Long at the vanguard of international efforts to answer questions like these, ORNL’s contributions remain strong today. David Radford, head of the lab’s Fundamental Nuclear and Particle Physics section, is an internationally renowned expert in the field who has had an indelible impact on the development of germanium detectors. Vital experimentation tools at the forefront of fundamental physics research, germanium detectors are large, single crystals of germanium — a metallic element — used to detect radiation and enable incredibly precise energy measurements.
Radford currently leads the DOE-funded portion of the Large Enriched Germanium Experiment for Neutrinoless Double Beta Decay, known as the LEGEND-1000 DOE project, or LEGEND, with ORNL as its lead lab. LEGEND is a multi-national, multi-institutional project that relies on germanium detectors to reveal more about the elusive nature of neutrinos. A better understanding of neutrinos — the most abundant, mass-containing particles that we know of in the universe — could help unlock physics’ greatest mysteries.
With a collaboration comprising more than 250 researchers from around 50 international institutions, LEGEND’s global physics experiment will rely on a one-ton germanium detector array, shielded from background radioactivity in an underground laboratory. The project also involves funding from the National Science Foundation and multiple European agencies.
Throughout the history of the pursuit of neutrinoless double beta decay, “ORNL was the lead lab for a predecessor experiment, the Majorana Demonstrator at the Sanford Underground Research Facility in South Dakota. We were also in friendly competition, working hand-in-hand with the European GERDA experiment,” said Radford. “We contribute a lot to our European and U.S. colleagues on design and analysis codes.”
For decades, Radford has been a key contributor to many impactful, international germanium-detector projects, including Majorana, GRETA and GRETINA. To advance capabilities for the study of nuclear structure and nuclear astrophysics, he has made major contributions to germanium detector design and use as these complex scientific sentinels have grown in both size and effectiveness over decades.
“After both GERDA and Majorana were successful, we merged the collaborations — the European and the U.S. experiments — and formed the LEGEND collaboration. ORNL contributed the detector design that’s being used for LEGEND,” said Radford.
Germanium detector history
Since the 1960s, one constant in this ongoing pursuit of elusive subatomic knowledge has been the chemical element germanium. Situated in the carbon column of the periodic table between silicon and tin, germanium has properties of both metals and nonmetals. Dmitri Mendeleev predicted its presence in 1869, and Clemens Winkler identified it in a mineral sample in 1886, naming it after his nationality. However, half a century passed before many of its potential uses were discovered and exploited.
During WWII, germanium was primarily used in point-contact diodes for radar pulse detection. After the war, from the 1950s to the early 1970s, germanium’s development as a semiconductor in transistors paved the way for its use in solid-state electronics, until it was replaced by its more plentiful, less expensive neighbor in the periodic table, silicon. Subsequently, germanium has also been used in fiber optics, solar panels, night vision goggles, polymerization catalysts for plastics, and the infrared optics of airport security thermal cameras and scanners.
However, germanium detectors, first grown from and built around a single crystal of high-purity germanium, did not arrive until the mid-1960s. These groundbreaking tools ushered in a new investigative technique for nuclear physicists: high-resolution gamma-ray spectroscopy.
This process determines the structure of nuclei or isotopic composition of materials by analyzing gamma-ray spectra — a quest in search of the unique gamma-ray fingerprints that atomic nuclei possess. Germanium proved ideal for use in gamma-ray spectroscopy because of its effective balance between high detection efficiency and high energy resolution.
This Oak Ridge National Laboratory news article "Germanium detectors help ORNL physicists unlock the mysteries of the universe" was originally found on https://www.ornl.gov/news
