Microdosimetric interpretation of the photon energy response of LiF:Mg,Ti detectors

Photon energy response of MTS-N (LiF:Mg,Ti) detectors (TLD Poland) and of MTS-N detectors sensitised with 200 Gy of 60Co gamma rays, followed by UV irradiation (sMTS-N), has been determined using X rays with narrow energy spectra, in the energy range from 20 to 300 keV. The over-response of LiF:Mg,Ti detectors for X rays (relative TL efficiency eta = 1.1) can be explained as an ionisation density effect. Low energy X rays produce short electron tracks, which locally deposit a high radiation dose and, consequently, lead to an enhanced (supralinear) response. This over-response has not been observed in sensitised MTS-N where supralinearity in the response after gamma ray doses above 1 Gy is not seen. Using the dose-response curves measured for MTS-N detectors after 137Cs gamma ray irradiation and local doses calculated using Monte Carlo generated electron tracks, it was possible to predict the relative TL effectiveness for different X ray energies. The calculation procedure can be applied to predict the photon energy response of LiF:Mg,Ti detectors in an arbitrary photon field.     

On the dose response of some CVD diamond thermoluminescent detectors

The linearity of dose response of chemical vapour deposition (CVD) diamonds grown at the Institute for Materials Research at Limburg University, Belgium, was investigated over a dose range relevant for radiotherapy. The following CVD diamonds were investigated: (1) a batch of square 3 x 3 mm2 detectors cut from a CVD wafer and (2) an as-grown CVD wafer of 6 cm diameter. A total of 20 CVD square detectors were irradiated with 137Cs gamma rays over the dose range from 200 mGy to 25 Gy. The CVD wafer, used as a large-area thermoluminescent (TL) detector, was exposed to a 226Ra needle. Very few square detectors showed linearity over a limited dose range, followed by saturation of the TL signal. The dose range of linearity was found to be strongly affected by the thermal annealing procedure of the detector. Owing to its high sensitivity and homogeneity of response, the large CVD diamond wafer was found to be very suitable as a large-area detector for 2-D dose mapping of the 226Ra brachytherapy source, possibly for Quality Assurance purposes.     

Dosimetry of low energy ions by means of solid state nuclear track detectors

This paper concerns applications of solid state nuclear track detectors (SSNTDs) of the CR-39 type for measurements of ion streams emitted from the rod plasma injector (RPI). The main diagnostic tool was a Thomson-type mass spectrometer, To detect low energy ions use was made of an additional ion-acceleration system, which enabled the registration threshold to be lowered to about 25 keV. Simultaneously with the time-integrated measurements, time-resolved studies were performed of ion streams by means of Faraday-type collectors. It was shown that the investigated plasma-ion source generates also high energy ions, e.g. protons of energy of 2.6-3.7 MeV. For the analysis of the irradiated and etched CR-39 detectors use was made of a computerised system, which enabled determination of the dimensions of the registered tracks produced by low energy protons, deuterons and nitrogen ions. It has extended the known characteristics of the CR-39 detector.     

Microdosimetric modelling of the response of thermoluminescence detectors to low- and high-LET ionising radiation

The microdosimetric one hit detector model was applied to calculate the dose response, energy response and relative thermoluminescence (TL) efficiency, eta, of high sensitive LiF:Mg,Cu,P and Al(2)O(3):C detectors after their irradiations by X rays, gamma rays, beta electrons and heavy charged particles (HCP). Microdosimetric distributions in 60 nm targets for photons and beta rays were calculated using the TRION MC track structure code, for HCP using the analytical model of Xapsos with modified transport of secondary electrons and the model of Olko & Booz. The calculated values of eta compare favourably with a broad spectrum of experimental data, including ICHIBAN experiments with HCP. The model offers a method for calculating the thermoluminescence response of TL foils applied to 2-D dosimetry of radiotherapeutic proton beams.     

A fast multianode detector for solid state ultraviolet photoelectron spectroscopy

A new angle-resolving photoelectron spectrometer has been developed which uses a fast multianode parallel readout. The detector has been designed for high resolution ultraviolet photoelectron spectroscopy from solid surfaces using synchrotron radiation. Examples of initial results obtained with the detector using a rare gas discharge lamp are presented.     

Single-electron response and energy resolution of a Micromegas detector

Micro-Pattern Gaseous Detectors (MPGDs) such as Micromegas or GEM are used in particle physics experiments for their capability of particle tracking at high rates. Their excellent position resolutions are well known but their energy characteristics have been less studied. The energy resolution is mainly affected by ionisation processes and gain fluctuations. This paper presents a method to separately measure these two contributions to the energy resolution of a Micromegas detector. The method relies on the injection of a controlled number of primary electrons in the gas. The Micromegas has a 1.6-mm drift zone and a 160-μm amplification gap. It is operated in Ne 95%-iC₄H₁₀ 5% at atmospheric pressure. The electrons are generated by non-linear photoelectric emission derived from the photons of a pulsed 337-nm wavelength laser coupled to a focusing system. The single-electron response has been measured at different gains (3.7×10⁴, 5.0×10⁴ and 7.0×10⁴) and is fit with good agreement by a Polya distribution. From those fits, a relative gain variance of 0.31±0.02 is deduced. The setup has also been characterised at several voltages by fitting the energy resolution measured as a function of the number of primary electrons, ranging from 5 to 210. An upper limit on the Fano factor (0.37) has been estimated for 5.9 keV X-rays absorbed in a Ne 95%-iC₄H₁₀ 5% gas mixture.     

Gamma-ray response function of some polymeric nuclear track detectors

The effect of gamma dose on the bulk-etch rate measurements for some gamma-irradiated polymeric nuclear track detectors was extensively studied. Various plastic samples of CR-39 allyl diglycol carbonate, Makrofol-E and Lexan polycarbonates were used and exposed to gamma doses up to 30.0 Mrad. The bulk-etch rate ratioV _BD/V _BO, i.e. the bulk-etch rate of irradiated samples to the unirradiated ones, was measured at the most recommended optimum etching conditions. Fading behaviour of irradiated CR-39 samples was also studied at room temperature and for a duration of up to 8 days. It was found that the etch-rate ratio for the CR-39 specimens was dose-dependent. In contrast, the polycarbonate samples showed an extremely weak response to gamma irradiation. The results of the present work reflected great evidence of the gamma dosimetric potential of CR-39 plastic detectors, which can indeed be recommended as gamma-dosimeters within the studied dose range.     

Electron dose radiation response of dyed PMMA detectors developed at IPEN

Dyed polymethylmethacrylate (PMMA) detectors using yellow, red, blue and green colouring compounds, commercially available in Brazil, were originally developed and characterised using the optical absorption (OA) technique for gamma radiation, with the aim of obtaining a sensitive, useful, practical and cheap dosemeter for use in the quality control of industrial gamma radiation processing. In this work these detectors were evaluated for electron OA response, for use in the quality control of electron accelerator radiation processing. The studied parameters were the absorption spectra, dose-rate dependence between 2.66 and 45.22 kGy s(-1); dose response between 1.2 and 110 kGy; and energy dependence of response between 0.8 and 1.5 MeV electron energy.     

Optically stimulated luminescence of some thermoluminescent detectors as an indicator of absorbed radiation dose

Stimulation spectra of several TLD materials in the short-wave spectral region are measured using the optically stimulated afterglow (OSA) method for determination of absorbed dose. Optical stimulation spectra are studied in the region of wavelengths lower than those of emission spectra. The effective optical stimulation hands have been found for examined materials in the regions of wavelengths which overlap with fluorescence excitation bands. Application of short-wave OSA bands for determination of absorbed dose is analysed.     

A Monte Carlo based development of a cavity theory for solid state detectors irradiated in electron beams

Recent Monte Carlo simulations have shown that the assumption in the small cavity theory (and the extension of the small cavity theory by Spencer-Attix) that the cavity does not perturb the electron fluence is seriously flawed. For depths beyond dmax not only is there a significant difference between the energy spectra in the medium and in the solid cavity material but there is also a significant difference in the number of low-energy electrons which cannot travel across the solid cavity and hence deposit their dose in it (i.e. stopper electrons whose residual range is less than the cavity thickness). The number of these low-energy electrons that are not able to travel across the solid state cavity increases with depth and effective thickness of the detector. This also invalidates the assumption in the small cavity theory that most of the dose deposited in a small cavity is delivered by crossers. Based on Monte Carlo simulations, a new cavity theory for solid state detectors irradiated in electron beams has been proposed as: Dmed(p) = meanDdet(p) x s(med,det)S-A x gamma(p)c x S(T) where Dmed(p) is the dose to the medium at point p. MeanDdet(p) is the average detector dose to the same point, s(med,det)S-A is the Spencer-Attix mass collision stopping power ratio of the medium to the detector material, gamma(P)c is the electron fluence perturbation correction factor and S(T) is a stopper-to-crosser correction factor to correct for the dependence of the stopper-to-crosser ratio on depth and the effective cavity size. Monte Carlo simulations have been computed for all the terms in this equation. The new cavity theory has been tested against the Spencer-Attix cavity equation as the small cavity limiting case and also Monte Carlo simulations.     

A large area solid state detector made of ultra high purity p-type Si

A Surface Barrier Detector for environmental monitoring was fabricated with an ultrahigh purity p-type Si crystal. The crystal had a nominal resistivity of 50 kΩ cm, and Al was evaporated on the outer surface to form a positive electrode of 50 mm ø. The excellent light-tightness and adhesivity of the Al layer enables direct mounting of samples on the detector and decontamination of the surface with wetted soft tissues.The energy resolution for α and β particles is 36 and 33 keV fwhm respectively and simultaneous measurement of both α and β particles can be carried out. The detector fabrication procedure, its characteristics and application are reported in this paper.     

X射线探伤机剂量检定系统研制

针对JJG 40-200i检定规程的要求,利用空腔电离理论测量X射线辐射剂量的原理,研制了一套智能化的X射线探伤机剂量检定系统.该系统包括0.6cm3、600 cm3电离室和监测用半导体探测器(Monitor Semiconductor Detector,MSD)、导轨运动系统以及一套自动化的软件系统.系统测量准确、快速、方便易用,主要用于X射线探伤机空气比释动能率、漏射线、辐射角、重复性等参数的检定.     

Operational comparison of TLD albedo dosemeters and solid state nuclear tracks detectors in fuel fabrication facilities

The authors carried out an operational study that compared the use of TLD albedo dosemeters and solid state nuclear tracks detector in plutonium environments of Japan Nuclear Cycle Development Institute, Tokai Works. A selected group of workers engaged in the fabrication process of MOX (Plutonium-Uranium mixed oxide) fuel wore both TLD albedo dosemeters and solid state nuclear tracks detectors. The TL readings were generally proportional to the counted etch-pits, and thus the dose equivalent results obtained from TLD albedo dosemeter agreed with those from solid state nuclear tracks detector within a factor of 1.5. This result indicates that, in the workplaces of the MOX fuel plants, the neutron spectrum remained almost constant in terms of time and space, and the appropriate range of field-specific correction with spectrum variations was small in albedo dosimetry.     

Evaluation of solid state nuclear track detector stacks exposed on the international space station

The aim of the study was to investigate the contribution of secondary neutrons to the total dose inside the International Space Station (ISS). For this purpose solid-state nuclear track detector (SSNTD) stacks were used. Each stack consisted of three CR-39 sheets. The first and second sheets were separated by a Ti plate, and the second and third sheets sandwiched a Lexan polycarbonate foil. The neutron and proton responses of each sheet were studied through MC calculations and experimentally, utilising monoenergetic protons. Seven stacks were exposed in 2001 for 249 days at different locations of the Russian segment 'Zvezda'. The total storage time before and after the exposure onboard was estimated to be seven months. Another eight stacks were exposed at the CERF high-energy neutron field for calibration purposes. The CR-39 detectors were evaluated in four steps: after 2, 6, 12 and 20 h etching in 6 N NaOH at 70 degrees C (VB = 1.34 microm h(-1)). All the individual tracks were investigated and recorded using an image analyser. The stacks provided the averaged neutron ambient dose equivalent (H*) between 200 keV and 20 MeV, and the values varied from 39 to 73 microSv d(-1), depending on the location. The Lexan detectors were used to detect the dose originating from high-charge and high-energy (HZE) particles. These results will be published elsewhere.     

Characterization of Platinum and Gold ions emitted from laser produced plasmas using solid state nuclear track detectors

Investigations on key characteristics of ions emitted from Laser Induced plasmas are reported. A Q-switched Nd: YAG pulsed laser at 1064 nm, 9-14 ns and 1.1 MW, is focused on 4 N pure Gold (Au) and Platinum (Pt) targets to produce plasma plume. The ions thus emitted are detected by CR-39 Solid State Nuclear Track Detectors (SSNTD’s), placed at angles 0°, 30°, 60°, and 90° with respect to the target normal. The distances between the targets and detectors are 9 cm. The experiments are performed under a vacuum ∼10⁻³ torr and the ion tracks are recorded on SSNTD’s for 300 laser shots. The etched detectors are analyzed with the help of Motic Images Optical Microscope (Motic Advance 3.1). The flux of ions exhibits anisotropic behavior where as maximum energies of these ions are not only anisotropic but also forward peaked.     

An absolute calibration of the solid state detectors in the narrow band neutrino beam at CERN

A method to calibrate in an absolute way the solid state detectors that are used to monitor the muon flux in the (anti)neutrino beam line at the CERN SPS is described. This calibration is one way that opens the possibility to measure the (anti)neutrino flux needed for the determination of the absolute total cross-sections of (anti)neutrino-nucleon interactions. Tracks of charged particles are recorded simultaneously in the solid state detectors and in Ilford G5 emulsions. The readings of the detectors are compared with a count of the tracks in the developed emulsions. Absolute calibration factors (number of passing muons per delivered pC of electric charge) under particular circumstances are given. The overall accuracy that can be obtained is 3%.