The Utrecht accelerator facility for precision dating with radionuclides

The Utrecht facility for accelerator mass spectrometry is described. The set-up with an EN tandem accelerator is designed for measurements of a broad range of long-lived radionuclides and of stable trace elements. In particular, dating measurements with ¹⁰Be and ¹⁴C can be performed with high precision by rapid switching between the measurements of the isotopes. Optimal beam transmission through the accelerator is achieved with a new injection system in conjunction with the installation of axially symmetric acceleration tubes with spirally inclined electrodes. The first ¹⁴C/¹²C measurement with this set-up is reported.     

Accelerator mass spectrometry at the rehovot pelletron tandem: Measurements of abundances of cosmogenic radioisotopes and future prospects

The accelerator mass spectrometry system developed at the Rehovot 14UD Pelletron tandem laboratory has been used in measurements of abundances of cosmogenic nuclei. Measurements of ³⁶Cl concentrations in natural water samples from the Jordan River and Dead Sea Basin are presented in the framework of a ³⁶Cl budget analysis of the Dead Sea. The feasibility of ⁴¹Ca detection at concentrations ranging down to 1 × 10^?13 by tandem accelerator mass spectrometry has been demonstrated.     

The accelerator mass spectrometry facility at the University of Washington: Current status and an application to the 14C profile of a tree ring

The University of Washington accelerator mass spectrometry system, based upon a Model FN tandem accelerator, is described. Preliminary data on ¹⁴C in thin sequential sections of a single Sitka spruce annual ring (1963) are presented; the ¹⁴C profile reflects the dramatic nuclear-weapons-induced changes in atmospheric ¹⁴C observed for 1963.     

Accelerator mass spectrometry at Chalk River

Accelerator mass spectrometry of ¹⁴C was studied with the Chalk River MP tandem from 1978 until the tandem was shut down in 1982 for the installation of a post-accelerator. The performance of the original system is reviewed and plans for AMS with the new accelerator facility are presented.     

14C dating of small archaeological samples: neolithic to iron age in the central alpine region

Accelerator mass spectrometry (AMS) radiocarbon ¹⁴C dating will widen enormously the range and scope of archaeological investigations. This is due mainly to 100- to 1000-fold sample size reduction over conventional dating. In order to determine the size and the quality of samples that can be accepted for AMS ¹⁴C dating, we have selected archaeological samples relating to the Neolithic to Iron Age. The basis of our AMS target preparations is the coking (pyrolysis) of organic matter after elimination of impurities by various physical and chemical treatments. The effect of the morphology as well as of the grain size distribution of the charcoal particles was determined in order to achieve optimal conditions for accelerator dating.     

Archaeological and geological interest in applying 14C AMS to small samples

One aspect of the accelerator mass spectrometry technique is that samples can be dated which are essentially smaller than required for conventional ¹⁴C dating. This two orders of magnitude expansion offers applications of ¹⁴C which are new and in some fields of great importance. This paper attempts to list and group the various types of sample materials, with special emphasis on their role in archaeology and geology.     

Accelerator-based research activities at “Centro Nacional de Aceleradores”, Seville (Spain)

In February 1998, almost 10 years ago, the set-up of the first IBA (ion beam analysis) facility in Spain took place with the arrival of a 3 MV tandem accelerator [J. García-López, F.J. Ager, M. Barbadillo-Rank, F.J. Madrigal, M.A. Ontalba, M.A. Respaldiza, M.D. Ynsa, Nucl. Instr. and Meth. B 161-163 (2000) 1137]. Since then, an intensive research program using IBA techniques has been carried out. Subsequently, a cyclotron for 18 MeV protons has been also installed at the “Centro Nacional de Aceleradores” (CNA), devoted mainly to isotope production for PET (positron emission tomography) techniques, but possibly applied to material analysis and damage studies on a dedicated beam line. Moreover, a 1 MV tandem has been recently installed for AMS (accelerator mass spectrometry) ¹⁴C dating and environmental research with other isotopes.In the present paper we describe the new facilities and the developments of the 3 MV tandem beam lines occurred during the past years, as well as some examples of the most recent research activities in our Center in the fields of Material Science, Archaeometry, Biomedicine and Environment.     

A new AMS beam line at the Erlangen tandem accelerator facility

An accelerator mass spectrometry beam line is presently being built up at the EN tandem accelerator in Erlangen. A new Cs sputter ion source is being developed, and mass separators on both the low- and high-energy sides of the tandem and an electrostatic sector field for charge-state selection have been installed. Optimization of the beam quality will be possible with a new emittance measuring device. The tandem is stabilized via a position-sensitive Faraday cup, which simultaneously measures the current of the abundant isotopes. The spectra of the rare-isotope ions are taken by differential energy loss measurements in a gas ionization chamber.     

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.     

Status and research programs of the multinuclide accelerator mass spectrometry system at the University of Tsukuba

We present the current status and research programs of a multinuclide accelerator mass spectrometry (AMS) system on the 12UD Pelletron tandem accelerator at the University of Tsukuba (Tsukuba AMS system), Japan. A maximum terminal voltage of 12 MV is available for the AMS system. The Tsukuba AMS system can measure environmental levels of long-lived radioisotopes of ¹⁴C, ²⁶Al, ³⁶Cl and ¹²⁹I by employing a molecular pilot beam. Recently, enhancements in AMS techniques and equipment, including sample preparation, the ion source and the data acquisition system, have improved the performance of ³⁶Cl-AMS. The standard deviation of fluctuations is typically ±2%, and the machine background level for the ³⁶Cl/Cl ratio is lower than 1 × 10^?15 with a halite sample. We have measured over 500 samples in 1 year, including samples for earth and environmental sciences and nuclear safety research.     

Graphite sample preparation for AMS in a high pressure and temperature press

A high pressure-high temperature press is used to make target material for accelerator mass spectrometry. Graphite was produced from typical ¹⁴C samples including oxalic acid and carbonates. Beam strength of ¹²C was generally adequate, but random radioactive contamination by ¹⁴C made age measurements impractical.     

Improved SSAMS performance

We operate a new NEC 250 kV single-stage accelerator mass spectrometer (SSAMS) next to our established 5 MV tandem. This permits good comparison of ¹⁴C-AMS and challenges SSAMS performance. Initial SSAMS ion-optical deficiencies have been addressed by shimming the injection magnet and 3‰ ¹⁴C/¹³C measurement with background limited by sample chemistry is routine. Higher-precision analysis is also achievable. A problematic measurement interference remains, however. The small spectrometer was procured to add measurement capacity, and for experiments with positive ions, but is now the preferred instrument for both convenience and measurement quality.     

Progress in 14C and 10Be dating at SFU

Since early 1982, a substantial upgrading of the Simon Fraser University radioisotope dating system at the McMaster FN accelerator has taken place. The accelerator itself was equipped with a new charging system and beam tubes, resulting in excellent stability and beam transmission. A new isotope filtering system of two magnets and a Wien filter has removed previously troublesome backgrounds: our carbon background from graphite is now ～ 47 ka BP, and is due to real ¹⁴C rather than scattered ¹³C. Measurement of ¹⁰Be in natural samples is now routine, with several hundred samples processed. Other work on ¹⁰Be has included studies which showed for the first time that ¹⁰Be could be measured at low energies (3 MV). We have also started work on ²⁶Al detection as a preliminary to the investigation of ²⁶Al/¹⁰Be dating. Finally, we present examples of our applications of this facility to studies in oceanography and archaeology.     

Accelerator mass spectrometry with completely stripped 36Cl ions at the Munich postaccelerator

An accelerator mass spectrometry (ams) system has been set up at the postaccelerator of the Munich tandem laboratory. This system allows background-free ams measurements with completely stripped ions of masses up to 40. In first experiments, the ³⁶Cl abundances of palaeontological samples and the cosmic ray induced ³⁶Cl contents in limestone as a function of depth have been determined. ³⁶Cl has been used as pilot beam for the stabilization of the system. The detection limit is ${}^{36}\text{Cl/Cl = 4 × 10}{}^{\mathrm{?15}}$. A search for negative ³⁶Ar ions has been undertaken.     

Accelerator mass spectrometry programme and related developments at the BARC-TIFR Pelletron accelerator

The accelerator mass spectrometry programme and the related developments based on the BARC-TIFR Pelletron accelerator is described. A segmented gas detector and beam chopper control electronics have been developed for conducting ³⁶Cl measurements. Distinct energy loss characteristics of the gas detector and beam chopper performance are presented. Also presented are the initial results for the measurement of ³⁶Cl in standard and samples of unknown concentration.     

Direct measurements of small 14C samples after oxidation in quartz tubes

Small ¹⁴C samples gain importance in environmental research and for dating purposes. However, throughput of such samples is limited by the preparation of graphite targets for accelerator mass spectrometry (AMS) measurements. In our approach, oxidation of samples with copper oxide in quartz tubes was applied to form CO₂ which was measured directly with the gas ion source of the small AMS facility MICADAS. The presented method was designed to meet the requirements for fast and easy handling of small samples (<100 μg carbon). As combustion byproducts are likely to interfere with ionisation processes in the gas ion source, we additionally investigated the effects of several gases on C^? currents.     

A review of ion sources for accelerator mass spectrometry

Accelerator mass spectrometry places unusually difficult demands on ion source design and possible ways of meeting these are discussed. A brief review of the state-of-the-art methods of generating negative ion beams of beryllium, carbon, aluminum, chlorine and calcium are presented. A new method of producing 20–25 μA of ¹²C^? ions from CO₂ gas is described in detail with emphasis on accelerator ¹⁴C dating. Ionization efficiency is high (～ 7.7%) and it may be possible to date samples containing 100 μg of ¹²C (i.e. ～ 0.2 at. cm³ of CO₂). Accelerator measurements with contemporary CO₂ followed by CO₂ from anthracite enabled the age of the latter to be determined to be > 39000 years without background subtraction.     

Measurement of Sm with the HI-13 accelerator mass spectrometry system

¹⁵¹Sm is an interesting nuclide in many research fields. Measurement methods of the long-lived ¹⁵¹Sm with accelerator mass spectrometry have been developed at China Institute of Atomic Energy. The chemical form of samples was Sm₂O₃ and the extracted ion was SmO⁻. To date, the sensitivity, that is, the isotopic ratio, of ¹⁵¹Sm measured using accelerator mass spectrometry is about 10⁻⁸. This method was also used to measure the concentration of tracer ¹⁵¹Sm in biological samples for clarifying whether the rare earth elements can enter into the brain. It is not possible at present to determine whether the tracer has penetrated the blood-brain barrier into the brain.     

Accelerator mass spectrometry of strontium-90 for homeland security, environmental monitoring and human health

Strontium-90 is one of the most hazardous materials managed by agencies charged with protecting the public from radiation. Traditional radiometric methods have been limited by low sample throughput and slow turnaround times. Mass spectrometry offers the advantage of shorter analysis times and the ability to measure samples immediately after processing, however conventional mass spectrometric techniques are susceptible to molecular isobaric interferences that limit their overall sensitivity. In contrast, accelerator mass spectrometry is insensitive to molecular interferences and we have therefore begun developing a method for determination of ⁹⁰Sr by accelerator mass spectrometry. Despite a pervasive interference from ⁹⁰Zr, our initial development has yielded an instrumental background of ∼10⁸ atoms (75 mBq) per sample. Further refinement of our system (e.g. redesign of our detector, use of alternative target materials) is expected to push the background below 10⁶ atoms, close to the theoretical limit for AMS. Once we have refined our system and developed suitable sample preparation protocols, we will utilize our capability in applications to homeland security, environmental monitoring and human health.     

Forensic applications of C at CIRCE

The decreasing trend of the radiocarbon pulse produced during the atmospheric tests of nuclear weapons (bomb-carbon) coupled with high sensitivity accelerator mass spectrometry (AMS) measurements, drastically increased the precision of radiocarbon age determinations since the second part of the sixties, allowing the application of radiocarbon AMS to a wide range of studies previously not directly involving conventional radiocarbon dating (i.e. food authenticity, forensic, biochemistry). In the framework of authenticity evaluation of artworks, high precision radiocarbon (¹⁴C) AMS measurements (ΔR/R < 0.3%) reduce the conventional uncertainty of the dating to few decades, allowing precise age estimation of materials containing carbon (C). The Centre for Isotopic Research on Cultural and Environmental heritage (CIRCE) during its activity on AMS ¹⁴C dating achieved high precision measurements opening the opportunity to these kinds of applications. This paper presents the main results obtained from radiocarbon measurements on a set of bone samples analyzed for the determination of the post-mortem interval in the framework of an unsolved case investigated by the Rome prosecutor office. The chronological characterization of the wooden support of the “Acerenza portrait” is also presented with the aim to evaluate its age and to further investigate the possibility to attribute this artwork to Leonardo da Vinci.Bomb-¹⁴C dating on the lipid and collagen fractions of bones allows the evaluation of the year of the death of the individuals by means of ad hoc calibration data sheet with the typical few years precision and difference between collagen apparent age and the year of death appeared in agreement with the age of one individual estimated by dating of tooth collagen. Conventional radiocarbon dating on both wood and wood extracted cellulose leads to an estimation of the portrait wood board age (2σ) of 1459-1524 AD (57% relative probability), 1571-1631 AD interval (42% relative probability).and 1559-1563 AD (1% relative probability). These results attribute with the highest relative probability an age comprised within the life span of Leonardo (1452-1519) to the support.