Scintillator Volume Research Articles

A fibre optic scintillator dosemeter for absorbed dose measurements of low-energy X-ray-emitting brachytherapy sources

A newly developed dosemeter using a 0.5 mm diameter x 0.5 mm thick cylindrical plastic scintillator coupled to the end of a fibre optic cable is capable of measuring the absorbed dose rate in water around low-activity, low-energy X-ray emitters typically used in prostate brachytherapy. Recent tests of this dosemeter showed that it is possible to measure the dose rate as a function of distance in water from 2 to 30 mm of a (103)Pd source of air-kerma strength 3.4 U (1 U = 1 microGy m(2) h(-1)), or 97 MBq (2.6 mCi) apparent activity, with good signal-to-noise ratio. The signal-to-noise ratio is only dependent on the integration time and background subtraction. The detector volume is enclosed in optically opaque, nearly water-equivalent materials so that there is no polar response other than that due to the shape of the scintillator volume chosen, in this case cylindrical. The absorbed dose rate very close to commercial brachytherapy sources can be mapped in an automated water phantom, providing a 3-D dose distribution with sub-millimeter spatial resolution. The sensitive volume of the detector is 0.5 mm from the end of the optically opaque waterproof housing, enabling measurements at very close distances to sources. The sensitive detector electronics allow the measurement of very low dose rates, as exist at centimeter distances from these sources. The detector is also applicable to mapping dose distributions from more complex source geometries such as eye applicators for treating macular degeneration.

Synergic quenching effects of water and carbon tetrachloride in liquid scintillation gel samples

Although both water and carbon tetrachloride induce chemical quenching when incorporated to Insta Gel, the quenching power of carbon tetrachloride is nearly two orders of magnitude greater than that of water. This huge difference shows how different the chemical quenching mechanisms among quenchers can be. One remarkable fact of all pure β-ray nuclides is that calibration curves do not depend on the water to scintillator volume ratio or on the nature of the quencher. The fact is clearly surprising, because two tritium samples of different water to scintillator and quencher to scintillator volume ratios may have identical counting efficiencies. As we shall prove, this fact is only possible when the external quench parameter of both samples is the same. We study the synergies in quenching generated when carbon tetrachloride is added to a sample in gel phase.

The three-dimensional scintillation dosimetry method: test for a 106Ru eye plaque applicator

The need for fast, accurate and high resolution dosimetric quality assurance in radiation therapy has been outpacing the development of new and improved 2D and 3D dosimetry techniques. This paper summarizes the efforts to create a novel and potentially very fast, 3D dosimetry method based on the observation of scintillation light from an irradiated liquid scintillator volume serving simultaneously as a phantom material and as a dose detector medium. The method, named three-dimensional scintillation dosimetry (3DSD), uses visible light images of the liquid scintillator volume at multiple angles and applies a tomographic algorithm to a series of these images to reconstruct the scintillation light emission density in each voxel of the volume. It is based on the hypothesis that with careful design and data processing, one can achieve acceptable proportionality between the local light emission density and the locally absorbed dose. The method is applied to a Ru-106 eye plaque immersed in a 16.4 cm3 liquid scintillator volume and the reconstructed 3D dose map is compared along selected profiles and planes with radiochromic film and diode measurements. The comparison indicates that the 3DSD method agrees, within 25% for most points or within ∼2 mm distance to agreement, with the relative radiochromic film and diode dose distributions in a small (∼4.5 mm high and ∼12 mm diameter) volume in the unobstructed, high gradient dose region outside the edge of the plaque. For a comparison, the reproducibility of the radiochromic film results for our measurements ranges from 10 to 15% within this volume. At present, the 3DSD method is not accurate close to the edge of the plaque, and further than ∼10 mm (<10% central axis depth dose) from the plaque surface. Improvement strategies, considered important to provide a more accurate quick check of the dose profiles in 3D for brachytherapy applicators, are discussed.

Plastic scintillation dosimetry: Optimal selection of scintillating fibers and scintillators.

Scintillation dosimetry is a promising avenue for evaluating dose patterns delivered by intensity-modulated radiation therapy plans or for the small fields involved in stereotactic radiosurgery. However, the increase in signal has been the goal for many authors. In this paper, a comparison is made between plastic scintillating fibers and plastic scintillator. The collection of scintillation light was measured experimentally for four commercial models of scintillating fibers (BCF-12, BCF-60, SCSF-78, SCSF-3HF) and two models of plastic scintillators (BC-400, BC-408). The emission spectra of all six scintillators were obtained by using an optical spectrum analyzer and they were compared with theoretical behavior. For scintillation in the blue region, the signal intensity of a singly clad scintillating fiber (BCF-12) was 120% of that of the plastic scintillator (BC-400). For the multiclad fiber (SCSF-78), the signal reached 144% of that of the plastic scintillator. The intensity of the green scintillating fibers was lower than that of the plastic scintillator: 47% for the singly clad fiber (BCF-60) and 77% for the multiclad fiber (SCSF-3HF). The collected light was studied as a function of the scintillator length and radius for a cylindrical probe. We found that symmetric detectors with nearly the same spatial resolution in each direction (2 mm in diameter by 3 mm in length) could be made with a signal equivalent to those of the more commonly used asymmetric scintillators. With augmentation of the signal-to-noise ratio in consideration, this paper presents a series of comparisons that should provide insight into selection of a scintillator type and volume for development of a medical dosimeter.

SU-FF-T-229: A Test of the 3D Scintillation Dosimetry Method for a Ru-106 Eye Plaque Applicator

Purpose: To describe and test a novel and potentially fast, 3D relative dosimetry method based on the observation of scintillation light from an irradiated liquid scintillator (LS) volume serving simultaneously as a phantom material and as a dose detector medium. Method and Materials: The method, named Three Dimensional Scintillation Dosimetry (3DSD), uses visible light images of the liquid scintillator volume at multiple angles and applies a tomographic algorithm to a series of these images to reconstruct the scintillation light emission density in each voxel of the volume. The method is applied to a Ru-106 eye plaque immersed in a LS volume and the reconstructed relative 3D dose map is compared along selected profiles and planes with radiochromic film (RCF) and diode measurements. Results: The comparison indicates that the 3DSD method agrees with the relative RCF dose distributions for a small (3 mm high by ∼12 mm diameter) part of the volume within 25% for most points. Larger, up to 45 % deviations are observed for fraction of the points due to elongation of the RCF transverse isodose contours, not seen by 3DSD. For a comparison, the spread of the RCF measurements ranges from 10 to 15% within this volume. The method is not accurate close to the edge of the plaque, close to the edges of the scintillator volume and further than ∼9 mm from the plaque surface. Conclusion: 3DSD shows potential for quick 3D relative dosimetry in a small volume with accuracy and resolution comparable to existent 2D techniques. More accurate determination of the point spread function of the system, of the light scatter within the cell, of the dose-rate and energy related quenching effects and enhancement of the algorithm for partially blocked projections are expected to extend accuracy to larger volumes and closer to the applicator edges.

Applications of a phoswich-based detector for fast (∼1–10 MeV) solar neutrons for missions to the inner heliosphere

We describe a phoswich-based detector concept for studies of low energy (∼1–10 MeV) solar neutrons in the innermost heliosphere ( R <∼ 0.5 AU). The detector has applications both as a very low mass (<∼1 kg), low power (∼1–2 W) stand-alone instrument, and as a component to enhance the capabilities of more sophisticated instruments, for example, the fast neutron imaging telescope instrument described by Moser et al. [Moser, M.R., Flückiger, E.O., Ryan, J.M., et al. A fast neutron imaging telescope for inner heliosphere missions. Adv. Space Res., in press, this issue, doi:10.1016/j.asr.2005.03.037]. In its most basic form, the detector consists of a small volume (∼1 cm 3) of fast organic scintillator completely surrounded by a slow inorganic scintillator. The dimensions of the organic scintillator are chosen to minimize multiple n–p scatterings while retaining adequate sensitivity. The inorganic scintillator provides anti-coincidence protection against energetic charged particles. A single PM tube views light from both scintillators. Pulse shape analysis identifies as potential neutrons those events where only the organic scintillator contributes to the signal. The signal size corresponds to the energy of the recoil proton from an n–p elastic scatter, on average half the energy of the incident neutron. An instrument based on this concept would provide measurements of the neutron flux and, through statistical analysis of recoil proton energies, basic information about the neutron spectrum.

Recent progress in the development of CsI(Tl) crystal–Si-photodiode spectrometric detection assemblies

Highly sensitive spectrometric γ-detection assemblies are developed using a comprehensive approach (optimization of crystal growth conditions as well as of treatment and packing of scintillators, creation of low-noise charge-sensitive preamplifiers and shapers). The detection assemblies with CsI(Tl)⩽100cm3 have a sensitivity of about 20pulse/s(mcR/h), their energy resolution with respect to 137Cs γ-line being ⩽8.5%. The assemblies with lesser scintillator volumes (1–5cm3) provide a resolution lower than 6% with respect to 137Cs and ⩽40% with respect to 241Am.

Statistics of the LS-detector in the case of low counting efficiency

In the case of high-quenched 3H and 63Ni sources a distinct incompatibility of theoretical and experimental detection efficiency in the triple liquid scintillation (LS) detector was observed (Appl. Radiat. Isot. 52 (2000) 643). The authors concluded, that the Poisson distribution does not properly describe the detection process, when less than one photoelectron is expected in one of the photomultipliers. Application of other distributions of photoelectrons, e.g. binomial, does not solve the observable problem of incompatibility. Measurements of a set of 55Fe sources have been performed with phototubes defocusing and grey filters for decreasing the counting efficiency of the TDCR detector. Differences between counting results of the 55Fe source and the light emitting diode (LED), simulating the scintillation source, excited by a pulse generator have been observed. Various distributions (Poisson, binomial and Polya) were used for the determination of the theoretical counting efficiency in both cases. The Poisson law gave a good result in the case of the LED but the Polya law had to be applied in the case of 55Fe. The results were independent of the scintillator volume. It seems that the validity of the Polya law in the case of LS-sources is related to the scintillator itself. Measurements of the 3H solution confirmed that conclusion.

Scintillation material for determination of radionuclides in water

This paper is devoted to the development and use in radiation monitoring of new sorption materials, together with methods of their application for selective determination of radionuclide 90Sr in water. The material comprises a matrix, which is transacted by pores. A selective sorbent is fixed onto the surface of these pores. The material structure allows the passage of the liquid to be analyzed through the pores. The element to be determined is accumulated in the scintillator volume. Preconcentration of 90Sr inside a scintillation composite material, rather than through sample manipulation (evaporation, etc.), will greatly simplify the analytical process. 4π-Geometry is ensured for radiation detection, and simultaneously the radiochemical problem of radionuclide concentration is solved. Crystals of p-terphenyl doped with diphenylbutadiene were used as the matrix, and synthetic hydroxylapatite as selective complex-forming agent. The proposed method based on using porous scintillators allows detecting concentrations of 90Sr in the potable water, which are less than the maximum acceptable concentration (i.e. 2 Bq/l).

A new X-ray scintillator for digital radiography

The authors report a new scintillator based on a transparent ceramic of Lu/sub 2/O/sub 3/:Eu. The material has an extremely high density of 9.4 g/cm/sup 3/ and a light output comparable to CsI:Tl. Its narrow-band emission at 610 nm perfectly matches the spectral response of charge coupled devices (CCDs). To enhance the spatial and contrast resolution, the authors have developed a special process to pixelate the scintillator and prevent the spread of light within the scintillator volume. The imaging performance of this pixelated device was evaluated using a thermoelectrically cooled CCD camera. The new scintillator is expected to play a major role in digital radiographic systems when readout technologies capable of taking advantage of the transparency are developed further.

Quest for double beta decay of 160Gd and Ce isotopes

The 2 β decay study of 160Gd has been performed in the Solotvina Underground Laboratory with the help of Gd 2SiO 5:Ce crystal scintillator (volume 95 cm 3). The background of the detector in the vicinity of the Q ββ energy of 160Gd was reduced to 1.0 cpd/(keV kg). The new improved half-life limits have been established for 0 ν2 β decay of 160Gd to the ground (0 +) and first excited (2 +) levels of 160Dy: T 1/2 0 ν ⩾2.3(1.3)×10 21 yr at 68%(90%) C.L. The T 1/2 bounds have been also set for 2 ν, 0 νχ and 0 νχχ modes of 160Gd decay, as well as for different 2 β decay processes in 136Ce, 138Ce and 142Ce.

Detection efficiency improvement of a large volume scintillation cell

A large volume scintillation cell (LVSC) for radon activity concentration measurements has been reported at MARC-IV. The present paper describes improvements in the detection efficiency of the LVSC and results of the radon activity concentration measurements for indoor air that were performed using the improved LVSC. The cell is a cylindrical shape and has two photomultiplier tubes that are attached to a condensing lens on the photocathode so as to provide good light collection. Individual counting efficiencies were determined to be 0.48 for 222Rn, 0.55 for 218Po, and 0.61 for 214Po. The average counting efficiency per alpha-particle from the radon and its short half-life progenies was 0.55. This value is smaller than the original value reported by LUCAS of 0.86. However, the sensitivity is approximately eight times higher than that of the Lucas cell, which has a smaller volume. A background counting rate of 0.015 cps was obtained. The lower limit of detection (LLD) for the measurements was estimated using the average background counts, the detection efficiency and measurement time. The LLD at 80% statistics confidence limits was less than 10 Bq/m3 when counted within two hours.

Efficiency of a large size scintillation cell

A large volume scintillation cell has been designed to detect low levels of radon and its progeny. The cell has a cylindrical shape (nominal volume 1.2 liters) with two photomultiplier tubes. In this study, the detection efficiency was estimated with Monte-Carlo calculations for 3-dimensional before fabrication. Counting efficiencies for241Am were measured along the axial of the cell with different distances between the source and the scintillation screen to confirm the calculation method. The counting efficiencies for the alpha particles from the226Rn and its short-live progenies were measured using a radon generator. The efficiency was estimated to be 0.36 count per alpha-particle as the average of three alpha-particles.

Detector optimization for hand-held CsI(Tl)/HgI/sub 2/ gamma-ray scintillation spectrometer applications

Gamma-ray spectrometers using mercuric iodide (HgI/sub 2/) photodetectors (PDs) coupled with CsI(Tl) scintillators have shown excellent energy resolutions and high detection efficiency at room temperature. Additionally HgI/sub 2/ semiconductor PDs allow for extreme miniaturization of the detector packaging compared with photomultiplier tube (PMT) based detectors. These advantages make possible the construction of a new generation of hand-held gamma-ray spectrometers. Studies of detector optimization for this application have been undertaken. Several contact materials including hydrogel and semi-transparent metal films have been evaluated and compared for their performances and long term stability. In order to provide higher gamma-ray detection efficiency (i.e. larger scintillator volume), but without causing significant degradation of the excellent response achieved with the matched scintillator/PD interface, the scintillator/PD configuration has been studied. A Monte Carlo simulation model has been developed so that the spectral shape can be predicted for various scintillator shapes and surface treatments.

A study of the light collection for avalanche photo diode readout of CsI(Tl)

Abstract In order to read out the large volume scintillation crystal by such a small photo-sensor as an avalanche photodiode, we have examined the light collection properties of different scintillator-to-sensor interfaces. A spiraled fiber attached on the readout plane of a 4 cm cubic CsI(Tl) scintillator was tried first as an application of the scintillating tile/fiber technique. A light collection buffer of a clear acrylic plate or a wavelength shifter plate was also tested. Its performance and the condition for the minimum enhancement of the light collection are discussed with reference to a Monte Carlo simulation result. The surface reflectivities of the crystal and the interface were the most effective parameter in the light collection.

The LVD experiment at Gran Sasso

The Large-Volume Detector (LVD) in the Gran Sasso underground Laboratory is a multipurpose detector consisting of a large volume of liquid scintillator (at present 562 tons are in data taking) interleaved with limited-streamer tubes. Several physical problems are investigated with LVD, the major being the search for neutrino bursts from gravitational stellar collapses in our Galaxy. In this paper we discuss some results on cosmic neutrinos and cosmic-ray muons obtained with the first of the five towers of LVD (operational since June 1992) and part of the second tower (operational since June 1994). The results of the search for supernovae neutrinos show that LVD is a neutrino observatory able to detect neutrinos of different flavours from gravitational stellar collapses in all our Galaxy, over a wide range of burst durations. Indeed, the carbon-based liquid-scintillator target gives a unique possibility to directly detect neutral- and charged-currents neutrino interactions with a very good signature. This characteristic of LVD allows us to make an indirect estimate of the neutrino rest mass and of neutrino oscillations from supernovae in our Galaxy. No evidence for burst candidates has been found in the data recorded from June 1992 to March 1995, for a total live time of 682 days and a total exposure of 613 tons per year. We present the results of a time coincidence analysis between low-energy signals, eventually due to neutrinos of different flavours, and γ-ray bursts (GRBs) detected by the BATSE experiment. This search covers the period from June 1993 to March 1995, during which 41 GRBs have been selected from the BATSE data. Since no excess of events in LVD has been found, upper limits on the neutrino fluxes are reported for (νe, p), and for neutral- and charged-currents neutrino interactions of different flavours with the C-nuclei of the scintillator. The muon intensity as a function of slant depth is presented. These measurements, obtained during a live time period of 11.556 hours, cover a slant depths range from about 3000 to about 20 000 hg/cm2 of standard rock and extend over five decades of intensity. An interesting result is that the muon flux is independent of slant depth beyond a depth of about 14 000 hg/cm2 of standard rock, and corresponds to near horizontal muons. This is direct evidence that this flux is due to atmospheric neutrinos interacting in the rock surrounding LVD.

LSC background prediction using three-dimensional modelling

A general 3-D surface B(Q, V) is proposed to describe, in liquid scintillation counting, the dependence of the background count rate B, on both the quenching level and the volume of sample, which avoids the need for preparing and measuring blank vials for each problem sample. The analytical function has four parameters which have been determined for Optiphase-Hisafe II® scintillator volumes between 2 and 20 mL and sample quench ranging from 25–50% 3H-equivalent efficiency. It has been successfully tested with 3H standard samples of activity down to 0.24 Bq, with significant background corrections, between 30 and 95% of the raw count rate.

Search for neutrinos from collapsing stars with the LVD at Gran Sasso

The Large Volume Detector (LVD) in the Gran Sasso underground Laboratory is a multipurpose detector consisting of a large volume of liquid scintillator interleaved with limited streamer tubes. In this paper we discuss its power to study low energy cosmic neutrinos. The results show that the first of the five LVD towers, operational since June 1992 with 368 tons of liquid scintillator, is well suited to detect neutrinos from collapsing stars with in all our Galaxy, over a wide range of burst duration (up to a few) hundreds seconds). One year data, collected since June 1992, have been analized and results are here discussed. No evidence for burst candidates has been found in this period of data taking.

On the dectection of neutrino oscillation effects during observation of neutrino burst from stellar collapse in the galaxy

The ability of large volume scintillation counters based on white-spirit (( CH 2) n ) to select charged current (C.C.) ν e, ν e interactions with 12 C while observing a neutrino burst from a stellar collapse in the Galaxy is discussed. If there exist neutrino flavour oscillations ν μ( τ) ↔ ν e , then the number of the C.C. interactions will increase, especially if neutrino oscillation parameters lie in the range of the neutron star matter oscillation effect. Scintillation counters have very good sensitivity to detect these oscillations.

First results of a search for neutrinos from collapsing stars with the LVD at Gran Sasso

The Large Volume Detector (LVD) in the Gran Sasso underground Laboratory is a multipurpose detector consisting of a large volume of liquid scintillator interleaved with limited streamer tubes. In this paper we discuss its power to study low energy cosmic neutrinos. The results show that the first LVD tower (368 tons of liquid scintillator) is well suited to detect neutrinos from gravitational stellar collapses within all of our Galaxy over a wide range of burst duration (up to a few hundred seconds). No burst candidates have been observed in the first two months of data taking.