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PubMed2005

Beam dumps design and local radiation protection at TERA synchrotron.

The realisation of the National Center of Hadrontherapy was funded by the Italian Government in 2002. The Centre will be built in the area of Pavia (Italy). The synchrotron designed in the framework of this programme will accelerate protons and carbon ions up to 250 MeV and 400 MeV u(-1), respectively. Some of the main aspects which were taken into account in the design of the acceleration system are the patient's safety and the beam control. From this point of view an important role is played by the beam dumps in the synchrotron ring and upstream of the extraction system. In particular, an horizontal and a vertical beam dump will be installed in the synchrotron ring: the former will be used for lowering the beam intensity and the latter for beam abortion. The dump at the extraction will absorb the particles during the mounting and the falling ramps of the synchrotron magnetic cycle, thus extracting only the flat top of the ion spill. Beam dumps can produce intense fields of secondary radiation (neutrons, charged light-hadrons and photons) and high rates of induced activity, since they can absorb the beam completely. Usually they have to be shielded to protect the electronics during machine operation and to attenuate the radiation dose below the limits imposed by the law when the personnel access to the synchrotron hall. The part of the shielding design of the beam dumps concerning with the acceleration of protons was made using Monte Carlo simulations with the FLUKA code. Both induced activity and secondary radiation were taken into account. The shields against secondary radiation produced by carbon ions were designed, referring only to secondary neutrons, taking double-differential distributions from the literature as sources for the FLUKA simulations. The induced activity from carbon ions interactions was estimated analytically, using the data generated by the EPAX 2 code. The dose-equivalent rates from the induced radionuclides were calculated at 1 m from the shielded dumps, taking into account the contribution of activated components of the synchrotron ring.

Computer Simulation↗
PubMed2005

The radon inverse dose rate effect and high-LET galactic hazards.

The lung dose rate per unit 222Rn concentration in enclosed spaces is shown to experience transitions at high radon concentrations. This has implications on the radon inverse dose rate effect. At an air change rate (ACH) of 0.194 h(-1) and relative humidity (RH) of 52.3% in a 0.283 m3 test chamber, the total human lung dose for an adult male in a residential setting (breathing rate 0.78 m3 h(-1)) would undergo a reduction of 2.5 using the ICRP 66 human respiratory tract model and the BEIR VI methodology. Using the same methodology of both Cross (Pacific Northwest Laboratory rat exposures) and Lubin et al. (miners dose rates), adjustments are necessary for effects of RH and ACHs. These adjustments, however, do not affect the reduction behaviour. It is thus shown that the enhanced deposition effect (EDE) must influence the magnitude of the purported inverse dose rate effect (IDRE). In the analysis of animal data, Cross rat exposures in a 2.0 m3 chamber, a reduction in lung dose is estimated to be over a factor of 3 the transition between the 50 and 500 WLM week(-1) dose rate range. For an estimation of the EDE, using a hypothetical 30 m3 enclosure for underground miners, we obtain a factor of approximately 4 in human lung dose reduction. Although the extensive analyses required make these results qualitative, the EDE behaviour is sufficiently conclusive that these estimates show that the radon IDRE for lung cancer must be an EDE dosimetric issue as well as a radiological lung cell dose response issue. The consequence of analysis of other animal data would achieve the same conclusion.

Adult↗
PubMed2005

Radiation protection standards: their evolution from science to philosophy.

The concept of applying constraints on individual sources to a small fraction of the public dose limit has been deemed inappropriate when shielding the medical X-ray sources. This represents a broad-based consensus of medical physics and radiological societies in the United States, and the report series on the shielding design for medical X-ray sources (including dental, X-ray imaging and therapeutic X ray) from the National Council on Radiation Protection and Measurements (NCRP) utilises 1 mSv y(-1) as a source control limit. In the present study, the rationale for such a conclusion is discussed, and a somewhat critical look at the current model of radiation protection of the public is made.

Environmental Exposure↗
PubMed2005

The PDS-XADS reference accelerator and its radioprotection issues.

At the start-up of the FP5 project PDS-XADS, the main initial specifications for the accelerator system (e.g. beam energy, beam intensity, beam profile, their stability and the accelerator availability and reliability) have been defined by Working Package 1 (WP1), 'Global Coherence', in connection with the other WPs of the project. From this, WP3 ('The Accelerator') has assessed the main requirements and the corresponding technical answers. A reference solution, based on a linear superconducting accelerator with its associated doubly achromatic beam line has been worked out to some detail. For high reliability, the proposed design is intrinsically fault tolerant, relying on highly modular 'de-rated' components associated with a fast digital feedback system. The proposed solution also appears to be robust in terms of operational aspects like maintenance and radioprotection. A programme for the remaining R&D required has been elaborated and is proposed within the FP6 project EUROTRANS.

Equipment Design↗
PubMed2005

Investigation of radiation fields outside the Sub-critical Assembly in Dubna.

The radiation fields outside the planned experimental Sub-critical Assembly in Dubna (SAD) have been studied in order to provide a basis for the design of the concrete shielding that cover the reactor core. The effective doses around the reactor, induced by leakage of neutrons and photons through the shielding, have been determined for a shielding thickness varying from 100 to 200 cm. It was shown that the neutron flux and the effective dose is higher above the shielding than at the side of it, owing to the higher fraction of high-energy spallation neutrons emitted in the direction of the incident beam protons. At the top, the effective dose was found to be -150 microSv s(-1) for a concrete thickness of 100 cm, while -2.5 microSv s(-1) for a concrete thickness of 200 cm. It was also shown that the high-energy neutrons (> 10 MeV), which are created in the proton-induced spallation interactions in the target, contribute for the major part of the effective doses outside the reactor.

Computer Simulation↗
PubMed2005

21st century challenges in radiation protection and shielding: draft 2005 recommendations of ICRP.

The International Commission on Radiological Protection regularly examines the status of its recommendations and reviews the increasing knowledge of the effects of exposure to ionising radiation in order to decide whether new recommendations are needed. The Commission strives to make its system more coherent and comprehensible, while recognising the need for stability in international and national regulations, many of which have, only fairly recently, implemented the 1990 Recommendations. However, new scientific data have been produced since 1990 and there have been societal developments in that more openness or transparency is expected in developing new recommendations and, in addition, there has been a move from the utilitarian approach of 'the greatest good for the greatest number', to one with more concern for the 'individual', all of which have inevitably led to some changes in the formulation of the recommendations. This paper outlines the proposals for the 2005 Recommendations.

Guidelines as Topic↗
PubMed2005

Shielding design for the front end of the CERN SPL.

CERN is designing a 2.2-GeV Superconducting Proton Linac (SPL) with a beam power of 4 MW, to be used for the production of a neutrino superbeam. The SPL front end will initially accelerate 2 x 10(14) negative hydrogen ions per second up to an energy of 120 MeV. The FLUKA Monte Carlo code was employed for shielding design. The proposed shielding is a combined iron-concrete structure, which also takes into consideration the required RF wave-guide ducts and access labyrinths to the machine. Two beam-loss scenarios were investigated: (1) constant beam loss of 1 Wm(-1) over the whole accelerator length and (2) full beam loss occurring at various locations. A comparison with results based on simplified approaches is also presented.

Computer Simulation↗
PubMed2005

Preliminary shielding assessment for the 100 MeV proton linac (KOMAC).

The Proton Engineering Frontier Project is building the Korea Multipurpose Accelerator Complex facilities from 2002 to 2012, which consists of a high-current 100 MeV proton linear accelerator and various beam-lines. This paper provides a preliminary estimate of the shielding required for the 20 mA proton linac and the beam-dump. For an accurate information on secondary neutron production from the guiding magnet and primary heat sink of the beam dump, proton-induced 63Cu and 65Cu cross section data were evaluated and applied to shielding calculations. The required thickness of the concrete was assessed by a simple line-of-sight model for the lateral shielding of the beam-line and the full shielding of the beam dump. Monte Carlo simulations were also performed using the MCNPX code to obtain the source term and attenuation coefficients for the three-dimensional lateral shielding model of the beam-line.

Computer Simulation↗
PubMed2005

Design of radiation shielding for the proton therapy facility at the National Cancer Center in Korea.

The design of radiation shielding was evaluated for a proton therapy facility being established at the National Cancer Center in Korea. The proton beam energy from a 230 MeV cyclotron is varied for therapy using a graphite target. This energy variation process produces high radiation and thus thick shielding walls surround the region. The evaluation was first carried out using analytical expressions at selected locations. Further detailed evaluations have been performed using the Monte Carlo method. Dose equivalent values were calculated to be compared with analytical results. The analytical method generally yielded more conservative values. With consideration of adequate occupancy factors annual dose equivalent rates are kept <1 mSv y(-1) in all areas. Construction of the building is expected to be completed near the end of 2004 and the installation of therapy equipment will begin a few months later.

Computer Simulation↗
PubMed2005

Calculation of the store house worker dose in a lost wax foundry using MCNP-4C.

Lost wax casting is an industrial process which permits the transmutation into metal of models made in wax. The wax model is covered with a silicaceous shell of the required thickness and once this shell is built the set is heated and wax melted. Liquid metal is then cast into the shell replacing the wax. When the metal is cool, the shell is broken away in order to recover the metallic piece. In this process zircon sands are used for the preparation of the silicaceous shell. These sands have varying concentrations of natural radionuclides: 238U, 232Th and 235U together with their progenics. The zircon sand is distributed in bags of 50 kg, and 30 bags are on a pallet, weighing 1,500 kg. The pallets with the bags have dimensions 80 cm x 120 cm x 80 cm, and constitute the radiation source in this case. The only pathway of exposure to workers in the store house is external radiation. In this case there is no dust because the bags are closed and covered by plastic, the store house has a good ventilation rate and so radon accumulation is not possible. The workers do not touch with their hands the bags and consequently skin contamination will not take place. In this study all situations of external irradiation to the workers have been considered; transportation of the pallets from vehicle to store house, lifting the pallets to the shelf, resting of the stock on the shelf, getting down the pallets, and carrying the pallets to production area. Using MCNP-4C exposure situations have been simulated, considering that the source has a homogeneous composition, the minimum stock in the store house is constituted by 7 pallets, and the several distances between pallets and workers when they are at work. The photons flux obtained by MCNP-4C is multiplied by the conversion factor of Flux to Kerma for air by conversion factor to Effective Dose by Kerma unit, and by the number of emitted photons. Those conversion factors are obtained of ICRP 74 table 1 and table 17 respectively. This is the way to obtain a function giving dose rate around the source.

Body Burden↗
PubMed2005

Shielding design for the PANDA spectrometer at the Munich high-flux reactor FRM-II.

The start-up of the Munich high-flux reactor FRM-II is in progress on. At the beam tube SR-2 the spectrometer PANDA has been installed. It is at three-axis neutron spectrometer looking onto a slightly under-moderated cold neutron source. For polarisation analysis, PANDA is equipped with a vertical cryomagnet producing fields up to 14.5 T for the sample. To get an appropriate shielding of the high-intensity instrument, one has to take into account the large cross section of the primary beam, several restrictions using magnetic materials, limitations in loading the site and finally, has to keep the lateral extent of the shielding small to allow for high-scattering angles. The shielding has been designed on the basis of the results, which were achieved by the combined use of both the Monte Carlo code MCNP-4B2 and an analytical method based on one-dimensional dose transmission functions.

Computer Simulation↗
PubMed2005

Shielding variation effects for 250 MeV protons on tissue targets.

This paper provides results of computer simulation studies with the goal to analyse issues regarding radiation protection for personnel, patients and third persons involved in hadron therapy treatment. The treatment room and the patient are modelled by simple cylindrical geometries at incident proton energies of 250 MeV. Monte Carlo simulations of the energy and angular dependence of proton, neutron and photon radiation fields and resulting ambient dose equivalent distributions outside the shielding walls are performed. In order to investigate systematic uncertainties due to the shielding materials and inherent to the computer models, various concrete compositions, densities and water contents are modelled, and the influence of simulation parameters on the results obtained is determined. Generally, good agreement is found between results provided by MCNPX and FLUKA computer codes. Variations in neutron ambient dose attenuation from -50 to +/-30% are found due to varying concrete composition. Changes in the water content of the concrete in the order of 8% may cause variations up to 20%.

Body Burden↗
PubMed2005

A very low-background gamma-ray counting facility in the Baradello underground laboratory.

An underground station for the measurement of low-level radioactivity is in operation in Northern Italy in the town of Como under the Baradello hill. The rock cover is -300 m water equivalent. This paper reports about the preliminary measurements carried out to characterise the site of the Baradello hill and the installation of a high-purity Ge detector with a radio-pure copper shielding. Features and levels of the achieved background are reported and discussed, in comparison with other above ground and underground low-radioactivity stations. Sensitivities to radioactivity in typical environmental matrices are evaluated, confirming the very low-gamma background attained in the laboratory.

Air Pollutants, Radioactive↗
PubMed2005

Calculations for the availability of photoneutron using synchrotron radiation.

The availability of the neutrons due to photonuclear reactions has been discussed by using synchrotron radiation with the beryllium targets. The superconducting wiggler with the magnetic field of approximately 10 T, which is installed into an 8 GeV class storage ring, can emit intense and high-energy photons to produce neutrons. By using MCNPX, the simulations were performed for the conceptual design of the neutron beamline to estimate the available intensity and to investigate the shield conditions. The results were discussed in comparison with other research reactors.

Computer Simulation↗
PubMed2005

Current developments at IRSN on computational tools dedicated to assessing doses for both internal and external exposure.

The paper presents the OEDIPE (French acronym that stands for tool for personalised internal dose assessment) and SESAME (for simulation of external source accident with medical images) computational tools, dedicated to internal and external dose assessment, respectively, and currently being developed at the Institute for Radiological Protection and Nuclear Safety. The originality of OEDIPE and SESAME, by using voxel phantoms in association with Monte Carlo codes, lies in their ability to construct personalised voxel phantoms from medical images and automatically generate the Monte Carlo input file and visualise the expected results. OEDIPE simulates in vivo measurements to improve their calibration, and calculates the dose distribution taking both internal contamination and internal radiotherapy cases into account. SESAME enables radiological overexposure doses to be reconstructed, as also victim, source and accident environment modelling. The paper presents the principles on which these tools function and an overview of specificities and results linked to their fields of application.

Academies and Institutes↗
PubMed2005

Shielding design of an underground experimental area at point 5 of the CERN Super Proton Synchrotron (SPS).

Increasing projected values of the circulating beam intensity in the Super Proton Synchrotron (SPS) and decreasing limits to radiation exposure, taken with the increasing non-acceptance of unjustified and unoptimised radiation exposures, have led to the need to re-assess the shielding between the ECX and ECA5 underground experimental areas of the SPS. Twenty years ago, these experimental areas at SPS-Point 5 housed the UA1 experiment, where Carlo Rubbia and his team verified the existence of W and Z bosons. The study reported here describes such a re-assessment based on simulations using the multi-purpose FLUKA radiation transport code. This study concludes that while the main shield which is made of concrete blocks and is 4.8 m thick satisfactorily meets the current design limits even at the highest intensities presently planned for the SPS, dose rates calculated for liaison areas on both sides of the main shield significantly exceed the design limits. Possible ways of improving the shielding situation are discussed.

Computer Simulation↗
PubMed2005

Target station shielding issues at the spallation neutron source.

Recent spallation neutron source shielding activities in support of the neutron beam shutters and the hot cell walls are presented. Existing neutron beam shutters can be replaced with concrete at low power or with concrete and steel at approximately 500 kW of beam power. Potential voids in the hot cell walls are analysed to determine the impact on dose rates as a function of void size. A change in the type of shielding work is noted as the project moved from the early design stages as a 'green field' site to the current stage as a construction project nearing completion, where issues to be addressed are approaching retrofit-type analyses.

Equipment Design↗
PubMed2005

Benchmarking of Monte Carlo based shutdown dose rate calculations for applications to JET.

The calculation of dose rates after shutdown is an important issue for operating nuclear reactors. A validated computational tool is needed for reliable dose rate calculations. In fusion reactors neutrons induce high levels of radioactivity and presumably high doses. The complex geometries of the devices require the use of sophisticated geometry modelling and computational tools for transport calculations. Simple rule of thumb laws do not always apply well. Two computational procedures have been developed recently and applied to fusion machines. Comparisons between the two methods showed some inherent discrepancies when applied to calculation for the ITER while good agreement was found for a 14 MeV point source neutron benchmark experiment. Further benchmarks were considered necessary to investigate in more detail the reasons for the different results in different cases. In this frame the application to the Joint European Torus JET machine has been considered as a useful benchmark exercise. In a first calculational benchmark with a representative D-T irradiation history of JET the two methods differed by no more than 25%. In another, more realistic benchmark exercise, which is the subject of this paper, the real irradiation history of D-T and D-D campaigns conducted at JET in 1997-98 were used to calculate the shut-down doses at different locations, irradiation and decay times. Experimental dose data recorded at JET for the same conditions offer the possibility to check the prediction capability of the calculations and thus show the applicability (and the constraints) of the procedures and data to the rather complex shutdown dose rate analysis of real fusion devices. Calculation results obtained by the two methods are reported below, comparison with experimental results give discrepancies ranging between 2 and 10. The reasons of that can be ascribed to the high uncertainty on the experimental data and the unsatisfactory JET model used in the calculation. A new dedicated JET benchmark experiment will be performed trying to solve these issues.

Algorithms↗