Scintillator Screen Research Articles

Diurnal variations in a sealed radon chamber

During experiments to calibrate a radon-in-air counter, some unexpected diurnal variations have been observed. Inside the sealed stainless-steel chamber of a nominal volume of 3 litres, ionised 218Po atoms from the alpha-decay of 222Rn are attracted by an electric field to a ZnS(Ag) scintillation screen via which subsequent α-decay events are detected. Results for this configuration are presented and also for a modified version in which the scintillation screen is replaced by a high-resolution α-detector. Ambient temperature changes were suspected to be responsible for the observed counting-efficiency variation and this has been confirmed by operating the wall of the chamber at various temperatures between 0°C and about 40°C, which revealed a positive temperature coefficient of ∼1%/°C at 25°C. Possible reasons for this effect are considered.

Real-time neutron radiography at Texas A&M University

A real-time neutron radiography imaging system has been installed at the Texas A&M University Nuclear Science Center. The system employs a scintillating screen viewed by a low-light TV camera with a front surface mirror placed at 45° to the neutron beam. The key components of the system are the neutron camera and the image capture and processing unit. The neutron camera uses an NE 426 scintillating screen (ZnS), front surface mirror, remote focus and zoom lens, intensified relay optics (IRO) and monochrome CCD television camera. The image capture and processing unit consists of an IBM PC AT-compatible computer, arithmetic frame grabber, frame processor and high-resolution color monitor. The neutron camera is similar to others using a silicon intensified target (SIT) television camera to provide a TV image of the low-level light from a NE 426 screen. The IRO and CCD camera are used in place of the SIT camera. The computer digitizes the TV image (512 × 512 × 8 bit) at a rate of 30 frames/s and provides a variety of image processing functions. The neutron beam has a total neutron flux of 1.2 × 10 7 neutrons/cm 2 s with the TRIGA reactor operating at 1 MW. A remotely operated sample handling devices is used to position an object in the neutron beam.

Simultaneous dynamic neutron and gamma radiography

Equipment for dynamic neutron and gamma radiography has been developed at the 4.6 MW research reactor in Budapest, using thermal neutrons and gamma radiation obtained from the reactor. Radiography images are detected by scintillator screens and by low-light-level TV cameras, providing the possibility of visualizing medium-speed movements inside the investigated objects. The images are displayed on monitors and stored on video recorders. Some applications for nondestructive investigations are given.

Development of New Techniques for Thermal and Fast Neutron Dosimetry Based on Scintillator-Filled Etched-Track Counting

The scintillation method of Harvey and Weeks (1982) has been extended to the counting of etched tracks in CR-39 made by thermal and fast neutrons. For thermal neutrons, CR-39 detectors placed in contact with both Li2B4O7 and BN1 converter screens have been exposed to neutrons from portable sources, with suitable moderation. For fast neutrons, beams of neutrons of different energies up to ~19 MeV from an accelerator have been used without moderation. The pits of the chemically etched 'intrinsic' tracks of fast neutrons, or the (n,a) tracks from the thermal neutrons, are filled with scintillator material, and the light pulses caused by a strong readout a source are detected by a photomultiplier. A number of new methods of producing convenient repositories for the scintillator paste (e.g. using electrochemical etching), and of readout (e.g. by using a separate scintillator screen underneath the etched-through holes produced by a spark counter, rather than filling the etch pits with a scintillator) have also been developed. The linearity of response by these methods has been tested for neutrons of different energies (thermal up to 19.2 MeV). The response (in terms of scintillation count rate) remains linear so long as serious overlapping of etch pits does not occur. The method promises to offer a quick and automatic technique for neutron dosimetry.

A low-energy beta-particle imaging system for measuring tritium distributions

A low-energy beta-particle imaging system was constructed for rapid measurement of the distributions of low-energy beta-emitting nuclides, especially tritium. The imaging system consists of a scintillator screen, two tapered fibers, an image intensifier, and a Polaroid film for image recording. The distortion of the observed image is less than 2.5% and the spatial resolution is more than 5 line pairs (lp)/mm. ZnS(Ag) screens with thicknesses of 5–7 mg/cm 2 have the highest scintillation light yield for low-energy beta-particles. The detectable flux densities for 14C and 3H were 7.3 and 80 s −1 cm −2, respectively.

Scintillation detector for escaping alphas and tritons in TFTR

A diagnostic for escaping charged fusion products is presently being tested on tokamak fusion test reactor (TFTR). It consists of a 1×1-in. ZnS scintillator screen located inside a movable probe at the bottom of the TFTR vacuum vessel. The alphas or tritons hit the scintillator screen where they create visible light pulses which are fiber-optically coupled to photomultiplier tubes and/or an intensified video camera for recording and analysis.

New methods of sample-preparation and readout for the scintillator technique of etched-track counting of plastic detectors

Abstract Several methods have been developed as variants of the original Harvey and Weeks (1982) technique in which scintillator-filled etched-track pits in a plastic detector are counted by exposure to a readout α-source, the resulting light pulses being detected by a photomultiplier (PM) placed underneath the detector foil. Our modifications concern both sample-preparation and readout methods. The first development is based on enlarging the track-pit cavity to make the scintillation-filling more secure either by preheating the detector at elevated temperatures for long periods (which enhances the bulk-etch rate in subsurface layers) or by successive chemical, electrochemical, and further chemical etching. The second modification is to produce through-holes in a thin plastic detector (containing tracks on its front surface) by irradiating its rear surface with a high dose of long-range particles of high track-etch velocity; subsequent etching then produces through-holes, via these “host etch-channels”, corresponding to the original tracks. The etched-through detector is then placed on a scintillator screen, which can receive the readout α-particles via the combined etch-channels, and thus generate light pulses.

A theory of particle interference based upon the uncertainty principle

In the original paper (i) it was denostrated that the wave explanation traditionally employed within quantum mechanics to account for particle interference is apparently untenable because it disagrees with the special theory of relativity! A superior explanat ion based on Heisenberg's uncertainty principle and in agreement with special relativity was set forth which also gi~es the correct positions of the so-called , interference maxima and minima ,. (The adjective (~ so-called )) is used here because, in the context of this alternative explanation, the maxima and minima are not produced by the interference of waves, but rather are produced by the grating interfering with the particles.) A problem for understanding will, no doubt, be that the reader is accustomed to thinking of the uncertainty principle as having been derived from the de Broglie wavelength. In contrast to this my approach has been to assume the primacy of the uncerta in ty principle so that the de Broglie wave-length appears as a sort of a reflection of it. However, that they are not equivalent is apparent from the reconsideration of the particle interference problem given in the original paper. In this second paper we will explore some important additional consequence of this alternative approach. One immediate consequence is that we obviate a difficulty that has long been worrisome in quantum mechanics; viz., the problem of the collapse of the wave system. In the wave approach to the interference problem it has been noted that , if the electron hits a scintillation screen after passing through the interference grating, then the de Broglie wave should instant ly collapse to that small region of the scintillation screen struck by the electron. Since the de Broglie wave is very extensive, for some portion of the wave to traverse each slit of the grating, this essentially instantaneous collapse of the de Broglie wave constitutes another disagreement with the theory of special relativity.

Survey of two-dimensional electro-optical X-ray detectors

Electro-optical devices offer a flexible and modular approach to quantitative imaging X-ray detection. Such a detector typically consists of an energy converter coupled to a gain element which is followed by a readout device. This may, for example, be configured by coupling a scintillating screen to an image intensifier which is read by a TV camera. The large variety of commercially available energy converters, gain elements, and readout devices serve to limit the design problem to one of selecting the components, coupling them together and designing the appropriate electronics and software. The design criteria follow most directly from the nature of the particular X-ray detection problem being considered which, in turn, dictates which of two general modes the detector shall be operated in. In the photon counting mode, the gain element is of sufficient magnitude that each absorbed X-ray transmits a large and clearly recognizable signal to the readout device. This signal is real-time detected and allocated to memory. This has the advantages of high spatial resolution and high noise immunity; it has the disadvantage of a low maximum count rate. In another mode, termed the analog mode, the gain element is adjusted so that an individual x-ray makes a contribution comparable with the per-picture element readout noise on a readout device capable of integrating the signal from many X-rays. The magnitude of the integrated signal corresponds to the number of quanta incident. Since X-rays are not individually processed extremely high count rates can be accommodated. The primary disadvantages here is that the readout time lowers the device duty cycle. Hybrid modes are possible. The survey will emphasize the characteristics and principal limitations of the available components as applied toward synchrotron X-ray detection. Methods of coupling the components and modes of reading the final signal will be discussed. The literature pertaining to electro-optical devices that have been constructed will be briefly surveyed. Finally, the need for particular avenues of research and development will be outlined.

Visual Search Using Microfiche: Effects of Microfiche Reader Screen Scintillation on Visual Fatigue, General Fatigue, and Performance

Nine subjects performed a visual search task for two 100-minute sessions using microfiche with positive appearing images and small, portable microfiche readers. During one session the subjects performed the task with a reader having a screen with highly visible scintillation. During the other they used a reader equipped with a screen that was nearly free from scintillation. Dependent variables were subjective visual fatigue, general fatigue, and number of targets located. Subjects reported significantly greater visual fatigue after viewing the “high” scintillation screen for 50–100 minutes than after viewing the “low” scintillation screen for the same length of time. When the high-scintillation screen was used, the subjects also reported an increase in general fatigue. Screen scintillation did not affect the subjects' performance on the search task, however.

ChemInform Abstract: X‐RAY IMAGING TECHNIQUE FOR OBSERVING LIQUID ENCAPSULATION CZOCHRALSKI CRYSTAL GROWTH

AbstractBei dem entwickelten Abbildungsverfahren auf einem Szintillationsschirm wird eine Röntgen‐Punktlichtquelle zur Erzeugung eines Schattenbildes des aus der flüssigen Phase wachsenden Kristalls verwendet.

X‐Ray Imaging Technique for Observing Liquid Encapsulation Czochralski Crystal Growth

An imaging technique has been developed to facilitate growth of uniform diameter crystals by the liquid encapsulation Czochralski method. A point source of x‐rays is used to produce a shadow image of the growing crystal on a scintillation screen. A high‐sensitivity TV camera converts the shadow image into a real‐time display on a TV monitor. System components are described, and results obtained from growing GaP crystals are presented.

Field evaluation of X-ray collimators

An X-ray collimator test tool comprising a metal framework incorporating a pinhole aperture, phosphor-coated lead slug and a self-contained photomultiplier tube phosphor scintillator amplifier assembly has been developed. A pinhole image of the X-ray focal spot is detected by the photo tube. The current representing the light output of the scintillator screen is fed into an operational integrator and read as a reference output signal. A second exposure is taken with the lead slug positioned to obscure the focal spot, to ensure that off-focus radiation is the principal contributor to second exposure signals. The ratio of focal spot signal minus background over focal spot signal plus background is taken as a measure of the off-focus radiation.

Sensitivities of some photographic films and screens for proton radiography

The sensitivity to proton radiation of a selection of photographic films and film-screen combinations was measured for applications in proton radiography. For the fastest emulsions, usable radiographic images require a proton fluence of around 5 × 106 protons/cm2. When the emulsion is placed near the end of range for high contrast imaging, the required dose level is at least 5 rad. Transparent scintillation screens offer a great advantage in speed with little impairment of resolution, providing usable radiographs at 0.1 rad dose level. Screen unsharpness is investigated for plastic scintillator screens of three thicknesses.

A simple method for making a fast inorganic scintillator screen for the detection of fission fragments

A simple method is described for making a fast inorganic scintillator screen for the detection of fission fragments. A suspension of ZnO:Ga in a solution of collodion in acetone is ultrasonically agitated and deposited upon a thin glass disc.

Very Long Baseline Interferometry of Decametric Radiation From Jupiter

Very long baseline Michelson interferometry measurements were made on Io‐related radio emissions from the planet Jupiter at 34 MHz. The data include a single baseline observation made on December 1, 1968, between the Arecibo Ionospheric Observatory (AIO) and Boulder, Colorado (436,000 λ), and a three‐station observation made on April 27, 1969, between the University of Maryland Radio Observatory in California, the University of Texas Radio Astronomy Observatory (UTRAO) in Texas, and Boulder, Colorado (typically 100,000 λ). Frequency analysis of the cross‐correlated signals shows that there is a tendency toward lower observed fringe rates than had been calculated. If we interpret the results entirely in terms of source motion, the data imply a velocity near 200 km/sec eastward. We attribute the phase fluctuations in the cross‐correlated signals to interplanetary scintillation; however, source motion effects cannot be distinguished from scintillation. The implied rms phase variations at the scintillation screen are 0.7 radian at an elongation of 65° (December 1, 1967) and 0.3 radian at an elongation of 145° (April 27, 1969).

Thoron half-life

The half-lives of thoron and actinon have been redetermined using a detector which depends on charcoal particle adsorption of the gas and measurement of the α-particles by scintillation screen, photomultiplier techniques. The new value for thoron half-life is 55·61 ± 0·04 sec, and the new value for actinon is 3·96 ± 0·01 sec.

Nuclear Physics in Photographs

THE epoch-making discoveries in the field of nuclear physics during the past thirty years have been predominantly due to the development and use of methods of detection of single fast-moving nuclei and electrons. In the experiments of Lord Rutherford upon the scattering of α-particles which established the concept of the nuclear atom, in the discovery of the neutron and of artificial transmutation, and in the more recent investigations upon cosmic rays leading to the discovery of the positron and the meson, the part played by the detectors of single charged particles and quanta has been universal and indispensable. It is, therefore, very surprising to reflect that practically all this work has been done with only four basic techniques : the scintillation screen, the Geiger counter, the ionization chamber plus amplifier and the expansion chamber. Nuclear Physics in Photographs Tracks of Charged Particles in Photographic Emulsions. By C. F. Powell and G. P. S. Occhialini. Pp. ix + 124 (50 plates). (Oxford : Clarendon Press ; London : Oxford University Press, 1947.) 18s. net.

The Nature of Statistical Fluctuations with Applications to Cosmic Rays

I. The square of the mean deviation D of the combined effect of several random processes releasing an average of x, y, z ... particles per unit time and producing a, b, c ... ion pairs, respectively, per particle, is D2=a2x+b2y+c2z+..., regardless of whether the separate effects are added or subtracted by the experimental arrangement. For tube-counters, point-counters, scintillation screens and particle counting chambers, a=b=c=1; for ionization chambers a, b, c ... are unequal. II. From the standpoint of statistical fluctuations, the use of two identical instruments in a differential circuit is inferior to the use of a single instrument. III. The natural observational limit for the measurement of x particles against a background of y particles is x=0.67(y)1/2. IV. The statistical fluctuations in the ionization produced by cosmic rays in a spherical ionization chamber are treated rigorously and the fluctuations due to heterogeneity of range and to showers are derived. V. Application to existing data shows that the showers observed in cloud-chamber photographs of the cosmic radiation are also present in the ionization chamber in about the same frequency and multiplicity as indicated by the cloud-chamber results. The tube-counter investigations of the cosmic-ray flux are also in agreement with the deductions from the statistical fluctuations in the ionization chamber. An upper limit of 70±10 ion pairs per cm in air at 1 atmosphere is set for the total ionization along the path of an individual cosmic-ray secondary. The size and the relative frequency of occurrence of showers is appreciably greater at 14,700 feet elevation than at sea level. These showers are quite distinct from the ionization bursts or Stosse observed by Hoffmann, Steinke and others.

Valve methods of recording single alpha-particles in the presence of powerful ionising radiations

In 1926, Greinacher showed that it was possible to detect single α-particles by linearly amplifying the ionisation current due to an α-ray by means of thermionic valves. Subsequently, he was also able to detect single H-particles by the same method. Other workers have since applied the method to various radio-active problems in which the counting would otherwise have had to be done by means of scintillation screens or Geiger counters, etc. The present writers, working in conjunction with H. M. Cave, also employed the method for determining the mean rate of emission of α-particles from radium C, by counting accurately the number of particles emitted within a defined solid angle. While the problem of encounting α- or H-particles can be a comparatively simple matter under certain conditions, there are many experiments necessarily carried out under conditions which render it utterly impossible to employ the Greinacher method in its original form. These experiments involve the counting of comparatively few particles in the presence of disturbances caused by powerful β- or γ- radiation, or by large groups of α-particles which it is not desired to count.