That was the question ISIS industrial placement student Ella Beck had just twelve months to answer when she started work with the Neutronics team at ISIS. The Target Operations team at ISIS had video footage from within the monolith, from which Ella hoped to estimate relative levels of gamma radiation by counting the brighter damaged pixels that appeared.
It might seem like a fairly simple problem; could Ella write software to count the number of bright pixels? It had been done before elsewhere, but often with footage that had a plain black background. The challenge facing Ella was that her footage was moving, with a shifting, coloured background, and full of reflections and other details.
“This project was something I could never do at university," says Ella. “We wouldn't have the footage, access to the computing cluster, or see the monolith first hand."
Inside the void vessel
At the heart of each of ISIS' two target stations stands the monolith. Within, through layers of concrete and steel shielding several meters thick, is the void vessel. The void vessel contains the target – a small cylindrical block made of tungsten and clad in tantalum. Bombarding the target with protons from the ISIS synchrotron generates neutrons, which are then channelled towards the instruments used for the ground-breaking research carried out at the facility. However, the stream of protons striking the target also generates a lot of radiation, so the entire void vessel is dangerously radioactive.
Periodic inspection using a remote-controlled robot equipped with a camera lets ISIS engineers monitor the condition of welds and looking for other signs of damage. That video footage is the only way to see inside. Understanding radiation levels inside the void vessel isn't essential to the day-to-day operation of ISIS, but it will be important information when ISIS is decommissioned.
Counting pixels
The Target Operations team had collected video footage from a maintenance inspection inside the monolith in target station one using a remote-controlled robot with a camera.
The footage appears grainy, full of bright static that partially obscures the images of the void vessel components as the camera moves around. The amount of static in the footage varies as the remote camera moves through the monolith. Some areas show very few bright dots, while others are blanketed in a static snowstorm. It was that variation that Ella and the team were interested in.
Each dot of static is a single bright pixel caused by a gamma ray striking the camera sensor and causing the pixel to brighten for a single video frame; the more bright dots, the more gamma radiation in that area. Counting all the bright pixels manually, frame by frame, would be unfeasible, but it is the sort of problem that theoretically could be automated.
A frame from the video footage showing the bright pixels as well as reflections and other details
Relative radiation levels
“It was quite satisfying to overcome those challenges and find a solution," says Ella. “We gleaned a lot of information we didn't even know was possible."
The code Ella developed can pick out the damaged bright pixels from the moving, colour video footage and provide an estimate of relative gamma radiation levels. It does so by comparing each pixel to its neighbours, and to itself in adjacent frames of the video. The code could filter out reflections, and was able to adapt to changes in brightness as well as movement in the footage.
Importantly, the code isn't specific to the ISIS video. “We can apply the code to any video with damaged pixels, for example footage from the Fukushima disaster in Japan," says Ella. It could provide a useful tool for surveying hazardous environments although, as gamma radiation is only a single type of radiation, the technique has its limitations.
The project is also an important first step. Future placement students will be able to calibrate the footage using known radiation sources to provide a measure of the absolute radiation levels in the void vessel.
A personal interest
For Ella, the project provided a unique insight into the workings of a large research facility like ISIS, and allowed her to follow her interests.
“I've always been interested in radiation monitoring," Ella explains. “But I had no idea what I would be doing on my placement. For placements at ISIS you can tailor it to your personal interests. Because I like dosimetry, that's where I took it!"
The placement may also help shape Ella's future career. “Working at ISIS definitely made a career in research feel more accessible," she adds.
