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  • Author or Editor: M. Nikkinen x
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Abstract  

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is setting very specific requirements to processing of gamma-ray spectra. All the data collected in 80 radionuclide particulate stations are transmitted to the International Data Centre (IDC), where they are analyzed. National Data Centres (NDC) are the users of IDC services. The NDC's are responsible of giving technical information to National Authorities, who have thepolitical responsibility of the compliance to the treaty. The IDC analysis is not directly informing if a nuclear test has been conducted; it is just categorizing the spectra to help the NDC's to make their decision. An NDC must have a high confidence on the correctness of the radionuclide analyses the IDC, and the NDC itself, are performing. Special attention must be paid to Event Screening, where the NDC, among other things, needs a historical record of the measured data to be able to ignore the occasionally occurring fission products, for example. The amount of data produced is too large for an NDC to process interactively. Therefore, batch-processing capabilities are required from the NDC. The Finnish NDC is involved in evaluating of the IDC processing and software and it is also proposing a radionuclide processing solution for other NDC's, as well.

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Summary  

{\rtf1\ansi\ansicpg1250\deff0\deflang1038\deflangfe1038\deftab708{\fonttbl{\f0\froman\fprq2\fcharset238{\*\fname Times New Roman;}Times New Roman CE;}} \viewkind4\uc1\pard\lang2057\f0\fs24 In many laboratories the number of measured routine gamma-spectra can be significant and the labour work to review all the data is time consuming and expensive task. In many cases the routine sample does not normally contain radiation above a detectable level, and still the review of the spectra has to be performed. By introducing simple rules for emerging conditions, the review work can be significantly reduced. In one case the need to review the environmental measurement spectra was reduced to less than 1% compared to the original need, which in turn made the review personnel available for more useful functions. Using the \scaps UniSampo\scaps0 analysis system, the analysis results of spectra that are causing alarming conditions can be transmitted via e-mail to any address. Some systems are even equipped with the capability to forward these results to hand-portable telephones or pagers. This is a very practical solution for automated environmental monitoring, when the sample spectra are collected automatically and transmitted to central computer for further analysis. The paper describes how to set up an automatic analysis system, rules for the emerging conditions, technical solutions for an automated alarming system and a generic hypothesis test for the alarming system developed for \scaps UniSampo\scaps0 analysis software. \par }

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Summary  

A novel method to measure beta-gamma coincidences using a phoswich detector with state-of-the-art pulse shape discrimination techniques has been investigated. A thin CaF2(Eu) and thick NaI(Tl) crystal phoswich detector has been built and tested using gamma and beta test sources as well as xenon gas. The two types of radiation are distinctly seen in the signal processing electronics based on pulse shape analysis. Preliminary results indicate that it will be difficult to achieve sufficient discrimination of the pulse types in application to beta-gamma coincident counting.

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Abstract  

UNISAMPO is a new member of the SAMPO family of gamma-spectrum analysis programs running on Linux. Its portable graphical user interface relies on Tcl/Tk running an X-client, which obtains services from an X Window System server, allowing natural access to UNISAMPO over the Internet. UNISAMPO features a scripting ability for analyses of thousands of spectra. Peak search is based on stringent statistical criteria and peak fitting has optional step function under each peak of a multiplet. UNISAMPO will analyze 32K spectra with up to 2500 peaks, and 32 peaks in a single multiplet extending over a fitting interval of 1024 channels. It has an interface to the expert system SHAMAN for extensive peak interpretation and radionuclide identification.

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Abstract  

SAMPO for Windows is a high performance gamma spectrum analysis program. All the measurement, analysis and NAA phases can be done either under full interactive user control or user defined tasks can be used for automated measurement and analysis sequences including control of MCAs and sample changers. High resolution gamma-ray spectroscopy together with the possibility to resolve complex multiplets with high accuracy makesSAMPO very suitable for INAA. On the other hand, the possibility to automate analysis sequences allows its use effectively also in all routine NAA measurements.NAA inSAMPO is accomplished using comparative methods. Spectra of standards, flux monitors, controls and actual samples are analyzed normally to obtain the peak areas which are optionally corrected for decay. In the comparison the flux monitor results are used to correct for variations in the effective neutron flux. An optional irradiation position correction can also be applied. The controls are used to alarm for possible deviations in the results.The sophisticated spectrum analysis methods used together with the comparative NAA and monitors give accurate results limited by the systematic effects only. The Windows environment provides ease of use and further processing power is available through the interface to expert system identification of nuclides.

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Abstract  

SAMPO 90 is a high performance gamma-spectrum analysis program for personal computers. It uses color graphics to display calibrations, spectra, fitting results as multiplet components, and analysis results. All the analysis phases can be done either under full interactive user control or macros and programmable function keys can be used for completely automated measurement and analysis sequences including the control of MCAs and sample changers. Accurate peak area determination of even the most complex multiplets, of up to 32 components, is accomplished using linear, non-linear and mixed mode fitting. Nuclide identification is done using associated lines techniques allowing interference correction for fully overlapping peaks. Peaked Background Subtraction can be performed and Minimum Detectable Activities calculated. The analysis reports and program parameters are fully customizable.

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Abstract  

The Preparatory Commission of Comprehensive Nuclear Test-Ban-Treaty Organization is setting up a global network capable to monitor treaty compliance. Specific monitoring systems and methodologies that match the needs of the International Monitoring System (IMS), namely to clarify the nuclear character of suspect explosions, had to be developed for monitoring purposes during the last decade. Four xenon isotopes, namely 133Xe, 135Xe, 133mXe and 131mXe play a key role here. A complex background from medical isotope production facilities and nuclear power plants, varying over four orders of magnitude, challenges the system’s capability to distinguish these from treaty-relevant events. Available measurement data are compared with model calculations. The importance of atmospheric transport modelling is demonstrated both for completely understanding the civilian background and for explaining peak concentrations and abnormal events. New methodologies for backtracking nuclide detections improved the capability to locate sources and corroborate the role of radioxenon monitoring.

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Abstract  

SHAMAN is an expert system for qualitative and quantitative radionuclide identification in gamma spectrometry. SHAMAN requires as input the calibrations, peak search, and fitting results from reliable spectral analysis software, such as SAMPO. SHAMAN uses a comprehensive reference library with 2600 radionuclides and 80 000 gamma-lines, as well as a rule base consisting of sixty inference rules. Identification results are presented both via an interactive graphical interface and in the form of configurable text reports. An organization has been established for monitoring the recent Comprehensive Test Ban Treaty. For radionuclide monitoring, 80 stations will be set up around the world. Air-filter gammaspectra will be collected from these stations on a daily basis and they will need to be reliably analyzed with minimum turnaround time. SHAMAN is currently being evaluated within the prototype monitoring system as an automated radionuclide identifier, in parallel with existing radionuclide identification software. In air-filter monitoring, very low concentrations of radionuclides are measured from bulky sources in close geometry and with long counting time. In this case true coincidence summing and self-absorption become important factors. SHAMAN is able to take into account these complicated phenomena, and the results it produces have been found to be very reliable and accurate.

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Abstract  

Using gamma-spectrometry systems on mobile units with accurate position information is a convenient means for surveying large areas for radioactive fallout or finding hot spots due to misplaced sources or releases from nuclear installations. Traditionally, large (tens of litres) high efficiency NaI(T1) detectors have been used for the purpose. HPGe detectors, however, offer certain advantages which can often compensate for their lower efficiency. This kind of remote sensing, regardless of detector type, requires specialized software. In order to provide accurate position information, the integration times must be kept as short as possible. This is especially true for fast air-borne measurements where counting periods below one second are desirable. We have constructed a special version of SAMPO software which controls data acquisition and runs real-time gamma-spectrum analysis including peak determination, nuclide identification, activity calculations, and reporting. The measurement/analysis cycle can be reduced down to 0.5 seconds on a standard Pentium-based PC. The analysis results are combined with accurate co-ordinates from a differential GPS system on a color coded map. The system is also able to give alarms based on different criteria. We have already measured and analyzed more than 500 000 spectra in field applications using jets, helicopters, cars, and also on-foot.

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Abstract  

SHAMAN is an expert system for radionuclide identification and spectrum peak interpretation in gamma-ray spectrometry. SHAMAN utilizes a comprehensive reference library with 2616 radionuclides and 81,642 gamma-ray lines, as well as a rule base consisting of sixty inference rules. Identification results are presented both via a graphical user interface and as configurable text reports. SHAMAN has been installed as an automated radionuclide identifier, handling the last phase of the gamma-ray spectrum analysis of air filter samples in the Comprehensive Nuclear-Test-Ban Treaty (CTBT) environment, both at the International and National Data Centre level. SHAMAN is a powerful tool in this environment: it is shown to reach a peak explanation percentage above 99% for routine CTBT air filter spectra. However, SHAMAN's true capabilities are revealed when anything unusual is detected in a spectrum.

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