Inability of the BrilLanCe® detector to measure U directly in-situ

B. L. Dickson

    Research output: Chapter in Book/Report/Conference proceedingConference proceeding contribution

    Abstract

    An AMIRA-funded project, begun in 2007, examined the potential for the new, high-resolution LaBr 3(Ce) (BrilLanCe®) 2 detector to directly measure uranium in situ. The detector has the potential to measure the 1.001 MeV gamma-ray emitted by 234mPa, an immediate daughter of 238U. Such a measurement would overcome problems associated with radiometric disequilibrium in conventional gamma-ray logging. Laboratory tests confirmed that this gamma-ray could be resolved and measured in small samples. Unfortunately, in trials of a downhole probe at the AMDEL test pits in Adelaide, the 1.001 MeV peak was not resolved. Modelling of the detection of U-decay gamma-rays using the GEANT4 gamma-ray transport code confirmed that the BrilLanCe detector could not resolve this gamma-ray. This is mostly due to the increased Compton-scattered radiation from higher energy gamma-rays from uranium decay obscuring the small 234mPa peak. However, very recent (<10 000 year old) deposits with extreme U-rich disequilibrium could be logged using this detector. The modelling shows that resolution of the order of 2.5 keV per channel, as obtained with cooled high-purity germanium detectors, would enable the 234mPa gamma-ray to be used measure U. Such measurements were demonstrated in the early 1980s and there may be scope to revisit that technology again. The properties of BrilLanCe® detector do have advantages for more accurate logging of U and Th where disequilibrium is not a problem, for example, logging in high count-rate environments and logging where only small detectors can be used. Unfortunately, the decay of naturally-occurring 138La emits a gamma-ray at 1.436MeV, which interferes with determination of K using the 1.46 MeV gamma-ray, so its use for lithological logging by measuring K-U-Th is limited.

    Original languageEnglish
    Title of host publicationAusIMM International Uranium Conference 2008 abstracts volume
    Place of PublicationCarlton, VIC
    PublisherAustralasian Institute of Mining and Metallurgy
    Pages7-7
    Number of pages1
    ISBN (Print)9781920806835
    Publication statusPublished - 2008
    EventAusIMM International Uranium Conference 2008 - Taking Best Practice and Education to a New Level - Adelaide, SA, Australia
    Duration: 18 Jun 200819 Jun 2008

    Other

    OtherAusIMM International Uranium Conference 2008 - Taking Best Practice and Education to a New Level
    CountryAustralia
    CityAdelaide, SA
    Period18/06/0819/06/08

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