RESUMO
RATIONALE: The measurement of (210) Pb provides an assessment of the risk an individual faces of developing lung cancer as a result of their exposure to radon and radon decay products. Existing radiometric techniques are not sensitive enough to detect (210) Pb in many exposures. This report describes the further development of a method of measuring (210) Pb using Accelerator Mass Spectrometry (AMS). METHODS: (204,205,208,) (210) Pb measurements were performed by AMS. Samples were prepared from stock solutions of (204) Pb, (205) Pb, (208) Pb and (210) Pb and measured by making PbF3 (-) ions at the IsoTrace AMS facility using a SIMS-type Cs(+) sputter source. Potential interferences in Pb(3) (+) isotope measurement and the overall efficiency of Pb beam production were determined experimentally. RESULTS: (204) Pb and (205) Pb suffer from molecular and atomic isobaric interferences that cannot be removed without sacrificing the efficiency of (210) Pb measurements whereas (208) Pb suffers from no interferences. The abundance sensitivity of (210) Pb/(208) Pb was 1.3 × 10(-12) . Keeping the (210) Pb/(208) Pb spike below this level resulted in a detection limit of 4.4 mBq of (210) Pb using the IsoTrace AMS facility. CONCLUSIONS: This study identified key interferences in the measurement of PbF3 (-) â Pb(3) (+) ions and demonstrated a new AMS method to measure (210) Pb. This new AMS technique is about five times more sensitive than gamma and beta spectroscopy measurements of (210) Pb and the measurement time is much shorter. Copyright © 2016 John Wiley & Sons, Ltd.
RESUMO
RATIONALE: The ability to measure both (135) Cs and (137) Cs can provide an estimate of the age and source of Cs isotopes in an environmental sample. Accelerator mass spectrometry (AMS) consistently reports lower abundance sensitivities than other techniques and, with the addition of an on-line reaction cell, simpler isobaric suppression. Therefore, an AMS methodology was developed to measure Cs isotopes using CsF2- as the initial anion. METHODS: The ion beam is passed through the Isobar Separator for Anions (ISA) where it is captured by radiofrequency quadrupoles in a gas cell before injection into the tandem accelerator. In the ISA, the beam reacts with O2 gas, selectively removing the BaF2- and leaving the Cs analyte to be reaccelerated and sent through the remainder of the AMS system. RESULTS: The BaF2- signal was attenuated by a factor of 10(5) in the ISA while 25% of the original CsF2- current was transmitted into the accelerator. (135) Cs was measured without any interference from (133) Cs to an abundance sensitivity of 1.3 × 10(-10) . The abundances of four stable Ba isotopes (masses 133, 134, 135 and 137) were measured and no isotope-dependent bias was detected using the ISA in vacuum. CONCLUSIONS: The results demonstrate the feasibility of measuring long-lived Cs isotopes without Ba interference by AMS with on-line isobar separation and the ability to use shorter lived Cs isotopes for yield tracing.
RESUMO
RATIONALE: An experimental Isobar Separator for Accelerator Mass Spectrometry (ISAMS) instrument has been used to demonstrate an on-line separation of HfF5(-) from its isobar WF5(-). This is necessary, in addition to sample preparation chemistry, for measuring (182)Hf at natural levels by Accelerator Mass Spectrometry (AMS). METHODS: The device utilizes a radiofrequency quadrupole (RFQ) controlled gas cell, wherein anion-gas reactions at eV energies attenuate the interfering isobars of the analyte molecular anions, leaving HfF5(-) for AMS analysis. The RFQ also helps to control the multiple scattering resulting from the ion-gas collisions. RESULTS: O2 gas was used in the HfF5(-)/WF5(-) separation and WF5(-) was attenuated by nearly 3 orders of magnitude while maintaining ~75% transmission of HfF5(-). It is expected that the transmission and attenuation can be increased by further research. CONCLUSIONS: This result advances the possibility of detecting natural (182)Hf when AMS is supplemented with an isobar separator in the injection system.
