Based on a functional description of the standard Ge(Li) spectrometer some of its shortcomings at high counting rates are
discussed and, as a possible solution to the problem, an outline is given of an experimental high rate gamma spectroscopy
with real time compensation of counting losses.
A Gamma Spectroscopy Logging System (GSLS) has been developed to study sub-surface radionuclide contamination. The absolute
counting efficiencies of the GSLS detectors were determined using cylindrical reference sources. More complex borehole geometries
were modeled using commercially available shielding software and correction factors were developed based on relative gamma-ray
fluence rates. Examination of varying porosity and moisture content showed that as porisity increases, and as the formation
saturation ratio decreases, relative gamma-ray fluence rates increase linearly for all energies. Correction factors for iron
and water cylindrical shields were found to agree well with correction factors determined during previous studies allowing
for the development of correction factors for type-304 stainless steel and low-carbon steel casings. Regression analyses of
correction factor data produced equations for determining correction factors applicable to spectral gamma-ray well logs acquired
under non-standard borehole conditions.
Authors:F. Bronson, V. Atrashkevich, G. Geurkov, and B. Young
To properly interpret the quality of a gamma-spectroscopy measurement, an uncertainty estimate must be made. The uncertainty
in the efficiency calibration is the dominant component to the total propagated measurement uncertainty for many types of
measurements. Any deviations between the as-calibrated geometry and the as-measured geometry contribute to the total uncertainty.
A mathematical technique has been developed to evaluate the variations between calibration and measurement conditions. A sensitivity
analysis mode identifies those variables with the largest contribution to the uncertainty. The uncertainty mode uses probabilistic
techniques for the combined variables to compute average efficiency and uncertainty, and then to propagate those values with
the gamma-spectroscopic analysis into the final result for that sample.
Gamma spectroscopy with a high resolution Ge(Li) detector is used to determine243Am by its 74.7-keV gamma transition in solutions containing much higher specific activities of other actinides and fission
products. As little as 100 ppm of243Am relative to244Cm can be determined. A relative standard deviation of 1.4% was obtained for routine samples. The method is well suited for
analytical control of curium process steps because of its simplicity, speed, and reliability.
The American National Standard "Calibration and Use of Germanium Spectrometers for the Measurement of Gamma-Ray Emission Rates of Radionuclides" has been reissued as N42.14-1999. The performance tests in it can be used to make sure that a gamma-spectroscopy program is set up correctly. The same tests can also be used to verify the improvements made by program developers. However, sometimes the tests in this ANSI standard are not enough. To satisfy certain quality assurance requirements, it is necessary to demonstrate that the results are correct either by hand calculations or by comparing the results to known values.
Normally, gamma-ray spectroscopy is performed by equipment positioned in the SLOWPOKE-2 Facility at the Royal Military College; however, there have occasionally been requirements for analyses externally. A transportable gamma spectroscopy system was thus assembled by acquiring a commercially available multichannel analyzer, analysis program and detector, and by designing and constructing a transportable shielding castle. It was then used to take measurements of fission product concentrations at several research reactors.
Utilizing a portable spectroscopy system, a quantitative method for analysis of samples containing a mixture of fission and
activation products in nonstandard geometries was developed. This method was not developed to replace other methods such as
Monte Carlo or Discrete Ordinates but rather to offer an alternative rapid solution. The method can be used with various sample
and shielding configurations where analysis on a laboratory based gamma-spectroscopy system is impractical. The portalle gamma-spectroscopy
method involves calibration of the detector and modeling of the sample and shielding to identify and quantify the radionuclides
present in the sample. The method utilizes the intrinsic efficiency of the detector and the unattenuated gamma fluence rate
at the detector surface per unit activity from the sample to calculate the nuclide activity and Minimum Detectable Activity
(MDA). For a complex geometry, a computer code written for shielding applications (MICROSHIELD) is utilized to determine the
unattenuated gamma fluence rate per unit activity at the detector surface. Lastly, the method is only applicable to nuclides
which emit gamma-rays and cannot be used for pure beta or alpha emitters. In addition, if sample self absorption and shielding
is significant, the attenuation will result in high MDA's for nuclides which solely emit low energy gamma-rays. The following
presents the analysis technique and presents verification results using actual experimental data, rather than comparisons
to other approximations such as Monte Carlo techniques, to demonstrate the accuracy of the method given a known geometry and
Authors:G. Troyer, E. Nordquist, D. Legare, K. Hillesand, S. Kessler, J. Nelson, R. Richard, S. Goodwin, and E. Killian
The cleanup of high-level defense nuclear waste at the Hanford Site presents many challenges. These include removing and disposing
of components from buried active waste tanks to allow new equipment insertion or hazards mitigation. This paper discusses
a unique automated system that provides for retrieval, high-pressure washing, inventory measurement, and containment for disposal.
Key to the inventory measurement is a three-detector high-purity germanium high-performance gamma-spectroscopy system capable
of recovering data at up to 90-percent saturation (200,000 counts/s). Data recovery is based on a unique embedded electronic
pulser and special software to report the inventory. Each detector has different shielding specified through simulation using
the Monte Carlo computer code for N-particle transport modeling. This shielding provides performance over a dynamic range
of eight orders of magnitude. This paper covers system description, calibration issues, and operation.
Compton suppression gamma-spectroscopy provides an efficient method for measuring the concentration of226Ra,228Ra, and210Pb in ocean sediments. The background reduction realized from the suppressed mode of operation provides an “active shield”
to allow for the low-level counting required for these measurements. We have used the method to study the possible accumulation
of radium from produced waters in sediments from Gulf of Mexico sites of varied distances from drill platforms. In addition,210Pb levels were determined to evaluate the use of our spectrometer for this purpose. Baseline undisturbed concentrations have
been obtained from the study of subsurface core material which predates drilling activities. Correlations of radium isotope
concentrations with iron and barium provide information concerning the possible relationships between radium levels and drilling
activity (excess barium) and natural variations in sediment texture (iron).
Authors:Laith Najam, Firas AL-Jomaily, and Enas AL-Farha
The activity concentration of radionuclides, such as 238U, 226Ra and 40K of limestone rocks in northern Iraq was measured using gamma spectroscopy. The radionuclide activities were obtained and
discussed. CR-39 nuclear track detector was used to measure the radon exhalation rates as well as the effective radium contents
of these samples and are found to correspond with uranium concentration values measured by NaI(Tl) detector in the corresponding
limestone rocks samples. The absorbed gamma dose rates in air due to the presence of 238U, 226Ra, 40K and cosmic ray contribution varied between 105.3 and 223.11 nGy/h. The annual effective dose of each sample has been calculated.
The correlation between activities of 226Ra, 222Rn exhalation rates and 238U is explained. Results show a symmetrical distribution of activity concentrations of primordial of radionuclides in selected
samples. The values of all studied radionuclides are considered to be a typical level of natural background and compared with
results of similar investigations carried out else where.