Particle Count Rate Research Articles

Measurement of LET distribution and dose equivalent on board the space shuttle STS-65

Space radiation dosimetry measurements have been made on board the Space Shuttle STS-65 in the Second International Microgravity Laboratory (IML-2). In these measurements, three kinds of detectors were used; one is a newly developed active detector telescope called “Real-time Radiation Monitoring Device (RRMD)” utilizing silicon semi-conductor detectors and others are conventional detectors of thermoluminescence dosimeters (TLDs) and CR-39 plastic track detectors. Using the RRMD detector, the first attempt of real-time monitoring of space radiation has been achieved successfully for a continuous period of 251.3 h, giving the temporal variations of LET distribution, particle count rates, and rates of absorbed dose and dose equivalent. The RRMD results indicate that a clear enhancement of the number of trapped particles is seen at the South Atlantic Anomaly (SAA) without clear enhancement of dose equivalent, while some daily periodic enhancements of dose equivalent due to high LET particles are seen at the lower geomagnetic cutoff regions for galactic cosmic ray particles (GCRs). Therefore, the main contribution to dose equivalent is seen to be due to GCRs in this low altitude mission (300 km). Also, the dose equivalent rates obtained by TLDs and CR-39 ranged from 146.9 to 165.2 μSv/day and the average quality factors from 1.45 to 1.57 depending on the locations and directions of detectors inside the Space-lab at this highly protected orbit for space radiation with a small inclination (28.5°) and a low altitude (300 km). The LET distributions obtained by two different detectors, RRMD and CR-39, are in good agreement in the region of 15–200 keV/mm and difference of these distributions in the regions of LET < 15 keV/mm and LET > 200 keV/mm can be explained by considering characteristics of CR-39 etched track formation especially for the low LET tracks.

Search for Gamma-Ray Bursts at Photon Energies E &gt;= 10 GeV and E &gt;= 80 TeV

The EAS-TOP extensive air shower array has been operating since 1992 in the search for gamma-ray bursts at primary energies E_1_ &gt;= 10 GeV and E_2_ &gt;= 80 TeV. The study is performed by searching for short transients in the cosmic-ray intensity in the single particle (E_1_) and extensive air shower (E_2_) counting rates at mountain altitude (2005 m above sea level). We discuss the method and the results obtained both in sky survey and in correlation with BATSE events. In both energy ranges, the observed fluctuations in the event rate obtained in the sky survey during 800 days of live time are compatible with the statistical fluctuations of the cosmic-ray background. A single candidate of time duration δt~2 s and energy fluence F(10 &lt;E &lt; 100 GeV) = 1.7 x 10^-4^/(cos{theta)^10.5^ ergs cm^-2^ (where D is the unknown zenith angle) has been observed on 1992 July 15 at 13:22:26 UT in the energy range E_1_ &gt;= 10 GeV with significance 10.6 and 20.1 σ in two measurement channels. In the analysis made in correlation with ~50 events detected by BATSE, no burst candidate was found in time coincidence or in the 2 hr interval around the BATSE detection time. The following ranges of upper limits F_max_ to the energy fluence in the time interval {DELTA}t_90_ in which BATSE detected 90% of the counts are obtained: F_max_ = 2.3 x 10^-5^ -7.4 x 10^-3^ ergs cm^-2^ (10 &lt; E &lt; 100 GeV) F_max_ = 1.6 x 10^-6^ -3.3 x 10^-5^ ergs cm^-2^ (100 &lt; E &lt; 1000 TeV).

Influence of climate on the radioactivity of lake and sea sediments: first results

SUMMARY Low-level nuclear counting has been carried out on sediment cores from Lake Bouchet in France and from the Black Sea. The cores span the past 20Ka. The variation of CY and p particle counting rates with core depth, i.e. with time, shows features which can reasonably be associated with climatic change. The discussion is augmented by some high resolution y ray spectrometry measurements of the specific activity of particular component radionuclides ('14Pb, 'Pb and 40K) in the Black Sea cores.

Simultaneous observations of quasistatic electric fields and large dust particles during the Vega-2 flyby of comet Halley

The quasistatic electric field records made in Halley's coma by the APV-V experiment represented a superposition of the overall negative variation with a number of positive spikes. A correlation has been found between the overall variation and the count rates of dust particles in the mass range 10 −11–10 −8 g. For interpretation purposes the impact-induced plasma cloud radius has been specifically defined. Owing to the asymmetry of the double-probe antenna with respect to the impact direction, the particles producing plasma clouds with radii greater than several metres induced impulsive negative potentials of different magnitudes on the two probes, thereby generating an apparent electric field. In the inner coma, the electron emission generated by impacts of cometary gas molecules maintained the sensitivity of the antenna to dust impacts, but implied that the lower mass limit of particles responsible for the apparent electric field varied proportionally with the secondary electron current. The linear dependence of the quasistatic signal on the particle flux breaks down for high fluxes ; hence, the positive spikes are interpreted as manifestations of smallscale, dense clouds of dust. The present study has shown that a long double-probe antenna can be used as a large dust particle detector, whose target area is comparable to the spacecraft projected area.

A CMOS analog-digital integrated circuit for charged particle spectrum measurements

The authors present a CMOS analog-digital integrated circuit implemented using metal oxide semiconductor implementation system (MOSIS) fabrication to be used for nuclear radiation measurements. They have implemented a charge sensitive preamplifier, operational amplifiers, RC filters, a peak detector, low-voltage comparators, a low-voltage analog switch, logic and control circuits, flip-flops, and counter cells. On the system level they have built an analog-digital block, suitable for charged particle spectrum measurements, using an external solid-state detector. The particle energy spectrum is measured in 10 channels and stored in equinumber 11-b registers, which can then be selectively addressed, read out, and reset. The overall noise performance with no detector connected is equivalent to 10-keV proton energy. The whole system can resolve particle counting rates as high as 1.5*10/sup 5/ counts/s, and as high as 10/sup 6/ in the pulse height analyzer (PHA) mode. >

Submicron Particles Observed during Etching Process

Submicron particle counts were taken by monitoring hole etching in the RIE (reactive ion etching) process for approximately 30 days. One particle sensor was installed in the exhaust pipe from a process chamber and the second one in the exhaust pipe from loadlock chambers. More than 1000 wafers were processed using five different etching processes. Differences in the particle count per minute were observed among the etching processes. Reactive gas pressure, 13.56 MHz rf power and gas composition significantly influenced the generation of particles. The particle count rate increased as the etching time for one wafer increased. A large number of holes were observed on the etched photoresist surface with a scanning electron microscope (SEM) after prolonged etching time.

Impacts of dust particles m > 10 −9 g in Halley's coma as seen in the electric field waveforms of Vega 2

In this paper we draw some inferences on the response of the APV-N antenna of Vega 2 to plasma clouds induced by dust particles. We show that: (1) electric impulses were mostly generated by impacts of particles bigger than ∼10 −9 g on the whole spacecraft, (2) in the case of large particle impacts the impulse amplitude was weakly dependent on the particle mass, (3) the antenna response to the impact plasma depends on the ambient plasma parameters, and (4) the sensitivity to impacts decreases when the impact rate becomes quasicontinuous. The conclusions are based on an analysis of the wide impulses in the outbound pass of Vega 2 through the outer coma and on a comparison of the electric field spectral densities with the count rates of dust particles in various mass channels. The lower limit, down to which the amplitude vs mass dependence is weak, has been defined as the “least effective mass”; its value has been deduced to be ∼3 × 10 −9 g in the outer coma, and ∼10 −7 g in the inner coma, while near the point of closest approach to the comet it was determined to be more than ∼10 −6 g due to the continuous impact of small particles. The spectral density of impact-generated impulses should be roughly proportional to the integral flux of particles bigger than the least effective mass. Some new peculiarities of the large particle distribution in the coma are derived. The interpretation of the impulse generation involves the response of the antenna to a negative pulse of the spacecraft potential and to electric fields associated with the electron density gradients in the expanding plasma cloud. The correlation between the count rates of the light ( m < 10 −14 g) particles and of the impulses (found in a previous investigation) is reinterpreted in terms of the hypothesis that the light particles were originated by disintegration of the big ones.

The characterisation of 10B and 6LiF reference deposits by the measurement of neutron induced charged particle reactions

Abstract This paper describes part of a project whose overall aim was the fabrication of a set of 10 B and 6 LiF deposits of known areal density for use in a measurement of the free neutron lifetime. (n, α) rates were measured in a neutron beam in a reproducible geometry and were related to the masses of several of the deposits (determined by isotope dilution mass spectrometry) so that the masses of the remaining deposits, and hence their areal densities, could be established. Details are given here of the detection arrangement and of the corrections which have to be made to the charged particle counting rates in order that the masses and counting rates be properly correlated.

The ONR-602 Experiment and Investigation of Particle Precipitation Near the Equator.

The global precipitation of radiation belt particles at low altitude was investigated, using the ONR-602 experiment on board U.S. Air Force mission S81-1. A combination of a main telescope, beginning analysis at a few MeV/nucleon, and a monitor system, giving results below 1 MeV/nucleon, was designed for measuring particle phenomena characterized by almost any energy spectrum. The monitor provides an indication of the presence of the particles at low energy, while the main telescope gives detailed flux and composition data for the higher energy events. Results of the instrument performance analysis indicate that, at the equator, the monitor telescope has the peak efficiency for particles of about 90 deg pitch angles. The large opening angle of 75 deg makes it possible to detect omnidirectional flux of quasi-trapped particles. The high-energy cosmic-ray background count is found to be very insignificant. It is demonstrated that the particle counting rates for the low-energy threshold have been almost entirely due to protons.

The use of alpha counting for determining the heat production due to the uranium and thorium decay chains

The count rate of alpha particles emitted form the surface of a sample can be readily used to determine the heat production rate due to U and Th in the sample. the conversion factor lies in the range 22–25 mJ/kg per year for an alpha particle count rate of 1.00 count/(ks cm 2), depending on the relative contributions of U and Th, and the extent of Rn escape. Use of a value of23 ± 1mJ/kg per year is recommended for most samples. Glassing the sample first overcomes errors due to inhomogeneity and Rn escape; in this case the conversion factor is about 10% higher. The apparatus is simple to use and is inexpensive.

Three-dimensional lithium microanalysis by the 7Li(p, α) reaction

In order to investigate the corrosive behaviour of lithium in stainless steel, an analysis method is required, which gives concentrations of lithium as well as the heavier constituents of the attacked steel with a positional resolution in the micrometer range. In the Karlsruhe ion microprobe the combination of the 7Li(p, α) reaction with PIXE (for heavier elements) and with RBS (for carbon and oxygen) covers all interesting elements. With 3 MeV proton impact energy, which is just above the broad reaction cross-section maximum, the alpha particle count rate is optimized. The horizontal and vertical sweeping of the proton microbeam ( ⋍ 2.5 μm diameter) across the specimen together with the energy loss of the alpha particles on their way through the specimen to the detector reveals a three-dimensional lithium concentration distribution in the micrometer range. In the investigated samples of stainless steel the positional correlation of lithium with oxygen and chromium indicates the formation of lithium chromate complexes at the expense of the chromium content in the neighbouring zone.

Acceleration of charged particles in Mercury's magnetosphere

High‐intensity bursts of electrons with energies up to ∼600 keV were discovered during two nightside encounters of the Mariner 10 spacecraft with the planet Mercury. During the first encounter, Mariner 10 passed through the magnetotail plasma sheet region on March 29, 1974, and during the third encounter, on March 16, 1975, the spacecraft passed through the near‐polar region. Initial reports on these results (Simpson et al., 1974), which were based on 6‐ and 1.2‐s averages of the counting rates, strongly indicated that impulsive electron acceleration, probably by magnetic field reconnection, occurred in the magnetotail of Mercury and that this phenomenon was similar to Earth's substorm effect. The present paper is a detailed analysis of the encounter measurements based on the highest time resolution available for the particle counting rates, namely 0.6‐s intervals, and the correlation of the counting rates with the 0.04‐s measurements of the magnetic field. This analysis shows that the time‐intensity characteristics of the charged particle bursts, whether occurring in sequences of bursts or as single bursts, are similar for both encounters; namely, (1) individual burst onsets are ∼0.5 s per decade of rising intensity, (2) exponential decay time constants are ∼1.5 s per decade, (3) the repetition period for the sequences of bursts is ∼5 to 6 s, and (4) the maximum observed intensity of successive bursts in a sequence decreases exponentially. These observations are not artifacts of the encounter measurements but are characteristics of the particles which arrive at the point of detection promptly from the acceleration source region. Magnetosonic waves have been found near the magnetotail plasma sheet which were associated with the onsets of the two most intense burst sequences. Assuming that these waves are similar to the injection fronts of substorms described at Earth and that they indicate the presence of a neutral sheet current, an estimate of the maximum cross‐tail potential yields &lt;2×104 V. Thus this mechanism could not account for the acceleration of the high‐energy electrons. Furthermore, acceleration mechanisms based on stochastic processes also appear to be excluded. On the other hand, the direct evidence at Mercury for the acceleration of electrons to 0.5 MeV within 1‐2 s argues for acceleration in an inductive electric field within the plasma sheet of Mercury's magnetotail produced during explosive reconnection of the magnetic field. It is pointed out that instabilities leading to explosive reconnection, such as via the tearing mode instability, could provide the required free energy for particle acceleration. The problem of how this mechanism could explain the observed quasi‐periodic electron burst sequences at Mercury is discussed. From measurements of the total electron energy in a sequence of bursts it is found that for 1% efficiency in the acceleration mechanism the required total magnetic free energy is of the order of 1012 joules, depending upon the assumed electron energy spectrum and the mode of particle propagation. From comparisons with the impulsive acceleration of charged particles to the order of MeV energies in the earth's magnetotail during magnetic substorms reported in recent years it is concluded that the rates of acceleration at Mercury are a factor of 200 to 300 times more rapid. The study reported here provides strong evidence for acceleration during explosive magnetic field reconnection within Mercury's magnetotail and places stringent, new constraints on the development of theories to explain the physics of the high‐energy charged particle acceleration in the magnetotails of planets.

Energetic neutral particles from Jupiter and Saturn

The Voyager 1 spacecraft has detected energetic neutral particles escaping from the magnetospheres of Jupiter and Saturn. These energetic neutrals are created in charge exchange reactions between radiation belt ions and ambient atoms or molecules in the magnetosphere. If the Io torus is assumed to be the dominant Jovian source region for energetic neutrals, the Voyager observations can be used to infer upper limits to the average ion intensities there below about 200 keV. No readily interpretable in‐situ measurements are available in the Io torus at these energies. The middle and outer Jovian magnetospheres may also be a significant source of energetic neutrals. At Saturn, the observed neutral particle count rates are too high to be explained by charge exchange between fast protons and H atoms of the Titan torus. Most of the energetic neutrals may be produced by charge exchanges between heavy ions and a neutral cloud containing H2O in Saturn's inner magnetosphere. If so, the Voyager measurements of energetic neutral fluxes would be the first detected emissions from this region of Saturn's magnetosphere.

Cosmic ray variations and turbulent flow systems: 0.3–1.0 AU; 1977–1980

Relations among the relative counting rates of cosmic ray protons and the magnetic fields and flows observed by Helios 1 between 0.3 AU and 1 AU in the period January 1977 to August 1980 are discussed. Isolated corotating or transient flows are associated with short‐term depressions in cosmic ray intensity, but the effects are localized in longitude. Systems of corotating streams do not produce a long‐term modulation effect, although temporary, short‐term depressions in cosmic ray intensity are associated with individual streams and interaction regions. Spectra of fluctuations of the magnetic field and magnetic helicity for systems of corotating flows often do not have the form f−5/3 at frequencies ≥10−5 Hz, and accordingly, the hydromagnetic fluctuations in corotating streams near the sun do not appear to represent fully developed turbulence at low frequencies. Systems of transient streams containing shocks that might encircle the sun are associated with long‐lasting decreases in cosmic ray intensity. The magnetic field fluctuations in such flow systems are often turbulent, with f−5/3 spectra extending from below 10−5 Hz to the Nyquist frequency of the data. The turbulence is likely to be confined to sheets with thicknesses of the order of 0.1 AU, possibly associated with shocks. We conclude that long‐term modulation of cosmic rays inside 1 AU is associated with turbulence in transient disturbances that probably encompass a large longitudinal extent around the sun. In mixed flow systems the effects are intermediate between those of corotating and transient systems. The net modulation may be relatively small, with large short‐term variations associated with individual streams.

Grain size distribution in ceramics and the beta dose-rate for thermoluminescence dating

The dependence of the alpha particle counting rate from samples of powdered sherds on the size of grains selected for counting is interpreted with the aid of photographs of polished sections of the sherds showing the sizes of the inclusions. The measurements are discussed in terms of the errors possible in thermoluminescence dating when determining the internal beta dose-rate due to the thorium and uranium series from alpha particle counting rates.

Continuous flow, single-particle-counting condensation nucleus counter

A new condensation nucleus counter (CNC) has been developed. It is capable of counting single particles, giving it an unlimited lower concentration range. The CNC uses butanol as its working fluid. The continuously flowing sample of aerosol is first nearly saturated in a 35°C butanol chamber, then cooled to 10° C, causing supersaturation with condensation of butanol onto the particles. A single-particle-counting light-scattering system detects the resulting larger droplets. In the single counting mode (below 1000 cm −3), the CNC measures aerosol concentration from the particle count rate of a constant aerosol flow rate, a primary method. This compares within 8% with the primary electrical method. In the photometric mode (above 1000 cm −3), the CNC was calibrated by the electrical method and exhibits good stability. In the 0.02–0.1 μm dia. range, nearly all particles are detected. Below 0.02 μm, detection efficiency depends on diameter.

Particle size and velocity measurement in flames by laser anemometer

The size and velocity of droplets are measured simultaneously by a particle counting Laser Doppler Anemometer (LDA) in kerosene fuel sprays under both burning and non-burning conditions. This measurement technique enables rapid measurement of size and velocity of particles in spray flames for particle diameters larger than the fringe spacing up to, at least, 300 μm. The time dependent variations in local spray structure can be measured at particle counting rates of 2 kHz with spray densities of, at least, 10 10 particles/m 3 . Particle sizes are derived from pulse height analysis of the mean LDA signals and velocities are determined simultaneously, by measuring Doppler shift frequencies. The performance and accuracy of the system is determined by analysis, using geometrical optics theory, coupled with calibrations using a monosized particle generator. The measurements demonstrate that droplet velocity is a function of droplet diameter for both burning and non-burning conditions. The technique enables temporally averaged local size distributions to be measured. Spatially averaged size distributions are derived from the simultaneously acquired velocity data. Comparison of results obtained under burning and non-burning conditions show changes in size distribution due to preferential vaporization of small droplets, acceleration due to thermal expansion of gases and corresponding changes in droplet momentum.

A Diagnostic Method for Time Resolved Spatial Profile Measurements of Proton and Impurity Density and Temperature

A new diagnostic technique, based on elastic scattering of neutral atoms off the plasma ions, is proposed and analyzed. Space and time resolved measurements of the number densities and temperatures of the various components of the plasma are possible by energy analysis of the scattered neutral atoms. The ability to resolve ions of different masses is limited by ion thermal motion and the energy and angular dependence of the scattering cross sections. In hydrogenic plasmas with impurities, the scattering by the impurities is easily resolvable from the scattering of protons, even when the individual impurity contributions cannot be separately resolved. Detected particle count rates are calculated for a conceputal system for a tokamak plasma (n ~ 1013 cm-3, Ti ~ 300 eV). Time resolution of ~ 10 ms with spatial resolution of a few cm are predicted.

Angular distributions of electrons of energyEe&gt; 0.06 MeV in the Jovian magnetosphere

Results of an angular distribution analysis of electron intensity data recorded by the University of Iowa experiment aboard Pioneer 10 are presented for the Jupiter encounter period November 26 through December 14, 1973. The data were from three directional particle detectors with effective integral energy thresholds of Ee = 0.06, 0.55, and 5.0 MeV, respectively. It is found that the central core of the magnetosphere for radial distances less than 12 RJ (Jovian radii) is dominated by pitch angle distributions strongly peaked at α = 90°, while the region of radial distances 12–25 RJ shows bidirectional and approximately equal maxima at α = 0° and 180°. Bidirectional angular distributions in the magnetosphere out to the radius of the magnetopause strongly suggest quasi-trapping on closed field lines as the predominant situation. Substantial field-aligned unidirectional streaming was detected on only two occasions, each of about 1-hour duration; one of these episodes immediately preceded the return of particle count rates to near-interplanetary values for 3 hours on December 1. No distinctive effects on angular distributions were discerned near the L shells of satellites. Some interpretative suggestions are made.

The magnetosphere of Jupiter as observed with Pioneer 10: 2. Nonrigid rotation of the magnetodisc

The maximum count rates of energetic particles are observed earlier on the inbound pass and later on the outbound pass than one would expect if the Jovian magnetodisk moved rigidly with the planet. This lead and lag cannot be explained by the observed azimuthal distortion of the Jovian magnetic field alone. A possible explanation is that the foot of a magnetic field line in the ionosphere slips with respect to Jupiter's surface. The rate of slippage and the electric field necessary for this is estimated. The electric field may be as large as 2 V/m in the Jovian polar ionosphere.