Ray Pulses Research Articles

Fast Diamond Photoconductors

ABSTRACTPreliminary results on the response of type Ib and IIa diamond photodetectors to fast laser pulse exposures at 265 and 530 nm are presented. The influence of the applied bias, the laser wavelengths and the light intensity on the detector sensitivity is studied. Also, recent measurements with 1.25 MeV gamma ray pulses are reported.

Ray-pulse matrices: a rational treatment for dispersive optical systems

A new formalism to describe beam propagation in paraxial optical systems with dispersive elements, including both spatial and temporal variations in the propagating signal, is presented. This formalism makes use of 4*4 ray-pulse matrices which take account of dispersive effects up to quadratic phases in both spatial coordinates (as in the usual paraxial ABCD matrix approach) and in the temporal domain. How to use these matrices to write a space-time integral analogous to a generalized Huygens integral is shown, and propagation laws for Gaussian ray pulses which are space- and time-varying analogs of the conventional results for Gaussian beams are derived. The formalism should be useful for analyzing dispersive optical systems such as prism beam expanders, femtosecond pulse compression systems, and dispersive mode-locked laser cavities.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Picosecond GaAs X- and gamma-ray photodetectors

GaAs, due to its high charge carrier mobility and its relatively large band gap, is a promising candidate for the detection of ultrafast gamma ray, X-ray and laser pulses, both for timing and for intensity measurements. Starting from high resistivity (> 107 ω cm) undoped GaAs, photodetectors of various shapes have been developed. Instabilities in bulk GaAs of high resistivity under electric field, previously described as low velocity domain propagation, and tailing in the pulse response are avoided by fast neutron irradiation. Time resolution (FWHM) in the 10 ps range and linearity of more than five decades have already been achieved.

７．５ｃｍφ球形ＮａＩ（Ｔｌ）シンチレーション検出器による地上レベルにおける５ＭｅＶ以下の宇宙線波高分布スペクトル

Ground level cosmic ray pulse height spectrum of a 7.5cm diameter spherical NaI (T1) scintillation detector was evaluated through stripping operation based on a pulse height spectrum measured on the sea and high precision response functions of the detector for U-series, Th-series and 40K. The exposure rate calculated from the determined cosmic ray pulse height spectrum was 0.21μR/h eq., which agreed well with that obtained from another method. The shape of the pulse height spectrum showed similarity to that measured at the altitude of 16, 000 ft, especially in the energy region of 0 to 3MeV. The principle of the adopted method is rather plain, however, the reliability of the spectrum is satisfactory. As the pulse height spectrum is a common information to any analytical method for environmental gamma ray using NaI (T1) scintillation detector, it is expected to be used for simple and precise separation of cosmic ray component involved in the enviromental pulse height spectrum.

Inner bremsstrahlung accompanying beta decay of 147Pm.

The inner bremsstrahlung spectrum associated with the nonunique first-forbidden \ensuremath{\beta} decay of $^{147}\mathrm{Pm}$ was measured employing the magnetic deflection method with a 4.5\ifmmode\times\else\texttimes\fi{}5.1 ${\mathrm{cm}}^{2}$ NaI(Tl) scintillation spectrometer in the energy region 30--200 keV. The contribution due to the 121 keV source gamma ray line was subtracted by normalizing its peak with that of the 122 keV $^{57}\mathrm{Co}$ gamma ray pulse height distribution recorded in the same experimental setup. The raw spectrum was unfolded following Liden and Starfelt and compared with theoretical spectral distributions. The measured spectral distribution does not match any of the theories in any part of the investigated energy region.

Time-Derived Sigma for Pulsed Neutron Capture Logging

Summary This paper reviews field applications of the Dresser Atlas Neutron Lifetime Log™ (NLL) service and examines recent technical advances in the instrumentation and data-analysis system. The major improvement discussed is a new method for computing S, the thermal neutron capture cross section of an earth formation. In the new method, the time after the neutron burst is measured for each gamma ray pulse detected by the instrumentation system within a gate of fixed width. This "average pulse time" is uniquely related to the thermal neutron decay rate observed in a borehole environment. The technique discussed is applicable for any condition where the neutron or gamma ray flux is time-dependent. The advantages of this signal-processing method, however, are most apparent for cases of rapid flux change with time, as in an exponential decay. A simple two-gate method of measurement suffers, statistically, from the lower count rate of the second gate. An average-pulse-time measurement over the same range covered by both gates of a two-gate system is less affected by statistical deviations than the ratio normally formed between the two gates. Some important advantages result from this type of signal processing when applied to the NLL service. First, the statistical accuracy of the log is improved; second, the instrumentation required for implementation of the method is not complicated. Also, the average-pulse-time measurement can be made with either digital or analog equipment, and since it involves only simple arithmetic computations, the method is much simpler to implement than either least-squares or correlation methods. Introduction The NLL service1 was introduced in the early 1960's; it was the first measurement through casing that could distinguish and quantitatively evaluate oil and gas in saline formation water environments. More recently, the Dual Detector Neutron Lifetime Log (DNLL) service2 has been used (1) to explore for hydrocarbon resources behind pipe, (2) to monitor the production behavior of wells, (3) to plan workovers properly, (4) to determine residual oil saturation for enhanced-recovery projects, etc. Although the carbon/oxygen3 (C/O) log provides a reliable cased-hole formation evaluation in fresh and brackish formation water environments, the DNLL service is applicable when logging through casing and/or tubing in saline environments. As discussed in detail in the literature, the basic measurement is the thermal neutron absorption (capture) cross section, S, of a subsurface formation. Advanced methods of processing the data recorded by such a pulsed neutron capture logging system are presently under development. These improvements include (1) the average-time technique4 and (2) the sigma-dependent positioning of a single gate exhibiting a fixed gate width of 600 µseconds. The basic theoretical considerations of these improvements are discussed, and supporting field data are presented.

Gamma ray intensity standards for calibrating Ge(Li) detectors for the energy range 200–1700 keV

Gamma ray pulse height spectra for seven radioactive sources have been analyzed for the full energy peak areas. Using these areas in conjunction with the results of an extensive compilation of relative gamma ray intensities, a relatively simple efficiency function has been used to calibrate a coaxial Ge(Li) detector. The resulting relative intensities for each source have been used in investigating the consistency of the weighted averages of the compiled relative intensities. Possible systematic errors are discussed and recommendations are made with respect to the choice of gamma ray intensity standards.

Tunnelling rays in graded-index fibres

An analysis of the role of tunnelling rays in pulse propagation in graded-index fibres is presented. Tunnelling ray attenuation is handled by using the generalized parameter technique which allows attenuation coefficients to be dispensed with and relevant families of tunnelling rays to be identified. Results are given for impulse response pulse widths and shapes. Incorporation of tunnelling ray pulse contributions into the formalism for determining optimum refractive-index profiles is presented. For most cases, tunnelling ray effects are small, but significant corrections may be necessary when measurements are made on short lengths of fibre.

Computed Tomography Using a Cs137 Source

The purpose of this work was to explore the use of a monenergetic gamma ray source and pulse counting techniques for use In a CT device. The ideal source for CT scanning is one with a 100-keV gamma ray, long lifetime and low-cost availabiltly in high specific activity. However, since the attenuation coefficient of tissue-like materials varies slowly with energy a Cs-137 source was used without significant disadvantage. Phantoms consisting of brass, aluminum and low-Z, organic polymers were scanned with 2.0 mm ray spacing and up to 60 angular orientations. The results from 0.1% statistical accuracy data obtained with the prototype scanner have demonstrated that a 2.5% density gradient can be detected. One of the advantages of a Cs-137 source is that the calculated attenuation coefficients are directly proportional to physical densities of the materials scanned.

A Stabilized Scintillation Crystal System for Monitoring Gamma Ray Exposure in the Environment

A 2 inch NaI(Tl) scintillator has been incorporated into a remote real time monitor for gamma ray background. The scintillator contains a small 241Am source which provides a high energy reference pulse for maintaining system gain. Gain is maintained automatically by a variable gain linear amplifier at the central station. The detector is connected to the central station by a single coaxial line which passes both the high voltage and the signal. Gamma ray pulses are processed in a modified Wilkinson analog to digital converter to provide an output count rate proportional to exposure rate (microR/hour). The system has been shown to be stable against temperature change, to be independent of gamma ray energy in the range 0.1 to 2.0 MeV, and to be useful in the range 1.0 to 10,000 microR/hour.

Nuclear goblins and cosmic gamma ray bursts

Among the cosmic and the macroscopic bodies composed of nuclear matter, the neutron stars and the nuclear goblins represent typical configurations. Nuclear goblins are stable only under large external pressure, in the interior of certain types of stars for instance. When propelled to the surface of their parent stars, and there exploding, they produce flares. When ejected from their parent stars and exploding in interstellar space they will give rise to short bursts of Gamma rays, with energies centered around 0.78 MeV and with characteristics which are in accord with the observations on the Gamma ray pulses detected in recent years by the four Vela spacecraft.

Pulse shape analyzer for fast neutron-gamma ray discrimination

A wide-band differential amplifier has been built to extract pulse shape information from photomultiplier dynode pulses. A zero-crossing is measured at ≈90% of peak pulse amplitude from pulses produced by neutrons and gamma-rays in a liquid scintillator. Subsequent logic circuits uniquely select and sort the gamma ray pulses and neutron pulses into separate channels for identification at rates of up to 50 kHz.

Low energy gamma radiation in the atmosphere during active and quiet periods on the Sun

Gamma ray pulse height spectra during active and quiet solar periods from midlatitude balloon flights

Gamma Rays in Coincidence withKX Rays from the La, Ce, and Pr Fission Fragments ofCf252

An experiment has been carried out to study the $\ensuremath{\gamma}$ rays from the fission fragments of ${\mathrm{Cf}}^{252}$. The $Z$ values of the fragments studied were determined by detecting their $K{\ensuremath{\alpha}}_{1}$ x rays with a Si(Li) x-ray speectrometer. A single-channel analyzer was used to accept only pulses corresponding to the $K{\ensuremath{\alpha}}_{1}$ x rays of the element under study. The $\ensuremath{\gamma}$ rays were detected with a Ge(Li) detector, and a time coincidence system was used to accept only the $\ensuremath{\gamma}$-ray pulses that occurred within 0.175 \ensuremath{\mu}sec of the preselected x ray. Energy transitions in three fission elements, $\mathrm{La}(Z=57)$, $\mathrm{Ce}(Z=58)$, and $\mathrm{Pr}(Z=59)$, were observed in an energy range 125-300 keV. Eleven $\ensuremath{\gamma}$ transitions were seen in La, fourteen in Ce, and four in Pr, although some of the weaker $\ensuremath{\gamma}$ rays attributed to La and Pr may belong to $\mathrm{Ba}(Z=56)$ and $\mathrm{Nd}(Z=60)$, respectively.

New Pulse Height to Clock Pulse Converter and its Application to Neutron Dosimetry

The pulse height to clock pulse converter is an electronic digital integrator and its application for gamma ray dosimetry (gamma ray pulse dosimeter) has been reported recently. In the present study, a new integration method was adopted for the pulse height to clock pulse converter in addition to its transistorization. The results of its application for neutron dosimetry are also described.

Sur la discrimination de forme, dans un spectrometre a coincidences, des impulsions livrees par un detecteur Au germanium

A simple and accurate pulse shape discrimination method is described for coincidence spectrometers using Ge(Li) detectors. Gamma ray pulses degraded by electron interaction in Ge(Li) detector's dead layers are rejected within 40% by delaying the Ge(Li) crossover signals. Spectra given by a Ge(Li)NaI(Tl) three-crystal pair spectrometer with and without rejection are shown. Results are compared with elaborated and much more expensive methods.

Internal Energy Standardization of Multichannel Gamma Ray Spectra by Use of the 0.511 MeV Annihilation and 40K Peaks

A computer method is described for making after-the-fact adjustments for incorrect zero energy intercept and instrumental gain to experimental gamma ray pulse height spectra from NaI (Tl) scintillation spectrometers. The method makes use of the 0.511 MeV annihilation peak and 1.46 MeV 40K photopeak as internal energy reference standards, both of which peaks are available to NaI (Tl) scintillation detectors. The technique has been tested experimentally and appears to be of practical use for routine energy standardization of long counting time gamma ray spectra between 0.1 and 2.0 MeV.

Cavitation in liquids demonstrated by ultrashort-exposure radiography.

Using a field-emission x-ray tube, giving a much shorter pulse of rays than does conventional apparatus, we have demonstrated around a water jet the presence of a toroidal cavity that could not be detected visually. One advantage of this method of demonstrating cavitation is that it may be used with fluids and vessels that are opaque to light.

Cosmic Ray Induced Dark Current in Photomultipliers

Čerenkov light flashes produced by cosmic rays traversing the window of an end-on photomultiplier create a fundamental noise limitation that cannot be reduced by cooling the tube. Although the cosmic ray pulse rate is only 1 or 2 cm−2/min, the individual pulses may be hundreds of times larger than single electron pulses. Thus in dc or charge integration photometry, cosmic ray noise can exceed thermionic dark current noise at temperatures as high as +10°C. These assertions are based on the observed behavior of EMI 6256 and 9558 tubes. The implications for photometry of faint astronomical sources are discussed.

Total Absorption Gamma Ray Spectrometer System for Pulsed Beam n, n′ γ Measurements

A gamma ray spectrometer that combines the techniques of neutron time-of-flight spectroscopy and gamma ray total absorption spectroscopy is described. Data on gamma ray pulse height resolution and photopeak efficiency are presented. Representative pulse height spectra from neutron inelastic scattering reactions are shown.