Search Results

You are looking at 1 - 8 of 8 items for

  • Author or Editor: C. Aalseth x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

This work addresses the energy spectrum correction due to increased charge carrier collection times in larger HPGe spectrometers. The energy of the radiation interaction is expected to be proportional to the total collected charge. This is increasingly not true with larger HPGe spectrometers. Some charge is lost as the total charge travels from the interaction location to the collection electrode. This path dependent loss of charge results in decreased energy resolution. In HPGe spectrometers, this process is characterized by the charge carrier lifetime constant and is given as an exponential function of the charge carrier collection time divided by this constant. Thus large detectors can experience exponential decrease in energy resolution as charge carrier collection time increases. We studied the effect of charge carrier lifetime on energy resolution for a p-type point contact HPGe spectrometers using pulse shape analysis. We present a method using the rise time to correct for the charge carrier lifetime on a pulse by pulse basis for a given HPGe spectrometer.

Restricted access

Abstract  

A fast digital oscilloscope based pulse shape discrimination (PSD) system has been tested with intrinsic germanium detectors large enough to allow ionizing events which generate localized electron-hole pairs at a single site to be segregated from those depositing energy at several different sites in the crystal. Drift velocities of the electrons and holes result in pulses several hundred nanoseconds long. Since the electric field varies by almost a factor of 10 between the outer and inner surfaces, collection of electrons and holes can frequently be dinstinguished, and pulses due to multi-site events can be distinguished from single site events.

Restricted access

Summary  

We have developed an analysis pipeline for air filter gamma-ray spectra, utilizing the software packages UniSampo for peak analysis and Shaman for nuclide identification. In an automated usage mode, spectra that are received via e-mail are processed into a directory tree, analyzed with UniSampo and Shaman, and finally categorized on the basis of the analysis results. Alarms are generated if anything out of the ordinary is observed. Typical applications for an air filter analysis pipeline are national radioactivity surveillance networks and the global radionuclide monitoring network being implemented for verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Our analysis pipeline system has been used by the Finnish national CTBT-authority, the Finnish National Data Center (FiNDC), since July 1999. Evaluation with a randomly selected set of 1518 air filter spectra showed that our pipeline system produces significantly better analysis results than that utilized by the CTBT Organization (CTBTO): our system found 4.2 more peaks per spectrum than the CTBTO system (9 & increase) and identified 5.6 more peaks per spectrum (14 & increase) on the average.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: P. Bachelor, J. Friese, C. Aalseth, J. McIntyre, H. Miley, R. Perkins, and G. Warren

Abstract  

In anticipation of a nuclear detonation, techniques to quickly assess the radiation exposure of evacuees should be developed. Based on experience relating neutron radiation exposures to activation products, measurement of activation products can be performed in a few minutes. Personal items exposed to significant levels of radiation allows neutron dose assessment via the activation products. This approach allows prompt collection of important data on human exposure following a nuclear attack. Data collected will facilitate triage decisions for emergency medical treatment to ameliorate the radiation effects on exposed individuals. Activation experiments with everyday items exposed to a neutron source are presented.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Douglas, J. Friese, G. Warren, P. Bachelor, O. Farmer, A. Choiniere, S. Schulte, and C. Aalseth

Abstract  

A project has been undertaken at Pacific Northwest National Laboratory (PNNL) to tailor a series of efficient chemical separations to allow the rapid quantification of gamma-ray emitting isotopes in mixed fission product (MFP) samples. In support of that goal, modeling of singles and coincident gamma-ray spectra that would result from various chemical separation strategies has been performed. These simulated spectra have identified likely instances of spectral interference and have provided an estimate of the time window available for the detection of radionuclides following various chemical separation schemes. A description of results to date is presented here, demonstrating the utility of this approach for improved processing and analysis of fission product samples.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: E. Hoppe, E. Mintzer, C. Aalseth, D. Edwards, O. Farmer, J. Fast, D. Gerlach, M. Liezers, and H. Miley

Abstract  

Copper is one of few elements that have no long-lived radioisotopes and which can be electrodeposited to ultra-high levels of purity. Experiments probing neutrino properties and searching for direct evidence of dark matter require ultra-clean copper, containing the smallest possible quantities of radioactive contaminants. Important to the production of such copper is establishing the location and dispersion of contamination within the bulk material. Co-deposition of contaminants during copper electrodeposition and its relationship to nucleation and growth processes were investigated using scanning electron microscopy (SEM), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and secondary ionization mass spectrometry (SIMS).

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: E. Hoppe, A. Seifert, C. Aalseth, A. Day, O. Farmer, T. Hossbach, J. McIntyre, H. Miley, J. Smart, and G. Warren

Abstract  

Spectrometers for the lowest-level radiometric measurements require materials of extreme radiopurity. Measurements of rare nuclear decays, e.g., neutrinoless double-beta decay, can require construction and shielding materials with bulk radiopurity reaching one micro-Becquerel per kilogram or less. When such extreme material purity is achieved, surface contamination, particularly solid daughters in the natural radon decay chains, can become the limiting background. High-purity copper is an important material for ultra-low-background spectrometers and thus is the focus of this work. A method for removing surface contamination at very low levels without attacking the bulk material is described. An assay method using a low-background proportional counter made of the material under examination is employed, and the preliminary result of achievable surface contamination levels is presented.

Restricted access

Abstract  

The search for neutrinoless double beta decay in 76Ge has driven the need for ultra-low background Ge detectors shielded by electroformed copper of ultra-high radiopurity (<0.1 μBq/kg). Although electrodeposition processes are almost sophisticated enough to produce copper of this purity, to date there are no methods sensitive enough to assay it. Inductively coupled plasma mass spectrometry (ICP/MS) can detect thorium and uranium at femtogram levels, however, this assay is hindered by high copper concentrations in the sample. Electrodeposition of copper samples removes copper from the solution while selectively concentrating thorium and uranium contaminants to be assayed by ICP/MS. Spiking 232Th and 238U into the plating bath simulates low purity copper and allows for the calculation of the electrochemical rejection rate of thorium and uranium in the electroplating system. This rejection value will help to model plating bath chemistry.

Restricted access