James R. Milch

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.

Slow‐scan silicon‐intensified target‐TV x‐ray detector for quantitative recording of weak x‐ray images

The construction and performance of a two‐dimensional x‐ray detector is described. X‐rays are detected as scintillations in a thin phosphor screen which is fiber‐optically coupled to a cooled SIT vidicon TV camera tube. The x‐ray image is analog integrated on the vidicon target during an exposure period; afterwards, the x‐ray signal is gated off and the target is read via a slow‐scan, low‐noise readout in a 256×256‐pixel raster. Test data are presented on the performance of a detector based on an 80‐mm SIT tube. The device is shown to be a quantitative, quantum‐limited detector suitable for recording x‐ray diffraction patterns over a wide range of x‐ray intensities. The detector is shown to be especially suited for high count‐rate applications. Current applications of the detector are described.

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.

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.

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).

Force measurement using an inductively coupled sensor

A low-compliance, high-bandwidth force sensor is described. The bending of a quartz plate is converted to an analog voltage by using a phase-locked loop to measure the change in frequency of two oscillators inductively coupled to the plate. The resolution of the sensor is approximately 10(-5) N, with a bandwidth of approximately 1 kHz.

Image Intensification of X-Ray Diffraction Patterns from Protein Molecules

An image intensifier film system has been used to obtain X-ray diffraction patterns suitable for quantitative measurements of protein structure. Relevant image tube characteristics have been measured, as have the corresponding TV vidicon parameters for extension of the systems to on-line digital recording and analysis.

The dynamical stability of isometrically contracting muscle and its relation to transient force response

Abstract The length-tension relation for tetanically contracting muscle indicates that for lengths longer than the resting length, the muscle should be dynamically unstable; i.e. some sarcomeres should lengthen and others shorten. This behavior is not observed experimentally. The theoretical behavior of muscle in this respect is determined both by the length-tension curve, and by the response of muscle to rapid changes in its mechanical state. In this paper it is shown that the force generated after a small step change in length is related to the dynamical stability of muscle. By means of a simple model, the behavior of isometrically contracting muscle is predicted based on in vitro mechanical studies and classical control theory. It is found that inhomogeneities in sarcomere length can develop only after many seconds, and that this relative stability is due entirely to the presence of the muscle transients.