Reduction of False Positives in the Identification of Nuclides in Environmental Samples

2003 ◽  
Author(s):  
Susan E. Haywood
Keyword(s):  
Environmental Samples ◽  
Free Parameter ◽  
Gamma Ray ◽  
Large Range ◽  
False Positives ◽  
Energy Calibration ◽  
Average Error ◽  
Peak Activity ◽  
Analysis Method ◽  
Decay Products

Gamma-ray spectra containing peaks that are too close in energy for deconvolution to be done accurately are best analyzed by a library-based method. However, a library-based analysis done with a large library may result an unacceptable number of false positives being reported. A normal working library suitable for analyzing environmental samples containing unknown materials may have over 1000 peaks, many of which are too close for deconvolution to be done accurately. A program has been written that uses a library-based analysis method that reduces the reporting of false positives, while retaining the ability to identify isotopes accurately from a large range of possibilities. In addition, the peak area calculation has been improved by allowing the energy calibration to be a free parameter in the fit of individual multiplets. This peak area improvement can result in a change of activity of several percent for some nuclides. In some cases, shifting the multiplet position can reduce false positives by identifying a peak in the multiplet as an unknown rather than associating it with a nuclide. One spectrum showed a marked peak activity improvement when the calibration was allowed to shift even though the the average error in the original calibration was 0.08%. Results obtained from a study on the identification of uranium decay products are presented.

An analysis method of gamma-ray pulse-height distributions obtained with a Ge(Li) detector

1975 ◽  
Vol 125 (4) ◽  
pp. 507-523 ◽  
Author(s):  
Nobuo Sasamoto ◽  
Kinji Koyama ◽  
Shun-Ichi Tanaka
Keyword(s):  
Gamma Ray ◽  
Pulse Height ◽  
Analysis Method

scholarly journals Nonintrusive Depth Estimation of Buried Radioactive Wastes Using Ground Penetrating Radar and a Gamma Ray Detector

2019 ◽  
Vol 11 (2) ◽  
pp. 141 ◽  
Author(s):  
Ikechukwu Ukaegbu ◽  
Kelum Gamage ◽  
Michael Aspinall
Keyword(s):  
Bulk Density ◽  
Ground Penetrating Radar ◽  
Gamma Ray ◽  
Depth Estimation ◽  
Average Error ◽  
Density Estimates ◽  
Material Density ◽  
Linear Correction ◽  
Ground Penetrating ◽  
Gamma Ray Detector

This study reports on the combination of data from a ground penetrating radar (GPR) and a gamma ray detector for nonintrusive depth estimation of buried radioactive sources. The use of the GPR was to enable the estimation of the material density required for the calculation of the depth of the source from the radiation data. Four different models for bulk density estimation were analysed using three materials, namely: sand, gravel and soil. The results showed that the GPR was able to estimate the bulk density of the three materials with an average error of 4.5%. The density estimates were then used together with gamma ray measurements to successfully estimate the depth of a 658 kBq ceasium-137 radioactive source buried in each of the three materials investigated. However, a linear correction factor needs to be applied to the depth estimates due to the deviation of the estimated depth from the measured depth as the depth increases. This new application of GPR will further extend the possible fields of application of this ubiquitous geophysical tool.

Energy spectrum from single TGFs detected by ASIM

2020 ◽  
Author(s):  
Anders Lindanger ◽  
Martino Marisaldi ◽  
Nikolai Østgaard ◽  
Andrey Mezentsev ◽  
Torstein Neubert ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Spectral Analysis ◽  
Energy Spectrum ◽  
Monte Carlo Simulations ◽  
Energy Range ◽  
Gamma Ray ◽  
High Energy ◽  
Energy Calibration ◽  
Energy Detector ◽  
Instrumental Effects

<p>Terrestrial Gamma-ray Flashes (TGFs) are sub milliseconds bursts of high energy photons associated with lightning flashes in thunderstorms. The Atmosphere-Space Interactions Monitor (ASIM), launched in April 2018, is the first space mission specifically designed to detect TGFs. We will mainly focus on data from the High Energy Detector (HED) which is sensitive to photons with energies from 300 keV to > 30 MeV, and include data from the Low Energy Detector (LED) sensitive in 50 keV to 370 keV energy range. Both HED and LED are part of the Modular X- and Gamma-ray Sensor (MXGS) of ASIM.<br><br>The energy spectrum of TGFs, together with Monte Carlo simulations, can provide information on the production altitude and beaming geometry of TGFs. Constraints have already been set on the production altitude and beaming geometry using other spacecraft and radio measurements. Some of these studies are based on cumulative spectra of a large number of TGFs (e.g. [1]), which smooth out individual variability. The spectral analysis of individual TGFs has been carried out up to now for Fermi TGFs only, showing spectral diversity [2]. Crucial key factors for individual TGF spectral analysis are a large number of counts, an energy range extended to several tens of MeV, a good energy calibration as well as knowledge and control of any instrumental effects affecting the measurements.</p><p>We strive to put stricter constraints on the production altitude and beaming geometry, by comparing Monte Carlo simulations to energy spectra from single ASIM TGFs. We will present the dataset and method, including the correction for instrumental effects, and preliminary results on individual TGFs.</p><p>Thanks to ASIM’s large effective area and low orbital altitude, single TGFs detected by ASIM have much more count statistics than observations from other spacecrafts capable of detecting TGFs. ASIM has detected over 550 TGFs up to date (January 2020), and ~115 have more than 100 counts. This allows for a large sample for individual spectral analysis.</p><p>References:</p><ol><li>Dwyer, J. R., and D. M. Smith (2005), A comparison between Monte Carlo simulations of runaway breakdown and terrestrial gamma-ray flash observations, Geophys. Res. Lett., 32, L22804, doi:10.1029/2005GL023848.</li> <li>Mailyan et al. (2016), The spectroscopy of individual terrestrial gamma-ray flashes: Constraining the source properties, J. Geophys. Res. Space Physics, 121, 11,346–11,363, doi:10.1002/2016JA022702.</li> </ol>

Dual 14C/residue analysis method to assess the microbial accessibility of native phenanthrene in environmental samples

2008 ◽  
Vol 30 (2) ◽  
pp. 159-163 ◽  
Author(s):  
Rosa Posada-Baquero ◽  
José-Luis Niqui-Arroyo ◽  
Marisa Bueno-Montes ◽  
Alfonso Gutiérrez-Dabán ◽  
José-Julio Ortega-Calvo
Keyword(s):  
Environmental Samples ◽  
Residue Analysis ◽  
Analysis Method

scholarly journals Establishing adequate conditions for mercury determination in environmental samples by INAA

2019 ◽  
Vol 7 (2A) ◽  
Author(s):  
Caroline Perez ◽  
Eliane Conceição Dos Santos ◽  
Mitiko Saiki
Keyword(s):  
Environmental Samples ◽  
Gamma Ray ◽  
Irradiation Time ◽  
Certified Reference Materials ◽  
Nuclear Research ◽  
Tree Bark ◽  
Good Precision ◽  
Experimental Conditions ◽  
Synthetic Standard ◽  
Adequate Method

Mercury (Hg) is a toxic element released into the environment mainly by anthropic activities. Consequently, the improvement for Hg determination in environmental samples is of great interest. Instrumental Neutron Activation Analysis (INAA) is considered an adequate method to determine several elements. However, Hg determination by INAA is often hampered by its volatility, which causes losses. The aim of this study was to establish adequate irradiation conditions for Hg determination in environmental samples by INAA. The following parameters were evaluated: irradiation time, container for irradiation and spectral gamma ray interferences. For the study, aliquots of certified reference materials (CRMs) and tree bark samples were irradiated together with Hg synthetic standard at the IEA-R1 nuclear research reactor. Gamma ray activities of 197Hg and 203Hg were measured in a spectrometer coupled to a HGe detector. Obtained results indicated that polyethylene capsules or envelopes can be used as container for sample irradiation and the Hg impurities in these containers were negligible. Irradiation time of one hour was adequate for Hg determination and in long irradiations of 8 h problems of spectral interference of 198Au and 75Se were observed. In addition, Hg loss during the irradiation of 1 h and after irradiation was not observed. Quality control of Hg results, obtained in the CRMs analyses using one hour of irradiation, indicated good precision and accuracy with HORRAT < 2 and |Z score| < 2. The experimental conditions established in this study were applied to tree bark samples. Detection limits in these analyses were between 0.14 and 1.9 µg g-1.

scholarly journals Minimum periodic function test of HPGe Detector Using 152Eu Certified Reference Materials

Wahana Fisika ◽  
2020 ◽  
Vol 5 (2) ◽  
pp. 83-90
Author(s):  
Yogi Priasetyono ◽  
Wahyu Retno Prihatiningsih
Keyword(s):  
Periodic Function ◽  
Environmental Samples ◽  
Hpge Detector ◽  
Certified Reference Materials ◽  
Energy Calibration ◽  
Channel Changes ◽  
Function Test ◽  
Efficiency Control ◽  
Measurement Validation ◽  
The Eu

The purpose of this research is to determine a minimum of periodic function tests for measurement validation for environmental samples. In this paper, the EU 152 is used as a source for measuring energy calibration as well as efficiency. Control quality on energy calibration monitor channel changes in energy 121.78 keV. In addition to calibration, testing Minimum Detectable Activity on this system. Results from measurements are then validated using environmental samples.

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