A large area liquid scintillation multiphoton detector

A 60 layer lead-liquid scintillator shower detector, which we call the SLIC, has been used for multiphoton detection in the Fermilab tagged photon spectrometer. The detector has an unimpeded active area which is 2.44 m by 4.88 m and is segmented, by means of teflon coated channels, into 3.17 cm wide strips. The 60 layers in depth are broken into three directions of alternating readouts so that three position coordinates are determined for each shower. At present the readouts are made by 334 photomultiplier tubes coupled to BBQ doped wavelength shifter bars which integrate the entire depth of the detector. It is relatively straightforward to increase the number of readouts to include longitudinal segmentation and to increase the segmentation of the outer region which are at present read out two strips to a readout. The energy and position resolutions of isolated showers are about and 3 mm., respectively. The SLIC has been used to study the K⁻π⁺π⁰ decay of the D⁰ [1], as well as for electron and muon identification in ψ → e⁺e⁻ and ψ → μ⁺μ⁻ plus π⁰ identification in γp → ψχ [8].     

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.     

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.     

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.     

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.     

Systematic studies of scintillation detector with timing resolution of 10 ps for heavy ion beam

We have tested Time-Of-Flight detectors consisting of several combinations of scintillators and photomultiplier tubes for the identification of produced heavy ion beam. Timing resolution of 6.8 ps (RMS) is achieved with energy deposited of 150–160 MeV in the plastic scintillator, where ⁴⁰Ar beam is used as a primary beam at the total energies of 3.8 GeV. Our systematic studies suggest the importance of maximizing the number of photoelectrons, where the timing resolution seems to be scaled by the pulse height according to the characteristic function of the photomultiplier tube. In addition, scintillator with faster timing property seems to be also essential for better timing resolution.     

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.     

X-ray and gamma-ray response of a 2″×2″ LaBr3:Ce scintillation detector

Advances in material growth techniques have recently made large volume LaBr₃:Ce crystals commercially available. These scintillators are currently being assessed by ESA for use as remote sensing gamma-ray spectrometers on future planetary missions. In addition to their superior scintillation properties (high light output, fast time response and good stopping power), they offer significant benefits when designing gamma-ray detection systems for resource-limited spacecraft—not only in terms of resources but also in terms of reliability and robustness. We present the results of an investigation into the gamma-ray detection properties of a 2″×2″ LaBr₃:Ce crystal, characterized using radioactive sources over the energy range 14–3220 keV. The response of the crystal was found to be largely linear over the upper 95% of the dynamic range, the deviations at lower energies can be attributed to the shortcomings of the PMT. Compared to smaller volume crystals, no substantial degradation in light output, or alternately, energy resolution has been observed. For example, at 662 keV, an energy resolution of 3% FWHM was measured. Experiments with monoenergetic protons show that they create approximately half the light output of gamma-rays.     

Use of a microplate scintillation counter as a radioactivity detector for miniaturized separation techniques in drug metabolism

In miniaturized separation techniques, such as capillary electrophoresis (CE) or capillary liquid chromatography (LC), conventional on-line radioactivity detection of labeled compounds is restricted, because of insufficient sensitivity. It will be shown that a microplate scintillation counter for 96-well plates (TopCount) can be used as a sensitive and easy-to-handle radioactivity detector for capillary LC and CE. The attractive combination of capillary LC, eluent fractionation, and subsequent off-line counting is described. The new method is applied for rapid and sensitive separation and detection of 3H-labeled parent drug and its metabolites at levels between 25 and 700 cpm in rat urine. The advantages of capillary LC coupled to the TopCount, and combined with LC-MS data, can be of benefit in many analytical areas, including the characterization of metabolites at low concentration within complex biological fluids. With the same setup, the fractionation with subsequent off-line counting is equally applicable to CE. This is demonstrated with electrophoretically separated 14C-labeled impurities, nicely resolved from a negatively charged main compound, at low levels.     

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.     

Polychromatic scintillation

A formula to compute the index of stellar scintillation detected with a finite spectral bandpass and with arbitrary aperture is derived in the limit of weak perturbations. It also applies to differential scintillation (relative fluctuations of light intensity in a pair of apertures), where the effect of finite bandpass turns out to be significant. The new formula is used for measurements of free-atmosphere seeing and low-resolution turbulence profiles with concentric-ring apertures.     

Evaluation of flow cell detector configurations combining simultaneous preconcentration and scintillation detection for monitoring of pertechnetate in aqueous media

Flow cell detectors were developed for simultaneous concentration and scintillation detection of technetium-99 in water. Evaluated flow cell geometries consisted of a coil and a fountain flow cell design; the latter is based on radial solution flow through a resin bed interfaced with a photomultiplier tube through a polycarbonate window. The sorptive scintillating media investigated were (1) an extractive scintillator combining a porous polystyrene resin with the extractant Aliquat-336 and fluor 2-(1-naphthyl)-5-phenyloxazole, (2) a mixed bed of organic scintillator (BC-400) and Tc-selective resin (TEVA), and (3) a mixed bed of inorganic scintillator particles (CaF2-Eu) with either TEVA resin or strong base anion-exchange resin (Dowex 1 x 8-400(Cl)). Depending on flow cell geometry and medium, the detection efficiencies for 99Tc ranged from 7.26 (BC-400/TEVA in coil geometry) to 50.20% (CaF2(Eu)/Dowex 1 x 8-400(Cl) in fountain flow cell geometry). The configuration with the highest sensitivity, CaF2(Eu)/Dowex 1 x 8-400(Cl) in coil geometry, can detect 99Tc as low as 3.78 Bq L(-1) for a 100-s count interval and a 200-mL sample, which is below the current regulatory level of 33 Bq L(-1). The issue of sensor reusability was addressed in this research, and its potential application at near neutral pH was demonstrated. The optimal sensor design was evaluated with a 99Tc-spiked synthetic groundwater matrix.     

Luminescence and scintillation properties of rare-earth-doped LuF3 scintillation crystals

The Nd-doped and Er-doped LuF₃ single crystals were grown by the micro-pulling-down method to study their scintillation properties in the vacuum-ultraviolet (VUV) region. The doubly Nd–Er codoped single crystal was grown to study possibility of scintillation performance improvement by energy transfer from Er³⁺ to Nd³⁺ ions. The LiF flux was to avoid phase transition below melting temperature. The 1%Nd-doped sample showed the highest overall scintillation efficiency under X-ray excitation which was 7 times as high as that of the LaF₃:Nd 8% standard. The leading Nd³⁺ 5d–4f emission was situated at 176 nm, while the Er³⁺ 5d–4f emission for Er-doped samples was observed at 163 nm, which better matches the sensitivity of some VUV-sensitive photodetectors. The optimum Er concentration was determined to be around 1–3 mol%. No Er³⁺ 5d–4f emission was observed for the doubly Er,Nd-codoped sample due to energy transfer from the Er³⁺ to Nd³⁺ ions. Slight improvement of the light yield was observed in the doubly-doped sample with respect to the Nd-only doped one.     

Choice of the detector scintillation crystal thickness in a spectrometer used for phase analysis of a substance by the gamma-resonance method

A discussion is given of the choice of the thickness of the scintillation crystal in a spectrometer used for phase analysis of a substance by the gamma-resonance method when the concentration of the investigated phase is low and the resonant gamma rays are recorded by measuring the total absorption peak.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 63–65, September, 1995.     

Response of a BaF2 scintillation detector to quasi-monoenergetic fast neutrons in the range of 45 to 198 MeV

We have studied the neutron response of a scintillation detector consisting of a 14 cm long, hexagonal-shaped BaF₂-crystal with an inner diameter of 8.75 cm coupled to an EMI9821QB photomultiplier tube. The detector was exposed to calibrated quasi-monoenergetic neutron fields obtained from ⁷Li(p,n)⁷Be reactions. The measurements were performed at neutron energies of 45, 60, 96, 147 and 198 MeV as given by the energies of the incident protons. The experimental pulse-height spectra of the BaF₂-detector are compared with Monte Carlo simulations using the FLUKA code. The detection efficiency of the BaF₂-detector in the energy range of 45–198 MeV was determined as a function of the discriminator threshold and compared to the literature data. At neutron energies above 100 MeV the detection efficiency of the BaF₂-detector was found to be a factor of two higher than that of an NE213-detector of comparable size.