Measurement Of Stray Radiation Research Articles

Assessment of ECH stray radiation levels at the W7-X Michelson Interferometer and Profile Reflectometer

Electron Cyclotron Heating and Electron Cyclotron Current Drive are key components for heating and control in magnetically confined fusion plasmas. The high power microwaves are not always completely absorbed leading to stray radiation [1], [2]. At W7-X, the total injected microwave power can be up to 7.5 MW @140 GHz while the entire Electron Cyclotron Emission picked-up by an observer at the edge of the plasma is a fraction of a mW. In the situation of a Michelson Interferometer, the principle measurement is the entire ECE spectrum. Thus, any stray radiation is bound to enter the spectrum. In this work initial stray radiation measurements without filters at the location of two microwave receivers -the Michelson Interferometer and the Profile Reflectometer -are discussed. The data is used to dimension a notch filter to be used with the broad band Michelson Interferometer.

Inference of the microwave absorption coefficient from stray radiation measurements in Wendelstein 7-X

The efficiency of electron cyclotron heating is determined by the microwave absorption of the plasma. Good microwave absorption is also crucial for the machine safety. In this paper we present a method of evaluating the microwave absorption coefficient from stray radiation measurements. The discussed method is computationally simple and can be applied potentially in real time. Evolution of the second harmonic extraordinary mode (X2) microwave absorption coefficient in Wendelstein 7-X during the start-up phase is presented, as well as an estimate of the absorption coefficient for the second harmonic ordinary mode (O2) wave.

Measurement of stray radiation within a scanning proton therapy facility: EURADOS WG9 intercomparison exercise of active dosimetry systems

To characterize stray radiation around the target volume in scanning proton therapy and study the performance of active neutron monitors. Working Group 9 of the European Radiation Dosimetry Group (EURADOS WG9-Radiation protection in medicine) carried out a large measurement campaign at the Trento Centro di Protonterapia (Trento, Italy) in order to determine the neutron spectra near the patient using two extended-range Bonner sphere spectrometry (BSS) systems. In addition, the work focused on acknowledging the performance of different commercial active dosimetry systems when measuring neutron ambient dose equivalents, H(∗)(10), at several positions inside (8 positions) and outside (3 positions) the treatment room. Detectors included three TEPCs--tissue equivalent proportional counters (Hawk type from Far West Technology, Inc.) and six rem-counters (WENDI-II, LB 6411, RadEye™ NL, a regular and an extended-range NM2B). Meanwhile, the photon component of stray radiation was deduced from the low-lineal energy transfer part of TEPC spectra or measured using a Thermo Scientific™ FH-40G survey meter. Experiments involved a water tank phantom (60 × 30 × 30 cm(3)) representing the patient that was uniformly irradiated using a 3 mm spot diameter proton pencil beam with 10 cm modulation width, 19.95 cm distal beam range, and 10 × 10 cm(2) field size. Neutron spectrometry around the target volume showed two main components at the thermal and fast energy ranges. The study also revealed the large dependence of the energy distribution of neutrons, and consequently of out-of-field doses, on the primary beam direction (directional emission of intranuclear cascade neutrons) and energy (spectral composition of secondary neutrons). In addition, neutron mapping within the facility was conducted and showed the highest H(∗)(10) value of ∼ 51 μSv Gy(-1); this was measured at 1.15 m along the beam axis. H(∗)(10) values significantly decreased with distance and angular position with respect to beam axis falling below 2 nSv Gy(-1) at the entrance of the maze, at the door outside the room and below detection limit in the gantry control room, and at an adjacent room (<0.1 nSv Gy(-1)). Finally, the agreement on H(∗)(10) values between all detectors showed a direct dependence on neutron spectra at the measurement position. While conventional rem-counters (LB 6411, RadEye™ NL, NM2-458) underestimated the H(∗)(10) by up to a factor of 4, Hawk TEPCs and the WENDI-II range-extended detector were found to have good performance (within 20%) even at the highest neutron fluence and energy range. Meanwhile, secondary photon dose equivalents were found to be up to five times lower than neutrons; remaining nonetheless of concern to the patient. Extended-range BSS, TEPCs, and the WENDI-II enable accurate measurements of stray neutrons while other rem-counters are not appropriate considering the high-energy range of neutrons involved in proton therapy.

WE‐D‐17A‐05: Measurement of Stray Radiation Within An Active Scanning Proton Therapy Facility: EURADOS WG9 Intercomparison Exercise of Active Dosimetry Systems

Purpose:Intercomparison of active dosemeters in the measurement of stray radiation at the Trento active‐scanning proton therapy facility.Methods:EURADOS WG9 carried out a large intercomparison exercise to test different dosemeters while measuring secondary neutrons within a 230 MeV scanned proton therapy facility. Detectors included two Bonner Sphere Spectrometers (BSS), three tissue equivalent proportional counters (TEPCHawk) and six rem‐counters (Wendi II, Berthold, RadEye, a regular and an extended‐range Anderson &amp; Braun NM2B counters). Measurements of neutron ambient dose equivalents, H*(10), were done at several positions inside (8 positions) and outside (3 positions) the treatment room while irradiating a water tank phantom with a 10 × 10 × 10 cc field.Results:A generally good agreement on H*(10) values was observed for the tested detectors. At distance of 2.25 m and angles 45°, 90° and 180° with respect to the beam axis, BSS and proportional counters agreed within 30%. Higher differences (up to 60%) were observed at the closest and farthest distances, i.e. at positions where detectors sensitivity, energy, fluence and angular response are highly dependent on neutron spectra (flux and energy). The highest neutron H*(10) value, ∼60 microSv/Gy, was measured at 1.15 m along the beam axis. H*(10) decreased significantly with the distance from the isocenter dropping to 1.1 microSv/Gy at 4.25 m and 90° from beam axis, ∼2 nanoSv/Gy at the entrance of the maze, 0.2 nanoSv/Gy at the door outside the room and below detection limit in the gantry control room and at an adjacent room. These values remain considerately lower than those of passively scattered proton beams. BSS and Hawk unfolded spectra provide valuable inputs when studying the response of each detector.Conclusion:TEPCs and BSS enable accurate measurements of stray neutrons while other rem‐meters also give satisfactory results but require further improvements to reduce uncertainties.

A Mobile Geiger-Müller Tube Counting System and some of its Medical Applications

The design and operation of a mobile counting system incorporating a Geiger counter are described. The instrument reads directly all counting rates up to 1000 periodic impulses per second, and correction graphs are drawn for the losses sustained when random impulses are counted. The instrument is calibrated in terms of tolerance dose-rate (T.D.R.) for the γ rays of radium and for 200 kV X rays. For radium γ rays, full scale deflection corresponds to about 1 T.D.R., while for X rays it is only about 0·4 T.D.R. Results of stray radiation measurements carried out in the teleradium treatment room (containing 1 gm. and 10 gm. teleradium units), and the floors beneath it, and also in the X-ray Therapy and Diagnostic Departments, are presented. A brief description of the use of the instrument in measuring activities in various parts of a patient's body after the administration of radio-iodine, is also given. Instruments of similar design may be widely used in the future for work of this nature.

A Negative Feed-back Dosage-rate Meter

A direct reading X-ray dosage-rate meter is described, which consists of a radiation transparent thimble ionization chamber (volume ½ c.c.), connected by a thin flexible cable to a negative feed-back D.C. amplifier. The instrument is robust and cheap to manufacture. An accuracy of better than ± 5 per cent. or 1 r/min. is achieved on all ranges, and the instrument is intended for routine measurements in a radiotherapy department. Standard radio components are used throughout and electrometer valves have been eliminated. The instrument is adaptable for radium dosage-rate measurements, stray radiation measurements, and as a radon balance.

A Stray Radiation Survey of Twenty High Voltage Roentgen Installations

THE problem of x-ray protection has received the attention of numerous investigators since the early days of roentgenology. As a result of such studies the various committees on x-ray protection have recommended certain minimum requirements (1) to prevent excessive stray radiation. Yet, the degrees of protection provided in different radiologic departments for the same operating conditions show surprisingly wide differences. While, in general, this variation is well on the safe side, there are, unfortunately, still installations where the protection is inadequate or ineffectively arranged. In many cases this lack of uniformity is due to differences in opinion as to how the protective material should be distributed on the walls, floor, and ceiling of the x-ray room in order to comply with the recommendation of the protection committees which is to limit the stray radiation to the now generally accepted tolerance dose of 0.2 r per day (2, 3). Earlier reports (4, 5) on stray radiation measurements have been ...