Scintillator Films Research Articles

Amorphous silicon pixel layers with cesium iodide converters for medical radiography

We describe the properties of evaporated layers of cesium iodide (thallium activated) deposited on substrates that enable easy coupling to amorphous silicon pixel arrays. The CsI(Tl) layers range in thickness from 65 to 220 /spl mu/m. We used the two-boat evaporator system to deposit CsI(Tl) layers. This system ensures the formation of the scintillator film with homogenous thallium concentration which is essential for optimizing the scintillation light emission efficiency. The Tl concentration was kept to 0.1-0.2 mole percent for the highest light output. Temperature annealing can affect the microstructure as well as light output of the CsI(Tl) film. 200-360/spl deg/C temperature annealing can increase the light output by a factor of two. The amorphous silicon pixel arrays are p-i-n diodes approximately 1 /spl mu/m thick with transparent electrodes to enable them to detect the scintillation light produced by X-rays incident on the CsI(Tl). Digital radiography requires a good spatial resolution. This is accomplished by making the detector pixel size less than 50 /spl mu/m. The light emission from the CsI(Tl) is collimated by techniques involving the deposition process on patterned substrates. We have measured MTF of greater than 12 line pairs per mm at the 10% level. >

Phoswich detectors combining doubly or triply ZnS(Ag), NE102A, BGO and/or NaI(Tl) scintillators for simultaneous counting of α, β and γ rays

Phoswich detectors for simultaneous counting of α, β and γ rays have been developed: ZnS(Ag)/Au Mylar/NE102A, ZnS(Ag)/Au Mylar/BGO and ZnS(Ag)/NaI(Tl) for α and β(γ) rays and ZnS(Ag)/Au Mylar/NE102A/BGO and ZnS(Ag)/NE102A/NaI(Tl) for α, β and γ rays. They were prepared by coupling a ZnS(Ag) film scintillator for α counting with a scintillator(s) for β and γ counting having different rise time. In order to adjust each component of pulse height within a given dynamic range, a sheet of Au-coated Mylar (Au Mylar) was used, if necessary, as an optical ND filter for lowering transmittance of scintillation of the ZnS(Ag). Characteristics of these phoswiches were examined by a technique of pulse-shape discrimination. Excellent discrimination among the radiations was attained and small tailings from each other peak were obtained for the prepared phoswiches.

Thin films of barium fluoride scintillator deposited by chemical vapor deposition

We have used metal-organic chemical vapor deposition (MOCVD) technology to coat optical substrates with thin (∼1−10 μm thick) films of inorganic BaF 2 scintillator. Scanning electron microscope (SEM) photographs indicate that high-quality epitaxial crystalline film growth was achieved, with surface defects typically smaller than optical wavelengths. The scintillation light created by the deposition of ionizing radiation in the scintillating films was measured with a photomultiplier and shown to be similar to bulk melt-grown crystals. The results demonstrate the potential of these composite optical materials for planar and fiber scintillation radiation detectors in high energy and nuclear physics, synchrotron radiation research, and in radiation and X-ray imaging and monitoring.

A large-area, scintillation telescope for heavy ions

The design and laboratory testing of a large-area, scintillation telescope (LAST) for the detection of heavy ions are discussed. This dual, thin-film detector is to be used as a fast event trigger, Delta E, and time-of-flight spectrometer at the focal plane of the Argonne Fragment Mass Analyzer (FMA). The thin scintillator films in each of the LAST detector modules have dimensions of approximately 1 in by 3 in. This is large enough to completely cover the active area of the focal plane of the FMA. Preliminary measurements indicate that Delta E measurements in each of the foils taken alone or in conjunction with data from other detectors could be used to determine the nuclear Z of the transisting ions. The durability and excellent timing characteristics of plastic scintillators make the LAST detector particularly valuable for high-rate applications such as secondary beam measurements. >

Mass identification in heavy ion collection with the spectrometer SOLENO

A detection system consisting of a thin film scintillator detector and a solid state detector has been set up and used to measure the time of flight and energy of the fusion evaporation residues collected with the magnetic spectrometer SOLENO at the Orsay tandem. The linear responses and the timing properties of the system were tested using a 252Cf source and beams of 16O, 32S and 58Ni. The system was used to study the mass identification and the collection yield obtained with SOLENO.

A position-sensitive n-detector for neutron-fragment correlation measurements

A position-determining device has been developed for studying neutron emission in fission processes. The detector essentially consists of two photomultipliers at the ends of a cylinder of NE213 liquid scintillator (about 82 cm in length and 3 cm in diameter), yielding a position resolution of 8 cm and a time resolution of 1.2 ns for 3 MeV neutrons. The quality of the performance is illustrated by measuring the velocity and angular distributions of neutrons associated with the fission fragments from spontaneous fission of 252Cf. The experimental setup, adaptable for use with other neutron emitting fragments (e.g. heavy-ion reaction products), consisted of the position-sensitive n-detector, a thin scintillator film, and a solid-state detector.

Response characteristics of thin film detectors to fission fragments

The dependence of the pulse height spectrum of a thin film detector (TFD) for fission fragments of 252Cf spontaneous fission on the thickness of scintillator film of the TFD was studied experimentally. The scintillator films used in the experiments were about 50, 100, 200 and 300 μg/cm 2 in thickness. The ratio of the yield of the heavy fragment peak to that of the light fragment peak became smaller as the film became thinner. The experimental result of the pulse height spectrum was analyzed by a luminescence production model which the present authors recently reported. The pulse height spectrum was represented satisfactorily by this model. The dependence of the pulse height spectrum on the incident beam position in the scintillator film was also investigated.

A new model of luminescence production in a very thin plastic scintillator film

A new model of luminescence production in a very thin (less than 100 μg/cm 2) plastic scintillator film is described. This model contains the thickness of the scintillator film and needs only one parameter to fit to the experimental data. Applications of this model are presented for the response of heavy ions as a function of the energy and for the double-valuedness of the luminescence production on the stopping power of the 16O ion. The calculated results show good agreement with the experiments reported by other authors. This model is useful for heavy ions with low energy.

Response of thin NE102A scintillator films to fission fragments

The pulse height response of NE102A plastic scintillator films to fragment ions from 252Cf spontaneous fission has been investigated as a function of fragment time-of-flight and film thickness t in the range 1–15 μm. For velocities close to the two peaks in the fragment velocity spectrum and for films of either t ≳ 9 μm or t ≲ 3 μm, an approximately linear relationship between response and fragment velocity is found. For films of thickness 3–6 μm or for fragments from symmetric or highly asymmetric fission. deviations from the linear dependence are observed. The response increases rapidly with film thickness in the range t = 3–6 μm and saturates at t ≳ 9 μm for both light and heavy fragments. The possible role of surface effects in these phenomena is discussed.

An on-line tritium-in-water monitor

The paper describes the development and operation of a continuous on-line tritium-in-water monitor for the detection of heavy water leaks into the secondary coolant light water of a heavy water power reactor. The heart of the instrument is its plastic scintillator sponge detector, made from 5 μm thick plastic scintillator films. The sponge weighs only about 1 g and is in the form of disc of 48 mm diameter and 8 mm thickness. The total surface area of the films is about 3000 cm 2. In the coincidence mode of counting, the detector gives 1000 cps for the passage of 3.7 × 10 4 Bq/cm 3 (1 μCi/cm 3) of tritiated water. The background in 6 cm thick lead shielding in the laboratory is 0.2 cps, and inside the reactor building it is below 1 cps. The monitor presently scans 18 sample lines in sequence for 5 min each and gives a printout for the activity in each line.

Passage of fission fragments through thin film plastic scintillators

The slowing down of fission fragments from the spontaneous fission of 252Cf has been studied in the self-supporting thin films of plastic scintillator NE 102A, using a surface barrier detector. The measured residual energies and hence the energy losses of the mean light and heavy fragments after passing through the thin films of thickness ranging from ∼-100 to 1200 μg/cm 2 of NE 102A are reported. These measurements were carried down to 20.0 MeV and ∼- 14.0 MeV for light and heavy fragments respectively. The shape spectrum parameters from the slowed spectra are determined. The measured energy straggling parameters obtained from these spectra show a maximum around 300 μg/cm 2 of NE 102A and the energy bunching effect due to fission fragments is observed in thicker plastic scintillator films (>300 μg/cm 2). The stopping power obtained from these measurements is compared with the theoretical predictions.

Light collection systems for thin film scintillation detectors

Three different designs for light guides used with thin film scintillators employed as ΔE detectors are described. Each system was tested in nearly identical conditions and configurations except for the light-gathering mechanism, using NE102A and Pilot B films and alpha-particles. Light-collection efficiencies, as well as energy and time resolutions are compared. It was found that a simple hollow cylindrical reflector in which the reflective surface was produced by vacuum evaporation of aluminium on a thin plastic sheet, was an efficient light guide for large-area thin-film scintillation detectors. Coupled to two matched and selected RCA 8850 phototubes operated in coincidence mode, this system was capable of giving a pulse height resolution of 21% and time resolution of 0.4 ns for a 1.1 mg/cm 2 NE102A detector and alpha-particles of 5.48 MeV incident energy. The TFD mounting feature of this design allows a comparison of different detectors without disturbing any other parameter. It thus provides a very effective system for testing and comparing the properties of thin scintillator films on a very reliable basis.

Fragment charge-mass-energy correlations in 236U fission using an ionization chamber-scintillation detector telescope

Fission fragment charge-mass-energy correlations have been obtained in the thermal neutron induced fission of 235U by measuring the responses of an ionization chamber and a thin film scintillation detector arranged in tandem using a single-sided source. Since the response of the ionisation chamber and also that of the thin film scintillation detector for fission fragments are functions of their charge, mass and velocity, information on these parameters is obtained from these responses making use of the conservation relations that are valid for the fission fragments with respect to their mass, charge and momentum. The distributions so obtained are compared with those obtained by double energy measurements using semiconductor detectors.

Thin film scintillation detector response to fragments from light charged particle accompanied fission of 236U

The thin film scintillation detector (TFSD) response to incident heavy ions is made use of to probe the difference in most probable mass and charge of fragments in binary and light charged particle accompanied (LCPA) fission. The response function of the detector is calculated semi-empirically and the detector calibration is done by using the peaks in the TFSD pulse height distribution due to binary fission fragments. The analysis indicates that in LCPA fission the shifts (with respect to binary fission) of the charge and mass of the most probable light fragment are larger than the corresponding shifts for the most probable heavy fragment.

Quantitative investigation of scintillator intensification for light and electron microscope radioautography.

Several reports have indicated that scintillators enhance the intensity of radioautographic reactions. If this were the case, the use of scintillators would shorten the exposure time of radioautographs and the production of radioautographs would be accelerated. It was, therefore, decided to examine the effect of scintillators on the intensity of radioautographs in a quantitative manner over uniformly labeled test specimens. Reaction intensities with or without scintillators were compared using Kodak NTB2 emulsion for light microscopy and Ilford L4 and Sakura NR-H2 emulsion for electron microscopy. In addition, the background fog was quantitatively evaluated. No increase in the intensity of the radioautographs was observed under the following conditions: pretreatment of tissue sections with scintillator solutions before emulsion coating and exposure; treatment with scintillator solutions after emulsion coating but before exposure; treatment with scintillator solutions during exposure; contact with a plastic scintillator film throughout exposure. Heightened reaction intensity was obtained only when scintillators were applied during the histological processing of tissues. The impregnation of tissue blocks with PPO (2,5-Diphenyloxazole) and POPOP (1,4-bis-2-(5-phenyloxazolyl)-benzene) during dehydration, infiltration and Epon embedding produced a 20% increase of reaction intensity in light microscope radioautographs using NTB2 emulsion and a 75% increase in electron microscope radioautographs using L4 emulsion.

Heavy ion identification using a thin film scintillator detector

The application of a thin film scintillator detector (TFD) for the identification of heavy ion products from the well-known reactions 12C+ 16O, 12C+ 14N, 12C+ 12C and 12C+ 7Li has been made. The TFD was used to measure values proportional to specific luminescence and a solid state detector was used for incident and residual particle energy measurements. In parallel experiments the TFD was exposed to a range of monoenergetic ion beams of 16O, 14N, 12C and 7Li, as well as to alpha particles from a 228Th decay source, in order to establish calibration curves. These spectra were collated with as to alpha particles from a 228Th decay source, in order to establish calibration curves. These spectra were collated with two-parameter plots of coincident signals from the solid state and scintillator detectors for each reaction. Trends in specific luminescence as a function of ion energy-loss and luminescence efficiency vs. ion energy are also presented. Calculations based on two different models of specific luminescence production are shown to agree with the general behavior exhibited by the five ions.

Discrimination between different ions using thin scintillator films as time-of-flight detectors

A time-of-flight telescope is described using two thin plastic scintillator films as start- and stop-detectors. The separation of different ions with different energies is achieved both by time measurement and by thin film light response. First experiences with the telescope, now installed at the velocity filter behind the UNILAC at GSI, are reported.

A detector for continuous monitoring of low levels of tritiated water activity in presence of high gamma background

Development of a flow cell type of detector for continuous monitoring of low levels of tritiated water activity in presence of high gamma background is being reported. The cell is packed with 50 mm dia. and 6 μm thick plastic scintillator films. The total surface area of the films is 2800 cm 2 and the total weight is 0.880 g. Background of the unshielded detector is 20 counts per minute which is equivalent to a passage of 0.3 nCi/ml of tritiated water. Gamma response of the detector in 6 cm lead shielding is equivalent to the passage of 0.2 nCi/ml of tritiated water for 1 mR/h field.

Energy loss and straggling of alpha particles in thin homogeneous NE-111 scintillator foils

A method for preparing thin homogeneous plastic scintillator films is described. The films were tested by measuring energy loss and straggling of alpha particles. The results are compared with theoretical predictions. In addition, the detection efficiency of the films was determined.

Optical characteristics of the thin-film scintillator detector

A study of the thin-film detector (TFD) was made in which various light guide and scintillator film support configurations were tested for efficiency of light coupling. Masking of selected portions of the photomultiplier (PM) tube face revealed the extent to which emitted light was received at the exposed PM surfaces. By blocking off selected areas of the scintillator film surface from direct view of the PM tube faces, a measure of the light-guiding efficiency of the film and its support could be estimated. The picture that emerges is that, as the light which is initially trapped in the thin film spreads radially outward from the ion entrance/exit point, it is scattered out of the film by minute imperfections. Optimum signals were obtained by a configuration in which the thin scintillator film was supported on a thin rectangular Celluloid frame inserted within a highly polished metal cylindrical sleeve.