A direct method for determining the altitude variation of the uranium stripping ratio in airborne gamma‐ray surveys

Geophysics ◽  
1989 ◽  
Vol 54 (10) ◽  
pp. 1350-1353 ◽  
Author(s):  
S. S. Raghuwanshi ◽  
B. K. Bhaumik ◽  
S. G. Tewari
Keyword(s):  
Potassium Channels ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Direct Method ◽  
Ground Level ◽  
Above Ground Level ◽  
Ground Clearance ◽  
Detector Distance ◽  
A Direct Method ◽  
The U.S

In airborne gamma‐ray spectrometric surveys, it is essential to calculate the net counts in the thorium, uranium, and potassium channels for quantitative analysis. The net uranium, thorium, and potassium counts are given by [Formula: see text], (1a) [Formula: see text] (1b) and [Formula: see text], (1c) where [Formula: see text], [Formula: see text], and [Formula: see text] are the background corrected counts per second for uranium, thorium, and potassium channels, respectively; α and β are the Compton contributions of thorium gamma rays in the uranium and potassium windows, respectively; and γ is the contribution of uranium gamma rays in the potassium window. In some countries, such as the U.S., Canada, and India, it is common practice to compute the stripping ratios by taking measurements over a set of calibration pads with known and varying amounts of uranium, thorium, and potassium (Grasty and Darnley, 1971; Grasty, 1975; Lovborg, 1984). These factors are determined by keeping the detector system inside the survey aircraft over the calibration pads. The stripping coefficients do not have fixed values but vary with source‐detector distance. Because most airborne surveys are conducted at about 120 m above ground level, the stripping ratios measured over the pads should be corrected for variations with ground clearance. In practice, the ground clearance in airborne gamma‐ray surveys may vary from about 40 m to 200 m depending upon the topography of the area flown. It is, therefore, necessary to know the values of the stripping coefficients as a function of ground clearance at least within the range of investigations. If this is known, it is possible to apply proper corrections while converting all data to a uniform datum of 122 m.

STUDIES IN THE ACTIVE DEPOSIT OF ACTINIUM: PART II: THE DECAY OF 211Pb (AcB)

1965 ◽  
Vol 43 (3) ◽  
pp. 383-403 ◽  
Author(s):  
C. R. Cothern ◽  
R. D. Connor
Keyword(s):  
Gamma Rays ◽  
Level Scheme ◽  
Gamma Ray ◽  
Ground Level ◽  
Conversion Line ◽  
Point Energy ◽  
Correlation Studies ◽  
Absolute Intensities ◽  
Gamma Coincidence ◽  
Conversion Coefficients

Studies of the active deposit of actinium using a Siegbahn–Slatis beta-ray spectrometer and scintillation counters together with gamma–gamma coincidence work and gamma–gamma angular correlation measurements have led to the establishment of a new decay scheme for 211Pb and a level scheme for 211Bi involving five excited states.The gamma rays have the following energies and absolute intensities:[Formula: see text]Conversion-line studies yielded energy values for the transitions marked with an asterisk as 403.3 ± 0.5 and 426.5 ± 0.5 keV respectively. The K conversion coefficients of the 400- and 430-keV transitions have been determined as 0.091 ± 0.018 and 0.117 ± 0.024 respectively.Fermi analysis yields 1.378 MeV as the highest end-point energy of the beta partial spectra. The remaining end points and the component intensities as deduced from the level scheme are as follows:[Formula: see text]The much less accurate results from Fermi analysis of the complete active deposit are in reasonable agreement with these data.Angular correlation studies of the 430–400- and 706–400-keV gamma-ray cascades have yielded spins for the levels concerned: ground level (9/2), 400-keV level (7/2), 830-keV level (9/2), and 1 100-keV level (7/2). These spins are the only ones consistent with the experimental evidence and the theoretical arguments presented.

Candidate Networks, Citizen Clusters, and Political Expression

2015 ◽  
Vol 659 (1) ◽  
pp. 149-165 ◽  
Author(s):  
Leticia Bode ◽  
Alexander Hanna ◽  
Junghwan Yang ◽  
Dhavan V. Shah
Keyword(s):  
Direct Method ◽  
Tea Party ◽  
The Political ◽  
Election Cycle ◽  
Political Actors ◽  
Political Left ◽  
Twitter Users ◽  
Political Right ◽  
A Direct Method ◽  
The U.S

Twitter provides a direct method for political actors to connect with citizens, and for those citizens to organize into online clusters through their use of hashtags (i.e., a word or phrase marked with # to identify an idea or topic and facilitate a search for it). We examine the political alignments and networking of Twitter users, analyzing 9 million tweets produced by more than 23,000 randomly selected followers of candidates for the U.S. House and Senate and governorships in 2010. We find that Twitter users in that election cycle did not align in a simple Right-Left division; rather, five unique clusters emerged within Twitter networks, three of them representing different conservative groupings. Going beyond discourses of fragmentation and polarization, certain clusters engaged in strategic expression such as “retweeting” (i.e., sharing someone else’s tweet with one’s followers) and “hashjacking” (i.e., co-opting the hashtags preferred by political adversaries). We find the Twitter alignments in the political Right were more nuanced than those on the political Left and discuss implications of this behavior in relation to the rise of the Tea Party during the 2010 elections.

Lifetimes and branching ratios of energy levels of 28Si. I

1969 ◽  
Vol 47 (6) ◽  
pp. 639-649 ◽  
Author(s):  
A. E. Litherland ◽  
P. J. M. Smulders ◽  
T. K. Alexander
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Energy Levels ◽  
Ground Level ◽  
Particle Beam ◽  
High Energy ◽  
Branching Ratios ◽  
Alpha Particles ◽  
Doppler Shift Attenuation ◽  
Energy Gamma

The gamma rays from the 25Mg(α,nγ)28Si reaction have been studied using alpha particles with energies ranging from 4.8 to 6.0 MeV. A 25 cm3 Ge(Li) gamma-ray counter was used to observe the complex high energy gamma-ray spectra at angles between 0° and 130° to the alpha-particle beam. Estimates of the nuclear lifetimes of the energy levels excited were obtained from Doppler shift attenuation measurements. The de-excitation branching ratios of the levels were also measured. The existence of a new level in 28Si at 6695 keV was confirmed. The recently reported 3− level at either 6880 keV or 6889 keV was observed and found to be the 6880-keV member of the doublet. The enhancement of the octupole transition to the ground level of 28Si was found to be 13 Weisskopf units.

scholarly journals Ground-Based Observations of Terrestrial Gamma Ray Flashes Associated with Downward-Directed Lightning Leaders

2019 ◽  
Vol 197 ◽  
pp. 03002
Author(s):  
Rasha Abbasi ◽  
John Belz ◽  
Ryan Le Von ◽  
Dan Rodeheffer ◽  
Paul Krehbiel ◽  
...  
Keyword(s):  
Electric Field ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Three Dimensional ◽  
Temporal Distribution ◽  
Cosmic Ray ◽  
Ground Level ◽  
High Energy ◽  
Lightning Strikes ◽  
Lightning Discharges

Terrestrial gamma-ray flashes (TGFs) are bursts of gamma-rays initiated in the Earth’s atmosphere. TGFs were serendipitously first observed over twenty years ago by the BATSE gamma ray satellite experiment. Since then, several satellite experiments have shown that TGFs are produced in the upward negative breakdown stage at the start of intracloud lightning discharges. In this proceeding, we present ground-based observation of TGFs produced by downward negative breakdown occurring at the beginning of negative cloud-to-ground flashes. The Terrestrial gamma-ray flashes discussed in this work were detected between 2014-2017 at ground level by the Telescope Array surface detector (TASD) together with Lightning Mapping Array (LMA) and the slow electric field antenna (SA). The TASD detector is a 700 km2 ultra high energy cosmic ray detector in the southwestern desert of Utah. It is comprised of 507 (3 m2) plastic scintillator detectors on a 1.2 km square grid. The LMA detector, a three-dimensional total lightning location system, is comprised of nine stations located within and around the array. The slow electric field antenna records the electric field change in lightning discharges. The observed Gamma ray showers were detected in the first 1-2 ms of downward negative breakdown prior to cloud-to-ground lightning strikes. The shower sources were observed by the LMA detector at altitudes of a few kilometers above ground level. The detected energetic burst showers have a footprint on the ground typically ~ 3-5 km in diameter. The bursts comprise of several (2-5) individual pulses, each of which have a span of a few to tens of microseconds and an overall duration of several hundred microseconds. Using a forward-beamed cone of half-angle of 16 degrees, GEANT simulation studies indicate that the showers are consistent with gamma rays of 1012 - 1014 primary photons. We hypothesize that the observed terrestrial gamma-ray flashes are similar to those detected by satellites, but that the ground-based observations are closer to the source and therefore are able to observe weaker sources and report on the structure of the temporal distribution at the source. This result and future studies will enable us to better identify and constrain the mechanisms of downward TGF production.

scholarly journals Wildlife at Airports

2017 ◽  
Author(s):  
Travis L. DeVault ◽  
Bradley F. Blackwell ◽  
Jerrold L. Belant ◽  
Michael J. Begier
Keyword(s):  
Ground Level ◽  
Civil Aviation ◽  
Aviation Industry ◽  
Above Ground Level ◽  
Tools And Techniques ◽  
Developed World ◽  
The U.S

Collisions between aircraft and wildlife (wildlife strikes) are common occurrences across the developed world. Wildlife strikes are not only numerous, but also costly. Estimates suggest that wildlife strikes cost the civil aviation industry in the U.S. up to $625 million annually, and nearly 500 people have been killed in wildlife strikes worldwide. Most wildlife strikes occur in the airport environment: 72 percent of all strikes occur when the aircraft is ≤500 ft (152 m) above ground level, and 41 percent of strikes occur when the aircraft is on the ground during landing or takeoff. Thus, management efforts to reduce wildlife hazards are focused at the airport. There are many techniques used to reduce wildlife hazards at airports, and these usually work best when used in an integrative fashion. Here, we discuss the available data on wildlife strikes with aircraft, summarize legal considerations, explain why wildlife are attracted to airports and how to identify important wildlife attractants, describe commonly-used tools and techniques for reducing wildlife hazards at airports, and explain how airports can enlist the help of professional wildlife biologists to manage wildlife hazards.

scholarly journals Solar Hard X-Ray and Gamma-Ray Observations from GRANAT

1994 ◽  
Vol 142 ◽  
pp. 611-621
Author(s):  
N. Vilmer
Keyword(s):  
Gamma Rays ◽  
Solar Flares ◽  
Gamma Ray ◽  
Ground Level ◽  
High Energy ◽  
Angle Distribution ◽  
X Rays ◽  
X Ray ◽  
Electrons And Ions ◽  
Solar Bursts

AbstractHard X-rays and gamma-rays are the most direct signature of the energetic electrons and ions which are accelerated during solar flares. Since the beginning of 1990 the PHEBUS instrument and the SIGMA anticoincidence shield aboard GRANAT have provided hard X-ray and gamma-ray observations of solar bursts in the energy range 0.075-124 and 0.200-15 MeV, respectively. After a brief description of the experiments, we present some results obtained on solar bursts recorded in 1990 and 1991 June. Special emphasis is given to the results related with particle acceleration during solar flares.The first part of the review is devoted to the constraints obtained on the electron acceleration timescale through the analysis of the temporal characteristics of the bursts. Combined studies of hard X-ray and gamma-ray emissions from PHEBUS and radio emissions from the Nançay Multifrequency Radioheliograph are used to infer constraints on the coronal magnetic topology involved in flares. The characteristics (location, spectrum) of the radio-emitting sources are found to vary within a flare from one hard X-ray peak to the other. Hard X-ray and gamma-ray burst onsets and rapid increases of the > 10 MeV emission are coincident with changes in the associated radio emission pattern. These results will be discussed in the context of the flare energy release.The second part of the paper concerns the heliocentric angle distribution of > 10 MeV events and presents more detailed observations of some of the largest flares in the gamma-ray line and the high-energy domains produced by ultrarelativistic electrons and > 100 MeV nucleon−1 ions. The PHEBUS observations of the gamma-ray line flare of 11 June 1991 have been used to deduce the hardness of the accelerated ion spectrum. The link between the main part of the flare and the late long-lasting >50 MeV emission detected by EGRET/COMPTON is discussed. Finally some observations of the large 1990 May 24 flare which produced a large neutron event at ground level are presented.Subject headings: acceleration of particles — Sun: flares — Sun: radio radiation — Sun: X-rays, gamma rays

Sign in / Sign up

Export Citation Format

Share Document