L.R. Kilius

129I from nuclear fuel reprocessing facilities at Sellafield (U.K.) and La Hague (France); potential as an oceanographie tracer

On the basis of measurements made on archived seaweed samples, together with available release data, we tentatively estimate that the input of 129I (half-life 16 m.y.) to the oceans from the nuclear fuel reprocessing facilities at La Hague, France and Sellafield, Great Britain, during the past 25 years has been ~ 5 X 1027 atoms, or ~ 1.2 ton of 129I. This is an order of magnitude larger than the total estimated 129I in the pre-nuclear era ocean, approximately 25 times the input due to nuclear weapons testing, and several hundred times that released by Chernobyl. Most of this 129I is transported up the West European coastline and into the North Atlantic and Arctic oceans. The technique of accelerator mass spectrometry (AMS) is capable of measuring 106 atoms of 129I, thus offering an extremely sensitive method of tracing this isotope in the oceans. We show, for example, that one can detect the reprocessing signal in 11 seawater samples from virtually anywhere in the North Atlantic. It thus should be possible to monitor not only surface circulation but also deep water formation in this latter area, which is believed to have considerable climatic influence. Given its high sensitivity for detection, and the well defined temporal and spatial distribution of its source function, 129I is a potentially attractive addition to the available suite of oceanographie tracers. We also discuss the potential of using this isotope to trace other possible intentional or accidental releases of fission products in the oceans.

129I from nuclear fuel reprocessing; potential as an oceanographic tracer

Abstract Using the technique of acceleraton mass spectrometry (AMS), we have measured 129 I in samples of seaweed and seawater taken at various distances along the coasts from the nuclear fuel reprocessing facilities at La Hague, France and Sellafield, Great Britain, as well as in the North Sea and in the North Atlantic. The deduced seawater 129 I/ 129 I ratios, which vary by 4 orders of magnitude, demonstrate the modest sized samples required for such measurements; less than 1 ml from the English Channel or Irish Sea, less than 1 litre in the North Atlantic. It thus should be possible to monitor not only surface circulation but also deep water formation in this latter area, which is believed to have considerable climatic influence. Given its high sensitivity for detection, and the well defined temporal and spatial distribution of its source function, 129 I is a potentially attractive addition to the available suite of oceanographie tracers.

The first detection of naturally-occurring 236U with accelerator mass spectrometry

Abstract The IsoTrace heavy element AMS system has been successfully used to detect naturally-occurring 236 U ( 236 U/ 238 U = (5.6 ± 1.5) × 10 −10 ) in samples of uranium ore from Cigar Lake, Saskatchewan, Canada. This level of 236 U agrees with that previously claimed for samples of a processed uranium ore (D.J. Rokop, D.N. Metta and C.M. Stevens, Int. J. Mass Spectrom. Ion Phys. 8 (1972) 259 [1]), and is consistent with the amount of 239 Pu found in pitchblende (W.A. Myers and M. Lindner, J. Inorg. Nucl. Chem. 33 (1971) 3233 [2]). This experiment illustrates the general capability of a small tandem-based AMS system for analyzing actinides, in particular 236 U. It can be shown that the isotope-ratio detection limit of this system, is at present 5 × 1o −8 for detecting a less abundant actinide isotope one mass unit above, and 5 × 10 −10 one mass unit below, a major isotope.

AMS of heavy ions with small accelerators

Abstract Recent advances in the detection and the routine measurements of heavy elements by accelerator mass spectrometry (AMS) are reviewed. Particular emphasis will be given to the measurement of low energy (⩽ 15 MeV) and high-Z ions using small (⩽ 3 MV) accelerators.

AMS measurement of environmental U-236 Preliminary results and perspectives

236U is a 23.4 Ma half-life radioactive isotope whose natural global abundance is expected to be overwhelmed in many places by its production and release during nuclear power generation. The detection of excess 236U in the environment is therefore a method of monitoring the presence of activated uranium. However, 236U has not been widely used for environmental studies due to the difficulties of measuring it at low levels with standard α-spectrometry or thermal ionization mass spectrometry. In principle, accelerator mass spectrometry can overcome some of the difficulties encountered in the traditional methods, making it possible to detect 236U at very low levels so that a large range of environmental samples can be analyzed. In this paper, we report some preliminary results of the 236U measurements of four water samples from the US Idaho Chemical Processing Plant. Limitations with our current AMS system and the perspectives for considerable improvements will be discussed.

Accelerator mass-spectrometric measurements of heavy long-lived isotopes

Abstract The potential for a systematic analysis of 129 I within the hydrosphere is explored using accelerator mass spectrometry. Examples are taken from measurements on pre- and post-bomb samples of marine organisms such as algae, sponges and some forms of coral.

The 12CH22+ molecule and radiocarbon dating by accelerator mass spectrometry

The 12CH22+ molecule has been studied and it was found that the molecule can be effectively eliminated thus allowing detection of 14C2+ at low terminal voltages of a tandem accelerator. Some implications of this discovery for radiocarbon dating are discussed.

The dispersal of 129I from the Columbia River estuary

129I/I isotopic ratios have been measured in algae samples, collected along the north-west portion of the Pacific coastline of North America, as part of a preliminary study, to determine the extent and concentration of 129I leaving the Columbia River. These isotopic ratios were found to be in excess of the nuclear weapons testing level, however all were significantly lower than those previously measured from European nuclear fuel reprocessing facilities.

Accelerator mass spectrometry of 129I at isotrace

Abstract 129I has been measured by an accelerator mass spectrometry (AMS) method which is compatible with the further development of small tandem accelerators for the study of heavy elements. The addition of an electrostatic analyser to the injector system, is a primary factor facilitating the detection of 129I at levels as low as 5 × 10−13 of 127I. The removal of a significant portion of the unwanted ions by this analyser results in a simplified high energy ion analysis system, because the possibility of mass, energy and charge ambiguities are reduced. The relevance of this and other improvements to heavy ion analysis at IsoTrace is discussed using the detection of 129I as a prime example.

MOLECULAR FRAGMENT PROBLEMS IN HEAVY ELEMENT AMS

Abstract Heavy element AMS is made more difficult by the presence of the molecular fragments of mass and charge (m, q) which come from negative ions entering the tandem accelerator together with the heavy element M. If the heavy element after atomic or molecular dissociation has charge Q then a useful quantity, to measure the degree of the molecular fragments as ambiguities to the detection of the ions of interest, is the near-integer n given by n = mQ − Mq. When n ≈ 0, a rare heavy element is accompanied by strong beams of lighter molecular fragments (pilot beams) which usually prohibit the measurement of the rare species. The same problem occurs for n ≈ ±1 (or larger) because molecular beams undergo Coulomb explosion even in a gaseous target and the energy spread results in the increase of the resolution requirement of the high energy analyzers. The resolution needed for both velocity and electric analyzers for removing any molecular fragments of [n, q], assuming that a much higher resolution (⪢ MQ) magnetic analyzer is also used, is given by Mq |n| . In the case of 129I+4 analysis, 97Mo+3 interference and the add-up from the other fragment can overwhelm the rare ions requiring charge +5 to be used. Fortunately, as an interference to 129I+5, 103Rh+4 is very rare. Strategies for solving this heavy element AMS problem and some recent results will be discussed.