The High-Intensity Proton Accelerator Facility at the Paul Scherrer Institute (PSI) accelerates protons to an energy of 590 MeV with currents up to 2.4 mA, i.e. 1.4 MW beam power. The beam feeds four main experiments using individual targets. The areas adjacent to these targets are heavily shielded by several meters of iron and concrete. The neutron stray field at different positions outside the shielding close to two of these targets has been investigated using the PSI extended range Bonner sphere spectrometer (ERBSS). It consists of 10 moderator spheres made of polyethylene and 4 spheres modified with metal shells, enhancing the sensitivity for neutrons with energies >20 MeV. The data was normalized to the proton current measured by a resonance chamber upstream of the first target. Two commercially available survey instruments for neutron radiation constantly monitored the stability of the field during the measurements. The spectral neutron distribution was determined by applying Bayesian methods, which were optimized for measurements of neutron stray fields behind shielding at high-energy accelerators. The measurements within restricted access areas resulted in ambient dose equivalent rates of 25-50 μSv (h mA)-1 with significant contributions of high-energy neutrons. The comparison to doses indicated by a commercially available survey instrument suitable for measurements in fields with a high-energy neutron component showed reasonable agreement with the dose values obtained from the ERBSS measurement. However, it is desirable to apply in-field calibration factors derived from spectrum measurements to reduce the uncertainty of dose values obtained with survey instruments.

The pulsed nature of laser-driven ion sources and their relative large emission angles result in the production of secondary, undesired, pulsed neutron (and photon) radiation. Conventional neutron monitors struggle to accurately measure in such environments, yet characterizing these fields is crucial for applications like hadron therapy. Parasitic neutron dose measurements were performed at the Petawatt beam of the Dresden Laser Acceleration Source (DRACO) employing laser energies from 4.5 to 18 J. An active extended-range neutron REM counter specifically developed for pulsed neutron fields, the LUPIN-II, was employed, as well as a passive extended-range neutron REM counter, the Passive LINUS. Neutron doses were recorded on a single-bunch level with values up to about 260 nSv per proton bunch characterized by a proton cutoff energy of about 60 MeV at about 2 m from the DRACO vacuum chamber, confirming the expected pulsed nature of the neutron field. Results of passive measurements were compared to the LUPIN-II results, integrated over the same period, and showed a reasonable agreement, confirming the presence of pulsed neutron radiation in the proximity of the DRACO ion source. These results demonstrate for the first time that this kind of radiation can be monitored, in terms of H*(10) on a single-shot basis by using the LUPIN-II neutron REM counter.

The latest large-scale research facility of the Paul Scherrer Institute, the x-ray free-electron laser SwissFEL, is installed in a 740 m long building. The facility accelerates electrons to a maximal energy of 5.8 GeV with repetition rates up to 100 Hz. The building is integrated in a regional recreation area with shielding of the accelerator vault dimensioned to tolerate temporary beam losses. An online dose monitoring system capable of shutting down SwissFEL ensures compliance with legal requirements. The studies present an overview of the evaluation of calibration factors for this system and results of dedicated benchmark measurements, carried out to verify underlying assumptions and simplifications.

Background and purpose: The investigation of the FLASH effect requires experimental accelerators capable of delivering ultra-high dose rate (UHDR) beams. Rapid widespread use of this technology could be achieved by modifying clinical electron linacs, originally designed to deliver megavoltage photon radiation up to a few Gy per minute to the isocenter, to deliver electron beams at 40 Gy/s and beyond. Only limited experience has been reported on the radiation safety of UHDR electron beams. This work aims to evaluate the performance and applicability of radiation detectors to quantitatively assess the radiation exposure in this context. Methods: A Varian TrueBeam linac has been modified to deliver 16-MeV electron UHDR with dose rates up to 3 & sdot;10(5) Gy/s (instantaneous) and 256 Gy/s (average) at the isocenter and used to investigate the detectors performances. A short-term survey was performed at the first UHDR beam-on with passive and active detectors. Then, a long-term survey was conducted with passive detectors during the first three months of operation of the UHDR linac. Moreover, linearity of detector response, activation of the linac components and secondary radiation inside the bunker were evaluated. Results: Selected active survey metres were shown to have a linear response for the detection of the ambient radiation outside the bunker when performing pulsed UHDR irradiations. The most critical locations outside the bunker were identified at the bunker door and at the control room. The results showed that the operation of the linac with a workload limit of 1000 Gy/week at the isocenter would allow respecting a limit of 0.02 mSv/week to the personnel. The activation of the linac head with 16-MeV electron beam was more than ten times greater with conventional beams compared to UHDR. The secondary radiation inside the bunker was also reduced by -27% when employing UHDR beams. Conclusions: This work provides a comprehensive evaluation of the suitability of active and passive detectors to perform a radiation safety assessment for a 16-MeV electron UHDR linac. The conditions under which commonly available survey metres for photons (FLUKE 451P) and neutrons (Ludlum Model 3007) can safely be employed in controlled areas outside the bunker were investigated. Moreover, we showed that if a radiation vault is safe for 16-MeV electron beams at conventional dose rates, this applies also to UHDR when fixing the linac weekly workload to a given amount of dose at the isocenter.

The Swiss Light Source (SLS) is an electron synchrotron at the Paul Scherrer Institute established in 2001. With an electron energy of 2.4 GeV and 16 operation beamlines, it provides photons for research in various fields of science. This paper describes the approach for the dismantling of the SLS storage ring from the material clearance point of view. It summarizes the general methods used for clearance and their application to the material to be cleared due to the SLS 2.0 upgrade. The experimental research described in this work confirms the applicability of the developed dismantling and clearance approach.

The Paul Scherrer Institute is a unique Swiss research institute that operates five large-scale research facilities in which different types of particles, such as electrons, protons, neutrons, pions and muons, are accelerated or produced. Depending on the facility and location, the operational radiation protection has to deal with challenging measurements of mixed radiation fields, which can be in addition pulsed and of high-energy. In this article, we provide insight into the associated demands and challenges using two examples with different requirements for the monitoring technology. Using the example of the high-intensity proton accelerator (HIPA), the measurement technology around high-energy accelerators is examined in more detail. On the other hand, the problems of measuring technology for pulsed radiation and its dynamic range are discussed using the example of the Swiss X-ray free electron laser SwissFEL. The aim of this paper is to highlight the different requirements and technical challenges in radiation measurements for such complex facilities and, thus, to raise awareness and provide a stimulus for further developments in measurement technology.

The Swiss Light Source (SLS) is a third-generation synchrotron light source with an electron energy of 2.4 GeV. It consists of a linear accelerator, a booster and a storage ring providing light for various applications. As SLS is a high-energy accelerator, its operation is accompanied with production of ionizing radiation fields, including neutrons. This leads to additional challenges from a radiation protection point of view. The long-term investigation of the radiation fields at this accelerator facility can provide useful information for the residual activation studies and optimization of shielding. This work describes measurements of the neutron radiation fields inside the tunnel and results of this study.

The international FCC study group published in 2019 a Conceptual Design Report for an electron-positron collider with a centre-of-mass energy from 90 to 365 GeV with a beam currents of up to 1.4 A per beam. The high beam current of this collider create challenging requirements on the injection chain and all aspects of the linac need to be carefully reconsidered and revisited, including the injection time structure. The entire beam dynamics studies for the full linac, damping ring and transfer lines are major activities of the injector complex design. A key point is that any increase of positron production and capture efficiency reduces the cost and complexity of the driver linac,

The Swiss Free Electron Laser is a new large-scale facility currently under construction at the Paul Scherrer Institute. Accessible areas surrounding the 720 m long accelerator tunnel, together with the pulsed time structure of the primary beam, lead to new challenges for ensuring that the radiation level in these areas remains in compliance with the legal constraints. For this purpose an online survey system based on the monitoring of the ambient dose rate arising from neutrons inside of the accelerator tunnel and opportunely calibrated to indicate the total dose rate outside of the tunnel, will be installed. The presented study provides a conceptual overview of this system, its underlying assumptions and measurements so far performed to validate its concept.

In the presented study, the relative response of a commercially available RPL glass dosemeter system, developed for individual monitoring of external ionizing radiation, was determined for different photon and beta radiation qualities, varying angle of incidence of photon radiation, and for combined photon irradiations. For Cs-137 radiation quality the H-p(10) and H-p(0.07) relative responses vary between 90% and 100% from 0.1 mSv up to 5 Sv. In the photon energy range from 33 keV to 1250 keV the H-p(10) variation is less than 10%. The H-p(0.07) variation is less than 10% for photon energies higher than 12 key. The response of both dose quantities varies less than 15% for angle of incidence up to 60 degrees for Cs-137 and N-80 photon radiation qualities. For beta radiation the relative response of H-p(0.07) was determined to be 1.03 for Sr-90+Y-90, 0.98 for Kr-85, and 0.48 for Pm-147. Under combined irradiation conditions with differing radiation qualities and angles of incidence, the dose accuracy was within +/- 50%. The precision of the RPL dosimetry system in H-p(0.07) and H-p(10) is better than 2% for radiation quality Cs-137 and doses greater than 0.5 mSv. (C) 2017 Elsevier Ltd. All rights reserved.

The measurement flights of the exercise ARM16 were performed between June 27th and July 1st, 2016. The exercise was organized by the National Emergency Operations Centre (NEOC) under coordination from the Expert Group for Aeroradiometrics (FAR). Representatives of KompZen ABC-Kamir participated with a second Super Puma helicopter carrying the prototype of a new airborne gamma-spectroscopy system (RLL) in parts of the exercise. According to the alternating schedule of the annual ARM exercises, the environs of the nuclear power plants Beznau (KKB) and Leibstadt (KKL) and the nuclear facilities of the Paul Scherrer Institute (PSI) and the Zwischenlager Würenlingen AG (Zwilag) were surveyed. Both reactor blocks of KKB were in maintenance shutdown during the flights. The series of radiological background measurements over Swiss cities was complemented with measurements over Luzern, Emmen, Cham, Baar and Zug. A permanent dose rate probe of the Swiss NADAM Network near Vicosoprano measures the highest values observed in this network. The vicinity of the probe was inspected with airborne gamma-spectrometry and the elevated dose rate was confirmed and could be attributed to elevated concentrations of natural radionuclides. The emergency exercise LAURA, consisting mainly of the search for radioactive sources, was conducted at Emmen military airfield in cooperation with local first responders. Several measuring flights were performed to test the evaluation procedures. Especially the parameters for background and altitude corrections were inspected.

Radiation survey instrumentation is adequate for the use around high-energy accelerators if capable to measure the dose arising from neutrons with energies ranging from thermal up to a few gigaelectronvolts. The SmartREM-LINUS is a commercial extended range rem-counter, consisting of a central (3)He-proportional counter surrounded by a spherical moderator made of borated polyethylene with an internal shield made of lead. The dose rate indicated by the SmartREM-LINUS was investigated for two different irradiation conditions. The linearity and the angular dependence of the indicated dose rate were investigated using reference neutron fields produced by (241)AmBe and (252)Cf. Additional measurements were performed in two different workplace fields with a component of neutrons with energies >20 MeV, namely the CERN-EU high-energy reference field and near the beam dump of the SwissFEL injector test facility. The measured dose rates were compared to a commercial rem-counter (WENDI2) and the results of Monte Carlo simulations.

The suitability of portable nuclide inspectors for incorporation measurements were tested with three probes (LaBr3(Ce), NaI(Tl) and HPGe) differing in sensitive volume and energy resolution. The efficiencies for the measurement of whole-body and lung radionuclide burden were calibrated using a whole-body block phantom with traceable radionuclide sources of 60Co, 133Ba, 137Cs, 152Eu and 40K. A standing geometry was chosen as it allows rapid positioning of persons for the measurements. Decision and detection limits were determined for the unshielded detector in a normal laboratory radiation environment according to ISO 11929 for 134Cs, 137Cs and 60Co. The detection limits of all three probes were significantly higher compared to well-shielded dedicated whole-body monitors (HPGe and NaI(Tl)) using a sitting geometry. Nevertheless, lung and whole-body burdens derived from dose constraints for routine and emergency conditions could be measured with all three probes with a counting time of one minute.

Since 2008 the Paul Scherrer Institute (PSI) has been using a microscope-based automatic scanning system for assessing personal neutron doses with a dosemeter based on PADC. This scanning system, known as TASLImage, includes a comprehensive characterisation of tracks. The distributions of several specific track characteristics such as size, shape and optical density are compared with a reference set to discriminate tracks of alpha particles and non-track background. Due to the dosemeter design at PSI, it is anticipated that radon should not significantly contribute to the creation of additional tracks in the PADC detector. The present study tests the stability of the neutron dose determination algorithm of the personal neutron dosemeter system in operation at PSI at different radon gas exposures.

Kandidaten für die vom 3. bis 21. März 2016 im Auftrag des Bundesamtes für Gesundheit (BAG) durchgeführte Vergleichsmessung waren vorwiegend Firmen, Institutionen oder Privatpersonen, welche die Anerkennung des BAG als Radonmessstelle besitzen und deshalb nachweisen müssen, dass die Qualität der Messresultate gewährleistet ist. Dem Aufruf des BAG zur Teilnahme folgten zwölf anerkannte Messstellen, beziehungsweise deren Auswertelaboratorien, sowie siebzehn weitere Messstellen. Acht Messstellen nahmen mit mehreren Messsystemen an der Vergleichsmessung teil. Sechs verschiedene Dosimeter- oder Messgerätearten waren vertreten. Neben Kernspurdetektoren wurden als Radondosimeter Elektret-Ionisationskammern und elektronische Dosimeter eingesetzt. In diesem Jahr nahmen Messgeräte mit Ionisationskammern, Szintillations- und Halbleiterdetektoren an der Vergleichsmessung teil. Die Dosimeter und Messgeräte wurden über 432 Stunden einer Exposition von 119 kBq h m-3 bei einer durchschnittlichen Radonaktivitätskonzentration von 276 Bq m-3 ausgesetzt. Die Durchschnittskonzentration war nahe dem Referenzwert von 300 Bq m-3 gewählt. Mit Ausnahme von einer anerkannten Messstelle erfüllen die in der Schweiz eingesetzten Messsysteme die Anforderungen.

The exercise ARM15 started with measurements in Switzerland performed on June 11th and 12th, 2015 organized by the National Emergency Operations Centre (NEOC) under coordination from the Expert Group for Aeroradiometrics (FAR). According to the alternating schedule of the annual ARM exercises, the environs of the nuclear power plants Gösgen (KKG) and Mühleberg (KKM) were surveyed. Additionally, the environs of KKG were inspected on September 16th during the emergency drill GNU15. Following a request of the University of Basel additional measurements were performed in the Urseren and Piora Valleys. Further tests with the prototype of a new airborne gammaspectrometry system and the associated data evaluation software were performed, showing performance improvements since 2014 and indicating areas, where further advancement is necessary. The major part of the exercise consisted of the participation in the International Airborne Gamma Counting exercise AGC15 organized by the Bundesamt für Strahlenschutz (BfS) in Germany from June 14th to 19th, 2015. The results of the intercomparison will be evaluated, interpreted and published in detail by BfS. Thus, the presented report is limited to the documentation of the measurements performed by the Swiss team.

The measurement flights of the exercise ARM13 were performed between June 24th and 27th, 2013. The exercise was organized by the National Emergency Operations Centre (NEOC) under coordination from the Expert Group for Aeroradiometrics (FAR). According to the alternating schedule of the annual ARM exercises, the environs of the nuclear power plants Gösgen (KKG) and Mühleberg (KKM) were surveyed. As in previous years, the distinction between pressurized and boiling water reactor is clearly identified from the photon spectra. Additional areas to the north and south of the routine measurement area of KKG and to the north-west of KKM were added during this exercise to improve information on the background radiation level. Measurements over the cities of Biel/Bienne and Thun were performed in the program to obtain radiation background values over Swiss cities. Further areas in the Kander valley were added to the program of the exercise. All of these areas showed background-level readings. A military training area near Thun was used to test parameters of the data evaluation and to intercompare air with ground measurements. A flight line from Berne to Zurich was used to increase the coverage of Switzerland with radiological measurements.

The measurement flights of the exercise ARM14 were performed between June 2nd and 6th, 2014. The exercise was organized by the National Emergency Operations Centre (NEOC) under coordination from the Expert Group for Aeroradiometrics (FAR). According to the alternating schedule of the annual ARM exercises, the environs of the nuclear power plants Beznau (KKB) and Leibstadt (KKL) and the nuclear facilities of the Paul Scherrer Institute (PSI) and the Zwischenlager Würenlingen AG (Zwilag) were surveyed. Following a request of the German authorities, the measuring area was extended beyond the Rhine River into German territory. As in previous years, the distinction between pressurized and boiling water reactor is clearly identified. The series of radiological background measurements over Swiss cities was complemented with measurements over Brugg, Baden, Schaffhausen and Winterthur. A new detector was characterised in the laboratory and tested successfully during the exercise. Test with the prototype of a new airborne gammaspectrometry system showed deficiencies in the proprietary software for data evaluation, which will be mended by the manufacturer. The raw measuring data rendered comparable results to the existing system when evaluated with the existing data evaluation software. Several source search exercises during ARM14, its sub-exercise RadEx14 and the international military exercise FTX14 yielded valuable information on the performance of the airborne gammaspectrometry system and its limitations.

Kandidaten für die vom 18. bis 24. März 2014 im Auftrag des Bundesamtes für Gesundheit (BAG) durchgeführte Vergleichsmessung waren vorwiegend Firmen, Institutionen oder Privatpersonen, welche die Anerkennung des BAG als Radonmessstelle besitzen und deshalb nachweisen müssen, dass die Qualität der Messresultate gewährleistet ist. Dem Aufruf des BAG zur Teilnahme folgten zwölf anerkannte Messstellen, beziehungsweise deren Auswertelaboratorien, sowie sieben weitere Messstellen. Acht Messstellen nahmen mit mehreren Messsystemen an der Vergleichsmessung teil. Sechs verschiedene Dosimeter- oder Messgerätearten waren vertreten. Neben Kernspurdetektoren wurden als Radondosimeter Elektret-Ionisationskammern und elektronische Dosimeter eingesetzt. In diesem Jahr nahmen Messgeräte mit Ionisationskammern, Szintillations- und Halbleiterdetektoren an der Vergleichsmessung teil. Die Dosimeter und Messgeräte wurden über 143 Stunden einer Exposition von 498 kBq h m-3 bei einer durchschnittlichen Radonaktivitätskonzentration von 3486 Bq m-3 ausgesetzt. Die Exposition und die Durchschnittskonzentration lagen bei einem gut messbaren Wert für alle teilnehmenden Messsysteme. Alle von anerkannten Messtellen in der Schweiz eingesetzten Messsysteme erfüllten die Anforderungen.

A new large-scale facility is currently in the design phase at the Paul Scherrer Institute.SwissFEL is foreseen to accelerate electrons up to an energy of 7 GeV with a pulsed time structure.Unavoidable interactions of the primary beam with beam line components create secondary radiation.The shielding of the accelerator vault has to reduce the radiation level for accessible areas in compliance with legal constraints.In addition, the position and layout of cable ducts and infrastructure shafts through the shielding of the accelerator tunnel have to be investigated from a radiation protection point of view.In this work, the dose rate distribution inside the accelerator vault has been evaluated for expected beam loss scenarios (normal and diagnostic mode of operation) based on Monte Carlo calculations.By means of the multi-particle transport code FLUKA, a simplified model has been defined and the results have been parameterized.From these, a dose rate evaluation has been extracted for different positions inside the accelerator tunnel.The results can be used to investigate the leakage of radiation through cable ducts and infrastructure shafts for different design layouts or modes of operation.