A few weeks ago, I wrote a C&EN Science Concentrate about a new californium complex with covalent bonds to its ligands rather than the ionic interactions traditionally expected for actinides. The work was led by Thomas E. Albrecht-Schmitt, a chemistry professor at Florida State University. His lab at FSU works with thorium, protactinium, uranium, neptunium, plutonium, americium, curium, californium, and-soon, for the first time--berkelium. His lab works with those elements safely by investing in protective equipment and meticulously planning experiments.
Most of the actinides in Albrecht-Schmitt's lab only present a concern if people inhale or ingest them, he says. It's when they get to americium that they have to start thinking about radiation exposure. For americium, the concern is gamma emissions; for curium it's spontaneous fission to release a neutron.
And for californium, the only isotope available in experimental quantity is 249Cf, which releases high-energy gamma radiation. "To shield to background levels we need 2 inches of lead," Albrecht-Schmitt says.
Safety in his lab starts with shoes. "The most common way in which radioactive material leaves a lab is when someone unknowingly steps in a contaminated area and walks out," Albrecht-Schmitt says. National labs tackle the problem by using foot covers, but his group members have dedicated lab shoes that they change into when they walk in and leave behind when they walk out.
His lab also has glove boxes dedicated to transuranium chemistry. Unlike standard glove boxes, which run at positive pressure to protect the box contents from air, Albrecht-Schmitt's has some that under negative pressure-sucking air in to prevent the spread of particulate matter. "The exhaust from the pumps and boxes is routed through a very sophisticated filter system," Albrecht-Schmitt says.
When doing lab work, Albrecht-Schmitt and his group members wear double gloves. They also use masking tape to tape the inner glove to their lab coats. That way they never have exposed skin, and if someone thinks their hands have been contaminated, they can remove the outer glove and still be protected. Working in a glove box adds a third layer to the hands.
The lab has several radiation counters, including general ones to detect any kind of radiation and specific ones to check for alpha, beta, and gamma emissions. There's also a special hand and foot monitor that people step on for a scan before leaving the lab. Lab coats get checked and replaced as needed. "Students who do low-level work may replace theirs once a year, but routine work with short-lived isotopes may mean replacing them 3-4 times a year," Albrecht-Schmitt says. Used coats go into radioactive waste.
And then there are the inspections. "Because people can be irrational about radiation, I would say a critical thing is that you have an unbiased radiation safety office that inspects your facility unannounced at least once a week," Albrecht-Schmitt says. He works with FSU's office to notify them in advance if his lab is doing "anything vaguely significant," he says, so that the office can send someone to supervise during or inspect after experiments, he says.
For the californium work in particular, the experiments were carefully choreographed in advance. "We went through and thought about each stage: =E2=80=98Where am I going to be and how am I going to shield myself?'" Albrecht-Schmitt says. "We had many different lead bricks cut by our machine shop into special configurations," such as one to hold a teflon liner containing californium while they loaded other reactants into it. They ran practice experiments with a stopwatch, to figure out how to minimize time spent on each procedure.
They also increased their PPE. "We put on full-length lead vests that go from the neck to past the knees," Albrecht-Schmitt says. "They weigh about 40 lbs. After a day of californium work, you're pretty tired."
To protect their hands, they work quickly. Albrecht-Schmitt and his group members wear dosimeters on their chests and on their hands. Albrecht-Schmitt wears his on his left hand, which is the one that he typically uses to hold bulk samples while manipulating tools with his right hand.
For experiments involving radioactive elements, Albrecht-Schmitt routinely handles the bulk material and then passes off smaller amounts to his students. Or, in his words, "I do stock and they get to do the exciting stuff." His extremities get a few hundred millirem/year of radiation, compared to a safety threshold of 50,000 mrem/year. His group members come out with no more than background-level exposure.
Some of his students, he notes, don't get to work with the more dangerous elements. "When a new graduate student comes in, they do nonradiation work," he says. "We watch how they perform. Students that demonstrate that they are careful and have a lot of forethought-'Where do I need to be at each stage and where do I need to be before I go home?'-will graduate from uranium to neptunium and then move up." Students that don't demonstrate that commitment stick with less hazardous chemistry-or Albrecht-Schmitt might dismiss them from the group entirely, as he's done with five graduate students in the last six years. He emphasizes that simple mistakes or unanticipated events are learning experiences and won't get someone in trouble. "What does get people in trouble is if they're showing disregard for safety."