Radiocarbon positive-ion mass spectrometry

Abstract

a b s t r a c tProof-of-principle of a new mass spectrometric technique for radiocarbon measurement is demonstrated. Interfering nitrogen and hydrocarbon molecules are largely eliminated in a charge-exchange cell operating on non-metallic gas. The positive-to-negative ion conversion is the reverse of that conventionally used in accelerator mass spectrometry (AMS) and is compatible with plasma ion sources that may be significantly more efficient and capable of greater output than are AMS sputter ion sources. The Nanogan electron cyclotron resonance (ECR) ion source employed exhibited no sample memory and the >50 kyrs age range of AMS was reproduced. A bespoke prototype new instrument is now required to optimise the plasma and cell physics and to realise hypothetical performance gains over AMS.

Preliminary results of positive ion mass spectrometry based on a 2.45 GHz ECR ion source and a non-metallic gas target

“…In the past ten years, to produce high-intensity C 3+ /C 2+ beams for PIMS, Australian Nuclear Science and Technology Organization (ANSTO), Oak Ridge National Laboratory (ORNL) and Scottish Universities Environmental Research Centre (SUERC) have carried out relevant researches on ECR ion sources with high microwave frequency of 7 GHz (C 3+ ), 14 GHz (C 3+ and 10 GHz (C 2+ , molecular cation 12 CH2 2+ is metastable, can be eliminated by change exchange target.) respectively [8][9][10]. The feasibility of high-frequency ECR ion sources in PIMS has been proven by these works.…”

“…However, due to its low optimal charge exchange energy, high maintenance and operation cost, and short service life of the alkali metal CXC, it is not convenient for the stable operation of PIMS. ANSTO, ORNL, and SUERC use Rubidium vapor target, single-crystal alkali halide (LiF) target, and non-metallic gas isobutane target to form Cion by charge exchange, respectively [8][9][10]. At present, there is still no consistent recommendation on the selection of efficient, stable, and reliable charge exchange targets, which also limits the development of PIMS.…”

Accelerator mass spectrometry: state of the art and perspectives

“…In rare cases, large accelerators requiring positive ions have been used for AMS experiments of noble gas isotopes [14,15], and of Sm isotopes [16]. It is interesting that an old idea of starting with positive ions, converting them to negative ions without using an accelerator [17], was revived recently [18].…”

“…Another step for small 14 C machines -still using negative-ion sputter sources -is the return to MS without an accelerator, which is pursued at the ETH Zurich (MμCADAS, [25]). Interestingly, as mentioned already above, there is also 14 C positive-ion mass spectrometry (PIMS) developed at SUERC Glasgow [18]. The basic idea of PIMS is to reverse the negative-to-positive ion conversion used in AMS (cf.…”

“…an electron cyclotron resonance ion source and then producing negative ions in a gas-filled charge exchange cell which suppresses 14 N − and dissociates molecules. It is argued [18] that such a system will be more efficient than standard AMS using sputter sources, especially if 14 C measurements of very small gaseous samples (CO 2 ) is of interest (see Section 2.2 below). Atmosphere Production of radionuclides by cosmic rays 14 c, 10 Be, 26 Al, 32 si, 36 cl, 39 Ar, 81 Kr, 129 10 Be, 26 Al, 41 ca, 53 Mn, 59 ni, 60 Fe Live supernova remnants in terrestrial materials 26 Al, 60 Fe, 244 Pu, ( 146 sm, 182 hf, 247 cm) stable trace isotopes in presolar grains 194,195,196,198 Pt Geochemical solar neutrino detection ( 97,98…”