Since our last report of December 2004, normal operations of the Fermi National Accelerator Lab (Fermilab) Tevatron Collider have resumed. This was done with surprising smoothness given the immense complexity of coordinating, after much invasive shutdown work, the resumption of the operations of the following: the antiproton production and collection machinery, the superconducting Tevatron, the two very sophisticated colliding beam experiments (Collider Detector at Fermilab [CDF] and DZero [D0]), the high-intensity MiniBooNE neutrino experiment, and the delivery of 120-GeV protons to our test beam area located in the meson experimental area formerly used for Tevatron fixed target experiments.
All of this went very well. However, at this point in time the most important new task is the commissioning and initial operation of the recently completed Neutinos at the Main Injector (NuMI) beamline to produce neutrinos for the Main Injector Neutrino Oscillation Search (MINOS). This new experiment involves the extraction of a high-intensity 120-GeV proton beam from the main injector and its transport downward to a target station where the protons end up being directed toward the Soudan Underground Laboratory in an old iron mine in Soudan, Minnesota.
As of this writing, this process is going quite well. Great care is being taken with the transport of the intense proton beam to the neutrino production target. Even losses of very small fractions of this beam can have significant radiological consequences. Thus, initial operations utilized very low beam intensities, followed by gradual increases toward the design intensity. With this approach, beam-loss problems were resolved with minimal impact as they were identified.
Otherwise, the initial operations of the new beamline are quite successful. The part of the MINOS detector located on the Fermilab site (the so-called "near" detector) detected neutrino interactions almost immediately upon commencement of low-intensity "test beam" proton targeting. The identification of the first neutrino events in the "far" detector at Soudan is anticipated soon, now that high-intensity operations have commenced.
The accomplishment of this success without the production of undue radioactivation is the result of a most extraordinary level of cooperation between experiment physicists, accelerator operations personnel, and radiation safety staff and technicians. As described in previous articles and in presentations at Health Physics Society (HPS) meetings, a great deal of work related to radiological safety has been applied to this project.
The NuMI facility was dedicated on March 4 in a ceremony attended by dignitaries including the director of the U.S. Department of Energy's (DOE's) Office of Science, Dr. Raymond Orbach; our local U.S. Representative, J. Dennis Hastert (who is also Speaker of the U.S. House of Representatives); and U.S. Representative James Oberstar, who represents the U.S. Congressional District that includes the Soudan mine. The event was announced in a press release.
It is surmised by many that Fermilab's future lies in the direction of more sensitive and sophisticated neutrino experiments. To accomplish this, much more intense proton beams are needed than can feasibly be delivered by the present chain-of-injector accelerators, some parts of which are well into their fourth decade of use without experiencing a major upgrade. In view of this, Fermilab, in collaboration with staff from other laboratories, is beginning a serious study of a new injector system that would replace the 400-MeV linac and the 8-GeV booster synchrotron with a new injector called the Proton Driver.
While numerous details are obviously unresolved and major decisions remain yet to be made at this early stage, present thoughts are centering around an 8-GeV superconducting linac. Work by members of the Accelerator Division and the Environment, Safety, and Health (ES&H) Section Radiation Physics Team staff on the assessment of the radiological issues posed by this new, high-intensity accelerator is underway. These issues will be challenging and it is appropriate that they be addressed early. Thus far, the work has been very enthusiastic and, somewhat surprisingly for a significant project at this early stage, an unusually good level of harmony is being achieved.
In our last report in December, we reported on some details of a number of radiological tasks performed during the major maintenance and development shutdown of calendar year (CY) 2004. We can now report on the total dose experience of that calendar year. Due to a great deal of work by all concerned, the total effective dose equivalent (TEDE) received by all personnel at Fermilab during CY 2004 was 21.18 person-rem, a decline from the 25.28 person-rem experienced in CY 2003.
During both years, "normal" accelerator operations, with occasional short periods of maintenance, occupied about nine months of the year while extensive and lengthy shutdowns occupied the remainder. During CY 2003, a large fraction of the shutdown work occurred in the Fermilab booster. Many of these tasks were directed toward the goal of reducing beam losses and their several undesired consequences of less beam available for the experiments, radiation damage to the booster components, and higher residual radioactivity levels and the associated doses to personnel.
Similar tasks were carried out during the shutdowns of CY 2004, but the reduced levels of exposures may be a direct result of the work done in CY 2003. During the past year there was much improved job planning, better scheduling of the "hotter" jobs later in the shutdown, and improved "staging" of assembly of parts outside of high-dose areas. These improvements certainly supported the objectives of keeping doses as low as reasonably achievable (ALARA). It should be stated that this success could not have been achieved without the enthusiastic support of these efforts by management at all levels, in the true spirit of integrated safety management.
Finally, we continue to follow a new figure of merit we have devised to monitor some aspects of our radiation protection program. This is the ratio of the TEDE to the number of protons accelerated to 8 GeV by the Fermilab booster. While acknowledging that there are limitations to its validity, like there are for nearly all such single parameter figures of merit, we continue to believe that this parameter is a reasonable one for us to track, at least at present, because the denominator includes all of the protons used in the Fermilab high-energy physics research program (in effect, the "product" of the laboratory's accelerator operations) while the numerator represents the "cost" of this product in terms of radiation exposure. In fact the intensive work performed in the booster during recent shutdowns to improve its performance has, at least for now, enhanced the value of this particular parameter. Figures 1 and 2 provide the results.
Figure 1 obviously reflects, rather dramatically, the advent of higher intensity operations of the booster in support of the MiniBooNe experiment, as well as other efforts to support improved Tevatron Collider operations, the Switchyard 120 program, etc. The doses received are obviously out of phase with the beam delivery, since by far the majority of the dose received is in the course of shutdown work; i.e., when the beam is actually off. Thus, in Fig. 1 the peaks in the doses received occur during the shutdown periods as expected.
Figure 2 shows the results of the normalization to the number of 8 GeV protons. In view of our present "custom" of having one or two large shutdowns each year, the four-quarter rolling average is undoubtedly a much better measure than are the individual quarter values as it smoothes out the phase shift between the periods of operations and work in the tunnels. (A long-term average would obviously have to be applied if one were to have a quarter of maintenance entirely devoid of 8 GeV protons, to avoid the obvious mathematical singularity!) We will continue to monitor this figure of merit for the foreseeable future. At present, we are encouraged by its continued downward trend.