This project run by Canadian Nuclear Laboratories (CNL) dates back to 2017, when the National Research Universal (NRU) reactor was still in operation at the Chalk River Laboratories, and neutrons were still being harvested for research by the Canadian Neutron Beam Centre (CNBC). Using those reactor beams, CNL scientists worked in collaboration with McGill University to expose blood samples to low-dose, thermal neutrons. Today, while the level of radiation has changed, as has the reactor and some of the research team, the goal of the project remains the same, which is to better understand whether this type of radiation exposure has an impact on cancer rates.
Recently, CNL published an article in Radiation Physics and Chemistry that details their most recent work in this field of research, which enabled CNL to study the impacts of fast neutrons on blood samples that are being irradiated in the ZED-2 reactor at the Chalk River Laboratories.
According to CNL’s Luke Yaraskavitch, a reactor physicist in ZED-2 who worked on the experiments, CNL researchers in the Radiobiology and Health group contacted his team to determine if there were opportunities to further evaluate the impacts of radiation on human blood.
In previous NRU reactor experiments, it was shown that low-energy neutrons are capable of generating DNA damage in human cells. This research contributed to our understanding of radiation-related cancer risks. With this new series of studies, the Radiobiology and Health team wants to go beyond the low-energy neutrons used in the previous NRU experiments and study more energetic neutrons, known as “fast neutrons.”
“Fast neutrons, as you would expect, move much more quickly than thermal neutrons, because they are more energetic,” commented Yaraskavitch. “Studying their impact on blood samples seemed like a very natural extension of the NRU reactor experiments, but it wasn’t without its challenges. Conducting this type of radiation exposure in ZED-2 would require a lot of creativity for the team, from loading and retrieving samples to simulations that made sure we understand the energy being deposited in the blood.”
With funding from Atomic Energy of Canada Limited’s Federal Nuclear Science and Technology (FNST) Work Plan, the CNL project team turned to the task of isolating the necessary fast neutrons for the experiment. Yaraskavitch explains that the ZED-2 facility, like the NRU reactor, is a thermal neutron reactor. However, the project team found new ways of using fast neutrons, produced during the fission process, before they get slowed down to thermal energies. This included shielding from other forms of radiation that are generated in the reactor, including thermal neutrons and conventional gamma radiation.
“A major part of our work was ensuring that the samples were exposed to as little gamma radiation and thermal neutrons as possible, since these forms of radiation have their own signature damage,” explained Yaraskavitch. “To prevent this, we put the samples in uranium metal annulus, which turns thermal neutrons into fast neutrons through the fission process. We also surrounded the samples with cadmium, which stops thermal neutrons, and lead, which limits gamma radiation. Together, these barriers ensured the samples were primarily exposed to the radiation we desired.”
Laura Paterson, an R&D Technical Officer in CNL’s Radiobiology and Health department, explains that, along with McGill University, they are interested in how this type of radiation exposure could contribute to cancer rates. According to Paterson, there are direct biological consequences associated with neutron irradiation, and they can vary depending on the type of neutron source. With some samples now in hand, Laura and her colleagues are turning their attention to the impact of these exposures.
“In post-irradiation, we allow the cells to incubate – known as cell culturing – where they can eventually be examined under the microscope,” comments Paterson. “At that point, we are looking for DNA double-strand breaks and mis-repairs. This occurs when there is a break in the DNA strand, and instead of reattaching itself at the breaking point, the broken DNA strand attaches itself to another broken piece of DNA strand, repairing itself incorrectly. We are most interested in mis-repairs that produce a dicentric chromosome. This is a very specific anomaly associated with radiation damage that has been theorized to lead to certain forms of cancer. If we can determine an association between neutron exposure and this type of DNA damage, it could shed light on the risks associated with this radiation exposure.”
In the end, the hope is that this research can inform Canadian and international radiation protection standards, while better protecting nuclear workers, medical patients and many others. But for now, there’s plenty of work left to be done to calculate doses, culture cells and, of course, conduct analysis at the microscope. It’s all in a day’s work for CNL researchers working to broaden our understanding of radiation, health and biology.
This research is funded by Atomic Energy of Canada Limited’s (AECL) Federal Nuclear Science & Technology (FNST) Work Plan, which connects federal organizations, departments, and agencies to the nuclear science expertise and facilities we have at Chalk River Laboratories.
Under the FNST Work Plan, researchers at Canadian Nuclear Laboratories (CNL) carry out projects to support the Canadian government’s core responsibilities and priorities across the areas of health, safety and security, energy, and the environment.
