The Jefferson Lab RadCon Group has recently had a flurry of activity (excuse the pun) at the lab. Recent experiments in Hall A again resulted in 7Be contamination of electronics in the hall that are powered and have forced air ventilation. As you might imagine, there are quite a few of these type of components. As usual, the technical and professional staff rallied to the cause and quickly controlled the potential spread of contamination by controlling access to the halls until the contamination areas could be identified and quantified.
This type of condition has happened previously in Hall C under similar conditions -- high current experiments run for a very long time. The Continuous Electron Beam Accelerator Facility (CEBAF) machine at the lab has a unique nature in that it is able to provide these high-current runs for a long period of time. Due to being superconducting, we can run 4 to 5 GeV at 100 or so microamps almost indefinitely. After several months of running, some of the more difficult to detect materials, such as 7Be, may be found in quantities that are unusual for other electron accelerators -- the fans in some of the electronics were reading on the order of 50,000 dpm per 100 cm2, though most of the contamination was on the order of about 5,000 dpm per 100 cm2, when it was detectable at all. (Here is the point where I brag about just how much the CEBAF produces for the physics world: we have delivered more polarized electrons to physics targets than all other machines, throughout all the world, throughout all time, combined. And we have done so only in the last five years!)
I have to credit our alert technologists with being able to find these lower levels at all . . . keep in mind that it is very difficult to see 7Be with a standard frisker, having only a 10.3% branching ratio and being a pure gamma emitter (E=477 keV). By some calculating (and measurements), the standard frisker level used for contamination detection (100 cpm) will be on the order of 30,000 dpm under ideal conditions. We routinely take contamination smears back to our radioanalytical laboratory to check for 7Be in the intrinsic germanium spectrometer. In this case, we set up a portable NaI detector in the field and set it up specifically for the detection of 7Be so that with a 3-minute count, we could tell on the spot whether or not a swipe was contaminated at the 1000 dpm per 100 cm2 level.
Another activity recently achieved was our second annual shipment of the very low-level radioactive materials that are now considered to be waste, in accordance with the year-old Department of Energy (DOE) order. This shipment was the culmination of a year's worth of effort in setting up a functioning program to identify, quantify, and move the waste. Last year's shipment was the first one ever and was more of a basic mission: get rid of it. We were pleased to have had the chance to set up a formal program this year so that future years may be easier to handle. Unfortunately, we also lost a very good term employee within a month of achieving this goal, so we'll have to see how well we can keep up in this area with a full-time equivalent position now gone.
The Spallation Neutron Source (SNS) work that Jefferson Lab is performing for the DOE has also kept the RadCon Group busy. The testing of the new superconducting cavities has provided us with unique new source terms and conditions that were, for the most part, expected. Nonetheless, the additional workload in dealing with a new source of radiation in addition to all of our previous work has been a source of, let's say, excitement.
We are also anticipating the startup of the newly improved Free Electron Laser (FEL) Facility here at the lab. It was previously the world's most powerful FEL machine but was providing infrared (IR) light only. It is now being configured to run up to ultraviolet (UV) frequencies; in fact, tunable anywhere between IR and UV. The maximum energy of the electrons in the machine was 50 MeV in the IR machine but will soon be 200 MeV. Fortunately, it is an energy-recovery machine, so the dumped electrons, which are the main source of our radiation concerns, are 10 MeV, as they were in the previous version of the machine. Energy recovery involves feeding the spent beam back into the radiofrequency (RF) cavities at 180 degrees out of phase, then using that energy to excite the in-phase electrons. This method produces much higher energy efficiency of the machine and much lower radiation levels from waste beam.
These are just a few of our activities here at Jefferson Lab, but I hope they have given you a flavor for some of the unique and interesting things going on here.