Counting Rate Meter Research Articles

Analysis of Spinal Interneurons Activated by Tactile and Nociceptive Stimulation

AbstractThe functional organization of spinal interneurons in the 6th and 7th lumbar segments responding exclusively to exteroceptive stimulation was studied in decapitate cats by means of intracellular technique. Seventy‐six neurons were classified according to their responses to three types of skin stimuli, viz. touch/pressure, movement of hairs and nociceptive stimulation, into one main group responding to only one, and a second main group responding to two modalities of skin sensation. Neurons responding to all three types of skin stimulation showed also proprioceptive influence and were not included. For each modality subgroup the excitatory and inhibitory response types, receptive fields, convergence patterns, discharge patterns and histological localization of the cells are described. The dorsal region of the spinal cord showed a predominance of neurons of more simple convergence and modality type, while the medial and ventral regions contained more complex cells with contralateral and suprasegmental connections. The receptive fields were generally larger for interneurons than for afferent fibers. Convergence of various types of tactile and nociceptive inflow both from the same field and from different, often widely separated areas was demonstrated. The discharge patterns, analyzed by means of a counting rate meter, showed characteristic features for various modalities of skin sensation, excitatory as well as inhibitory responses being determined mainly by the peripheral receptor discharges. Typical phenomena of postsynaptic activity, such as spatial summation, afterdischarges and inhibitory rebound, have been exemplified and one type of selective inhibition has also been described. The various types of convergence patterns observed in neurons influenced by tactile stimulation of the paws are schematically represented in a diagram.

Increase of the nucleonic intensity on May 4, 1960

An increase in the cosmic-ray intensity at the earth was observed on May 4, 1960, ∼16 minutes after a class 2 solar flare at ∼1015 UT in region H42 on the west limb, Nl0° heliographic latitude (Preliminary Report of Solar Activity, High Altitude Observatory, Boulder, Colo.). This intensity increase was very rapid and was recorded only at certain stations within well-defined regions on the earth (K. G. McCracken and R. Palmeira, private communica tion; H. Carmichael and J. F. Steljes, preliminary report). We report here the observations on the increase in the nucleonic intensity at Mt. Washington (elevation, 1909 m) and Durham (sea level), and some tentative conclusions regarding the rigidity spectrum of the flare-produced particles. The nucleonic intensity at Mt. Washington for the period of the major increase is plotted in Figure 1. Also given are the times of the flare and the 27.6-Mc/s riometer events at Kiruna, Sweden (J. Ortner, private communication) and the 18-Mc/s events at Rensselaer Polytechnic Institute, Troy, New York (R. E. Falconer, private communication). The cosmic-ray increase started at 1031.5±1.0 UT and reached a maximum increase of 214 per cent between 1040 and 1042, falling off to 18 per cent between 1125 and 1130. In the period 1830 to 1930, the intensity was still ∼2.4 per cent above the preincrease level. At Durham the onset time was 1032 +2 or −1 UT, and the magnitude as determined from a calibrated counting rate meter was 140±10 per cent, reaching a maximum at ∼1040. From the calculations by Frior [1954] we estimate that both these stations were in the 0400 zone.

Use of magnetic tape for recording radioactivity.

Radioactive isotopes are frequently used as tracer material for diagnostic purposes. The principle employed for determining rate of blood flow is based on a dilution or elimination rate of the administered tracer dose. Activity rate is measured with a suitable detector and recording system. Interpretation of disappearance curves is at times rendered difficult because of a weak dose of radioactive material introduced into the system or inadequate settings of the rate meter as to scaling and time factors. To obviate loss of valuable data, a recording system that could register all impulses emitted by the detector probe would be of value. These could then be reproduced at leisure through a scaler or integrating rate meter. Commercial tape recorders have proved adaptable for registering radioactive disintegration impulses. Method A suitable detector probe is activated to the proper voltage level by an appropriate power supply source, either from a scaler or rate-meter unit. The output from the scaler or rate meter is directly attached to the microphone input of the tape recorder. The simultaneous use of tape recording does not interfere with the routine recording system obtained directly from a rate meter or while the counting of radioactivity is in progress. Rate Meter 1. Nuclear-Chicago Rate Meter, Labitron, or Survey Meter. The speaker leads, or phone plugs, are tapped and connected directly to the microphone input of the tape recorder (Fig. 1). 2. Picker Rate Meter. The amplifier output, contact point 8 on the J4 amplifier plug in the socket, is tapped and connected to the microphone input of the tape recorder. Settings of the rate meter, sensitivity, and scaling rate are immaterial for magnetic tape recording purposes (Fig. 2). Tape Speed for Recording Tape speed for recording is dependent on activity rate. A three-speed Norelco Phillips tape recorder offers wider flexibility in recording and for replay. Normally a 3 3/4 inch per second tape recording is adequate. Replay of Tape Recording Tape recordings can be replayed by simply connecting the tape recorder output to the input of the rate meter. For counting purposes, it may be connected to the input of a scaler. 1. Nuclear-Chicago Rate Meter (Model #1620): A small Fisher transistor preamplifier is employed. The tape recorder speaker output is connected to the preamplifier input and the preamplifier output to the scaler or rate-meter input (Fig. 3). 2. Nuclear-Chicago Labitron (Model #1619A): No preamplifier is necessary. The recorder output is directly connected to the input. 3. Picker Counting Rate Meter (Model #2805): Tape recorder output is attached directly to the rate-meter preamplifier input; contact point 2 on the J4 amplifier plug in socket. The count rate can be doubled or halved depending on the tape speed at which the recording is replayed. With a replay speed twice the recording speed, counts are doubled and counting time is halved.

Transistor Circuitry for Radiation Counting

The transistorized circuits described here have been developed to provide more reliable instrumentation for the experimental nuclear physicist. These devices are a pulse amplifier, a pulse‐height analyzer, a scaler, and a linear count rate meter. The basic operating principles are discussed briefly. The electrical characteristics of these instruments compare favorably with their vacuum‐tube counterparts and they have the additional advantages of improved reliability, small size, and low power consumption.

Response of a Counting Rate Meter to an Input Signal A exp(−βt2)

Response of a Counting Rate Meter to an Input Signal <i>A</i> exp(−β<i>t</i>2)

Photoscanning after simple changes in present equipment.

The utility of photoscanning methods has been established by Bender, Kuhl, Rejali, and others (1–5). In a small hospital it is not always possible to obtain readily the new equipment required for new procedures. Consequently, instrument modifications for the production of photoscans may be of interest to those already possessing a Tracerscanner. Several types of equipment which are used for other studies in the isotope department were combined and modified to produce a photoscanning unit. The Scanner: Time constants in the count-rate meter and recorder require that the data be obtained with the scan occurring in one direction only. A Tracerscanner was modified as indicated in Figure 1 to produce a slow scan of 1.5 to 4.0 mm. per second and a rapid return of 50 to 178 mm. per second. These changes affect only the return speed. Forward speed, spacing, reset, motion limits, etc., are not affected. The small film density produced during the rapid return of the carriage has not been sufficient to cause concern but, if necessary, an additional relay could be connected in parallel with the solenoid to shut off the light during the return. The rapid return mechanism, illustrated in Figure 2, consists of a simple spring return which is easily installed as a consequence of the clutch mechanism already contained in the Tracerscanner. In operation, the motor drives the counter support to the back stop bar; instead of reversing the motor, the microswitch operates the solenoid which releases the clutch. The spring tension returns the counter support to the front stop bar, where a small compression spring eases the deceleration of the support system at the front stop bar. Count-Rate Meter: A Nuclear Chicago count rate meter was modified according to the diagram of Figure 3 to remove the load resistor, which produces the 10-mv. signal, without disturbing its operation in a normal manner without a recorder, or with a 0-1-ma recorder. In addition, the selection of a one-second time constant was incorporated into the instrument. Recorder: In place of the usual Esterline Angus or Houston Technical Laboratories chart recorder used in kidney function studies, a Varian 0-10-mv. recorder may be obtained at nearly the same cost. This equipment was selected because its motor-driven pen has sufficient power to turn the potentiometer, which is a vital part of the light control circuit. A 50-ohm potentiometer was mounted in the chart drive unit and connected to the potentiometer of the servo unit with a slotted shaft. It may be possible to obtain an instrument from the manufacturer with the second potentiometer already mounted in tandem with the servo unit potentiometer, thereby eliminating a mounting problem. Scintillation Probe: The shielding of a scintillation probe was changed to a focusing collimator by inserting concentric lead cones as shown in Figure 4.

Logarithmic-diode count-rate and period meter

THE DESIRE to achieve safe automatic start-up of nuclear power reactors — especially where rapid starting of marine or airborne reactors is required — has led to attempts to measure transients in neutron flux at power levels that correspond to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−10</sup> , or less, of full operating power. At these levels, one uses instruments such as counters and count-rate meters, that operate on individual neutron detections. Logarithmic count-rate meters are frequently used for convenience in monitoring wide ranges of neutron flux. Furthermore, the variable most commonly used for control during reactor start-up is the time derivative of the logarithm of the neutron flux, which is by definition proportional to the reciprocal of the period.

Random Interchange of Circuits with Applications to Counting Rate Meters and Function Generators

Two identical linear circuits are excited by generators furnishing equal and opposite voltages. Homologous portions of the two circuits are interchanged at random times with, on the average, r interchanges per unit time. Because of these interchanges, the currents in the remaining portions are irregular. A theorem is derived that permits one to calculate the statistical averages of these currents. It states that one may disregard the interchanging; instead, one merely replaces the complex frequency s by s+2r in the circuit functions [e.g., the impedances Z(s)] of the portions that were being interchanged. On the basis of this theorem one may design counting rate meters with nonlinear (e.g., logarithmic) scale, useful in reactor instrumentation, and function generators for functions of practical importance, such as the logarithmic and exponential functions, and powers with arbitrary exponent. The nature of the function depends only on linear passive circuit elements, such as resistors and capacitors.

The logarithmic-diode counting-rate meter and period meter

This paper analyzes the logarithmic-diode counting-rate meter and the logarithmic-diode period meter, treating the problem of obtaining rapid response to reactor-flux transients while minimizing the spurious fluctuations caused by the random character of neutron detections in a fission counter. A procedure for choosing design parameters is discussed.

Some nucleonic instruments for clinical use

The electrical and mechanical requirements are discussed from the points of view of designer and user. Instruments described in detail are: (1) A 4-channel logarithmic ratemeter employing Geiger counters and used typically for blood circulation investigations; (2) Clinical monitor using a Geiger counter, for tests not requiring high accuracy and where compactness and porta. bility are desirable; (3) Recording count-rate meter employing a scintillation counter, particularly useful for recording transient phenomena lasting only a few seconds; (4) Standard s-y ionization chamber for checking the activities of solutions of radioactive isotopes.

Comparison of liver blood flow values estimated by the bromsulphalein and by the radiogold method.

In a previous paper (1) we have described a method of following the disappearance of intravenously injected colloidal radioactive gold from the circulation in man and have discussed the possibilities of calculating liver blood flow from the disappearance rate constant as the fraction of blood volume perfusing the liver per unit time. If liver blood flow values estimated in this way could be demonstrated to be correct this method should have many advantages over other methods currently in use: it does not require hepatic vein catheterization; with only one blood sample withdrawn for determination of hematocrit and plasma volume, it does not involve any undue blood loss to the patient; being exceedingly simple and mechanized to a considerable extent by the use of counting rate meters and recorders, it can be carried out by a single technician; it can be repeated several times without exposing the patient to any risk thereby enabling observation of changes in hepatic circulation over any period of time. Hepatic blood flow values estimated by this method in 25 normal subjects (18 males and 7 females) were found to average 1310 ml. per min. (1) and thus to be somewhat lower but still within the range of normal values reported by other groups who used the bromsulphalein or other methods. However, even this difference might not have been a real one. In this laboratory the observed venous hematocrit is corrected for trapped plasma and for the uneven distribution of cells and plasma within the whole body circulation. This leads to a blood volume which is about 14 per cent lower than that which is calculated from the uncorrected hematocrit. None of the groups of investigators whose results have been compared

A study of the dynamics of K42 uptake by sunflower plants with the aid of a scintillation count-rate meter

The time sequential mechanism of K42 uptake by sunflower plants from an osmotic pressure series of K42 HCO3 solutions was analyzed with the aid of a localizing scintillation count-rate meter. A range of osmotic pressures from 0.3 to 28.2 atm was selected. Three phases of potassium uptake could be distinguished; an initial, exponential, rapid uptake; a period of saturation; a final phase, of renewed rapid uptake. Solutions with osmotic pressures of < 1.5 atm did not cause appreciable leaf scorching but tended to reduce uptake rates. An osmotic pressure of 7.6 atm resulted in a maximum potassium accumulation in the damaged leaves. All kinetic trends were reversed at 28.2 atm, causing rapid death by dessication. Plasmolytic effects of potassium were discussed in view of uptake stimulation.

Electronic Device for Measuring Reciprocal Time Intervals

A device is described which converts a train of electrical impulses into a succession of hyperbolic wave forms of amplitude proportional to the interval between successive impulses. These wave forms when applied to an oscilloscope furnish a display capable of showing rapid changes in the frequency of an electrical signal. Unlike conventional counting-rate meters response to sudden changes in frequency is immediate so that averaging over several cycles is not required. The instrument as constructed operates in the lower audio-frequency range and is being used in the study of the electrical discharge of single fibers of the optic nerve.

A spectrometric method for the study of radon partition in radium-burdened animals.

The Radium burden of living mammals is usually obtained by measuring both the gamma-ray activity of the Ra(B + C) retained in the body and the time rate at which radon is lost in the breath. Whereas the first can be done consistently with satisfactory accuracy (1), relevance of the latter measurement is predicted on the assumption that, at the time of sampling, the rate of radon exhalation equals the rate of radon release from the radium deposits in the body. Since the radon exhalation rate of a single subject may vary over short periods of time (2), experimental results are beset by annoying uncertainties, which can be minimized at best by repeated sampling in the case of man and can be effectively eliminated only by periodic sacrifice and Ra assay when dealing with laboratory animals. The method to be discussed here consists in comparing with a scintillation spectrometer the relative intensities of the Ra226 and RaB gamma rays emitted by an animal to those of suitably prepared standards, and in evaluating by these means the fraction of radon retained. It should be realized at the outset that whereas RaB emits gamma rays of 240, 295 and 350 kev in numbers comparable to its rate of disintegration, Ra226 emits instead a 50 per cent internally converted gamma ray of 186 kev in only approximately 6 per cent of its disintegrations. Despite this small probability of emission, the gamma ray in question is easily detected by scintillation spectrometers in Ra sources where radon is present in amounts lower than 50 per cent equilibrium, as is true of radium-burdened mammals. Some idea of the possibilities involved can be gathered by inspection of Figures 1 and 2, which show some preliminary results obtained under conditions described in the legends. Apparatus Either NaI(T1) or CsI(T1) cylindrical crystals, 1.5 inches in diameter, sealed in aluminum containers (3), were used as scintillators. They were coupled optically to a 6292 Dumont photomultiplier tube connected in turn to the inputs of two single-channel analyzers. One of these was adjusted to cover a 35-kev-wide band of the spectrum centered over the 186-kev photopeak of Ra26, and the other to record pulses over a 200-kev band astride those emitted by RaB. Correct adjustment of the channels was effected by motorized scanning of the spectrum of a Ra source in air with the instruments feeding a count rate meter and strip chart recorder. The simultaneous reading of the two bands curtailed the necessary recording time and eliminated errors arising from uncontrollable motions of the animal. Before proceeding further, it is well to recall that the interaction of monoergic photons with a scintillator leads to the production of light pulses by photoelectrons and Compton-recoil electrons released in the crystal.

Studies with radioiodine. IV. Collimating cones for crystal counters.

In a clinical radioiodine laboratory it is important frequently to determine the frontal area of a thyroid gland as a guide to its size, and to find out whether or not an area of the body or abnormal mass such as a metastatic thyroid tumor or a brain tumor contains I131 in excess of that in the surrounding tissue. If such a mass does exist, it is then important to record the fact of its existence and to establish its size, shape, position, and radioiodine content. Unshielded and partially shielded collimated Geiger and scintillation counters, either held by hand or by some kind of scanning rack, have been used for these purposes by most workers in the field of radioactivity. Uncollimated scintillation counters have a high sensitivity to gamma rays but have poor “localizing ability” at any appreciable distance. It is possible, by limiting the acceptance angle of the crystal for radiation through the use of a collimating cone, to gain a higher order of “localizing ability,” at the expense of sensitivity. Single-channel collimators with small apertures have the disadvantage of using only a small portion of the crystal and therefore are of low sensitivity. In addition, the sensitivity of the counter falls off as the distance between the radioactive source and crystal is increased. Better “localizing ability,” greater sensitivity of the counter with distance, and the use of as much as one-half of the crystal can all be achieved by the use of multichannel collimators. The theoretical background for the design of multichannel collimators was presented by Newell, Saunders, and Miller. Consideration of the problems involved led to the fabrication and study of various types of collimators. The effective use of collimating devices demands that there be a satisfactory apparatus for moving the counter and collimator over the area in which the radioactivity is to be measured and that there be apparatus to record properly the position of the counter and the radiation which falls on it. This paper presents a description of such an apparatus and the results of studies with different collimators. Apparatus Figure 1, a photograph of the apparatus, shows a counter assembly mounted on a scanning rack, which in turn is mounted on an x-ray tube stand. The counter is connected to two scalers arranged in series. The lower scaler contains a counting rate meter; its responses are measured and recorded on the Speedomax recorder. The switch box on the top of the upper scaler permits the simultaneous starting of the recorder chart and the moving of the counter. The counter assembly (Fig. 2) comprises a crystal scintillation counter, lead shield, collimator, and lead filter (0.5 gm.∕cm.2).

The determination of iodide‐iodate activity in sodium radio‐iodide (I131) by automatic scanning of paper chromatograms

Rf values of different width filter paper chromatograms using 75 per cent methanol in an ascending system are presented for iodide and iodate. The chemical identity of the spots is determined by the use of carrier iodide and iodate. The iodide spot was developed by spraying the dry chromatogram with starch hydrogen peroxide solution. The iodate spot was developed with a spray of ascorbic acid‐starch solution. Description of the equipment is given. The relationship of the chart drive speed and the optimal slit width to the time constant of the counting rate meter is discussed and the minimal slit width calculated for the instrument used. Integration of the curves gave areas representing the total activity at each spot. The ratio of the iodide‐iodate activities thus determined differed from the relative readings of the counting rate meter.

Instrumentation and control of the Brookhaven nuclear reactor

Safe startup and operation of the nuclear reactor require neutron-sensing instruments to cover a range of about 109. This coverage is obtained by a counting rate meter, a period meter, and a high level power indicator. At normal operating levels, the reactor is regulated by the high level power controller and protected by the high level trips. Emergency shutdown of the reactor can be initiated by any one of 54 different conditions. Since these safety circuits are almost 100% “fail safe”, careful design, good maintenance, and cautious operation have been necessary to avoid accidental shutdowns. The period trips and high level trips are provided in triplicate for safety and are coincidence-connected in pairs to guard against accidental shutdown. The use of suppressed-zero circuits has proved helpful. The theory of coincidence-connected trips is briefly discussed.

A scintillation counter for radioactivity prospecting

A transportable scintillation counter instrument, sensitive to gamma rays, has been designed for use in surveying for radioactivity. Use of a single cold cathode valve in the counting-rate meter circuit, which is triggered directly by the counter, and a new form of recording microammeter leads to simplicity and compactness. Recordings are shown of radioactive anomalies detected from the air. The stability and reliability of the instrument have proved satisfactory and have been further tested by use in a geological survey by car for 500 hours over rough road surfaces in tropical climates.

Counting rate meter

Counting rate meter

Mesures directes d'intensité de raies spectrales à, l'aide de photomultiplicateurs

By calculating approximately the amplitude distribution of the pulses forming the background noise of a photomultiplier tube, it appears possible to eliminate most of this by introducing an amplitude-discriminating step into the system and then using a counting rate meter as the indicating instrument. This method has considerable advantages over the normal use of a photo-multiplier cell and the integration time of the counting rate meter can be adjusted to give appropriate sensitivity to the detector even for very faint sources. The linearity of the system has been checked, and its performance is illustrated by the record of the spectrum of a mercury vapour lamp.