb and re-emit lower energy, or redder light. 

In their experiments the MIT team suspends quantum dots in the scintillating or spark-producing liquids used for neutrino detectors. They then test the effects of the dots on the liquids' luminescent or light-emitting properties. The quantum dots shift the frequency of the emergent light as expected without interfering with the timing properties of the detectors. They can, therefore, be used to tune the scintillator to optimally match the photon detectors that read out the signals. 

Because quantum dots can be manufactured with high precision and a variety of materials, researchers can use them to dope the scintillators with the heavy metals and rare-earth elements that are particularly interesting for double-beta decay nuclear physics experiments, but have been difficult to use in the past.