Application of large area avalanche photodiodes for alpha liquid scintillation counting

In order to improve the resolution in alpha liquid scintillation and to promote this method for the measurement of actinides in environment, a silicon Large Area Avalanche Photodiode (LAAPD) has been tested as liquid scintillation detector. The set-up consists of a LAAPD (16 mm diameter) coupled to a thin vial containing alpha-emitters and a liquid scintillation cocktail. After optimization of several parameters like bias voltage, temperatures, counting geometry and composition of scintillating cocktail, energy resolutions are found to be better than those obtained with photomultiplier tubes: 5% (200 keV FWHM) for ²³²Th and 3.9% (260 keV FWHM) for ²¹⁶Po. The improvement in energy resolution is not due to higher quantum efficiency of the silicon device but to better uniformity of the spatial photoresponse. A few energy spectra of thorium, plutonium and americium are given as example.     

A three dimensionally position sensitive large area detector

A large area detector consisting of a parallel plate avalanche counter (PPAC) and a trapezohedral ionization chamber (TIC) is described. Its active area is 184 cm². The time resolution of the PPAC is 175 ps. The energy resolution of the TIC is 0.4%, the energy loss resolution 2.8%, the nuclear charge resolution 2.3%. The TIC is position sensitive in three dimensions. The position x is measured via a saw-tooth anode with a resolution of 0.7 mm; the drift time coordinate shows a resolution of δy ? mm. The range z is determined by a new technique, a graded density Frisch grid. It enlarges the dynamic range of the charge measurement down to the Bragg maximum at E/A ～ 1 MeV. The resolution is δZ/Z ? 3.5%     

Thermostable scintillation detector

A design of a scintillation detector of ionizing radiation based on a Tl-activated NaI single or polycrystal is proposed. The detector is equipped with a unique compensator of inconsistent variations of the axial dimensions of the scintillator and its container. Khar’kov Institute of Electrification and Mechanization of Agriculture, Khar’kov, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 4, pp. 577–581, July–August, 1996.     

Amadeus - a new type of large area scintillation detector with position-, energy- and time-of-flight determination

The Amadeus detector consists of a scintillator plate, a Plexiglas plate and a matrix of photomultiplier tubes oriented opposite to the particle direction. A charged particle traversing the scintillator emits scintillation light which is seen only by the nearby phototubes. In a first approximation the sum of the pulse height seen by these tubes is proportional to the deposited energy and the center of gravity of the detected light distribution corresponds to the particle impact position. This approximation allows a fast determination of particle parameters with sufficient accuracy for online applications. In connection with the time-of-flight the particle identification and the complete determination of the four-momentum vector is given. For the off-line analysis a more refined algorithm can be used resulting in energy-, position- and time-of-flight resolution values in the range of σ_x = 3–5 mm σ_E = 3–5 MeV, σ₁ = 150–250 ps, respectively.     

Efficiency calibration of large volume liquid scintillation detectors

An array of seven large (10 cm thick by 20 cm diameter) NE213 scintillation detectors for use in neutron time-of-flight experiments has been calibrated to determine a matrix of relative detection efficiency as a function of incident neutron energy and detector bias. This matrix is then used to determine the relative efficiency for neutron groups in time-of-flight spectra to which an efficiency-optimizing dynamic bias has been applied.     

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.     

Parameters of various types of light guides for large area scintillation counters

The properties of a variety of different light guides used in conjunction with a large area scintillator (180 cm × 48.5 cm × 1 cm, SCSN-38) have been studied. The performance of a Y7 wavelength-shifter bar, a fishtail, a separated twisted and an all area coupled twisted lucite light guide were compared.The best performance was found for the all area coupled twisted guide. For this, we observed an average of 50 photoelectrons per minimum ionizing particale and a mean time resolution (σ) of 0.4 ns. for constant impact point of the particles.A Monte Carlo simulation of photon transmission in the counters has been done; the measured results on the performance of the various counter configurations agree well with the predictions of the simulation.     

Measurement of the spectral fluence rate of reference neutron sources with a liquid scintillation detector

Reference neutron sources such as (241)AmBe(alpha,n) and (252)Cf are commonly used to calibrate neutron detectors for radiation protection purposes. The calibration factors of these detectors depend on the spectral distribution of the neutron fluence from the source. Differences between the spectral fluence of the neutron source and the ISO-recommended reference spectra might be caused by the properties of the individual source. The spectral neutron fluence rates of different reference neutron sources used at PTB were measured with a liquid scintillation detector (NE213), using maximum entropy unfolding and a new, experimentally determined detector response matrix. The detector response matrix was determined by means of the time-of-flight technique at a pulsed neutron source with a broad energy distribution realised at the PTB accelerator facility. The results of the measurements of the reference sources are compared with the ISO-recommended reference spectra. For the PTB (241)AmBe(alpha,n) reference source, the spectral neutron fluence was determined by means of a high-resolution (3)He semiconductor sandwich spectrometer in 1982. These measurements were the basis for the ISO recommendations. The current measurements confirm the high-energy part (E(n) > 2 MeV) of this spectrum and demonstrate the suitability of this new method for high-resolution spectrometry of broad neutron spectra.     

Characterization of large area APDs for the EXO-200 detector

Enriched Xenon Observatory (EXO)-200 uses 468 large area avalanche photodiodes (LAAPDs) for detection of scintillation light in an ultra-low-background liquid xenon (LXe) detector. We describe initial measurements of dark noise, gain and response to xenon scintillation light of LAAPDs at temperatures from room temperature to 169 K—the temperature of liquid xenon. We also describe the individual characterization of more than 800 LAAPDs for selective installation in the EXO-200 detector.     

Performance of a large liquid argon shower detector used at Fermilab

Details of the construction and operation of a lead, liquid argon electromagnetic calorimeter used in Fermilab experiment E515 are presented. The system had an active projected area of 1.2×2.4 m². Its performance in low intensity electron beams and in exposure to intense, high multiplicity 200 GeV/c π^? Be interactions are described.     

Two-dimensional neutron scintillation detector with optimal gamma discrimination

For a two-dimensional scintillation neutron detector based on position-sensitive photomultipliers a digital differential discrimination unit has been developed which minimizes the gamma sensitivity of the detector and was necessary because of position- dependent PM gain. The digital upper and lower discrimination levels are set position-dependent due to the position-dependent photomultiplier gain which is obtained from calibration measurements. Narrow discriminator windows can be used to reduce the gamma background drastically without affecting the homogeneous neutron sensitivity of the detector. The new discrimination method is described and its function is tested with neutrons.     

Characterization of liquid scintillation detectors

Five scintillation detectors of different scintillator size and type were characterized. The pulse height scale was calibrated in terms of electron light output units using photon sources. The response functions for time-of-flight (TOF)-selected monoenergetic neutrons were experimentally determined and also simulated with the NRESP code over a wide energy range. A comparison of the measured and calculated response functions allows individual characteristics of the detectors to be determined and the response matrix to be reliably derived. Various applications are discussed.     

A Raman waveguide detector for liquid chromatography

A novel real-time liquid core Raman waveguide detector designed for liquid chromatographic applications is described. The Raman waveguide detector provides enhanced selectivity over typical high-performance liquid chromatography (HPLC) detectors. The waveguide detector also greatly improves the sensitivity of a typical Raman measurement without resorting to surface enhancement or resonance approaches and is compatible with the typical peak width volumes eluted by microbore and minibore HPLC (packed 1-2-mm-i.d. columns). Detection limit enhancements of over 1000-fold have been achieved for the measurement of alcohols in the aqueous phase with the Raman cell utilizing liquid core waveguide technology. The liquid core waveguides demonstrated in this study were constructed using Teflon AF 2400 tubing with a refractive index of 1.29. The low refractive index of the polymer material allowed HPLC separations with Raman detection to be performed with an aqueous mobile phase. A calibration curve for aqueous solutions of 2-propanol was generated and a limit of detection (LOD) of 2 ppm was determined. The Raman waveguide detector is demonstrated for the HPLC analysis of alcohol test mixtures, with LODs in the low-ppm range at the detector. By coupling the temporal separation achieved by HPLC with the vibrational information gleaned from Raman detection, an information-rich multivariate data matrix is obtained that can be deconvoluted to provide chemical speciation even when the HPLC resolution is poor. In this paper, we will discuss the physical and optical design of the Raman waveguide detector and the demonstration of the detector for HPLC detection.     

大面积塑料闪烁探测器剂量线性测量及修正

针对γ射线剂量增大时,大面积塑料闪烁探测器剂量线性会变差这一问题,采用能谱测量方式对塑料闪烁探测器的剂量线性进行修正。首先在单能辐射场中,探测器通过能谱测量电路在上位机形成辐射场能谱,然后按照能量线性规律算出每道址的权重因子,以标准剂量仪所测剂量率为参考值得到修正公式,接下来对待测辐射场进行能谱采样,根据每道计数和修正公式,得到修正后的总计数率和剂量率,从而对塑料闪烁探测器的剂量线性进行修正。结果表明:经过修正以后,在137Cs辐射场中剂量测量最大相对误差由-24.32%变为-6.90%,在60Co辐射场中最大相对误差由-72.22%变为-27.78%。可以看出,经过修正的探测器剂量线性得到很大改善,可为辐射场中γ射线剂量的准确测量提供技术参考。     

SENTIRAD—An innovative personal radiation detector based on a scintillation detector and a silicon photomultiplier

The alarming personal radiation detector (PRD) is a device intended for Homeland Security (HLS) applications. This portable device is designed to be worn or carried by security personnel to detect photon-emitting radioactive materials for the purpose of crime prevention. PRD is required to meet the scope of specifications defined by various HLS standards for radiation detection. It is mandatory that the device be sensitive and simultaneously small, pocket-sized, of robust mechanical design and carriable on the user's body. To serve these specialized purposes and requirements, we developed the SENTIRAD, a new radiation detector designed to meet the performance criteria established for counterterrorist applications. SENTIRAD is the first commercially available PRD based on a CsI(Tl) scintillation crystal that is optically coupled with a silicon photomultiplier (SiPM) serving as a light sensor. The rapidly developing technology of SiPM, a multipixel semiconductor photodiode that operates in Geiger mode, has been thoroughly investigated in previous studies. This paper presents the design considerations, constraints and radiological performance relating to the SENTIRAD radiation sensor.     

A small spherical NE213 scintillation detector for use in in-assembly fast neutron spectrum measurements

A small spherical 14 mm diameter NE213 scintillation spectrometer has been developed. Its linearity, gain stability and pulse shape discrimination were examined through experiments using a 14 MeV neutron field. The pulse responses were analyzed by a Monte Carlo code and compared with the measured ones. The detector proposed by us is superior in in-assembly measurements.     

Design and test of a large-area scintillation detector for fast neutrons

A plastic scintillator array of 3.4 m² total area for the detection of neutrons in medium-energy nucleon–nucleon reactions was constructed and built. Calibration procedures for the detector were developed which allow the monitoring of gain shifts by means of muons from the cosmic radiation. Experiments were performed in order to calibrate the efficiency simulations and study the performance of the detector using the d+t→+n reaction at 14.7 MeV neutron energy and proton-induced deuteron breakup at 300 MeV.