Neutron spectrometry with a monolithic silicon telescope

A neutron spectrometer was set-up by coupling a polyethylene converter with a monolithic silicon telescope, consisting of a DeltaE and an E stage-detector (about 2 and 500 microm thick, respectively). The detection system was irradiated with monoenergetic neutrons at INFN-Laboratori Nazionali di Legnaro (Legnaro, Italy). The maximum detectable energy, imposed by the thickness of the E stage, is about 8 MeV for the present detector. The scatter plots of the energy deposited in the two stages were acquired using two independent electronic chains. The distributions of the recoil-protons are well-discriminated from those due to secondary electrons for energies above 0.350 MeV. The experimental spectra of the recoil-protons were compared with the results of Monte Carlo simulations using the FLUKA code. An analytical model that takes into account the geometrical structure of the silicon telescope was developed, validated and implemented in an unfolding code. The capability of reproducing continuous neutron spectra was investigated by irradiating the detector with neutrons from a thick beryllium target bombarded with protons. The measured spectra were compared with data taken from the literature. Satisfactory agreement was found.     

A solid state microdosimeter based on a monolithic silicon telescope

A monolithic silicon telescope, consisting of a DeltaE and an E stage-detector ( approximately 1.9 microm and 500 microm thick, respectively), was coupled to a polyethylene converter in order to investigate the feasibility of a solid state microdosimeter with respect to the field-funnelling effect. This work discusses the preliminary results of an analytical approach for the correction of a spectrum measured with this silicon-based microdosimeter for tissue-equivalence and geometrical effects. The device was irradiated with 2.7 MeV monoenergetic neutrons at the INFN-Laboratori Nazionali di Legnaro (Legnaro, Italy). The non tissue-equivalence of silicon was corrected by exploiting the signals generated in the E-stage. The correction for the sensitive volume geometry was optimised by taking into account the track length distribution of the recoil-protons generated in the converter. The derived dose distribution of the energy imparted per event was compared to the one measured with a cylindrical tissue-equivalent proportional counter (TEPC). The agreement is satisfactory.     

All-spherical catadioptric telescope design for wide-field imaging

The current trend in building medium-size telescopes for wide-field imaging is to use a Ritchey-Chrétien (RC) design with a multilens corrector near the focus. Our goal is to find a cost-effective alternative design to the RC system for seeing-limited observations. We present an f/4.5 all-spherical catadioptric system with a 1.5° field of view. The system consists of a 0.8 m spherical primary and 0.4 m flat secondary mirror combined with a meniscus lens and followed by a three-lens field corrector. The optical performance is comparable to an equivalent f/4.5 RC system. We conclude that, for telescopes with apertures up to 2 m, the catadioptric design is a good alternative to the RC system.     

Mirrors for an imaging gamma ray telescope

A method is given for making mirrors suitable for large parabolic light collectors. The present application is for collecting Cherenkov light from air showers.     

Computation of the basic parameters for a telescope of a radiation pyrometer with a thermistor

Conclusions Laboratory tests of an experimental model pyrometer using a thermistor type TSh-1 agree well with the calculated values. The above technique of preliminary calculation of the telescope's basic characteristics can be recommended for designing radiation pyrometers with different thermistors.     

Correction for detector uniformity of a gamma-ray telescope using coded aperture imaging

A hard X-ray/medium energy gamma-ray telescope is being developed using coded aperture imaging. The image recorded on the detector has to be corrected before being cross-correlated, because it suffers from nonuniformity which generates large defects in the reconstructed image. A correction method has been developed and tested with the help of a laboratory model of the experiment.     

Validation of interferometric imaging from a pupil-masking experiment on a solar telescope

We present the results of a pupil-masking experiment that uses the Sun as the source object. The goal of our experiment was a proof-of-concept validation for a Fizeau (image-plane) interferometric beam combination with a complex source that overfilled the field of view. We employed a phase-diversity technique to measure the optical phases required to recover the instantaneous optical transfer function for the masked pupil. We used a Wiener filter to deconvolve the dirty images.     

International standards for radiation protection

International standards for radiation protection are issued by many bodies. These bodies differ to a large extent in their organisation, in the way the members are designated and in the way the international standards are authorised by the issuing body. Large differences also exist in the relevance of the international standards. One extreme is that the international standards are mandatory in the sense that no conflicting national standard may exist, the other extreme is that national and international standards conflict and there is no need to resolve that conflict. Between these extremes there are some standards or documents of relevance, which are not binding by any formal law or contract but are de facto binding due to the scientific reputation of the issuing body. This paper gives, for radiation protection, an overview of the main standards issuing bodies, the international standards or documents of relevance issued by them and the relevance of these documents.     

Neutron spectrometry for radiation protection

The various instruments used for neutron spectrometry can be divided into four categories. Within each of these categories, the underlying measurement principle for all devices is essentially the same. The applications of the instruments within each group to spectrometry for radiation protection are reviewed.     

Analytic diffraction analysis of a 32-m telescope with hexagonal segments for high-contrast imaging

Large segmented telescopes cannot be modeled accurately with fast-Fourier-transform techniques since small features such as gaps between the segments will be inadequately sampled. An analytic Fourier-transform method can be used to model any pupil configuration with straight edges, including tolerance analysis and some types of apodization. We analytically investigated a 32-m segmented primary with 18 hexagonal segments for high-contrast imaging. There are significant regions in the image in which extrasolar planets could be detected. However, the hexagonal profile of the pupil was not as useful as expected. The gaps between the segments, the secondary obscuration, and the secondary spiders must be as small as possible and their edges must be apodized. Apodizing the edges of the individual segments reduced the useful regions in the image since the gaps appeared to be wider.     

Adaptation of the present concept of dosimetric radiation protection quantities for external radiation to radiation protection practice

The present concept of dosimetric radiation protection quantities for external radiation is reviewed. For everyday application of the concept some adaptations are recommended. The check of the compliance with dose limits should be performed either by the comparison with values of the respective operational quantities directly or by the calculation of the protection quantity by means of the operational quantity, the appertaining conversion coefficient and additional information of the radiation field. Only four operational quantities are regarded to be sufficient for most applications in radiation protection practice. The term equivalent should be used in the connection dose equivalent only. Proposals are made for names of frequently used operational quantities which are denoted up to now by symbols only.     

Front-end receiver electronics for high-frequency monolithic CMUT-on-CMOS imaging arrays

This paper describes the design of CMOS receiver electronics for monolithic integration with capacitive micromachined ultrasonic transducer (CMUT) arrays for highfrequency intravascular ultrasound imaging. A custom 8-inch (20-cm) wafer is fabricated in a 0.35-μm two-poly, four-metal CMOS process and then CMUT arrays are built on top of the application specific integrated circuits (ASICs) on the wafer. We discuss advantages of the single-chip CMUT-on-CMOS approach in terms of receive sensitivity and SNR. Low-noise and high-gain design of a transimpedance amplifier (TIA) optimized for a forward-looking volumetric-imaging CMUT array element is discussed as a challenging design example. Amplifier gain, bandwidth, dynamic range, and power consumption trade-offs are discussed in detail. With minimized parasitics provided by the CMUT-on-CMOS approach, the optimized TIA design achieves a 90 fA/√Hz input-referred current noise, which is less than the thermal-mechanical noise of the CMUT element. We show successful system operation with a pulseecho measurement. Transducer-noise-dominated detection in immersion is also demonstrated through output noise spectrum measurement of the integrated system at different CMUT bias voltages. A noise figure of 1.8 dB is obtained in the designed CMUT bandwidth of 10 to 20 MHz.     

天文学自适应光学成像望远镜的模拟

为分析天文学自适应光学(AO)望远镜中AO系统的校正性能,利用Matlab仿真其成像过程。采用正交基为Zernike多项式的自相关法产生符合大气统计特性的大气相位屏,仿真平行光通过大气后的瞬时畸变波前相位;采用快速傅里叶变换仿真哈特曼-夏克波前传感器的成像光斑,根据实际成像与参考平面波成像的质心坐标之差,计算波前传感器子孔径内的平均波前斜率。模拟比较了1.2m望远镜两种AO系统布局的校正性能,结果表明,子孔径为正六边形AO系统的校正性能略优于子孔径为正方形AO系统的校正性能,两种AO系统的SR比(StrechlRatio)分别为0.872和0.859。     

Neutron spectrometry for radiation protection purposes

Determination of the dose equivalent is required for radiation protection purposes, however such a determination is quite difficult for neutron radiation. In order to perform accurate dosimetric determinations, it is advantageous to acquire information about the neutron fluence spectrum in the workplace as well as the reference radiations used to calibrate dosimetric instruments. This information can then be used to select the appropriate dosimetric instrument, the optimum calibration condition or to establish correction factors that account for the differences in calibration and workplace conditions. For quite some time, neutron spectrometry has been used for these purposes. A brief review of the applications of spectrometers in radiation protection and some recommendations for further development are given here.     

Assessment of sun protection for children's summer 2005 clothing collection

Overexposure to solar ultraviolet radiation (UVR) in childhoodis considered to be a critical factor for developing skin cancerin later life. Clothing may offer a simple and effective meansof protection against overexposure to the sun, but its use hasoften been underrated in public opinion. The Health ProtectionAgency, in close collaboration with a number of UK retailers,conducted a study to evaluate the UVR protection characteristicsof the summer 2005 collection of children's clothing for outdooractivity. The current paper presents a summary of the assessmentand the effects of stretching and wetting on the UltravioletProtection Factor (UPF) rating of children's clothing. The resultsdemonstrate the need for better public guidance in sun protectionof children and more comprehensive evaluation procedures forsun protection provided by clothing.     

ICRP special radiation protection issues in interventional radiology, digital and cardiac imaging

The International Commission on Radiological Protection (ICRP) has published two reports giving recommendations dealing with the avoidance of deterministic injuries in interventional radiology and the management of patient dose in digital radiology in 2001 and 2004, respectively. Another document, on radiation protection for cardiologists performing fluoroscopically guided procedures, will be produced during 2005. This paper highlights some of the topics of the published reports, their relevance to European legislation on medical exposures and the importance of radiation protection research in underpinning the ICRP task groups' work in to producing these documents. It is also anticipated that the results, obtained in the cardiology work package of the European research project, will be used in the new document on radiation protection for cardiologists.     

Biological and physical dosimetry for radiation protection

In the 5^th Framework Programme (5FP) of the European Commission(EC), the European Late Effects Project Group (EULEP) and theEuropean Radiation Dosimetry Group (EURADOS) were funded toco-ordinate research in radiation protection based on theirwell-established experience. This was termed ‘clustering’and was intended to encompass research funded by National Agenciesand that funded directly by     

Optical designs for ultrahigh-flux infrared and solar energy collection: monolithic dielectric tailored edge-ray concentrators

A new class of optical designs is developed for attaining ultrahigh flux in infrared and solar energy concentrators. These concentrators are required to satisfy simultaneously three criteria: (1) being monolithic, i.e., comprising a single piece of dielectric such that no mirrored surfaces or air spaces between concentrator elements are introduced; (2) attaining at least 90% of the thermodynamic limit to concentration; and (3) being relatively compact, e.g., aspect ratios of the order of unity or less. Our inventions are rooted in the recently developed formalism of tailored edge-ray concentrators.