INTERNATIONAL ACCELERATOR RADIOLOGICAL PROTECTION (IARPE) NEWSLETTER MARCH 1992 FROM THE EDITOR'S TERMINAL (Nisy Ipe ) ========================================================================= March, the end of winter, the onset of spring, a time for new beginnings! And so, spring ushers in a new feature for the newsletter. We are pleased to introduce our very first feature article (on the SSC) by Jeff Bull. Once again, I am deeply indebted to each of our correspondents wihout whom this newsletter would cease to be a reality. Those of you who wish to contribute news/articles (horizontal length <70 characters) to the newsletter, but do not have a correspondent at your facility, can send the information directly to me by E-Mail. I am soliciting feature articles (maximum length = 3 pages, minimum length = 1 page, horizontal length <70 characters) for the newsletter. You may send the article directly to me by E-Mail, or send it through your correspondent. Please feel free to circulate or post the newsletter on your bulletin boards. This may be of benefit to those who do not have E-Mail addresses. NEWS FROM BROOKHAVEN (Carl Schopfer ) ========================================================================= The Environmental Assessment of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (DOE/EA #0508, December 1991) has been released. The 31 page report describes the land use and demography, ecology, geology and seismology, archaeology and hydrology at the site. The baseline radiological characteristics are discussed. Potential environmental effects are described, including direct impacts to the site, effects from operation, waste generation and management, soil activation and groundwater effects, and airborne radioactivity. Shielding is expected to reduce the RHIC's average contribution to the dose rate, outside the RHIC areas of transient occupancy, to less than 0.5 mrem/hr. Annually, dose received at the Collider Center building is expected to be no more than 8.0 mrem/yr. The maximum onsite dose from direct radiation would be 36 mrem/hr on the berm near the beam dump, based on a maximum RHIC energy of 100 GeV/amu, with the equivalent of 8.6E14 Au ions accelerated per year. On February 28, silicon ions were accelerated for the first time in the Booster from 4 MeV per nucleon to about 20 MeV. Using harmonic switching and bunch coalescing, work is now going on to accelerate silicon to the top energy of 900 MeV/nucleon. The Booster is a pre- accelerator for both protons and heavy ions and is designed to increase the intensity of the AGS's proton and polarized proton beams, and allow th AGS to accelerate beams of heavy ions up to Au. This spring it is expected that Booster operations will be integrated into AGS operations for the physics program. From a 3/6/92 Brookhaven Bulletin Article by M. Belford. NEWS FROM CERN (Alberto Fasso' ) ========================================================================= The winter shutdown has come to an end. Dismantling work in the neutrino cave has been completed, but there is still a lot of work to be done to cut and condition the most radioactive pieces for disposal. All the accelerators have been closed and interlocks tested. The first test with beams have been started at the upstream end of the PS-SPS-LEP accelerator chain and are being progressively extended to all machines. Physics is scheduled to begin officially at the beginning of April. It will include 46+46 GeV electron-positron colliding beams in LEP, 200 GeV sulphur ions in SPS and low-energy antiprotons in LEAR. The PS, as usual, will handle all these particles at the same time. The SC, the old 600 MeV synchrocyclotron ended its glorious career at the end of 1990, but physics with ISOLDE will start soon again with new vigour. ISOLDE is an Isotope Accelerator On Line which has been fed by the SC beam for several years: it has now been moved to a new building and it will soon resume operation with a 1 GeV proton beam extracted from the PS Booster. A new radiation monitoring system has been installed and connected to the ARCON data-logging system. A meeting was held from 5-8 March in Evian-les-Bains, a holiday resort on the French side of the Lake of Geneva, 50 km from CERN, to discuss possible experiments on CERN's new accelerator project, the Large Hadron Collider (LHC). More than 600 physicists from nearly 30 countries examined four proposed experiments, two of which will be possibly selected. LHC is a proton-proton collider at about 8+8 TeV, to be installed in the same underground tunnel presently used by LEP. Its high energy and luminosity will present several interesting problems of radiation physics and radiation resistance of materials. The Annual Report of the Radiation Protection Group is close to completion. It describes the activities of the Group in 1991 and gives statistics of personnel and environmental doses. Copies of it are sent every year to the Authorities of CERN's host States, France and Switzerland. NEWS FROM CEBAF (Robert May ) ========================================================================= Construction of the Continuous Electron Beam Accelerator Facility is 65% complete and on track for accelerator completion in the first quarter of 1994 and first physics operations in the second quarter. The 45-MeV, 2 and one quarter cryomodule (containing 18 superconduct -ing cavities) injector, klystrons, and recirculation arc magnets have been received, successfully tested and installed. Three linac cryomodules had been installed in the 1400 meter circumference tunnel, and cryomodule production -- the accelerator's critical-path activity -- is accelerating. The 4800-watt helium refrigeration plant is in commissioning and supporting injector operations. Helium transfer line installation is over 2/3 complete. The personnel safety and accelerator control systems are operational for the injector and are being installed in the accelerator. A second round of experimental proposals has been presented to the Program Advisory Committee, and major experimental equipment procurements are advancing for all three end stations. Project civil construction is complete except for the end stations, where the underground portion is complete and the above-ground portion is one-quarter complete. Hall C spectrometer carriage component fabrication and deliveries are well advanced, with mechanical installation in process since mid-January. The end station refrigerator building will soon be occupied. Mechanical installation in Halls A and B will start in May. CEBAF has an opening for a Health Physicist in the Radiation Control Office. Duties will include dosimetry oversight, radioanalytical and environmental services, source control, safety system QA, hand- held and fixed instrumentation calibration and repair oversight. Duties also include participation in project documentation in the definition of and implementation of safety measures, shielding, barriers, and installed monitors and rendering advice on and gauging the effectiveness of radiation safety measures. Candidates are expected to have a BS degree in a scientific discipline with specialization in health physics or the equivalent combination of education, experience, and specific training; an advanced degree is desirable. Submit a resume and or application for position AR2121 to Employment Manager, SURA/CEBAF, 12000 Jefferson Ave., Newport News, Virginia, 23606. CEBAF is an equal opportunity employer. NEWS FROM LBL (Tony Greenhouse ) ======================================================================== The Advanced Light Source Accelerator at Lawrence Berkeley Laboratory recently achieved an important milestone when the booster ring accele- rated electrons to its rated energy (1.5 GeV) on February 11, 1992. The accelerator consists of three components: a 50 MeV linac, a 12 m radius "booster ring" 1.5 GeV synchrotron, and a 31 m radius storage ring (still under construction) which is expected to have a 12+ hour beam lifetime. Commissioning activities are continuing on the booster ring during swing shift so as not to interfere with on-going work on the storage ring. Completion is scheduled for June '92. A review is planned by DOE for May '92, and synchrotron radiation in the UV and soft x-ray regions will be available for users by April 1993 if construction and commissioning proceed on schedule. The LINAC and Booster shielding caves consist of monolithic reinforced concrete walls, and roof shielding is provided by removable concrete blocks. A ratchet wall design allows beam lines to carry synchrotron radiation tangentially away from insertion devices and bending magnets to experiment areas outside. Lead lined beam dumps have been provided for the LINAC and Booster ring, and lead sheeting will be added to the inside of the outer shielding ring wall when it is completed. Thus far the shielding has met or exceeded design expectations. The next milestone will be extraction of the full-energy beam from the booster into the booster-to-storage (BTS) extraction line. This is scheduled for March, '92, and will provide a test of the shielding design for the beam dump and surrounding areas. The following are recent publications by LBL health physicists and colleagues: J. Liu, S. Mao, R. McCall (SLAC) and R. Donahue (LBL). "The Effect of Magnetic Fields on the Response of Radiation Survey Instruments", SLAC-PUB-5670, 10/91. M. James (Reed College), R. Donahue (LBL), R. Miller and W. Nelson (SLAC), "A New Target Design and Capture Strategy for High-Yield Positron Production in Electron Linear Colliders", NIM A307 (1991) 207-212. R. Donahue (LBL), W. Nelson (SLAC), "Alternative Positron Target Design for Electron-Positron Colliders", LBL-30724/UC-414, 4/91. NEWS FROM TEXAS (Wes Dunn ) ======================================================================== The CRCPD (Conference of [State] Radiation Control Program Directors) is currently in the process of reviewing the SSRCR (Suggested State Regulations for the Control of Radiation) section dealing with accelerators. Current areas being looked at include dosimetry, interlock systems, and self-shielded accelerators. If you have any suggestions to make, please refer them to me or Jon Sharp (Texas Bureau of Radiation Control - 512-834-6688) or Gwen Gallaway (Utah state program...Gwen is the Chair of the committee reviewing these regulations). ANNOUNCEMENTS ======================================================================== Accelerator Section Meeting (Wade Patterson ) ------------------------------------------------------------------------- The Section will meet in Columbus, Ohio, during the Annual HPS meeting, on Monday, June 22 1992, as follows: Officers and Directors. 4-5 PM Meeting room posted on-site General Membership. 5-6 PM Same meeting room as above We will be electing Officers for the coming year and discussing matters pertaining to the newsletter and our membership. We will also be discussing future activities in which we may wish to engage. Please let me know of any thoughts or ideas you may have about these,or any other items you would like to see on the agenda. In particular, if you wish to be considered for office, or, if you'd like to take on some task for the Section, please tell me. A complete agenda will be posted, in the newsletter, after we have heard from you. (H. Wade Patterson is the President of the Accelerator Section of the Health Physics Society.) ANS Topical Meeting, Pasco, Washington (Nisy Ipe ) ------------------------------------------------------------------------ If any of you IARPERS are planning to attend the ANS Topical Meeting ( New Horizons in Radiation Protection and Shielding ) in Pasco, Washington, from April 26 - May 1, 1992, and are interested in in an informal get-together, please let me know. In this way, I can put a face to the E-Mail address, and, it is a wonderful opportunity for you to give me some feedback on the newsletter (face to face)! For those of you who are wondering how one becomes an IARPER, if you have read the newsletter thus far, you are now an IARPER! (IARPER = International Accelerator Radiological Protection E-Mail Newsletter Reader) Accelerator Section (Jerry Miller) ------------------------------------------------------------------------- From the HPS Secretariat, paid membership in the HPS Accelerator Section, as of February 20, 1992, stands at 74. A review of the membership list indicates that there are a number of Health Physicists working at accelerator facilities who had not signed up for membership in the Accelerator Section during the 1992 Annual HPS membership renewal period. On a related subject, in keeping with the Accelerator Section's Executive Board's interest in establishing a liaison with the National Registry of Radiation Protection Technologists (NRRPT), our membership list was forwarded to Paul C. Lovendale, the current Board chair of the NRRPT. At their Board Meeting during the Montreal IRPA Congress, the NRRPT is expected to discuss selection of an individual who is both NRRPT registered and also an Accelerator Section Member. Selection of an Accelerator Section - NRRPT liaison individual should be finalized at the Section Meeting during the Annual HPS meeting in Columbus in June. (Jerry Miller is a member of the Board of Directors of the Accelerator Section.) QUESTIONS? QUESTIONS? QUESTIONS? ========================================================================= Ozone Monitoring (Nisy Ipe ) ------------------------------------------------------------------------- I would appreciate hearing from those of you who have had experience with ozone monitoring at accelerator facilities. What are the instruments that you would recommend, and what has been your operational experience (advantages, disadvantages, etc.) with them? ANSWERS! ANSWERS! ANSWERS! ========================================================================= The synchrotron radiation debate continues......... In Reply To Rindi (Rick Donahue ) ------------------------------------------------------------------------- We are dealing with this problem at LBL's Advanced Light Source (ALS). I completely agree that it is incredible to imagine the possibility of a beam travelling down a synchrotron beamline - once beam has been stored. This is due to the reasons mentioned by Nisy: slow time constants (on the order of seconds) for failed bend magnets, beam scraping, etc. But there is another scenario not yet mentioned which may be more important. This assumes that you are injecting beam into the storage ring and one of the bend magnets at the end of a straight section has failed in such a way that the other magnets in series are still operational. This could happen from the magnet inadvertently being short-circuited during a shutdown period. Therefore, the beam is injected into the storage ring and, instead of being given its kick at the site of the failed magnet, goes straight down the synchrotron beamline. The ALS has 7 meter straight sections. The beam waist is at its minimum (~100um) at the midpoint and has a divergence of about 0.1 mrad. Therefore, the beam could travel 10 meters (3.5 meters to the end of the section, 6.5 meters down a synchrotron line) and its size would stil l only be ~1mm. The synchrotron lines have diameters which are about two orders of magnitude larger, so there would be little scraping of the beamline. There are two beam-absorbing devices in the ALS synchrotron lines: photon shutters, and personnel safety shutters. Photon shutters consist of about 1.25 cm Cu and 1.25 cm SS and are designed to prevent synchrotron light from exiting the storage ring when access is required to any of the experimental setups outside the shield wall. They are located about 2 meters downstream of the storage ring exit flange. Personnel safety shutters are located downstream of the photon shutters and just inside the storage ring shield walls (the ratchet walls). They consist of thick tungsten plugs and are designed to reduce any 0 degree bremsstrahlung which might find its way down a synchrotron beamline. During injection, both are closed. In the above postulated scenario the beam would therefore hit the photon shutter. This results in two additional source terms: 1.) The 0 degree bremsstrahlung is created at the photon shutter, instead of the storage ring 2 meters upstream. This reduces the geometric attenuation of the brem. spike. It takes < 1 radiation length of material to create the forward brem. spike (see for example, Yung-Su Tsai, "Pair production and bremsstrahlung of charged leptons", Rev. Mod. Phy., Vol. 6, No. 4, October (1974) pg. 834). 2.) Neutron production from the forward-directed shower into the personnel safety shutter (high-energy and giant resonance) is increased. The first component can be reduced by taking this into account in the design thickness of the personnel safety shutter. The second component is a little trickier since the source is now just inside the shield wall. Bulk wall shielding is conservatively designed. Problem is streaming through the synchrotron beamline penetration, since access into the experimental setups may be allowed during injection. The injected current is much less than the fully stored current, but the ALS has plans of being able to completely fill the ring (with practice) in a few minutes, so it would be possible to "fill" the synchrotron line (up to the photon shutter) with the equivalent of the entire design current of 400 mA within a few minutes. Radiation monitors, if located properly, should stop the fill shortly, but this is a passive solution, not an active one. I have been promised by the head of accelerator operations that I will to be able to set up some of these scenarios with the synchrotron lines during the commissioning phase, which is scheduled to start late summer, early fall, and last at least 6 months. Contributions and ideas (and publications!) are welcome. In Reply To Donahue (Nisy Ipe ------------------------------------------------------------------------- At SSRL we have a moveable mask and two injection stoppers which are are interlocked such that you cannot inject a beam until stoppers are in. In this way even if an injected beam tries to travel down the synchrotron beamline, it will be intercepted by these stoppers, and one can design the stoppers for whatever accidental dose rate limits one wants. The moveable mask (0.75 to 1.5 inches of copper) is water cooled and protects downstream components from synchrotron radiation. The injection stoppers (17 inches of lead or 12 inches of tungsten) are downstream of the moveable mask, but in most cases inside the storage ring. In addition each synchrotron beamline hutch has two shutters, whose material and thickness varies depending on the beamline. These shutters are interlocked such that the shutters have to be in, before an experimenter can enter the experimental hutch. They protect the experimenter in the hutch from gas bremsstrahlung and/or synchrotron radiation depending on whether the beamlines are in the median plane or not. If one is concerned about part of the stored or injected beam being channeled down the synchrotron beamline, a permanent magnet can be added at the start of the synchrotron beamline so that the primary charged particle beam is is deflected down into some kind of a shielded absorber. Care must be taken to ensure that the permanent magnet is of sufficient strength to deflect the beam well below the opening in the ratchet wall. In Reply To Ipe, Donahue,Ban ------------------------------------------------------------------------- (Alessandro Rindi ) ------------------------------------------------------------------------- I want to thank Nisy Ipe, Rick Donahue and Syuichi Ban who expressed their opinions on the problem I raised in the February issue of this newsletter. I, also, received the copy of an interesting "conversation" between Nisy and Rick on that matter. I will try to comment. For those who are not familiar with Synchrotron Radiation (SR) facilities, a SR " beam line" may be seen as a kind of large opening in the vacuum chamber and in the shielding of an electron storage ring, located just before a bending magnet, in line with the straight section that precedes the magnet. The question I raised was: Shall we (health physicists) consider, during the radiation safety planning phases, the possibility that the stored beam (or part of it) can be channeled into the SR beam line because of a failure of the bending magnets or of the RF that keeps the stored beam at the given energy; or the channeling of the beam during the injection into the storage ring? What are the realistic scenarios, are such "accidents" possible, and if so what are the solutions? I think there is a consensus amongs the SR health physicists (and the accelerator physicists) that IT IS POSSIBLE that, during injection, part of the injected beam can be channeled into a beam line. We have to figure out precisely, together with the accelerator physicists, what kind of machine conditions allow for such an "accident" and determine the measures that will prevent it. In any case, one can always install suitable thick beam stoppers in the SR beam lines that are closed during injection, as described by Donahue (we have alreay installed beam stoppers for the gas bremsstrahlung); or fence out the experimental areas along the SR beam lines during injection. It is not easy but ...... it will make us safe. On the contrary, I understand there is no agreement among the health physicists and, in particular, among the health physicists and accelerator physicists that it it is impossible for the stored beam (or part of it) to be channeled into a SR beam line. I stress A PART of the stored beam because, even though just 1/1000 of the stored beam of a "third generation" SR facility is extracted, it can be very dangerous. I had "timeless" discussions with our accelerator physicists who opposed all my arguments (well summarised by Nisy). However, they were not able to completely convince me and provide me with a written demonstration of that "impossibility" that I could show to our government "tiger teams" that "watch over me" very closely. When I asked them "Will you sign a paper which establishes numerically the probability of such an event, so that I may balance the risk versus the cost?", they refused. In conclusion, I still fear that it is not unlikely that A PART of the stored beam can be transported down a beam line when some accidental failures of some storage ring components occur. However, I also think that it is now up to us health physicists to prove (or disprove) theoretically and experimentally that this event could take place. We have to work together to envision some experiments which can be performed at the existing facilities. Somebody should run one of the several computer programs that simulate the position of the beam in a storage ring (very familiar to accelerator physicists) and see what happens under extreme accidental situations. And one should sort out and put together the calculations already performed on these topics ( I know of something done at Saclay in France). Syuichi Ban's comment is very interesting. If the scraping of the electron beam on the wiggler aperture cannot be avoided, one is forced to an intervention on the interested beam line. However, this is a "local" problem. It would be very expensive to surround all the beam lines with some 20 cm of lead or more to cope with the problem of channeled electrons. A permanent magnet on the line may be cheaper (admitting it is feasible), we are trying to determine this. It may be interesting to organize a workshop for the interested people. However, one has to prepare the workshop beforehand such as to present results of experimental and theoretical work for discussion. I am looking forward to seeing some preliminary reports on the topic. NOTE: The editor wishes to apologize to Dr. Ban for inadvertently erasing his reply to Dr. Rindi (this was an eraso, not a typo!!). ======================================================================== FEATURE ARTICLE OF THE MONTH ======================================================================== RADIATION SHIELDING AT THE SUPERCONDUCTING SUPER COLLIDER by Jeff Bull ------------------------------------------------------------------------ The Superconducting Super Collider (SSC) is the most recent in a line of particle accelerators which accelerate subatomic particles to record energies. The SSC facility will consist of a series of five proton accelerators, culminating with the 20 TeV collider. The booster complex, consisting of a linac, two resistive magnet synchrotrons, and a superconducting magnet synchrotron, will provide 2 TeV proton beams for injection into the collider, as well as 200 GeV protons for a test beam facility. The collider itself will be a pair of superconducting magnet accelerators contained in an underground tunnel 87 km in circumference. The proton beams will be steered to interact at several experimental halls, which are also located underground. All of the injector accelerators, experimental halls, and test beam facilities will be located on two main campuses placed on the either side of the accelerator ring. The majority of the collider tunnel, however, will be constructed underneath farms and residences of Ellis County, Texas. Additional emphasis on radiation control must considered to allay the concerns of the residents living above the collider. RADIATION DESIGN CRITERIA Since the its beginnings, it has been the goal of the SSC to keep the dose equivalent at the site boundary to less than 0.1 mSv/yr from all radiation sources due to facility operations. Since several major roads cross the SSC campuses, access by the general public will not be restricted. In fact, the SSC intends to maximize public access on the site and plans to limit the number of radiologically restricted areas. Therefore, all open areas on site are being designed such that the annual dose equivalent is less than 0.2 mSv per year during normal operations, and less than 0.1 mSv due to a catastrophic accident. Wherever possible, the accelerator shielding is being designed such that outdoor areas, including berms, meet this criteria. In these guidelines, normal operating conditions as well as accidental rates are considered. Dose rates during normal operations are calculated from high, but not unexpected, beam losses in the accelerators. Estimates for this normal losses range from less than 1% for the SSC to 20% in some of the resistive magnet boosters. Beam accidents are occurrences which are not expected to happen at all, but which must still be considered due to the high doses which could occur. For warm magnet accelerators, such beam accidents are often defined as the full loss of beam anywhere in the machine for a significant amount of time, up to one hour for some transport lines. In the superconducting accelerators, accidents are limited to one machine pulse, since such a high intensity loss would severely damage the machine. HADRON AND MUON SHIELDING Although empirical formulas for hadron shielding exist, much of the shielding calculations are performed with Monte-Carlo computer programs which simulate the hadronic cascade and muon production induced by accelerator beams. Most of the shielding design at the SSC has been analyzed with CASIM[1], developed at Fermilab by A. Van Ginneken, and MARS[2], written by N. Mokhov of Serpukhov. These codes utilize weighted techniques in which each particle generated by the program is weighted to represent several particles as it is tracked though the problem geometry. In typical tunnel sections of the collider, the major source of radiation will be the interaction of the beam with the residual gas in the beam tube. This loss is estimated at 10E3 protons/(m sec), resulting in a dose at the tunnel wall of 1.5 Gy/yr.[3] Of greater importance to radiation protection is the beam accident scenario described earlier. Such a catastrophic loss has been modeled with CASIM. Using 4 x 10E14 protons per ring and rock with a density of 2.3 g/cm3, these calculations show that 6.7 m of rock shielding is sufficient to reduce the dose equivalent to 0.1 mSv. The dose equivalent falls off approximately one order of magnitude per meter of shield, a useful rule of thumb used for high energy accelerator shielding estimates. To comply with the site boundary requirements, the state of Texas has purchased for the SSC a strip of land underground 24.5 m thick for the sections of the collider not beneath SSC property. Within this stratified fee land, the 4.25 m diameter tunnel will be bored, with the additional restriction that at least 9 m of rock is maintained between the tunnel and the edge of the stratified fee. However, to reduce the possibility of a landowner digging a basement or other structure into this radiation zone, at least 13.75 m of cover will be maintained over the collider in areas where the land surface is not controlled by the SSC. The closest the collider does come to the surface is 13 m, at the bottom of a couple creek beds which cross over the ring. Muons produced from beam losses have an even greater impact on the land requirements. The easiest method to shield muons is to range them out. Since muons are produced in a highly directional forward cone, the distance they travel until the dose equivalent is reduced to a specific value (0.1 mSv for this discussion) is commonly called the muon vector. The lengths of these muon vectors for the collider have been estimated to determine the land acquisition requirements[4]. As an example, for the catastrophic accident described above, the muon vector length is 2 km. This vector, however, is tangent to the beam direction, and since the collider has such a large radius, the muon vector ends only a distance of 165 m away perpendicularly from the tunnel wall. The stratified fee area is 300 m wide, which includes the muon vector and allows some lateral adjustment of the accelerator within the stratified fee. The muon vectors are largest beyond the expected loss points. The longest of these muon vectors extends 5.1 km behind the collider backstops. The muon vectors caused by the beam collisions in the interaction regions are 4.2 km long, while the muons from the beam scrapers, which remove particles which have strayed from their normal orbit, travel 3.6 km. The High Energy Booster, which provides the 2 TeV injection beam into the collider, has a 2 km long muon vector for each of its beam absorbers. As in the collider tunnel, stratified fee land has been purchased beyond these loss points to contain all the muon vectors. To insure that the site boundary radiation limits are not exceeded, surface land has been bought at both the end and half-way along the lengths of the muon vectors for the installation of muon monitoring stations. DESIGN OF PENETRATIONS The access shafts for the collider have been studied using the MARS program[5]. Again, the beam loss scenario which determines the radiation shielding requirement is the catastrophic beam accident. The largest of these shafts is the magnet delivery shaft, sized to accommodate the 16.7 m long dipole magnets. These shafts will be located directly over the collider tunnel. In addition to a 2 m thick ledge preventing a direct view of the accelerator from the surface, the top of these shafts will be covered with a removable concrete shield. For the shortest magnet delivery shaft, 21 m deep, a concrete cover 3 m thick is required to reduce the dose equivalent above ground to 0.1 mSv per accident. Personnel and utility access to the collider will be provided by service areas spaced approximately every 4.3 km around the ring. There will be three basic types of shafts, a personnel shaft (6.5 m diameter) provided with an elevator and stairs, a large utility shaft (5.5 m diameter) which includes a 4.5 m diameter drop zone for cryogenic equipment, and a smaller utility shaft (4.5 m diameter) which is equipped with emergency stairs. The personnel and large utility shafts will be connected underground by a 25 m long hallway parallel to the collider. A 9 m connecting tunnel will provide access to the collider. This 3- legged labyrinth provides sufficient attenuation to reduce the dose equivalent at the surface to 0.1 mSv per accident. GROUNDWATER ACTIVATION AROUND THE BEAM ABSORBERS One major radiation source which has yet to be discussed is the beam absorbers. Since these absorbers are located more than 45 m below the surface, they will not be a radiation hazard above ground. However, they must be shielded to prevent a significant amount of groundwater activation. To first order, the rock through which the collider tunnel will be built displays excellent hydrogeological characteristics. The rock surrounding the tunnel has a low hydraulic conductivity, and an estimated water velocity of 3 mm per year[6]. The nearest aquifer is more than 180 m below the tunnel depth, allowing for a decay time of several thousand years before the radionuclides reach the aquifer. However, due to the settling of the rock formations over time, several rock discontinuities exist throughout the rock, providing the potential for quick transport of any radionuclides to the aquifer or to an individual's well. In consideration of the geology and the public's concern for drinking water contamination, the SSC is using a conservative model to determine the shielding requirements for groundwater activation, especially at known loss points. For the beam absorbers, enough shielding is to be provided such that the leachable activity produced in the soil, if diluted in 55,000 liters of water, will not exceed of the federal radionuclide concentration limits for community water systems. The volume of water is based on an individual pumping 150 liters a day from a well. A calculation was performed using CASIM to determine the groundwater activation produced around the beam absorber. A 10 m long, 2 m diameter carbon core, surrounded by Al jacket which extends 2 m beyond the end of the carbon was used as the core of the absorber. Steel shielding was added to the back and sides, making the whole absorber and shield 5 m x 5 m x 14.5 m long. A total of 1.1 x 10E16 stars are produced in the rock surrounding the absorber, assuming 2 x 10E17 protons per year (500 aborts) hit the absorber. Due to their long half lives and comparatively high leachability factors, the only nuclides which contribute significantly to the groundwater activation around accelerators are 3H and 22Na. Production factors of 0.075 atoms/star for 3H and 0.006 atoms/star for 22Na have been recently determined from irradiation of SSC rock[7]. Using a leachability factor of one for 3H and 1% for 22Na, and diluting this activity in 55,000 liters, the activity concentration is 270 mBq/ml for 3H and 10 mBq/ml for 22Na. Combined, these concentrations will result in a dose equivalent of 0.05 mSv/yr. This has been only a brief description of some of the issues at the SSC regarding radiation protection. Since the laboratory is still mostly in the design stage, modifications to the accelerator and its layout is still being performed in several areas which impact the shielding design. In addition, each of the booster accelerators provide their own unique shielding problems. There is still a lot of work to be completed before colliding beam experiments are scheduled to begin in 1999. References: 1. A. Van Ginneken, "Program to Simulate Transport of Hadronic Cascades in Bulk Matter," FN-272, Fermi National Accelerator Laboratory, 1975. 2. N. I. MOKHOV, "The MARS10 Code System: Inclusive Simulation of Hadronic and Electromagnetic Cascades and Muon Transport," FN-509, Fermi National Accelerator Laboratory, 1989. 3. D. E. Groom, "Radiation Effects at the SSC," SSC-SR-1035, Superconducting Super Collider Laboratory, 1988. 4. J. D. JACKSON, "SSC Environmental Radiation Shielding," SSC-SR-1026, Superconducting Super Collider Laboratory, 1987. 5. I. BAISHEV, et. al., "The SSC Access Shafts Calculational Study," SSCL-496, Superconducting Super Collider Laboratory, 1991. 6. Osburn, Mike, The Earth Technology Corporation. Memorandum to Mack Riddle and Jeff Bull, December 1990. 7. Baker, S., Internal Memo. (Jeff is a physicist working on shielding design and dose estimates in the Project Management Office at the SSC. Jeff's paper entitled "Radiation Shielding for the Superconducting Super Collider", to be presented at the ANS Topical Meeting, Pasco, is one of the five papers that have been nominated for an award. Jeff's E-Mail address is BULL@SSCVX1.) CLOSING THOUGHTS ========================================================================= " The wise man is one who knows the difference between good sound reasons and reasons that sound good." from PEARLS OF GREAT PRICE, Minneoplis: Wright-Mohr Enterprises,1989