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) ====================================================================== July/August 1995 Circulation: 197 Vol. 4, #4 ====================================================================== OFFICERS ====================================================================== President: Bob May, CEBAF President-Elect: Lutz Moritz, TRIUMF Past President: Nisy Ipe, SLAC Secretary: Steve Musolino, BNL Treasurer: Carter Ficklen, CEBAF Newsletter Editor: Vashek Vylet, SLAC Directors: Jeff Leavey (1998) Tracy Tipping (1998) Lorraine Day (1997) Don Cossairt (1997),FNAL De Vaughn Nelson (1996) Paula Trinoskey (1996),LLNL ====================================================================== CONTENTS From the Editor From the President Minutes of meetings in Boston Feature article: Proton Therapy News from correspondents: CEBAF, DESY, CERN, ESRF, SLAC New jobs: see news from CERN How to subscribe or update subscription Closing thoughts >From the Editor Vashek Vylet ====================================================================== For more than three and half years now the IARPE Newsletter has been alive and in good health thanks to the efforts of its three successive editors - Nisy Ipe, Bob May and Lutz Moritz. I am very pleased to join the ranks of my distinguished predecessors by becoming the fourth Editor of IARPE and I am grateful for the confidence of all those who voted me into this office. Since this is the first IARPE issue after the HPS meeting in Boston, it contains the minutes of the Accelerator Section Meeting. Bob May, in his first address as the new Section President, presents a lucid analysis of the current situation in our field and his view of the priorities for the Accelerator Section. This issue also contains a feature article by Marco Silari on Proton Therapy. I hope that we will be able to secure one topical article for each future issue. As you can notice in the header, IARPE has currently 197 subscribers. If you could help to enroll a few additional souls (try friends/colleagues), we will soon get over the magic number of 200. Instructions how to subscribe are included at the end of this issue. I will conclude with a request for suggestions and contributions. Your views and opinions how to improve this Newsletter are always welcome. Besides the regular contributors, I would like to encourage all readers to feel free to send me anything that would be of interest to others in our field. Although we have contacts in several countries all over the world, I believe there is still a potential for expansion. I would be grateful for names (and e-mail addresses, if possible) of individuals who might be willing to become regular correspondents. >From the President Bob May ====================================================================== We find ourselves at a crossroads... The end of the cold war, the sky rocketing cost of environmental restoration, and a fiscally conservative legislature have resulted in a new, harder look at the cost of doing EH&S. None of us can avoid the influence of these circumstances. Additionally, the legislature is down playing the technology transfer aspects of laboratory operation... leaving technological development to "big business" and focusing the national laboratories on maintaining core expertise. Nowhere is basic science and research given a priority. The DOE, in state of flux, has been placed in a position to reevaluate programs and accept reasonable and cost effective means of achieving safety. Many of us welcome the opportunity to inject a healthy dose of reality into programs containing what we have long considered non-value added activity, or worse, wasteful activity. This is tempered by the possibility that it may cost some of us our jobs in the worst case. It may also force some of us to expend a substantial amount of effort justifying or defending what we consider reasonable programs against an undiscriminating budget ax. Amidst the turmoil there is a temptation for each to look after their own interests. We've seen this occur with respect to the DOE RadCon Manual. Our efforts at accelerator related categorical exemptions fell on deaf ears. We did not, as a community, continue to push the DOE envelope of acceptance. I believe we have an unprecedented opportunity to affect changes in the EH&S regulatory framework. I also believe that we have little time. Some may say we're already too late in key areas. I believe that we should use the block of time remaining in a strategic fashion. A coherent effort is needed on the part of the Accelerator Section. We need to actively promote reasonable standards for safety. We need to clearly define these standards. They must be generally applicable to accelerator labs and supported with sound technical bases. They must be accepted by a clear majority of professionals and proffered by the Accelerator Section as "position papers". The prime areas of concern are: Standards for hazard analysis and classification - generally accepted or low hazard facilities which are non-nuclear Standards for active and passive protection measures and against prompt radiation from beam loss Standards for removable radioactivity control and airborne radioactivity control at accelerators Calibration and performance standards for dosimeters and active monitors for high energy neutrons and for pulsed radiation fields These concerns stand out whether we attempt to apply newly promulgated laws or existing standards. We have a clear example of success - the CASOG. I propose that we learn from their success and form similar groups to address these key issues. We should also attempt to gain international cooperation in this effort from the International Advisory Board. I feel like I've been the recipient of one of Ben Franklin's cash loans to young entrepreneurs in Boston - a legacy identified in his will. A tremendous amount of hard work and development has gone into the accelerator section by those preceding me. This legacy is a loan... to all of us. I believe it's time for a return on this investment. There is one caveat however - and I believe Ben Franklin said it best in an address to the First Continental Congress - "We must hang together or we shall surely hang separately". MINUTES OF MEETINGS IN BOSTON Steve Musolino ====================================================================== Accelerator Section Board Meeting Minutes ----------------------------------------- Present: C. Ficklin, N. Ipe, R. May, J. McDonald, L. Moritz, S. Musolino, D. Nelson, G. Stapleton, P. Trinosky, L. Day Topical Midyear Meeting The Board vote unanimously to go ahead with planning the Midyear meeting in San Jose to be on the topic of Radiation Producing Machines, similar to the 1987 Reno meeting. Lutz volunteered to be Co-Chairman of the technical program, Nisy was proposed as a second Co-Chair but she deferred her decision to a later time, and Bob will work on logistics with the Secretariat. It was also proposed that the technical sessions at the Annual meeting before and after the Midyear be reduced in scope. History Committee Carter reported in Wade Patterson's absence. Wade requested funds to scan hard copy of documents into digital files. Paula volunteered to assist in lieu of paying for the service. The letter from Newell Stannard re history will be sent to Wade. Logo Contest: Scott Schwahn won the logo contest. Accelerator Section Meeting Minutes ----------------------------------- Approval of Minutes from Previous Board Meetings' Carter moved that the minutes from the Charleston and San Francisco meetings be approved as previously distributed in the Section Newsletter. Roger Kloepping seconded. President's Report Nisy reported the following were accomplished during the past year: HPS Meeting San Francisco - Thank you letters re the 1994 San Francisco meeting were sent out. HPS Meeting Boston - Bob May was asked to coordinate the technical program for Boston Public Relations Link between Section and International community - The liaisons are N. Ipe, M. Hoefert, M. Pelliccioni, T. Nakamura, D. Perry ANS Collaboration - Section is co-sponsor of Radiation Protection and Shielding for 4/96 meeting. N. Ipe is on Technical Program Committee. IRPA-96 - Session on Accelerators M. Hoefert is Liason Four invited papers Report of the Nominating Committee Carter reported the following nominations Section Officers: President Bob May Newsletter Editor Vashek Vylet Treasurer Carter Ficklen Directors Jeff Leavey Tracy Tipping Nomination were opened up to the floor. Al Evans moved that the election be approved by acclamation. Seconded by Lorraine Day. CASOG Subcommittee Report Geoff reported on the activities of the subcommittee and the content and status of the report. A meeting to discuss the report was scheduled for later in the day and was open to any interested persons. Treasury Report Joe Mcdonald gave a status report on the treasury. Section membership is 168, 24 are IRPA affiliates. Joe and Lutz emailed the new membership directory. it also exists in Wordperfect format. There is a balance of $2657.51. Training SLAC has versions of GERT in English, Spanish, Japanese, and Chinese available to anyone interested. SLAC is leading the development of the RCM Core Accelerator Facility Training and the working group is very interested in pictures to scan into it. Pictures can be sent to Paula Trinoskey at LLNL for scanning. DOE Core material for Rad Worker/High Radiation Area training is available. LLNL and SLAC are offering a 2 week RCT fundamentals training class. Midyear Meeting Don Cossairt moved and Lorraine seconded to not have a technical session at the 1996 Seattle meeting if the Midyear is on accelerators. The Midyear will publish proceedings. The vote was unanimous to proceed. New Business Geoff moved and Scott Schwahn seconded to support Bob as delegate to IRPA-96. Steve was requested to write a letter to the HPS Board to that effect. Don brought up the issue of compliance with the HPS policy on use of slides for oral presentations. Ken Kase who is a Program Committee member permits the Section to allow the use of overhead graphics. There was a motion for the Board to clarify Section policy in this regard. Al Evans brought up that a new Chairperson is needed for the committee to rewrite ANSI N43.1. Bob May will seek out a person. The Moyer Award was to be presented by Bill Mills to Justin Mohler. Justin was not present at the meeting so it will be forwarded to him. Bob May reported that Wess Dunn asked him to mention that the Conference of Radiation Control Program Directors will issue for comment, in the fall of 1995, the suggested state regulations for accelerators. Meeting Adjourned Action Items: Lutz Moritz - Serve as Technical Co-Chairman for the Midyear Meeting Bob May - Coordinate logistics for the Midyear Meeting with the Secretariat. Search for a new ANSI N43.1 Committee Chairperson. Board - Clarify policy on use of overhead projectors in oral presentations Steve Musolino - Send a letter to the HPS Board to request support of Bob May to IRPA-96 Addendum by the Editor: Shortly after the meeting Nisy Ipe decided not to co-chair the planned mid-year 1997 HPS meeting in San Jose, due to increased workload in her new position at SLAC. She proposed Vashek Vylet for this function and her proposal was approved by the Section Board. FEATURE ARTICLE Marco Silari ====================================================================== PROTON THERAPY Marco Silari CNR, I.T.B.A., Via Ampere 56, 20131 Milan, Italy The use of hadron beams (protons, neutrons and light ions such as carbon, oxygen and neon) in cancer radiation therapy has grown considerably since the first trials in the mid-fifties and now a few hospital-based facilities are in operation in the North America, Russia, Japan, Europe and South Africa, with a few others being built or designed. A very comprehensive and up-to-date review of the field can be found in ref. [1]. About 17'000 patients have been treated worldwide. Pathologies for which protons have a clear clinical indications are: uveal melanomas, chordomas and chondrosarcomas of the skull base, spinal and paraspinal tumours, parasellar meningiomas, optical nerve gliomas, craniopharyngiomas, acustic nerve schwannomas, artero-venous malformations and hypophysis adenomas. There are other classes of tumours for which protons should prove superior to conventional radiotherapy but still need clinical investigation. The rationale for the use of protons in radiation therapy relies on the superior dose distribution which can be achieved with respect to photons and electrons: this is due to the low lateral scattering undergone by heavy charged particles, their well-defined range and the increasing ionisation (i.e., dose deposition) with increasing penetration in tissue, which produces the well-known Bragg peak. The depth of the Bragg peak depends on the initial energy of the protons and its width on the energy spread of the beam. By varying the energy during the irradiation in a well-controlled manner, one can superimpose many narrow Bragg peaks and irradiate an extended region in depth. All the clinical needs can be satisfied with proton energies in the range 60 - 250 MeV and beam intensities of the order of 5x10^10 - 10^11 protons/s. To achieve a conformal irradiation of the target volume, the beam also has to be spread transversally. This can be achieved either with "passive" or "active" methods. The former makes use of a double scatterer: the first spreads the incoming pencil beam, the second flattens the dose distribution in order to obtain a large and uniform irradiation field. Lateral and distal shaping are achieved by means of a collimator and a compensating bolus. With raster scanning the beam is scanned continuously across a slice at a given depth and the dose delivery is controlled by the scanning speed and/or by the beam intensity. Present facilities still make use of passive systems for conforming the dose to the tumour. We shall briefly discuss the dosimetry of therapeutical proton beams with reference to such systems. The dosimetry instrumentation depends on the time structure of the proton beam, which is a function of the type of accelerator employed (i.e., a cyclotron, a synchrotron or a linac). Dosimetry of the therapeutical beam is needed for: 1) control of position and intensity of the proton beam emerging from the modulation and spreading devices; 2) control of the uniformity of the proton fluence in the cross- section of the therapeutic beams; 3) absolute beam calibration, i.e. knowledge of the absorbed dose in a tissue element exposed to the beam at the isocentre under standard physical conditions; 4) knowledge of the relative tri-dimensional distribution of the absorbed dose in the irradiated region; 5) knowledge of the values of microdosimetric quantities in the irradiated region. The primary purpose of a monitoring system is to ensure the correspondence between prescribed and delivered dose at a reference point, within a given overall uncertainty which needs to be +/- 2.5%, according to clinical requirements. Dose delivery must be promptly stopped as soon as the prescribed dose is reached. The agreement between nominal and actual proton range in water has to be periodically tested with a relative system. Instrumentation for on-line monitoring of the beam includes ionisation chambers, multiwire ion chambers, secondary emission monitors (SEM) and silicon diodes. Instrumentation for reference dosimetry includes water calorimeter, ionisation chamber and Faraday cup. Medium energy proton medical accelerators produce secondary radiation, mainly neutrons, from beam interaction with accelerator components (the magnets in particular), beam delivery devices (such as collimators) and the patient. Although the beam intensity is much lower than that typical of research accelerators, yet the fact that such accelerators may be installed inside a hospital or in highly populated areas calls for a shielding design which should reduce virtually to zero the radiological impact on the external environment. Typical shielding thickness ranges from about 1.5 m of ordinary concrete (for shielding of the treatment room from the beam transfer line, where beam losses are limited) up to 4 m (for shielding the forward secondary emission in the case of a treatment room with a fixed horizontal beam). Shielding thickness obviously also depends on whether one should ensure dose equivalent limits compatible with occupationally exposed workers or with the general public. A particular situation with a medical proton facility is the use of an isocentric gantry in one or more treatment rooms. A "gantry" is a large mechanical structure which allows the rotation of the terminal tract of the beam transport system around the patient, in order to accurately point the proton beam to the tumour from any desired angle of irradiation. The fact that the beam can be rotated 360 degrees in one plane imposes specific requirements on the shielding walls of the room, as well as accurate assumptions on the use factor of the shields. Access to the treatment rooms needs to be a two or three leg maze, several metres long, to avoid the use of a massive shielding door which would not be compatible with the clinical use of the facility. At most, a polyethylene door like those used in conventional radiation therapy units provided with electron linacs may be used. Interlocks must obviously prevent access to the accelerator hall and to any room when beam is present, but the possibility of fast beam abort and immediate entrance into the treatment room must be ensured in the case the patient needs assistance. [1] Hadrontherapy in Oncology, U. Amaldi and B. Larsson (editors), Excerpta Medica, International Congress Series Volume 1077, Elsevier (1994). NEWS FROM IARPE CORRESPONDENTS ====================================================================== News from CEBAF Bob May ---------------------------------------------------------------------- Tenth Annual Summer Graduate Program Held at CEBAF Nineteen graduate students representing twelve U.S. and three European institutions recently completed the tenth annual Hampton University Graduate Studies (HUGS) at CEBAF, held May 30 to June 16. Topics included nuclear chromodynamics, nuclear currents and dynamics, probing nucleon structure with polarized electrons, nucleon resonances in pi nucleon scattering, introduction to color transparency, and hypernuclear physics. T. Eden and R. Williams of Hampton University served as co-chairs; lecturers included P. Bosted of American/SLAC, S. Brodsky of Stanford, M. Manley of Kent State, G. Miller of the University of Washington, B. Jennings of TRIUMF, and D. Riska of the University of Helsinki. Participants were A. Rakotovao of Old Dominion, R. Woo of William and Mary, J. Bauer and Y. Kolomensky of the University of Massachusetts, A. Cichoki and V. Gladyshev of the University of Virginia, C. Rankins and W. Tun of Hampton University, R. Suleimann of Kent State, J. Li of Vanderbilt, Z. Bucalo of Catholic, R. Mohring of the University of Maryland, T. Vrana of the University of Pittsburgh, R. Erbacher of Stanford, H. Choi of North Carolina State, A. Longhi and M. Battaglieri of Genova, D. Marchand of Saclay, and F. Neumeyer of Darmstadt. News from DESY (Herbert Dinter ) ---------------------------------------------------------------------- Since May '95 the DESY accelerators are again in operation after a 4-month shut down. The shut down mainly was used to install the new experiment HERMES in the HERA storage ring. HERMES plans to clarify open questions concerning interactions of polarized electrons (or positrons) with polarized nucleons. From the point of view of radiation protection the experiment does not cause major problems. It is shielded with straight side walls and a roof and on top and the radiation background in the hall is expected to be comparable to that in the other halls. The other 2 experiments at HERA, ZEUS and H1, even if not shielded in such a clear way as HERMES run since a few years without requiring 'radiation controlled areas' in their halls. Permanent monitoring shows dose levels of less than 0.3 mSv per month. The second 'working horse' at DESY, the e-storage ring DORIS, presently provides nearly 50 experiments of the 'Hamburg Synchrotron Radiation Laboratory' HASYLAB with radiation without problems for the Radiation Protection Group. Parallel to these operations machine physicists are concerned how to satisfy the steadily growing demands of experimentalists for higher beam energies and luminosities. Presently the interest focuses to linear electron-positron colliders with lengths up to 30 km, energies of 500 GeV (center of mass), and luminosities of more than 10**33 cm-2 s-1. Working groups at several high energy accelerator centers are engaged in the development of the technical conditions to meet such a challenge. At DESY 2 competing projects are in progress with the aim to find out the most promissing technical solution that could lead to a linear collider. One project is based on a 3 GHz-RF-stucture ("S-band linac"), together with a normal conducting cavity system developed at DESY. The second one is an international collaboration ('TESLA') that investigates the use of superconducting accelerator components such as quadrupoles and cavities with very high field gradients (25 MV/m are envisaged). Both projects are planning to build test linacs for elec- trons with lengths of about 50 m, energies up to 500 MeV and beam powers of 20 kW and 50 kW, respectively. The last two figures show that these objects even represeting only "test facilities" are of high relevance with respect to radiation protection. The design of the shielding, the access possibilities and their interlock systems, water and air control were subjects of intensive work in the last months. Both linacs will be operational in 1996. After a certain period of time for tests and operation, and when enough experience will have been acquired, a decision is to be made which of both techniques will be followed for a possible realisation of a linear collider. The Radiation Protection Group is glad to have support of Dominik Dworak from Institute of Nuclear Physics, Krakow, for another half year. Dominik will be concerned with calculations to get information about shielding of stray radiation of a hadron beam in forward direction. News from CERN Alberto Fasso and Manfred Hoefert ---------------------------------------------------------------------- The good news first. Following the resignation of Catherine Vaerman after only 15 months of service for CERN's RP-Group her job was finally authorized to be filled. The description of the post for a senior physicist or an engineer, which has already been announced in a previous Newsletter, is now available on the World Wide Web. The URL is: http://www.cern.ch/CERN/Divisions/PE/HRS/Recruitment/vn/TIS-95- 44.html The request for another more junior physicist or engineer was already approved by our technical Director but still has some hurdles in front of it before publication. This post is in particular meant to provide the technical support for RP in the fields of individual dosimetry and calibration. The main general news from CERN concern of course the preparation for the LHC project. Negotiations are going on with several non-member States concerning their participation. A major step has already been achieved with the recent agreement and a substantial financial contribution from Japan. The reorganization of CERN in view of the project is slowly taking shape. A new LHC Division will be created in 1996, with the task of assembling the engineering activities related to the project. The responsibilities for safety issues (including radiation), however, will continue to remain with TIS (Technical Inspection and Safety Division). The civil engineering design of the two major LHC experiments (ATLAS and CMS) has started and a call for tender for digging out CMS is prepared. Initial radiation studies concerned the thickness of the shielding walls separating the huge experimental caverns from the control rooms and passage ways, streaming of radiation through ducts and shafts, and activation of experimental apparatus. Further calculations are under way with respect to air and rock activation, etc. Some of the results obtained will be included in the radiological environmental impact report which is part of the general environmental impact report under preparation and that shall be ready by the end of the year. But while the future is being built, RP Group has still to care about the routine control of radiation produced by the existing accelerators. Some facilities (the Low Energy Antiproton Ring LEAR and the SPS West Hall) will be shut down by the end of 1996 to liberate resources, i.e. money and staff, for the LHC. However, most of the other accelerators, like our work horse PS and the SPS, will continue to serve as proton, heavy ion (lead) and lepton injectors. LEP, the Large Electron-Positron Collider, will be boosted up to a maximum energy of possibly exceeding 90+90 GeV. This has to go fast as it will already be dismantled at the end of 1999 to make room for the LHC, which will be installed in the same 26 km tunnel. In the meantime, machine engineers are busy trying to improve the performance of present accelerators, in some cases pushing hard on the resistance of materials and on the help of radiation protection technicians. Since a few months, the SPS is running at record intensities (up to 4.0E+13 protons per pulse) to provide beams for the neutrino experiments. RP Group has had a hard time convincing the Control Room operators that such an intense proton beam has to be fully mastered. In fact, as a result of increased beam losses several magnet coils failed one after the other due to radiation damage and repairs had to be carried out in a rather "hot" radiation environment. Intensities are also up at LEP (although fortunately without any radiation consequences), where a new injection scheme (the so-called "bunch train") is giving record luminosities but also an unusual rate of failures. In addition, new superconducting cavities are steadily installed, in view of the next increase in energy (from 45+45 to 70+70 GeV). Such an increase will bring about a much more than proportional increase in energy and intensity of synchrotron radiation, which will require a lot of attention by RP Group. In preparation for that, a detailed map of present synchrotron radiation levels has been carried out around one of the LEP straight sections and in the nearest arc, in order to study the propagation of synchrotron radiation in the tunnel, in ducts and mazes. An identical experiment will be performed next November, when for the first time the circulating beam energy will be raised to 70 GeV. A recent incident at the ISOLDE (Isotope Separator On Line) has brought to our minds that radiation protection at CERN is not limited to shielding calculations or the measurement of dose equivalent. During the decoupling of an uranium target that had been hit by intense proton beams of 1 GeV from the booster using the built-in robot an important amount of gaseous activity was released and the target area became contaminated. After a first shock it became obvious that the CERN release limits had not been exceeded but nevertheless such an incident appearing in the books is nothing that will impress the CERN's Host state authorities positively. It is now time that the whole complex of release limits be revised taking into consideration the new Swiss Radiation Protection Ordinance and the recent ICRP Publication 68. This also in view of the LHC project. The Group is looking forward to two visitors (one senior physicist and a graduate student) starting their contract at the beginning of September who shall look particularly into this problem. A few announcements: The abstracts of the four summary papers to be given at the IRPA9 Congress next year in Vienna in a special symposium on accelerator health physics have been sent to the Programme Committee. Preparations are going on for the second SARE Workshop (Simulation of Accelerator Radiation Environments) which will take place at CERN the next 9th to 11th of October. Several applications have been received but interested persons are still in time to apply, proposing a paper or only to participate. For information, contact Graham Stevenson, . SARE will be followed by SATIF2 (a 2-days Meeting on Shielding Aspects of Accelerators, Targets and Irradiation Facilities). All SARE participants are invited. Interested people may contact Enrico Sartori . News from ESRF Elke Braeuer ---------------------------------------------------------------------- The European Synchrotron Radiation Facility is by now fully operational for 18 beamlines, which are "open" to external users. 10 other beamlines are under construction or in their commissioning phase. The machine is normally running at 160 mA with a lifetime of at least 50 hours. At the end of the year the maximum current shall be at its final value of 200 mA. There are some Radiation Protection challanges to shield the high energy beamline, since the superconducting wiggler will produce a very hard spectrum with e.g. 10E10 photons per second at 300 KeV. News from SLAC Vashek Vylet ---------------------------------------------------------------------- 1. SYNCHROTRON RADIATION CALCULATIONS FOR THE B-FACTORY B-Factory (i.e., PEP-II) at SLAC has one high-energy electron ring (HER, 12 GeV) above a low-energy positron ring (LER, 4 GeV), located in an underground tunnel with 2200 m in circumference. One detector will be used to study CP violation by means of B-meson production and decay following the collisions of the two stored beams. One of the main differences between SLAC's B-Factory and other accelerator storage rings currently running (or in design) is that PEP-II has a designed stored beam of 3 A - one order of magnitude higher than the others. Consequently, the radiation environment in the tunnel, resulting from both synchrotron radiation escaping vacuum chambers and from shower radiation (photons and neutrons) due to beam losses, is expected to present difficulties for instrumentation and components (e.g., cables and hoses) located in the tunnel. The ring vacuum chambers and related components are also subject to potential damage by synchrotron radiation, if not properly designed. One of the missions of the SLAC Radiation Physics Department is to support and assist the physicists designing the machine. That is, in addition to our normal radiation-safety related responsibilities, we are called upon to employ many of the same codes and techniques that are used in shielding and dosimetry to help figure out and solve interesting engineering problems involving heat transfer, radiation damage and detector backgrounds. A couple of examples of what we are currently doing are given below. In the original design proposal for PEP-II the vacuum chambers for the arcs of both the LER and HER were made of copper, an excellent (but expensive) material. Based on support calculations from our group, the latest LER now uses aluminum for the vacuum chamber, which allows for a much better vacuum. In order to handle the leakage problem resulting from the switch-over to aluminum, synchrotron radiation is purposely directed into copper absorbers located within antechambers that are part of a new vacuum-chamber design. Studies have now been done to demonstrate that the radiation environment - both synchrotron radiation and shower leakage - is acceptable for magnetic coil insulation and, with judicious shielding, also for electronic equipment that we plan to locate directly below the long C-shaped dipoles in the HER. The synchrotron radiation environment in the straight sections of the HER ring, in which copper beam pipe is replaced with stainless steel, has also been studied using the EGS4 Monte Carlo code. Another example involves the use of a wiggler magnet for beam dampening, whereby very sensitive silicon detectors, located inside a well shielded lead block under a copper chamber, are used to monitor very high power synchrotron radiation striking a dump within the vicinity of the wiggler. The problem has been to find (i.e., design) an appropriate geometry such that the Si detectors will function properly. This is a complex problem involving issues related to the so-called deep-peneration problem, forcing us to introduce severe biasing-weighting techniques in order to solve the problem using EGS4. There are several PEP-II technical notes and two papers published in NIM that document our efforts in this area. Readers who are interested are welcome to contact us for further information or for discussions. James Liu Ralph Nelson 2. SUPERCHARGED MODE IN PHOTOCATODE RF GUNS As part of a feasibility study/experiment, the LCLS (Linac Coherent Light Source) collaboration is planning to build a test stand for a photocatode rf gun, followed by a short accelerator section and producing 50 MeV electrons. The test stand will be located in the existing SSRL linac enclosure and should be operating by the end of this year. An iteresting aspect from the radiation point of view is a so called "superchaged mode" of operation, during which the average current can increase by orders of magnitude. During normal operation, free electrons are created at the photocatode surface by a short laser pulse (on the order 10 picoseconds) and accelerated by the rf field. In the supercharged mode, which can occur at very high field gradients, a plasma is maintained at the photocatode surface for periods much longer than the duration of the laser pulse. It is thought that the rf field smashes some of the free electrons back into the photocatode with enough energy to keep the plasma alive. This production is thus maintained purely by the oscillating rf. Since the rf macropulse is relatively long (2 microsec.), additional electrons are accelerated whenever the rf field points in the right direction, which is every 0.35 ns for a 2856 MHz klystron. This continues as long as the plasma is maintained, for a few hundred nanoseconds. The machine designers are currently studying ways to prevent this mode and to limit the resulting average current. If you had to deal with this issue in the past, I would appreciate any information about your Beam Containment System and other useful comments. Vashek Vylet 3. RECENT PAPERS N. E. Ipe, H. Bellamy, J. R. Flood, K. R. Kase, R. P. Phizckerely, K. J. Velbeck and R. Tawil, ``Low-Energy X-ray Dosimetry Studies (7 to 17.5 keV) with Synchrotron Radiation'' to be published in the Proceedings of the 11th International Conference on Solid State Dosimetry, Budapest, July 1995 [Also SLAC PUB 6939] J. C. Liu and W. R. Nelson, "Synchrotron Radiation Calculations using the EGS4 Code", Nucl. Inst.&Meth. A 360(1995),626-633 J. C. Liu, S. Mao, W. R. Nelson, K. R. Kase, N. E. Ipe, "Calculations of the Radiation Doses to the Electronic Equipment and Magnet Coil Insulation in the PEP-II Tunnel", Nucl. Inst. &Meth. A 359 (1995), 463-473 HOW TO SUBSCRIBE / UPDATE YOUR E-MAIL ADDRESS ====================================================================== To add yourself to the mailing list for the IARPE Newsletter, send an e-mail message to listserv@slac.stanford.edu The body of your message should contain the following command: subscribe iarpe-l name where 'name' (your full name, such as Joe Smith) is optional. Please don't forget to update your e-mail address if you move, change jobs or just due to changes in your computing environment. The update consists in canceling the old by 'unsubscribe' and submitting a new subscription, as illustrated below: unsubscribe iarpe-l old_email_address subscribe iarpe-l name end If the body of your message, as in this example, contains more than a single line/command, it is good practice to finish with the 'end' command, especialy if your mailer adds a signature. If you experience problems with subscribing/updating, please send me an e-mail to and I will do it for you. CLOSING THOUGHTS ====================================================================== Remember, where there is no solution, there is no problem. -- Shimon Peres