Radiation protection at Hadron therapy facilities

The Italian National Centre for Oncological Hadrontherapy is currently under construction in Pavia. It is designed for the treatment of deep-seated tumours (up to a depth of 27 cm of water equivalent) with proton and C-ion beams as well as for both clinical and radiobiological research. The particles will be accelerated by a 7-MeV u(-1) LINAC injector and a 400-MeV u(-1) synchrotron. In the first phase of the project, three treatment rooms will be in operation, equipped with four fixed beams, three horizontal and one vertical. The accelerators are currently undergoing commissioning. The main radiation protection problems encountered (shielding, activation, etc.) are hereby illustrated and discussed in relation to the constraints set by the Italian national authorities.     

Radiation protection at nuclear fuel cycle facilities

Radiation protection methodologies concerning individual monitoring, workplace monitoring and environmental monitoring in nuclear fuel facilities have been developed and applied to facilities in the Nuclear Fuel Cycle Engineering Laboratories (NCL) of Japan Atomic Energy Agency (JAEA) for over 40 y. External exposure to photon, beta ray and neutron and internal exposure to alpha emitter are important issues for radiation protection at these facilities. Monitoring of airborne and surface contamination by alpha and beta/photon emitters at workplace is also essential to avoid internal exposure. A critical accident alarm system developed by JAEA has been proved through application at the facilities for a long time. A centralised area monitoring system is effective for emergency situations. Air and liquid effluents from facilities are monitored by continuous monitors or sampling methods to comply with regulations. Effluent monitoring has been carried out for 40 y to assess the radiological impacts on the public and the environment due to plant operation.     

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.     

Present and future synchrotron radiation facilities in Japan

I was very pleased to be invited by Takehiko Ishii to spend 4 months (September–December 1985) as a visiting scientist at the Institute for Solid State Physics (ISSP) of the University of Tokyo. This visit, co-sponsored by Kazuo Huke of the Photon Factory, gave me an excellent opportunity to find out first hand about the status and prospects for synchrotron radiation research in Japan.This article summarizes my observations and discussions during this visit. In an appendix an update on the present status of these facilities is presented, with particular emphasis on the Photon Factory, the largest and most capable facility. The interested reader is referred also to annual activity reports published by the SOR-Ring and Photon Factory labs and planned for 1986 by the UVSOR lab and also to other references listed at the end of this article.     

A new beam position monitor for X-ray synchrotron radiation facilities

We present here a simple device which can detect one-dimensional beam mition over a large range, with a spatial resolution of a fraction of a percent of its range, a time resolution of a few seconds, and good long-term stability. Its resolution is statistically limited, and could be improved by careful detector design.     

Characteristics of radiation safety for synchrotron radiation and X-ray free electron laser facilities

Radiation safety problems are discussed for typical electron accelerators, synchrotron radiation (SR) facilities and X-ray free electron laser (XFEL) facilities. The radiation sources at the beamline of the facilities are SR, including XFEL, gas bremsstrahlung and high-energy gamma ray and photo-neutrons due to electron beam loss. The radiation safety problems for each source are compared by using 8 GeV class SR and XFEL facilities as an example.     

Radiation protection at medical accelerators

This paper focuses on radiation protection at proton and light ion accelerators for radiotherapy. The National Centre of Hadrontherapy, which is planned to he built in Italy in the next five years, is considered as a reference facility for applying the various methodologies presented. The shielding design is firstly discussed, together with that of the access maze to the treatment rooms. Subsequently, the main aspects for the estimate of the air activation in the environment hosting the accelerator system are described. The estimate of the dose equivalent due to the activated air transferred to the neighbourhood population is also treated. Outlines are given of the radioactivity induced by the primary beam in the materials constituting the magnets and the patient's personal collimator.     

Dosimetry at 28 keV synchrotron radiation for cell irradiations

Accurate dosimetry is a prerequisite for reliable comparisons between radiobiological irradiation experiments. Parameters affecting the determination of absorbed dose to cells in the shape of a small cell pellet in a centrifuge tube, irradiated by 28 keV mono-energetic photons from a synchrotron, were investigated. Thermoluminescent dosimeter (TLD), diode and ion chambers were utilized to monitor the irradiations. The distribution of the absorbed dose and such parameters as scatter, attenuation and interface dosimetry in the target, which influence the dose, were studied. A method for inter-calibrations of two different calibration sources by using TLD and TLD readers is given. Characteristics of the TLD, that is, fading, supralinearity, energy response, self-attenuation and mini-dosimetry were considered for the dosimetry. A method for correcting photon fluence attenuation in cylindrical TLDs is presented. The study shows that the absorbed dose to cells irradiated at low photon energy at a synchrotron irradiation facility can, using accurate dosimetry protocol, be correctly and reproducibly determined.     

Individual monitoring for external radiation at accelerator facilities

Individual monitoring at accelerator facilities is discussed, within the framework set out by the International Commission on Radiological Protection and with reference to the implementation of the recommendations of that body within the European Basic Safety Standards. Legislation in other parts of the world may differ, but a worldwide perspective on this subject would be too exhaustive. The fields at accelerator facilities are contrasted in terms of particle type and energy with those encountered at more conventional sites within the nuclear fuel cycle, medical applications and general industry. The implications for individual monitoring are discussed in relation to the dose quantities for these accelerator fields and also with respect to the personal dosemeters options.     

UHV-type synchrotron radiation reflectometer

We designed a reflectometer for grazing-incidence X-ray measurements with a rotational feedthrough consisting of three welded bellows and a circle-type goniometer. This apparatus does not require differential pumping and is suitable for ultra-high-vacuum applications. With this reflectometer, we successfully performed high-precision synchrotron radiation X-ray reflectivity measurements on a thin iron-film under an ultra-high-vacuum condition.     

Focusing of synchrotron radiation

Focusing of the synchrotron radiation from a storage ring using a convex lens is geometrically analysed and tested. The source radiation is supposed to have a bivariate normal distribution in its phase space both vertically and horizontally. Its modification caused by a lens is calculated as a function of distances among the source, the lens and the image plane. It is shown that the horizontal image becomes sharpest when the source is focused on the image plane. The vertical image, however, is not sharpest under this condition. The vertical distribution has more information than the horizontal; we can derive the orbit dependence of the vertical profile and the angle distribution of the radiation changing focusing.     

Radiation protection at low energy proton accelerators

A sample is provided of the radiological safety issues particular to low energy proton accelerators. 'Low' energy in this context is taken to mean proton energies of less than about 1 GeV. Many of the radiation issues are common to all particle accelerators. Here, those issues are addressed that may require perhaps not unique treatment but those which benefit from a different approach. Among the problems discussed are the generation of prompt radiation and its transmission through shielding, the estimation of induced radioactivity, and the assessments of both the off-site prompt radiation hazard and the effect of releases of radioactive effluents to the environment.     

Radiation protection at high energy proton accelerators

The radiological problems associated with proton accelerators having maximum energies higher than a few GeV are discussed. Examples are given from accelerators where the authors have had practical experience for a number of years. The main focus will be on those problems which are unique to high energy proton accelerators, and which may not be necessarily associated with the proton beam operation itself.     

Quantum efficiency measurement of CsI photocathodes using synchrotron radiation at BSRF

A quantum efficiency(QE) measurement system has been established for CsI photocathodes in the wavelength range of 120-210 nm by using the synchrotron radiation light source at Beijing Synchrotron Radiation Laboratory (BSRF). An AXUV100G photodiode calibrated by Physikalisch-Technische Bundesanstalt (PTB) was used as the transfer detector standard to ensure the accuracy and reliability of the QE measurement. The dependencies of QE measurement on beam energy, vacuum pressure and bias voltage were studied in detail. The influence of photoionization in gas on the QE measurement was observed and is described. The surface morphological characteristics of both substrate and CsI film were analyzed by atomic force microscopy (AFM). The QE results of differently prepared CsI photocathodes were compared, including: the printed circuit board (PCB) of FR-4 (Woven glass and epoxy)+Cu, FR-4+Cu/Ni/Au, and stainless steel substrates; a series of thickness from 60 to 600 nm; and the resistive and electron beam evaporation techniques.     

Spatial coherence of synchrotron radiation

The spatial coherence properties of a monochromatic component of synchrotron radiation from an insertion device in the Fraunhofer limit are analyzed in the general case when the coherence distance is comparable with the beam width, expressing them by simple products and convolutions of Fourier transforms and autocorrelations on the single-electron field amplitude and the electron-beam position and angular distributions. In particular, the Gaussian approximation is discussed, in which case the far-field amplitude satisfies the Schell condition (its statistical properties can be described by a coherence factor depending only on the difference of the reciprocal space coordinates), and this discussion leads to simple estimates of the coherence widths. The coherence widths deviate from the Van Cittert-Zernike values when one or more of the phase space widths of the electron beam are close to (or smaller than) the diffraction limit.     

Radiation protection aspects of the cosmic radiation exposure of aircraft crew

Aircraft crew and frequent flyers are exposed to elevated levels of cosmic radiation of galactic and solar origin and secondary radiation produced in the atmosphere, the aircraft structure and its contents. Following recommendations of the International Commission on Radiological Protection in Publication 60, the European Union introduced a revised Basic Safety Standards Directive, which included exposure to natural sources of ionising radiation, including cosmic radiation, as occupational exposure. The revised Directive has been incorporated into laws and regulations in the European Union Member States. Where the assessment of the occupational exposure of aircraft crew is necessary, the preferred approach to monitoring is by the recording of staff flying times and calculated route doses. Route doses are to be validated by measurements. This paper gives the general background, and considers the radiation protection aspects of the cosmic radiation exposure of aircraft crew, with the focus on the situation in Europe.     

Hard X-ray polarization measured with a Compton polarimeter at synchrotron radiation facility

A hard X-ray polarimeter with CdTe detectors has been developed for measurement of the degree of X-ray polarization at synchrotron radiation facilities. It utilizes 90° Compton scattering from the low Z targets. Measurements were performed at both facilities of the beamline BL38B1 in SPring-8 and the beamline BL14A in KEK-PF. The degrees of X-ray polarization for 20 keV X-rays are 99% and 82% at the BL38B1 in SPring-8 and BL14A in KEK-PF, respectively. The polarization degrees in the energy range of 15 and 40 keV correspond to 99.6±0.2% and 96.1±0.2% at the beamline BL38B1 in SPring-8. The analyzing power of the polarimeter was estimated by the Monte Carlo simulation with EGS4. The synchrotron radiation facilities provide highly polarized X-ray beams at energies above 15 keV.     

Radiation protection for accompanying person and radiation workers in PET/CT

The purposes of the present study are to measure the total radiation doses for the radiation workers and for the accompanying person to the patients in positron emission tomography (PET)/computed tomography (CT) imaging. Urines samples from the patients were collected at 43, 62, 87, 117, 238, 362 min after the 555-MBq (18)flour-fluorodeoxyglucose ((18)F-FDG) injection and activities were measured. Dose rates were recorded using a Geiger-Muller counter and the total radiation doses were measured with using an electronic personnel dosemeter. According to the results here, 18.4 % of (18)F-FDG was excreted in the urine in 117 min after injection. At 117th min after injection, dose rates were determined as 345, 220, 140, 50 and 15 μSv h(-1), at proposed distances. The radiation doses after 117 min were measured as 3.92 mSv at 0.1 m, 2.11 mSv at 0.25 m and 1.08 mSv at 0.5 m. In conclusion, radiation protection will be sufficient within 2 h after (18)F-FDG injection for PET/CT imaging in daily practice.