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| Titel |
Feasibility study for the preparation of plutonium reference materials for nuclear age dating |
| VerfasserIn |
Monika Sturm, Stephan Richter, Yetunde Aregbe, Roger Wellum, Timotheos Altzitzoglou, Andre Verbruggen, Klaus Mayer, Thomas Prohaska |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250052728
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| Zusammenfassung |
| Plutonium is an antropogenic element which is formed by multiple neutron capture reactions
starting with uranium. Beyond this textbook knowledge, the element plutonium only existed
in minute traces in (fairly rich) uranium ores. Nowadays, traces of plutonium are more widely
spread in the environment due to the numerous atmospheric and underwater nuclear weapons
tests in the late 1950’s and early 1960’s as well as due to the few nuclear accidents. The total
amount of plutonium is growing continuously due to the production of plutonium in
nuclear reactors. Although the nuclear fuel cycle is subject to strict regulatory control
schemes (nuclear safeguards), nuclear material (uranium, plutonium) is occasionally
discovered outside this regulatory control system. In these cases nuclear forensic
investigations are applied in addition to traditional forensics in order to provide clues on the
history of the material and to possibly identify the last legal owner of the material.
The isotopic and elemental composition, the physical appearance of the material
(dimensions of larger objects; particle form and size of powders) and its “age” are
determined.
In order to determine the age of nuclear material, the relationship between amounts of the
originating so-called mother isotopes and amounts of daughter isotopes continually being
formed by radioactive decay is used. This principle has been applied for the age
determination of minerals and rocks by geologists for many years; the isotopic composition
of rocks changes with time after their formation, thus the age can be derived from measuring
the ratio of mother to daughter nuclide. Similarly, the "age" of nuclear material is defined as
the time that has passed since the last chemical separation of the daughter nuclides from the
mother nuclides (e.g. in-grown uranium and americium from plutonium). The ratio of
mother to daughter nuclides depends on the half-lives of the radio-nuclides involved
and the time that has passed since the purification of the mother isotopes. For the
determination of the age of a plutonium material different pairs of mother and daughter
radio-nuclides can be used: 241Pu/241Am, 238Pu/234U, 239Pu/235U, 240Pu/236U, and possibly
242Pu/238U.
At the moment no uranium or plutonium reference materials certified for "age" are
available, although they are needed in order to provide a more solid metrological basis for
nuclear forensics and environmental measurements. Addressing these present needs the
Institute for Reference Materials and Measurements (EC-JRC-IRMM) is closely
cooperating with the Institute for Transuranium Elements (EC-JRC-ITU). As part of the
presented feasibility study for the development of plutonium reference materials for
age dating the well known and widely distributed isotopic abundance reference
materials NBS SRM 946, 947 and 948 (NBL CRM 136, 137 and 138) are investigated.
The "ages" of these materials (with known separation dates) of differing ages and
isotopic compositions will be verified by measuring amount concentrations of mother
(238Pu, 239Pu, 240Pu, 241Pu, 242Pu) and daughter (234U, 235U, 236U, 238U and
241Am) isotopes. Proper sample preparation and elemental separation is a prerequisite
for accurate isotope ratio measurements. Thermal ionisation mass spectrometry
(TIMS) is applied for the measurement of the plutonium and uranium isotope amount
concentrations via isotope abundance measurements and isotope dilution mass
spectrometric (IDMS) measurements while 241Am is measured by gamma-ray spectrometry. |
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