M-J. Nadeau

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.

A negative ion survey; towards the completion of the periodic table of the negative ions

Abstract The negative ion properties of many of the elements of the periodic table have been known for some years, however, there were some 36 elements for which conclusive experimental evidence for the existence of a stable negative ion had not been found. After a brief overview of the experimental method used, we will present the results obtained for the three elemental groups studied (Group II, lanthanides, actinides a total of 24 elements). We will then conclude by stressing the similitudes between different elements and different elemental groups.

Radium, actinides, and their molecular negative ions from a cesium sputter ion source

Abstract The negative ions of the isotopes 226 Ra, 231 Pa and 244 Pu, produced by a Cs sputter ion source, have been observed for the first time using the IsoTrace heavy element AMS system. The properties of these negative ions have been compared with those of Th and U, and the electron affinities of all these elements (Ra, Th, Pa, Th and Pu) have been found to be similar and greater than 50 meV. Some molecular negative ions of these elements, in particular carbides and oxides, have also been measured. It was found that di-carbide is generally a profitable molecule form for measuring Ra, Th and Pa, while mono-oxide is more efficient for measuring U and Pu.

Quantum mechanical effects on sputter source isotope fractionation

Abstract The negative ion production probabilities for ions of differing masses have been calculated for a simplified sputter source geometry using the formalism developed by Norskov and Lundqvist. The isotope fractionation derived from this probability is, as expected, a strongly varying function of the sputter cathode surface conditions. The results of these calculations using the carbon isotopes as an example are discussed with regard to their implications for accelerator mass spectrometry (AMS).

Heavy element analysis by low energy accelerator mass spectrometry

Improvements have been made to the mass and energy analysis system at the IsoTrace Laboratory that have resulted in a factor of 30 increase in detection efficiency for some heavy ions and have reduced interference from the fragmentation of hydrides and other molecules. The implications of these improvements for the detection of rare atomic negative ions and radioisotopes such as 129I will be discussed. Evidence is also presented for the existence of a barium negative ion that is completely resolved from barium mono-, di- and trihydride interferences and which is clearly distinguished from any interference due to the fragmentation of BaH−2 to BaH− before the first analyzing magnet.

Electric dissociation of negative ions — II

Abstract As an alternative to naturally occurring negative ion discrimination, we consider the possibility of electric dissociation to discriminate between isobars, by destroying the weaker negative ion of a pair. The theoretical basis of negative ion dissociation using high electric gradients and an appropriate experimental setup are discussed. The possibility of negative ion destruction by electric dissociation during the first stage of tandem acceleration and at the ion source is also considered. In consequence, it is possible to place a limit on the electron affinity of some elements considering their survival in the AMS system. Mn−, Ca− and C−∗ among others are considered.

Lanthanide negative ion detection using accelerator mass spectrometry

Abstract Accelerator mass spectrometric methods have been used in the detection of the negative ions of the lanthanides. All of the lanthanide negative ions (La−−Lu−) have been observed except Pm−, Ho−, and Er−. The heavy element analysis line at the IsoTrace Laboratory was used to count the positive ions resulting from the atomic negative ions produced in a Cs sputter ion source and passed through the tandem accelerator. Because of its very low electron affinity, Dy− had a terminal voltage dependent yield, and its study required the reduction of the electric field gradients used to accelerate the ions. The relative negative ion yields among the lanthanides will be discussed. Both Yb− and Lu− have recently been theoretically predicted to exist in negative parity ground states.

The negative ions of strontium and barium

Abstract Recent theoretical calculations have predicted a tendency toward higher electron affinities for heavier alkaline elements. Experimental evidence has been obtained for the existence of strontium and barium negative ions created from pure elements in a caesium sputter ion source. Accelerator mass spectrometric techniques were employed to resolve the above elemental negative ions from the interfering molecular species.

Detection of naturally occurring 236U in uranium ore

Abstract The IsoTrace heavy element AMS system has been successfully used to detect the naturally occurring 236 U ( 236 U/ 238 U= (5.6 ± 1.5) × 10 −10 , based on a single measurement with a 1σ confidence level) in samples of the uranium ore from Cigar Lake, Saskatchewan, Canada. This level of 236 U agrees with that previously claimed for samples of a procressed uranium ore [1], and is consitent with the amount of 239 Pu found in pitchblende [2].