INTERNATIONAL ACCELERATOR RADIOLOGICAL PROTECTION E-MAIL (IARPE) NEWSLETTER "The Official Publication of the Accelerator Section of the Health Physics Society" (with Contributions from International Correspondents) ====================================================================== October/November 1993 Vol. 2, #7 ====================================================================== OFFICERS ====================================================================== President: Geoff Stapleton, SSC Past President: Ralph Thomas, LLNL President Elect: Nisy Ipe, SLAC Secretary: Bob May, CEBAF Treasurer (designate): Joe McDonald, PNL Directors (1 year): Paula Trinoskey, LLNL Gerry Fallon, MIT BATES Directors (2 year): Jerry Miller, LAMPF Carter Ficklen, CEBAF Directors (3 year): Steve Musolino, BNL De Vaughn Nelson >From the Editor (Lutz Moritz ) ====================================================================== The big news last month was of course the demise of the SSC. So immense was this project that a large fraction of the world accelerator community, including many of us, had at least some peripheral involvement in its planning. Whether the cancelling of the SSC heralds a fundamental change in US science policy or reflects the public perception that funding for basic research needs to be redirected towards research with more immediate 'practical' results, will emerge in the next few months. What effects this closure may have on science policy in countries other than the US is even more difficult to discern. For some thoughts on 'big' science one can re-read Freeman Dyson's essay 'Quick is Beautiful' in his book 'Infinite in all Directions', especially his. As you can see from the submissions of our correspondents, there are still many new smaller projects which are going forward with all speed. I would like to introduce Vashek Vylet, who has agreed to serve as assistant editor of the Newsletter. Vashek works with the Radiation Physics Department at SLAC and you will probably hear from him in the coming months as he tries to solicit your contributions. Some of you have experienced problems receiving the Newsletter. These problems may be related to the phasing out of BITnet if you subscribed from a BITnet node. If you are having problems you can communicate with the SLAC Listserver directly by sending commands or queries. Some of the most useful commands are: SUBscribe IARPE-L (Subscribe to the Newsletter) SIGNOFF IARPE-L (Remove your name from distribution list) QUERY IARPE-L (Query personal distribution options) SET IARPE-L (Set personal distribution options) HELP (Obtain list of most commonly used commands) INFO REFCARD (Obtain complete reference card) These commands must be sent to (not to me! and not to iarpe-l@slacvm!). To diagnose a problem send the QUERY IARPE-L command to the Listserver to see if you are in fact on the distribution list. You may have to SIGNOFF and then SUBSCRIBE from an INTERnet account to straighten things out. >From the President (Geoff Stapleton ) ====================================================================== This is an extremely hard letter to write because of course we are all totally preoccupied with the closure of the Superconducting Supercollider Laboratory (SSCL). The SSCL was the most exciting and forward looking of any accelerator project in history and its closure must therefore be viewed with very serious concern by all of us who work on accelerators. To add further flavor to this letter I am personally affected and my own involvement makes it extremely difficult for me to be objective about the affair. I do not believe that the present worries of my SSCL colleagues and myself are in any way unique in the overall ebb and flow of labor round the country but it is unusual to find a situation where so many people with such highly specialized knowledge and skills have all been thrown on to the job market. I do not judge it appropriate for me to debate the wisdom of funding the SSCL nor on the decision to place it in Texas, however, I can say that there must be serious concerns about any future project of comparable size, especially where there is a wish to obtain foreign contributions; any foreign contributor is going to want rather good guarantees of continuing support from the US congress. However, the main tragedy of the SSCL is that by tradition the high energy physics community has always been rather well focused in pooling its resources to provide central facilities. The theme is that the equipment needed to do HEP research is so big that it is beyond the means of a single institution but not beyond the means of the pooled resources of a large number of institutions. This has happened all over the world in separate countries and also internationally at CERN with, it must be stated, resounding success. In the case of the SSCL the institutions are varied and legion. What a pity that such a wonderful opportunity for cooperative effort and shared resources should end in such a squalid way. I have received many messages from colleagues around the country and overseas which have invariably expressed dismay and sympathy; on behalf of my colleagues and myself at the SSCL I express my profound thanks for this support. I apologize for my preoccupation with the trials and tribulations of the SSCL and I hope by next issue that things will have improved to the extent that I can write about more mundane matters including those of the Accelerator Section. Geoff Stapleton NEWS FROM IARPENL CORRESPONDENTS ====================================================================== News from CEBAF (Bob May ) ---------------------------------------------------------------------- CEBAF Commissioning Preparations Under Way With the superconducting electron accelerator nearing completion at the Continuous Electron Beam Accelerator Facility (CEBAF) in Newport News, Virginia, activities preliminary to commissioning the five-pass recirculating machine are intensifying. CEBAF will send electron beams of energy greater than 4-GeV into three experimental halls in order to explore the region between nuclear and particle physics; between seeing the nucleus as a bound state of nucleons and seeing it as an assembly of quarks and gluons. CEBAF's first major commissioning goal: a single-pass beam to Hall C in 1994. By October, only the final four of 42 1/4 eight-cavity, nominally 20 MeV, cryomodules remained to be installed in the racetrack-shaped machine. Each of the antiparallel linacs will have 20 cryomodules, with the remaining 2 1/4 in the 45-MeV injector. Also nearly complete is the beam transport system, with over 2300 room-temperature magnets and 4.5-km of beamline under vacuum. Nine recirculation beamlines in two semicircular arcs link the linacs for five passes. During linac testing earlier this year, one cryomodule accelerated beam with an energy gain of over 32-MeV. This was 160% of the specified energy gain per module, showing that a final energy well above the design value of 4-GeV may be reached. Indeed, in vertical dewar tests prior to cryomodule assembly, cavity pairs have averaged 10.5-MeV/m accelerating gradient and a Q of 5.7 X 10^9, well above the specified 5-MeV/m and 2.4 X 10^9. No significant degradation in cavity performance has been observed between vertical tests and pre-operational tests of installed cryomodules. During the most recent round of testing, which ended in April, installation proceeded in the main accelerator and in the end stations while cw beam with energy up to 120-MeV was run in the first linac and its spreader/extractor region. The first recirculation beamline was operated with beam at low average current. There were several highlights: o The linac was operated at relatively high current (>100 microamperes) for extended periods. This demonstrated the accelerator's substantial inherent operating stability, given the minimal involvement of active correction mechanisms, which were still being implemented. o The external Q of two cavities was increased, permitting study of the rf control module under conditions equivalent to full beam loading in the complete five-pass accelerator. The module worked well under these conditions. o The high-precision calibration of rf control modules was demonstrated. After the exchange of two calibrated modules, the beam returned with precision to its previous state. o A precise method for measuring the recirculation beam transport isochronicity, the degree to which rays of different momenta are synchronized upon emerging from an arc, was demonstrated. The isochronicity was shown to be better than needed. o For both the linac and the arc, optics tune-up procedures were developed. Another recent highlight has been the reconfiguration of the 45 MeV injector into a three-beam system permitting independent control of the cw beam current to each experimental hall. A port was added to accommodate a polarized source developed at the University of Illinois to support parity-violation-based studies, and a bypass chicane was installed to accommodate a 10-MeV source for both high-micropulse-charge experiments and a possible future free electron laser system. (A wiggler magnet would receive beam diverted from the injector for infrared light production.) Development of the cryomodules has progressed since the first systems were installed on the injector. Although the early modules performed well, they have now been replaced with units containing higher performance cavities. CEBAF's experimental equipment commissioning will begin in Hall C, the first end station to receive beam. The equipment in Hall C consists of the High Momentum Spectrometer (HMS), a QQQD design using superconducting magnetic elements, and the Short Orbit Spectrometer (SOS), a QDD(bar) design (similar to the Medium Resolution Spectrometer at LAMPF) using resistive elements. The 450-ton HMS dipole was recently mounted on the spectrometer carriage and tested to full current (2.0-tesla), and field mapping is imminent. The first of the superconducting quadrupoles was received in October. The detector elements -- drift chambers, scintillators, gas Cherenkov counters, and Pb glass shower counters -- will be mounted in a massive concrete and lead shield house. The SOS DD(bar) dipole is planned to be mapped and mounted on its carriage shortly. Currently approved for Hall C, with 307 days of beam time awarded, are 15 experiments in areas as diverse as the neutron electric form factor, color transparency, high Q^2 deuteron photodisintegration, and hypernuclear production. News from DESY (Herbert Dinter ) ---------------------------------------------------------------------- The Radiation Protection Group of DESY participated in a collaboration initiated by the CERN RP-group to study the neutron field behind lateral shielding of a high energy proton accelerator. As Manfred Hoefert announced in the IARPE Newsletter issue of April 1993, three measuring periods took place at the CERN-SPS during 1993. Our main interest was the measuring of neutron fluence spectra and the determination of dose equivalents. We used a set of passive detectors, consisting of 8 Bonner spheres and 2 solid state track detectors. After unfolding the measured responses we found clearly different spectra behind concrete and iron (as expected). In each spectrum we found two separated peaks, one slightly below 1 MeV, produced by evaporation neutrons, and a second around 60 MeV. In the case of iron shielding (40-cm) the high energy peak contains only approximately 6% of the total fluence while in the case of concrete shielding (80-cm) it contains 40% of the total. Detectors used for routine surveys at our facility, such as Andersson-Braun rem-meters and C-11 activation detectors accompanied the measurements. In this way we are able to assess the efficiency of these detectors in neutron fields of these types, a very important problem around high energy proton accelerators. The evaluation work is not yet finished. I would like to thank the RP-group at CERN (especially Manfred Hoefert and Graham Stevenson) for the opportunity to perform these measurements and for bringing together colleagues from many European institutes for a fruitful exchange of experiences. NEWS from KEK (Hideo Hirayama ) ---------------------------------------------------------------------- All KEK Accelerators are now preparing for operation after a long summer shutdown. During the shutdown, a 'self-inspection' of all accelerator facilities at KEK was performed. This self-inspection was included as a new regulation last year and is obligatory for all users of radio-isotopes or accelerators. The results of the inspections must be reported to the Science and Technology Agency once a year. The inspection of the accelerator tunnel, the interlock system, the signs at the entrance of the radiation control area and the facilities related to the cooling water or air conditioning are all included in this self-inspection. A new accelerator, the injector for the ATF (Accelerator Test Facility) passed the government inspection and started operation. This injector is an 80-MeV high-gradient electron linac. The maximum energy will eventually be extended to 1.54-GeV. The ATF is composed of this linac and a dumping ring. The construction of the dumping ring has already started. Here is a list of reports published by members of the Radiation Safety Control Center recently. Interested people can request copies from H. Hirayama (hh02@kekcc.kek.jpn). M. Miyajima et al., Absolute Number of Scintillation Photons in Liquid Xenon by Alpha-Particles, IEEE Trans. on Nucl. Sci. 39, 4 (1992). M. Miyajima et al., Absolute Number of Photons produced by Alpha- Particles in liquid and gaseous xenon, Nucl. Instr. Methods, B63, 297 (1992). Y. Oki et al., Evaluation and Measurement of 55Fe Radioactivity in Accelerator Hardware Activated at High Energy Accelerator Facilities, Appl. Radiat. Isot. Vol. 43, 1355 (1992). T. Suzuki et al., Delayed Neutron Emitted from Cooling Water at a High Energy Proton Accelerator Facility, Radiat. Prot. Dosim. 46, 111 (1993). T. Miura et al., Relative Abundance of HT and HTO in the Accelerator Tunnel Air and Atmospheric Air, Appl. Radiat. Isot. Vol.44, 499 (1993). T. Suzuki et al., Positron annihilation and polymerization of epoxy resins, Polymer, Vol. 34, 1361 (1993). S. Ban et al., Measurement of the Photon Energy-absorption Coefficient for Air, Nitrogen and Argon at 30 keV, Appl. Radiat. Isot. Vol. 44, 769 (1993). Y. Namito et al., Implementation of Linearly-Polarized Photon Scattering into the EGS4 Code, Nucl. Instr. Methods. A332, 277 (1993). News from LBL (Rick Donahue ) ---------------------------------------------------------------------- 88" Cyclotron Still Ticking After 30+ Years Of Operation Researchers at the LBL 88" cyclotron have confirmed the existence of element 106 (A=263). The following is an excerpt from the LBL Currents newspaper explaining some of the details... "The nuclear properties and half-life (0.9s) of the isotope observed in this experiment confirmed the original discovery of element 106 by Albert Ghiorso and his co-workers at the LBL Heavy Ion Linear Accelerator (HILAC) in 1974. The confirmation of element 106 was based on the identification of correlated parent-daughter alpha decays in the energy range predicted for element 106 (A=263) and its daughter element rutherfordium-259 (Z=104). Target nuclei of californium-249 were bombarded with oxygen-18 ions. The reaction products - containing a few nuclei of element 106 - recoiled out of the target, were swept away by a jet of helium gas, and came to rest in one of 80 plastic foils positioned around the periphery of a rotating horizontal wheel. There, an atom of element 106 underwent an alpha decay, which was recorded by one of the detectors positioned in pairs above and below the wheel. The daughter isotope, rhutherfordium-259, recoiled into an opposing detector. The foil was then moved to a new position and the decay of the rutherfordium-259 was recorded. Nine such correlated pairs of parent-daughter alpha decays were detected during a run of approximately 80 hours." (Piruz Vargha) NEWS FROM SLAC (Vashek Vylet ) ---------------------------------------------------------------------- 1. DISTINGUISHED VISITORS We in the Radiation Physics Department were pleased to host two of our international colleagues, Dr. S. Tanaka and Dr.N. Sasamoto from JAERI. Dr. Tanaka, who is the head of the Shielding Group visited us in September and gave a very interesting talk on some of the radio- logical aspects of the JAERI facilities and some experimental work. Dr. Sasamoto, who visited us in October gave a very informative talk on SPRING8, the new synchrotron radiation facility, currently under construction at JAERI. We look forward to more visits from other national and international colleagues. There is so much we can learn from each other. (Nisy Ipe ) ...................................................................... 2. FFTB (FINAL FOCUS TEST BEAM) The latest beam line at SLAC, the Final Focus Test Beam (FFTB) was commissioned in August 1993. Beams were delivered to the main dump for the first time and radiation safety aspects of this beam line were investigated. FFTB is a 1-kW, 50-GeV/c electron beam line that will be used to test new optics designs, alignment techniques and instrumentation that are required to achieve small spot sizes (~tens of nano meters) in electron linear colliders. Controlled tests were performed in which low power beams were targeted off collimators and dumps in the beam line while the photon dose and neutron dose/flux were measured around the shielded enclosure which houses the beam line. At forward angles muon flux down beam of the main dump was also measured. Various components of the Beam Containment System (BCS) were also checked during these tests. The BCS is composed of ion chambers, toroids and other devices that would shut off the beams when the beam parameters (e.g. average current, pulse rate) or the measured radiation levels around the collimators exceed prescribed levels. The results of the beam tests were satisfactory and showed that measured and calculated radiation levels around the shielding enclosure are in good agreement. Following certification of the Radiation Safety aspects of FFTB, two weeks of beam time were allocated to complete successful checks of beam components (magnets, power supplies, Beam Position Monitors), initiate optics studies to check the alignment of the beam line, and observe first signal on newly designed and constructed beam spot size monitors. In these initial studies a spot size of 1.4 micron was measured with wire scanners. The FFTB will run for up to six weeks in 1994 with the goal of controlling and measuring a 60 nanometer beam spot size. (Sayed Rokni ) ...................................................................... 3. SEARCHING FOR MILLICHARGED PARTICLES (The mQ Experiment) Members of the Radiation Physics Department recently joined a SLAC collaboration to search for millicharged particles. Together with John Jaros, Martin Perl (discoverer of the tau), and others, an experiment is being set up to look for particles having a mass greater than 0.511-MeV, but with an electronic charge less than e/1000. Three key reasons for doing this experiment are: 1) mQ particles are NOT precluded by the Standard Model of physics. 2) Recent theoretical papers even suggest that they may exist. 3) The existence of such particles could help explain why the universe contains such a large amount of Dark Matter (over 80%). Why are accelerator health physicists involved in this search? The answer is rather simple once the experimental method is explained. To begin with this is a ``beam-dump'' experiment that runs in a parasitic mode with the current operation of the SLC and its major detector, the SLD. Positrons for the SLC are created in a target located at the 2/3 point of the two-mile accelerator, where a 30-GeV electron beam is extracted just for this purpose. The forward-directed beam energy, primarily in the form of electromagnetic and hadronic cascades, is quickly attenuated in a concrete-soil shield. High-energy muons are also readily produced in the target and they can penetrate as deep as 60-m into the soil. Because the range of a charged particle is proportional to the SQUARE of its charge, mQ particles will travel much much further---about 64,000-km (even past Berkeley!). How are we looking for mQ particles? We have dug a series of 30-cm diameter holes into the earth in order to intersect the direction of the beam. Using scintillation counters we have determined where the muons range out and, most important, we have established where we should place the primary detector in order to line up with and identify mQ particles without interference from muons produced by the beam. The mQ detector itself is a two-meter long, 400 sq.cm chunk of plastic scintillator with two very low-noise photomultiplier tubes attached. For the same reason that mQ particles do not ionize very much, their signal will also be very small in the scintillator---about a million times smaller than from cosmic-ray muons! So the most difficult part of this experiment will be to look for a very tiny signal amongst a huge background caused by a variety of sources. However, we are most fortunate to have an electron beam pulse that is a few picoseconds wide and occurs at a rate of 120 Hz, allowing us to open up a small time window (10 nsec) when the mQ particles arrive at the detector and providing us with a rejection factor of about a 1/million. >From this description you can probably guess why our group has become involved in this particle physics experiment. Besides calculating and measuring muon transport, with particular emphasis on range straggling, we are working on the general background issue and the best way to shield the detector from the soil radiation. Using the EGS4 Monte Carlo code we are trying to fully understand the detector response function for the mQ detector. Most of all...we are having fun. (Ralph Nelson ) ...................................................................... 4. B-FACTORY GOES TO SLAC It seems that SLAC employees and supporters can finally relax and celebrate, after lengthy months of uncertainty, expectations and contradictory rumours. Both the House of Representatives and the Senate passed a bill including $36 million for the B-factory at SLAC (votes were 229-190 and 89-11, respectively). The total cost of the project will be $237 million, extended over a period of 5 years. As many of you probably know, the location of the B-Factory site was decided recently by DOE Secretary Hazel O'Leary, after studying reviews of two competing proposals from Cornell University and SLAC. The SLAC project was proposed in collaboration with LBL and LLNL. In a conciliatory gesture after a tough competition, SLAC director Burton Richter offered Cornell to join in the collaboration. The purpose of this new facility is to produce over 100 million pairs of neutral B-meson particles per year, by colliding electrons and positrons. Measurements of the B-meson decay will help to test the theory of CP violation. The project will require upgrading the existing PEP ring (Positron Electron Project, 2.2-km circumference) by adding a new low energy ring and building a new particle detector. Half of the money to finance the detector will come from Canada, Europe and Russia. The project will attract about 300 physicist from around the world. Four members of the Radiation Physics Department are busy working on some unique challenges presented by this new machine. You will certainly hear from them in future issues. (Vashek Vylet ) News from TRIUMF (Lutz Moritz ) ---------------------------------------------------------------------- The most recent news from TRIUMF is that we now have another operating cyclotron, bringing the total to four. This most recent addition, truly a 'baby' cyclotron, is a 13-MeV machine specifically designed to be used for the production of radioisotopes for Positron Emission Tomography (PET). Like all the other cyclotrons at TRIUMF, it is a sector-focusing isochronous cyclotron that accelerates negative hydrogen ions. The 'TR13' will be capable of accelerating up to 100 microamperes of beam and of simultaneously extracting 50 microamperes of proton beam into each of two external radioisotope production targets. Commissioning started on the afternoon of October 19th, and by 18:00 1 microampere of beam had been accelerated to 13-MeV. During these tests the local shielding which will be an integral part of the cyclotron was not yet in place and instead a bunker made of concrete shielding blocks borrowed from the 500-MeV facility was constructed around the cyclotron. Needless to say this ad hoc shielding arrangement was not entirely satisfactory and, as predicted, a 'gas' of neutrons emerged from all gaps between the blocks. The neutron field was especially high because of a last minute short-cut which substituted copper for carbon as an internal beamstop, accentuating the neutron production. Last spring, the TRIUMF Safety Group hosted Igor Kopeikin from the Institute for Nuclear Research at Troitsk, near Moscow. The Institute hopes to operate a meson facility at Troitsk. However during the political and economic upheavals of the last few years they have not been able to obtain sufficient funds to complete the construction of the accelerator. Igor brought with him some interesting computer codes which he installed at TRIUMF. One of these is an analytic shielding code applicable to proton accelerators with energy below approximately 5-GeV. This code appears to be a useful calculational tool for deep penetration problems, as the execution time is independent of shield thickness. The physical principles behind the calculation have been published as 'Propagation of an internuclear hadron cascade at energies below 5-GeV' in Nuclear Instruments and Methods A301 (1991) pp.246-264. The other major development Igor and his colleagues have pursued is a code which grew out of a simpler program to display the results of their shielding calculations. It is a graphical interface that uses object oriented programming techniques to display 'geographical' information. This code has grown into a full Geographical Information System (GIS) and they have been able to market this software in Russia. Users are organizations which need to catalogue, display and manipulate geographical information, e.g. government forestry services, geological exploration companies, emergency response planners etc. There are already a number of such systems which have been developed in the West and the Russians are not trying to penetrate the western market with their software. But at TRIUMF we have used this software, tailored by Igor, for displaying the results of shielding calculations and the results of calculations of the atmospheric dispersion of radioactive gases and aerosols. The most novel application however has been as a display for our access control system. This is a unique application which allows for a visual appreciation of the interconnections of the various control devices such as beamblockers, switching magnets and accelerator parameters. It is also possible to display the Boolean Logic which governs the relation between the devices. Another version of the program allows the designer to write the interlock logic and debug it visually by 'operating' the system. We are now looking at the possibility of transferring the code to a DECWindows environment which would make it more compatible with the TRIUMF 500-MeV accelerator control system. FROM THE MEMBERSHIP ====================================================================== We welcome the following new subscribers to the IARPE E-mail Newsletter: Daniel Chen Andy Hurst David Marshall Rhoe CLOSING THOUGHTS ====================================================================== "The House of Representatives has discovered that the Superconducting Supercollider will reveal the true nature of inert matter - and, out of self defense, voted to kill it." Barron's National Business and Financial Weekly, Oct 25th, 1993 (with thanks to Bob May).