Measurement Of Radiation Field Research Articles

X波段高功率微波辐射场测量角锥天线特性

X波段高功率微波辐射场测量角锥天线特性

Angular distribution measurement and simulation of M band X-ray from the half- hohlraum

Measurement of radiation field near a implosion pellet M band X-ray is a important area in ICF research. On the SG Ⅱ laser facility, M band X-ray from Au plasma was measured in half-hohlraum radiation from the end. The experimental set-up and typical result were given. And weve also used the view-factor program to simulate this experiment. The results indicate that angular distribution of M band X-ray from the end of half-hohlraum doesnt assume linear relationship with the cosine of eradiating angle. The results are useful for the research of implosion experiment and target design.

WE‐E‐BRB‐05: The Effects of Low Dose Regions On 3D IMRT QA Delivery Using a MatriXX 2D Array and MULTICUBE

Purpose: IMRT quality assurance performed at treatment gantry angles using 2D arrays allows for the evaluation of rotational aspects of beam delivery. We investigate aspects of angular‐based IMRT QA that contribute to lower‐than‐average passing rates when compared to treatment planning calculations. Method and Materials: Planar dose profiles calculated on a CT of the IBA MatriXX 2D array device with the MULTICUBE phantom at iso‐center were exported from the Philips Pinnacle TPS. Beam angles of 0, 90, 180, and 270° were delivered using a Varian Clinac 2300iX. IBA OmniPro‐I'mRT software was used for analysis. Individual beams of 4×4 and 10×10 cm2 were compared to calculated profiles using gamma index criteria of 3 % and 3 mm. Additionally, composite profiles of 0 and 90° beams were assessed for each field size. Finally, IMRT‐delivered clinical beams were assessed. Results: The gamma index pass rates of individual 4×4 and 10×10 cm2 beams at 0° were greater than 98%. However, 90° beams were found to achieve below 90% pass rates, with the 4×4 being below 85%. The measured and calculated results compared worse in the exit dose region. Composite profiles of 0 and 90° beams agreed with calculated to within 98 % for both field sizes. Clinical IMRT beams showed good agreement in high‐dose regions, but passing rates in exit‐dose regions demonstrated reduced passing rates. Conclusion: An angular dependency is evident in the measurement of radiation fields when using the MatriXX device. Gamma index pass rates can show significant improvement through composite dose comparison. However, individual beam information can be lost, particularly the low‐dose beam exit contribution, when applying composite evaluation. This becomes important when considering the dose to organs‐at‐risk which lay in these low dose regions.

High Count Rate Neutron Spectrometry With Liquid Scintillation Detectors

Liquid scintillation detectors are widely used in nuclear/high-energy physics and nuclear fusion for spectral measurements in mixed radiation fields due to their compactness, fast response and neutron/gamma discrimination capabilities. The use of response functions evaluated for the specific system and of appropriate methods of data analysis allows such systems to be used as broadband spectrometers for photons and neutrons. System stability and ability to reach high throughput count rates are key challenges for several applications (e.g., neutron spectrometry for nuclear fusion devices), but standard analog electronics limits the operation of liquid scintillation neutron spectrometers to low count rates ( ~ 3 ldr 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) . The count rate capabilities of a liquid scintillation neutron spectrometer (NE213 detector) from the Physikalisch-Technische Bundesanstalt (PTB) has been extended up to ~ 4.2 ldr 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , by coupling it to a digital acquisition system developed at ENEA-Frascati. Measurements have been carried out at PTB using gamma sources and accelerator-produced 2.5 MeV and 14 MeV neutrons. For 14 MeV neutron measurements, digital pulse height spectra (PHS) obtained at high count rates have been compared to PHS recorded with standard analog electronics. The results show that stable PHS (within 1%) can be obtained at high count rate despite the high sensitivity of the gain of photomultiplier tubes to count rate variations.

Development of ion chambers for the measurement of low energy synchrotron radiation

Measurement of radiation fields due to low energy synchrotron radiation (SR) needs special considerations. The photoelectric interactions, which are mainly responsible for signal generation in this case, result in electron emission in a direction nearly perpendicular to the direction of incident photon. A free air ionisation chamber was designed and used for measurement of intensity of SR in the beam line and a methodology has been developed to measure SR fields away from the beam line using large volume ion chambers. Studies with spherical and cylindrical ion chambers in X-ray beams obtained at a tube potential of 15 kV (3 mm Be inherent filtration) showed that the chamber sensitivity at low energy strongly depended on curvature of the chamber wall especially in thick walled chambers. Our studies further showed that large volume thin and plane walled (0.01 mm thick aluminium wall) chambers could be used for measurement of SR fields away from the beam lines, with reasonably good accuracy (±10%) by calibrating them against the free air ion chamber through a similar chamber of smaller dimensions.

A SURVEY ON ACTUAL CONDITIONS OF PLATEAU RESIDENTIAL ENVIRONMENT IN TIBET OF CHINA

In this paper, we declare the intensity of solar radiation, UV strength, inside temperature, humidity, illumination intensity, CO and CO2 concentration field measurements for apartment building located in Tibet's capital and in traditional houses in order to evaluate their levels in the living environment. The Tibetan plateau is characterized by high altitudes, low oxygen concentration, atmosphere is transparent, wide diurnal range temperature, special culture and life style, so UV and solar radiation, thermal environment and IAQ are claimed attention. Also the questionnaire survey was carried out jointly with Xi'AN University of Architecture and Technology for considering improvements.

Characterizing a UV chamber with mercury lamps for assessment of comparability to natural UV conditions

UV radiation conditions in a UV chamber equipped with four 300-W mercury vapour lamps have been characterized to assess the exposure received by the specimens aged in the chamber. Spectrally resolved measurements were performed on UV radiation emitted by new lamps and lamps operated for 4850 h in the chamber. An intensity decrease of as much as 75% with a strong wavelength dependency was detected. By linking the measurements with independent broadband measurements of the UV radiation field emitted by a single lamp, the UV dose rate distribution on the specimen plane of the chamber was derived. A method for true exposure accumulation estimation, accounting for the fading of the lamps, was developed. Accumulated UV radiation exposures on material samples in the chamber were derived and compared to long-term (1995–2007) average UV exposures received in natural sunshine at Jokioinen, Finland (lat. 60.4°N, long. 23.5°E, 104 m a.s.l.). Acceleration factors for the exposure in the UV chamber were derived in terms of doses integrated over different wavelength ranges. The acceleration factor was found to depend strongly on the wavelength range of the dose considered, presenting an extra challenge to the assessment of the artificial material exposure duration.

Proposal of radiation fluxmeter for asymmetric thermal radiation field measurement

AbstractIn this study, a compound parabolic concentrator (CPC) radiation fluxmeter is proposed for measuring an asymmetric radiation field such as that in an urban outdoor environment with strong solar radiation in summer. The proposed CPC fluxmeter, which consists of multiple sets of a CPC mirror and a radiation flux sensor, can measure directional radiation from a solid angle limited by the acceptance half‐angle of the CPC. Using the data measured by the CPC radiation fluxmeter, a methodology to estimate the incident radiation flux distribution on an arbitrary three‐dimensional body was described in detail. A prototype CPC fluxmeter was fabricated and its essential parameters were calibrated based on the heat balance at the radiation flux sensor. Finally, actual field measurement and estimation of the radiation flux distribution on a human body model were demonstrated in a summer urban outdoor environment. Results show the validity and advantage of the proposed CPC radiation fluxmeter as compared with the conventional globe thermometer. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(5): 259–274, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20209

Study of reliability of TLDs for the photon dose mapping in reactor neutron fields for BNCT

Photon dose measurements in radiation fields having the proper characteristics for boron neutron capture therapy (BNCT) present several troubles. The thermal neutron flux is very high and produces a significant contribution to the response of most dosimeters. The consistency of photon dose measurements with CaF 2 :Tm and LiF:Mg, Ti thermoluminescent dosimeters has been studied. A method is described for obtaining the gamma dose with TLD-700 and some results are presented to test its reliability.

Dosimetry with a transportable water calorimeter in neutron, proton and heavy-ion radiation fields

A compact and transportable water calorimeter has been developed and extensively tested in the intensive, collimated neutron field of the PTB. It has been applied for absorbed dose to water measurements in the neutron therapy field of the University of Essen, in the proton therapy fields of the HMI in Berlin and at the iThemba therapy centre near Cape Town, South Africa, as well as in the (12)C-beam of the therapy facility at GSI in Darmstadt, Germany. Absolute dosimetry with relative standard uncertainties of less than 1.8% was achieved in all radiation fields. The results obtained using the water calorimeter are compared with the ionisation chamber measurements in the same radiation fields. The heat defect for the water in the calorimeter core was determined separately in independent measurements by irradiation with different charged particle beams covering a wide range of linear energy transfer.

Relative output factor and beam profile measurements of small radiation fields with an L‐alanine/K‐Band EPR minidosimeter

The performance of an L-alanine dosimeter with millimeter dimensions was evaluated for dosimetry in small radiation fields. Relative output factor (ROF) measurements were made for 0.5 x 0.5, 1 x 1, 3 x 3, 5 x 5, 10 x 10 cm(2) square fields and for 5-, 10-, 20-, 40-mm-diam circular fields. In beam profile (BP) measurements, only 1 x 1, 3 x 3, 5 x 5 cm2 square fields and 10-, 20-, 40-mm-diam circular fields were used. For square and circular field irradiations, Varian/Clinac 2100, and a Siemens/Mevatron 6 MV linear accelerators were used, respectively. For a batch of 800 L-alanine minidosimeters (miniALAs) the average mass was 4.3+/-0.5 (1 sigma) mg, the diameter was 1.22+/-0.07 (1 sigma) mm, and the length was 3.5+/-0.2 (l sigma) mm. A K-Band (24 GHz) electron paramagnetic resonance (EPR) spectrometer was used for recording the spectrum of irradiated and nonirradiated miniALAs. To evaluate the performance of the miniALAs, their ROF and BP results were compared with those of other types of detectors, such as an ionization chamber (PTW 0.125 cc), a miniTLD (LiF: Mg,Cu,P), and Kodak/X-Omat V radiographic film. Compared to other dosimeters, the ROF results for miniALA show differences of up to 3% for the smallest fields and 7% for the largest ones. These differences were within the miniALA experimental uncertainty (-5-6% at 1 sigma). For BP measurements, the maximum penumbra width difference observed between miniALA and film (10%-90% width) was less than 1 mm for square fields and within 1-2 mm for circular fields. These penumbra width results indicate that the spatial resolution of the miniALA is comparable to that of radiographic film and its dimensions are adequate for the field sizes used in this experiment. The K-Band EPR spectrometer provided adequate sensitivity for assessment of miniALAs with doses of the order of tens of Grays, making this dosimetry system (K-Band/miniALA) a potential candidate for use in radiosurgery dosimetry.

Estimation of a &amp;quot;radiatively correct&amp;quot; black carbon specific absorption during the Mexico City Metropolitan Area (MCMA) 2003 field campaign

Abstract. During the Mexico City Metropolitan Area (MCMA) field campaign of 2003, measurements of the shortwave radiation field allowed the inference of the black carbon (BC) specific absorption, αλ, defined as the monochromatic absorption cross section per unit mass (with units of m2/g). The averaged values of αλ derived from the method here are either 8.9 m2/g or 8.2 m2/g at 500 nm, depending upon the physical and optical parameters assumed for BC. These results are reasonably consistent with those of Schuster et al. (2005), 9.5 m2/g, and Baumgartner et al. (2002), 7.0 m2/g, both measured at 550 nm. The αλ values reported in this paper should only be considered effective, "radiatively correct" values because when used in radiative transfer calculations the calculated irradiances match the measured irradiances at 500 nm. The specific absorption so defined can assume a wide range of values, depending upon: (1) the assumptions made prior to the retrieval (e.g., shell/core aerosol configuration), and (2) values chosen for BC density and refractive index. The range of possible values is large, corresponding to a "worst case" uncertainty of about ±70%, assuming that all errors are additive and of the same sign so that no error cancellation occurs.

Radioluminescence of some optical fibres

Measurement of radiation fields with small scintillators as detectors for radiation dose is an attractive method provided that the scintillator luminescence can be discriminated against other unwanted signals. In diagnostic radiology radioluminescence of the optical fibres required for a transmission of the luminescence to an optical detector is the only source for such an impairment of the signal. To find fibres with low radioluminosity a survey of ten commercial fibres including polystyrene (PS), polystyrene wavelength shifting fibres, poly-methylmetacrylate (PMMA) and silica as fibre core material was made. Measurements were made with two photomultipliers of different spectral response and a clinical x-ray unit. Lowest radioluminosity was obtained with PMMA fibres. Depending on spectral sensitivity of the multiplier clear PS fibres give five to ten times the luminescence of PMMA. From the silica fibres only one high-OH fibre gave comparable results for wavelength up to 520 nm. Wavelength shifting fibres and silica fibres with low OH-content show strong fluorescence and are not suitable fibre materials.

Ionisation Chambers Containing Boron as Neutron Detectors in Mixed Radiation Fields

Ionisation Chambers Containing Boron as Neutron Detectors in Mixed Radiation Fields The paper presents a newly designed ionisation chambers containing boron, operated in the initial recombination regime. The chambers were either filled with BF3 or the chamber electrodes were covered with B4C. The chambers can be placed in paraffin moderators. The sensitivity of the chambers was investigated depending on gas pressure, moderator thickness and polarizing voltage. The results showed that it was possible to obtain nearly the same sensitivity of the chamber to H* (10) for photons and neutrons in restricted energy range, however further investigations are needed to make an optimum design. The examples of applications for dosimetric measurements in mixed radiation fields near medical linear accelerator and in the vicinity of high-energy proton accelerator are presented.

Proposal of Radiation Fluxmeter for Measurement of Asymmetric Radiation Field

In this study, CPC (Compound Parabolic Concentrator) radiation fluxmeter was newly developed for the measurement of the asymmetric radiation field such as urban street canyon with the strong solar radiation especially in summer. The developed fluxmeter consists of the CPCs and radiation flux sensors, and can collect the limited directional radiation from solid angle decided by the acceptance half-angle of the CPC. The optical characteristics of the CPC and the heat balance at the radiation flux sensor were numerically analyzed from a viewpoint of radiative heat transfer. Furthermore, a prototype CPC radiation fluxmeter was made and validated by fundamental experiments.

Investigation of radiation fields at different altitudes in near-Earth orbit

Space radiation dosimetry presents one of the greatest challenges in the field of radiation safety. In the present paper the dosimetric data collected over the last 20 years of radiation field measurement on near-Earth orbits are presented. The measurements were carried out aboard “Cosmos” spacecrafts (1979–1989), “Mir” station (1988 and 1991), as well as on board the ISS (2002). For determination of important characteristics of cosmic rays (particle fluxes, LET and fast neutron spectra, equivalent doses and heavy ion fluxes) a nuclear emulsion has been used as a controllable threshold detector. An integral LET spectrum was measured in the range of 0.5–3.5 × 10 3 keV/μm. The energy spectra of fast neutrons with E = 1–15 MeV have been also studied and induced equivalent doses calculated.

Bubble detector measurements of a mixed radiation field from antiproton annihilation

In the light of recent progress in the study of the biological potential of antiproton tumour treatment it is important to be able to characterize the neutron intensity arising from antiproton annihilation using simple, compact and reliable detectors. The intensity of fast neutrons from antiproton annihilation on polystyrene has been measured with bubble detectors and a multiplicity has been derived as well as an estimated neutron equivalent dose. Additionally the sensitivity of bubble detectors towards protons was measured.

Nanodosimetric cluster size distributions of therapeutic proton beams

As we move into the new millennium, it is important that we improve our understanding of radiation effects on humans and nanoelectronic systems. This understanding is essential in a number of areas including radiation therapy for cancer treatment and extended human presence in outer space. Nanodosimetry in low-pressure gases enables measurement of the energy deposition of ionizing radiation on a scale equivalent to the dimensions of the DNA molecule. This is extremely important for not only biological applications but also electronic applications, as the effect of radiation on nanoelectronics needs to be determined before they are installed and deployed in complex radiation fields. However, before nanodosimetry can be widely applied, further investigation is required to link the output of gas-based nanodosimeters to the actual effect of the radiation on a biological or electronic system. The purpose of this research is to conduct nanodosimetric measurements of proton radiation fields at the proton accelerator of Loma Linda University Medical Center (LLUMC) and to develop a Monte Carlo simulation system to validate and support further developments of experimental nanodosimetry. To achieve this, measured ion cluster size distributions are compared to the output from the Monte Carlo simulation system that simulates the characteristics of the LLUMC beam line and the performance of the nanodosimeter installed on one of LLUMC's proton research beam lines.

Measurements of radiation fields around high-energy proton accelerators

Monitoring of ionising radiation around high-energy particle accelerators is a difficult task due to the complexity of the radiation field, which is made up of neutrons, charged hadrons, muons, photons and electrons, with energy spectra extending over a wide energy range. The dose-equivalent outside a thick shield is mainly owing to neutrons, with some contribution from photons and, to a minor extent, the other particles. Neutron dosimetry and spectrometry are thus of primary importance to correctly evaluate the exposure of personnel. This paper reviews the relevant techniques and instrumentation employed for monitoring radiation fields around high-energy proton accelerators, with particular emphasis on the recent development to increase the response of neutron measuring devices > 20 MeV. Rem-counters, pressurised ionisation chambers, superheated emulsions, tissue-equivalent proportional counters and Bonner sphere spectrometers are discussed.

Neutron/ [formula omitted]-ray digital pulse shape discrimination with organic scintillators

Neutrons and γ -rays produce light pulses with different shapes when interacting with organic scintillators. This property is commonly used to distinguish between neutrons (n) and γ -rays ( γ ) in mixed n/ γ fields as those encountered in radiation physics experiments. Although analog electronic pulse shape discrimination (PSD) modules have been successfully used for many years, they do not allow data reprocessing and are limited in count rate capability (typically up to 200 kHz). The performance of a n/ γ digital pulse shape discrimination (DPSD) system by means of a commercial 12-bit 200 MSamples/s transient recorder card is investigated here. Three organic scintillators have been studied: stilbene, NE213 and anthracene. The charge comparison method has been used to obtain simultaneous n/ γ discrimination and pulse height analysis. The importance of DPSD for high-intensity radiation field measurements and its advantages with respect to analog PSD are discussed. Based on post-experiment simulations with acquired data, the requirements for fast digitizers to provide DPSD with organic scintillators are also analyzed.