1. HRIBF Update and Near-Term Schedule
(J. R. Beene)
There is much to celebrate concerning recent accomplishments at HRIBF. Researchers have produced exciting new scientific results, and the facility has produced important beams at record intensity. There is also ample cause for concern. Once again we face funding uncertainty in fiscal 2009, and we face uncertainty associated with recovery from an "operational emergency" which was declared on the morning of July 28, 2008. While this event did not occur during the period normally covered by this newsletter (the six months from January 1 to June 30), it is so important to the near-term future of the facility that it is impossible to ignore it here. I will therefore include a brief summary of the event and what we know of its impact on operations at the end of this article.
We are coming off a record year in FY2007 in terms of hours of radioactive ion beam delivered to experiments. Furthermore, the facility achieved a major milestone as the astrophysics group completed a direct measurement of the 17F (p,γ) 18Ne capture reaction, using the DRS to detect the 18Ne. This achievement adds another important result to the study of reactions that create and destroy 18F in stellar explosions. The experiment was made possible by an improvement of a factor of 50 in the intensity of the 17F beam over our previous facility record. Another important milestone was achieved by the decay spectroscopy group who capped a truly remarkable year of scientific results with the completion and first use of the new Low Energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS). We have also made excellent progress toward the completion of the IRIS2 project, though delays in funding have resulted in postponement of the completion date (see IRIS2 article).
In the six month period ending June 30, HRIBF provided 1667 hours of beam on target for research, including 795 hours of ISOL RIB (including 131 hours of low-energy RIB), 180 hours of "in flight RIBs" (stable beam for experiments using the RMS to select and propagate beams of radioactive species for implantation decay studies at the focal plane of the RMS), and 294 hours of stable beam in direct support of RIB measurements (setup tests, calibrations, etc.). A total of 399 hours were devoted to stand-alone stable-beam experiments.
In the January Newsletter, I discussed the expected impact of the FY2008 continuing resolution (CR), which included up to two months budgetary shutdown of the facility. Such a shutdown was planned for August 4, 2008. The budget situation for FY2009 is again troubling. A likely scenario is a six month CR (i.e. operation at FY2008 budget levels), followed by six months at the levels of whatever FY2009 budget is enacted. We have also been instructed to develop plans for a twelve month CR. Either case would require substantial reductions in facility operations.
Now I turn to a discussion of the event that has introduced great uncertainty into our near term schedule. At approximately 8 AM on Monday, July 28, during operations with approximately 12 μA of 50-MeV protons on a uranium carbide target, delivering neutron-rich 81Zn beam to the new LeRIBSS facility, a radiological control technician (RCT) reported higher than normal radiation levels just outside the shield door to the IRIS1 vault (the room in which RIBs are produced at HRIBF). The measured dose rate equivalent was 4 mrem/hr. The presence of radiological contamination on the floor just outside the shield door was subsequently noted, as was the possible presence of airborne radioactivity. These observations were reported to facility management. Accelerators were shut down immediately and the building evacuated. The event was subsequently declared a laboratory operational emergency. Parts of the building were cleaned for reentry to collect belongings on Monday afternoon. The entire building was cleared for reoccupation on Tuesday morning after a detailed radiological survey found no contamination outside the shielded vaults. No decontamination was required.
A "recovery team" was constituted by the laboratory consisting of HRIBF staff members supplemented by a few other ORNL staff members with relevant expertise. ORNL management also commissioned an investigative team who are charged with determining causes of the event and another team to develop corrective action. The function of the recovery team is to carry out a systematic collection of information under direction of the investigative team, and subsequently, to implement corrective actions and prepare for resumption of facility operations. The investigative team will report their findings in early October. Though the recovery team is convinced that the physical basis of the event is now understood, it would be inappropriate to discuss causes in any detail prior to the investigation team report. It is appropriate, however, to catalog a few facts about the event.
The first and most important fact is that no individual received any detectable radiological dose as a result of the event. Six individuals were sent for whole body counts on the morning of the event; all were negative. All seventy-one individuals who had been inside the HRIBF building (Building 6000) during the day of the evacuation and three days prior to it had their thermo luminescent dosimeters (TLDs) collected and read the morning of the event. Readings were all consistent with zero doses. All subsequent analysis is consistent with a release that consisted entirely of noble gasses (Xe and Kr isotopes). One of the several samples collected after the event contained some 131I (all others exhibited only Xe and Kr daughters). If we accept this single iodine sample, the suppression of iodine compared to its total inventory at the time of the event compared to that of Xe isotopes is on the order of a factor of 107. Four high-volume charcoal filter air samples were taken soon after the event to search for 131I. The largest air concentration measured was on the order of 10-12 μCi/ml (i.e., background). At this time, only the RIB production vault (C111S) remains classified as a contamination area (as it was before this event). The only measurable contamination present that is attributable to this event is low levels of 137Cs (from 137Xe) and 140Ba and 140La (from 140Xe). As noted earlier, it is inappropriate to discuss causes in any detail at this point. We believe we have identified two unrelated failures, one associated with the HVAC system and the other with the roughing system exhaust which accounts for both the escape of noble gasses into the IRIS1 vault and their migration outside the vault.
It is very difficult to guess when we will be able to resume
radioactive beam operation. The barriers to operation are not
technical. The plan to begin operation on batch mode beams may help
us start a little sooner, but we may well be down through November, or
perhaps even longer. We have recently been given permission to
resume operation of the HRIBF tandem for stable beams. When we are
given permission to resume radioactive beam operations, we will
begin with a two-month campaign of "batch mode" operations with
beams of 10Be and 26Al. This
will be followed by an extended period
of operation with neutron-rich radioactive beams that will probably
fill the remainder of our FY2009 operating time.