Geo. T. Reynolds

High sensitivity image intensifier‐TV detector for x‐ray diffraction studies

A sensitive, efficient image intensifier-TV x-ray detector is described that has been optimized for a large class of diffraction studies of biological structures. All of the major components are commercially available. The system is well suited to measuring the intensity of diffraction patterns that are weak, or changing with time. Because there is no count rate limitation, it is particularly well suited for studies utilizing the high fluxes of synchrotron sources.

The development of bioluminescence in the ctenophore Mnemiopsis leidyi

Abstract The photocytes of the ctenophore Mnemiopsis have a discontinuous distribution along the radial canal between the sites where the comb plate cilia cells are located on the side of the canal which contains the testes. They are separated from the lumen of the canal by a population of gastric cells. Cytologically these cells are characterized by a condensed nucleus and cytoplasm which stains lightly with basophilic dyes. The ability of the ctenophore embryo to produce light appears at the developmental stage when the comb plate cilia first begin to grow out. At this stage four light-producing areas are present; each area corresponds to one quadrant of the adult animal. At the sites of light production, a population of cells can be identified that have some of the cytological properties of the photocytes of the adult animal. Within 8–10 hr after light production begins there is a 10-fold increase in the amount of light produced by an embryo and a cytological maturation of its photocytes; during this time period there is no increase in photocyte number. At about the time the embryo begins to feed, each light-producing region splits into two regions, each of which corresponds to a radial canal. During the process of embryogenesis the photocyte cell lineage is first segregated from non-photocytes at the differential division which gives the 8-cell stage embryo. The M macromere lineage goes on to form photocytes, but the E macromere lineage does not. The M macromeres form a micromere at the aboral pole of the embryo at each of the next two cleavages; during these cleavages the potential for photocyte differentiation continues to segregate with the M macromeres. During the division which gives the 64-cell stage the M macromeres divide equally; the potential for photocyte differentiation segregates with the M macromeres nearest the oral-aboral axis. M macromeres which are isolated from the embryo at the 8-, 16-, or 32-cell stage of development will continue to cleave as though they were part of a normal embryo and differentiate to form photocytes. The events that are responsible for the differential division during the formation of the 8-cell stage embryo have been studied by centrifuging eggs to produce fragments of different cytoplasmic composition. Egg fragments which contain only cortical cytoplasm differentiate comb plate cilia cells, but do not produce photocytes. Cortical fragments with a small amount of yolk differentiate comb plate cilia cells and photocytes. Both the M and E macromeres from cortical fragments with no yolk produce comb plate cilia. Only M macromeres containing yolk form photocytes; if an M macromere forms photocytes it does not form comb plate cilia.

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

Abstract 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.

Interference effects produced by single photons

SummaryInterference patterns produced by low-intensity photon beams passing through a Fabry-Perot interferometer have been studied. Photons were detected by means of an image intensifier tube of high quantum detection efficiency. No change in the nature of the pattern was observed when the intensity of the beam was reduced from 5·104 to 15 photons per second in the entire pattern.RiassuntoSi sono studiate le figure d’interferenza prodotte dai fasci di fotoni di bassa intensità passanti attraverso un interferometro di Fabry-Perot. Si sono rivelati i fotoni tramite un tubo che intensifica l’immagine con alta efficienza nella rivelazione dei quanti. Non si è osservata alcuna variazione nella natura della figura una volta ridotta l’intensità del fascio da 5·104 a 15 fotoni per secondo nell’intera figura.РеэюмеБыли исследованы интерференционные диаграммы, обраэованные фотонными пучками с ниэкой интенсивностью, при прохождении череэ интерферометр Фабри-Перо. Фотоны детектировались посредством злектронно-опт ического усилителя иэображения с высокой зффективностью детектирования квантов. Не наблюдалось никакого иэменения природы диаграммы, когда интенсивность пучка уменьщалась от 5·104 до 15 фотонов в секунду.

Secondary Electron Multiplication in Image Intensifier Dynode Structures

The distribution in the number of photons in the light pulses from the phosphor of a five dynode transmission secondary electron image intensifier (TSEM) has been measured for single photoelectrons emitted from the cathode. This distribution reflects the distribution in the secondary electron multiplication in the dynode structure. The distribution is monotonically decreasing, but deviates significantly from a simple exponential. The noise distribution has also been studied and several different components distinguished. The effects on these components of cooling the cathode has been investigated.

Image Intensification of X-Ray Diffraction Patterns from Biological Structures

An image intensifier has been used to record two dimensional X-ray diffraction patterns. The details and characteristics of the system in current use are described. This system provides for the conversion of X-rays to visible light, intensification of this light for integration on a TV vidicon target, on-line computer controlled scan and readout to disk, and subsequent computer analysis of the data. The system is particularly useful for the study of weakly diffracting specimens, samples where radiation damage dictates minimal exposure, and structures where dynamic processes are involved. Results obtained to date are discussed. Comparisons are made of this system with alternate recording systems, including film and electronic devices. The potential usefulness of this system for studies utilizing high intensity synchrotron radiation is discussed.

A High Gain Image Intensifier - Spectroscope System for in Vivo Spectral Studies of Bioluminescence

In bioluminescence the amount of light emitted in vivo from a single specimen is in general so small that conventional spectral recording techniques are not useful. A specially designed fast input lens grating spectroscope has been combined with a high gain image intensifier. The light from the specimen is directed to the input slit of the spectroscope by means of a fiber optics light pipe. The system is calibrated by means of a standard lamp. A digitized densitometer provides input to a computor program which corrects for system non-uniformities and prints out spectra at 150 intensity levels every 4 Å from 4000 Å to 6000 Å. The system has been applied to the observation of in vivo spectra from many different species of bioluminescent organisms.

Area detectors capable of recording X-ray diffraction patterns at high count-rates☆

Abstract The Princeton SIT X-ray detector is an electro-optical system designed for recording X-ray diffraction patterns from biological structures. The detector, based on a silicon intensified-target vidicon (SIT), can measure X-ray intensities over an 80 mm diameter area without the count-rate limit characteristic of a photon counting system. Over a wide range of intensities, the accuracy of measurement approaches the quantum limit. Several versions of the device have been constructed, tested and applied to important biophysical problems. The SIT detector has proved particularly useful for the study of dynamic systems with the aid of the intense synchrotron radiation X-ray beams available at EMBL/DESY and SSRL/SLAC. The detectors used in such experiments at future synchrotron radiation sources are likely to be similar to the SIT detector, but based instead on a newer electro-optical device, the solid state imager (e.g. CCD).

Image Intensification Techniques Applied to the Study of X-Ray Diffraction Pattens

The usefulness of image intensifiers in the study of X-ray diffraction patterns has been demonstrated in a number of laboratories. Advantages arise from the fact that usable patterns can be obtained with a marked economy of X-ray exposure campared with conventional film recording or sequential diffractometer techniques, making possible the study of materials very susceptible to radiation damage and systems exhibiting dynamic characteristics which limit permissible dosage or exposure times. In addition, the reduction of time required for the recording of a pattern permits studies of families of crystals with large unit cell size containing many diffraction spots. Various X-ray sensitive cathode arrangements are described and compared. Image intensifiers and read-out techniques available are discussed. Results have been obtained for certain organic crystals demonstrating the capabilities of a system that has reduced the time required for certain exposures by a factor of several hundred.

Spatial distribution of light in luminescent fungal mycelia

SummaryThe spatial distribution of light in luminescent mycelia of Armillaria mellea and Panus stipticus grown on agar plates was examined by image intensification microscopy. Although, at any instant of time, not all parts of the mycelia emitted light, all kinds of hyphae—primary, secondary, tertiary, aerial, submersed, or superficial—were observed to emit light sometime during the lifetime of the colony. In the individual hypha, light emission was confined to a segment removed from the growing point. The growing point was dark so long as it remained a growing point.