Physics faculty and students mining for neutrino answers

During the manufacturing process, many medical devices or equipment for use on humans must be sterilized according to recognized standards. This includes gowns, surgical drapes, syringes and implantable medical devices. In fact, the United States has a huge medical device sterilization industry, regulated by the U.S. Food and Drug Administration. The industry is expected to grow considerably in the coming years.

The most common medical device sterilization methods will unlikely be able to handle that continued growth, say experts in the field. In addition, the industry is looking for alternatives since the two leading technologies use substances—ethylene oxide and cobalt-60—that present safety issues.

Researchers at U.S. Department of Energy’s Fermi National Accelerator Laboratory believe they can help. Using funding provided by the National Nuclear Security Administration, Fermilab researchers are building a prototype electron beam accelerator that integrates four emerging accelerator technologies into a single, efficient accelerator system. Industrial partners could use such a machine to make X-rays for sterilizing equipment.

“The focus of our effort is to develop a high-power electron beam that can serve as an alternative to large-scale cobalt facilities,” said Thomas Kroc, applications physicist and principal investigator of the Fermilab medical device sterilization efforts. “In doing that, we exploit the superconducting accelerator experience that we developed here at Fermilab. We think that technology provides the efficiency that makes it feasible to run electron accelerators that can sterilize medical equipment as well as existing large facilities that use other methods.”

Evolving sterilization methods

Electron beams first were used to sterilize medical equipment in the late 1950s, but their use was hampered by equipment reliability issues. Instead, gamma rays—high-energy photons produced by the radioactive decay of cobalt-60—became the go-to radiation sterilization technology. Since that time, and especially in the last decade, electron beam technology and X-ray technology have vastly improved. Kroc believes they now are viable alternatives to gamma rays. Fermilab received NNSA funding to look into the development and commercialization of these alternatives.

Today, around 50% of medical devices in the United States are sterilized using ethylene oxide, which is a colorless gas that kills microorganisms. It is extremely effective at sterilizing heat- or moisture-sensitive medical equipment without damaging it. Much of the remainder, around 40%, are sterilized using ionizing radiation like gamma rays created from cobalt-60, a radioactive isotope of cobalt. The rest use X-rays or electron beams.

Health and environmental concerns regarding the use of the highly regulated ethylene oxide are driving a search for alternatives. The use of radioactive isotopes like cobalt-60 is not a good alternative as it presents health and national security concerns. It also has practical issues such as how to transport and dispose of the residual radioactive waste safely and efficiently. In addition, there is a worldwide shortage of cobalt itself.

The NNSA Office of Radiological Security has been promoting the use of alternative technologies, including electron beams, for radiation sterilization to reduce U.S. reliance on cobalt-60. Given its strong foundation in particle beam technology, Fermilab is a leader in this effort.

Medical device sterilization with cobalt is performed on a large scale because of the penetrative power of the gamma rays that cobalt creates. The gamma rays can traverse and sterilize pallets full of medical equipment.

X-rays offer penetration as effective as gamma rays. Scientists can operate electron beam accelerators and force the electrons to emit X-rays without creating the residual waste associated with gamma-ray production. But the current accelerator technology for these systems is not energy—and hence cost—efficient.

The Fermilab team aims to change that. They work on developing a new type of electron beam accelerator system. At the core of their system is a superconducting radio frequency cavity that is used to propel charged particles. Their key to creating a more efficient accelerator system is managing the cavity’s heat budget.

Combining multiple emerging technologies

The typical SRF cavity used in most science facilities today is made of niobium. It requires liquid helium to keep it cold enough to conduct electric currents without resistance, the hallmark of superconducting material. Rather than building a helium liquification plant and all the associated infrastructure, the innovative design developed at Fermilab uses commercially available cryocoolers. These are also used in MRI machines, which need cooling for their superconducting magnets. But to keep the heat produced by equipment within a level that the cryocoolers can handle, the total heat generated by the system during operation must be within approximately five watts—less than the heat typically created by a light bulb.

To stay within that limit, the Fermilab team combines four technologies. Each of these has been independently demonstrated to work. Their prototype will integrate these patented technologies into an energy-efficient accelerator system.

First, they use niobium SRF cavities coated with tin, which increases the operating temperature of the superconducting cavity and puts it within a cryocooler’s operating range. Next, they embed the source of the electrons, the beam gun, directly into the cavity rather than transporting the electron beam from an external source via a transport line. This minimizes the amount of external heat that can leak into the superconducting cavity system. Similarly, they designed the coupler that transfers the radio frequency power into the cavity to minimize the amount of heat that can enter from the outside. Finally, they use conduction cooling in the commercial cryocooler and aluminum to connect the cryocooler to the SRF cavity. Together, this system will efficiently accelerate electrons to the energies needed for X-ray production.

To make X-rays, the beam from the electron accelerator is directed onto a target made of tantalum, tungsten or another heavy element. The material quickly slows down the electrons, and the particles emit X-rays in response, a process known as Bremsstrahlung radiation. The energy of the resulting X-rays is equal to the energy lost by the electrons as they slow down.

Application beyond physics

To advance the use of electron beam accelerators for medical device sterilization, Fermilab hosts an annual medical device sterilization workshop. The fifth such workshop, held Sept. 20-21, 2023 at Fermilab, brought together more than 200 stakeholders, in person and online. Participants came from Brazil, Canada, Germany and across the United States. They included representatives from major contract medical device sterilization companies, accelerator manufacturers, medical device manufacturers, academia, industrial regulators and federal regulators.

“This workshop brings together multiple stakeholder groups; stakeholders who do not often have the opportunity to meet and discuss cross-cutting issues in a pre-competitive environment. Similarly, it gives FDA an opportunity to engage and share information with these stakeholders in a manner that we don’t really get otherwise,” said Ryan Ortega, a regulator from the U.S. Food and Drug Administration who spoke at the event.

“Participation in the workshop has been a very beneficial and positive experience for me and my FDA colleagues. We get a significant amount of actionable information and stakeholder engagement from the workshop every year,” said Ortega.

By enabling this multidisciplinary discourse, the workshop organizers aim to facilitate the switch from ethylene oxide and gamma ray-producing cobalt-60 to accelerator-based technology and lay the groundwork for commercializing this technology.

“We want to leverage Fermilab’s expertise and the power of electron beam technology to spur economic growth, foster community development, meet national security needs and create an environment of innovation,” said Fermilab’s William Pellico, director of the Illinois Accelerator Research Center. “The scientists at Fermilab who work on this emerging accelerator technology are encouraged by the NNSA support and commitment to this endeavor.”

The road to commercialization

While the technical team focuses on getting the prototype electron beam accelerator up and running, another component of the recent NNSA grant is to look at commercialization avenues.

One of the commercialization hurdles that must be overcome is the ability for small- and medium-sized companies to do accelerator-based sterilization in house. Companies are looking for cost-effective accelerator options that are sized to meet their needs.

A team of scientists and engineers at Fermilab is building a compact prototype accelerator that can propel electrons to the energy of 1.6 million electron volts and has beam power output of 20 kilowatts. The prototype will enable them to validate the integration of the various technologies they are bringing together. It also is a step toward smaller sterilization applications. The final goal is an accelerator with 7.5 MeV beam energy and 200 kW beam power, which would be a valid alternative to large cobalt-60 facilities.

“The prototype is not the final goal, but there are companies that are interested in building this kind of accelerator for small, compact, end-of-line-type use cases such as blood kit sterilization,” said Kroc. “While we’re trying to facilitate specific requests, this development also serves the industry as a whole.”

Kroc also pointed out that these accelerator-beam radiation sterilization applications are not limited to medical equipment. Representatives from the bioprocess industry, which makes single-use systems for manufactures of vaccines and pharmaceuticals, participated in the Medical Device Sterilization Workshop. They are users of gamma-ray sterilization who are looking to transition to X-rays.

Once the 1.6-MeV prototype is built and tested, Kroc expects to hold a workshop specifically for companies and industries that have the potential of being commercialization partners. “We’ll present our progress and results and get feedback on whether we’re meeting their demand, what adjustments we might have to make, and then try to stimulate further interest,” said Kroc.

The Illinois Accelerator Research Center, also known as IARC, was established with support from the State of Illinois to industrialize Fermilab’s technologies and, together with other partners, to advance the next generation of technologies, products and applications to assist U.S. industry and support the U.S. Department of Energy’s science mission.

Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

New media artist Agnes Chavez will bring her creative approach to integrating art, science and technology to the U.S. Department of Energy’s Fermi National Accelerator Laboratory. She has been named 2024 guest artist by the Fermi Research Alliance.

Based out of Taos, New Mexico, Chavez will focus on particles called neutrinos during her tenure, creating an extended reality experience that will stand alone as well as travel with her existing immersive mixed reality art installation called Space Messengers.

Launched at the Festival Internacional de Ciência in Oeiras, Portugal, in 2021, Space Messengers connects New Mexico students ages 14-25 with students around the world through an international ambassador program. Students from Portugal, Mexico, Austria and Ireland have participated so far. Other activities include space-themed curriculum lessons and an international youth exchange program. A focal point of the display is a message board where students write about science they learned as well as their hopes for a sustainable interplanetary future, a topic especially important to Chavez.

“My work integrates art, science and technology as tools to inspire artistic, scientific and humanistic literacy, and to raise awareness of humanitarian and ecological issues,” she explained in her guest artist proposal. Chavez especially noted the opportunity she will have to further develop extended reality education techniques. Extended reality encompasses augmented reality, virtual reality, and mixed reality, where digital and physical elements can interact.

“My goal is to discover new ways to use augmented technologies to communicate the importance and relevance of neutrino astronomy, and science in general. I believe that it is essential for citizens to understand the value of artistic and scientific research to become more informed interplanetary citizens.”

Chavez is founder and director of the non-profit STEMarts Lab. With this program, she and her team design and deliver sci-art installations to schools, science organizations and festivals for STEAM education. In 2017, Chavez was commissioned to co-design a permanent art installation called Fluidic Data at the data center of the European laboratory CERN. The STEMarts Lab has also developed STEAM programs for CERN’s ATLAS experiment and for the Department of Energy’s Los Alamos National Laboratory. Most recently, Chavez’s lab was invited to participate in the Ars Electronica Festival, held September 6-10, 2023, in Linz, Austria.

“Agnes Chavez’s work epitomizes a harmonious blend of human inspiration, technology and outreach,” said Visual Arts Coordinator Georgia Schwender, who manages the FRA guest artist program at Fermilab on behalf of FRA. “Her impactful creations are poised to inspire a diverse audience, fostering a deeper comprehension of the groundbreaking research conducted at Fermilab.”

Editor’s note: Work created by former FRA guest composers and artists are featured in the public exhibition Beyond the Visible at the Schingoethe Center of Aurora University Jan. 29 – May 10, 2024. The exhibition will highlight Fermilab-inspired work by Mare Hirsch, David Ibbett, Jim Jenkins, Chris Klapper & Patrick Gallagher, Ricardo Mondragon, Ellen Sandor and Roger Zare.

The FRA guest artist program at Fermilab is funded by the Fermi Research Alliance, which manages Fermilab for the U.S. Department of Energy’s Office of Science. Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

The Short-Baseline Near Detector collaboration is preparing for an exciting year at the U.S. Department of Energy’s Fermi National Accelerator Laboratory. After nearly a decade of planning, prototyping and construction, the team is in the final stretch of commissioning of their detector.

In January, engineers began introducing gaseous argon into SBND to push air out of the cryostat. Now that the detector is mostly free of impurities, the team has begun filling it with liquid argon.

“We’re all excited to get to this point. It’s one of the last steps before we see our first particle tracks,” said Roberto Acciarri, the detector assembly and installation co-coordinator for SBND.

SBND is one of two detectors that will collect data in the coming years as part of the Short-Baseline Neutrino Program at Fermilab. Scientists will use SBND and ICARUS to examine the collisions of neutrinos with atoms and search for a new type of neutrino known as a sterile neutrino. A third detector, called MicroBooNE, finished recording particle collisions with the same neutrino beamline in 2021.

“Prior experiments showed hints of a fourth type of neutrino, which is not in line with the Standard Model,” said Peter Wilson, deputy head of the Fermilab Neutrino Division. “The SBN program is aimed at definitively determining whether or not the sterile neutrino exists.”

Projecting neutrinos

SBND is a liquid-argon time projection chamber, or LArTPC. Time projection chambers have been used to record particle tracks since their invention in the 1980s.

“You can think of a TPC like a 3D digital camera,” said Acciarri. Where a 3D camera captures multiple pictures to create a 3D image, the TPC captures all the electrons produced in the wake of a neutrino interaction “to reconstruct, in 3D, the trajectory and energy of a particle.”

On one end of the SBND TPC lie three staggered sets of wires on three different planes. A high voltage field inside the detector gives the wires a positive charge. That positive charge attracts the electrons created when a neutrino hits an atom and produces other particles inside the SBND detector.

“Since the detector has an electric field, the electrons will drift towards the array of wires and create a signal on each plane of wires,” said Ornella Palamara, co-spokesperson for SBND. Researchers then combine the three signals and the arrival times of the electrons to create a 3D projection of where the interaction took place in the detector.

Put together, the signals enable the scientists to recreate the paths of the emerging particles and determine the location of the neutrino collision. Based on the strength of the signal, researchers also know how energetic each of the emerging particles was.

However, the size of that signal is very small; it could easily be drowned out by electronics noise both from inside and outside of the detector. SBND scientists are using a relatively new method to reduce that noise.

In early iterations of TPCs, the electronics that identifies and amplifies the signals was located outside of the detector and connected to the wire planes via long, noise-introducing cables. “By moving the electronics inside, you can eliminate those wires and hence that noise,” said Wilson. “The challenge, of course, is designing electronics that can function at liquid-argon temperatures.”

Scientists at Brookhaven National Laboratory have developed so-called cold electronics for LArTPCs and designed the electronics that will be used in SBND to readout the interaction signal. Researchers also successfully deployed this same electronics setup in one of the prototype detectors for the Deep Underground Neutrino Experiment.

The future of neutrino physics

Beyond searching for sterile neutrinos and other unexpected neutrino behavior, SBND also serves as a state-of-the-art training ground for the Fermilab-hosted Deep Underground Neutrino Experiment. Like the Short-Baseline Neutrino Program, DUNE will consist of both a near and far detector, just on a much larger scale.

“The drift technology used in SBND is the same as what will be used in DUNE,” said Palamara. “Young researchers will learn the technology now on SBND and will be then capable to guide the show in the future.”

Once the SBND collaboration has finished filling the cryostat, the team will turn on pumps to circulate the liquid to filter the argon. This will ensure the system remains free of impurities that would prevent electrons from drifting to the sets of charged wires.

“When we start up, that filtering process will be making the argon more and more pure,” said Wilson. “Within a couple of weeks of that, we’ll be in a state where we can turn on the high voltage of the detector and see if everything works.”

Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.