Accelerator Mass Spectrometers AMS

The development of accelerator mass spectrometry goes back to the early days of ion accelera- 

Cs-Beam Sputter Source for Negative Eons 40 Samples 

Instrumental layouts and developments in AMS are reviewed by Kutschera.195 Today AMS is the most powerful, sensitive and selective mass spectrometric technique for measuring long-lived radionuclides at the level of natural isotopic abundances (10-16 to 10-12). Accelerator mass spectrometry (AMS) allows uranium isotope ratio measurements with an abundance sensitivity for 236U in the range of l(rlo-10 l2.l98J  

9 Electron Ionization Mass Spectrometers for Stable Isotope Ratio Measurements 

The development of accelerator mass spectrometry goes back to the early days of ion accelerators. Accelerator mass spectrometry (AMS) was developed in 1977 by introducing accelerators (cyclotron and tandem accelerator ) into mass spectrometry. A schematic diagram of a powerful 

Cs-Beam Stnjtler Source for Negelive Ions 40 Sampler 

Ions formed in an electron ionization mass spectrometer possess a relatively low initial energy spread, therefore single focnsing magnetic sector field instruments are sufficient to separate ion beams with different m/z ratios. Commercial stable isotope ratio mass spectrometers (SIRMS) allow highly precise and accnrate isotope ratio measnrements e.g., with the Finnigan MAT 253, of H/D, C/ C, N/ N, 0/ 0, jQj and SFg) Si/ Si as weU as Ar, Kr and 

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Another combination of magnetic and electric sector fields, together with a tandem accelerator, is realized in different types of accelerator mass spectrometers (AMS)17 applied for carbon-14 dating and extreme ultratrace analysis of long-lived radionuclides at natural isotope abundances (see Chapter 5). 

Accelerator mass spectrometer (AMS) A huge scientific instrument used for sorting and counting isotopes. AMS dating allows much smaller samples to be used in archaeology. 

There are several other types of MS instruments like the Fourier transform MS (FT-MS, which was originally called an ion cyclotron resonance or ICR-MS) or the accelerator mass spectrometer (AMS) in which the ion beam is accelerated by an extremely high electric field and then separated by a strong magnetic field (see next section). 

A reasonably common technique for the determination of many isotopes is mass spectrometry. This technique is very sensitive and isotope specific. It is especially suitable for heavy elements like the actinides, where isobaric disturbances are few. Three different t5q3es of mass spectrometers have been used for the determination of radionuclides in the environment. These types are the thermal ionization mass spectrometer (TIMS), the inductively coupled plasma-mass spectrometer (ICP-MS), and the accelerator mass spectrometer (AMS). The AMS is used mainly for the determination of geologic age or for the study of radionuclide production in the atmosphere. Thermal ionization mass spectrometry is a very sensitive technique with very low detection limits however, TIMS... 

Plate 22 Radiocarbon dating. View of a linear accelerator used as part of an accelerator mass spectrometer (AMS). This device is capable of counting the relatively few carbon-14 atoms in a radioactive sample. The proportion of carbon-14 to carbon-12 atoms in the sample may be used to determine the radiocarbon age of an organic object. This is then adjusted by various corrections to give the true age. See Isotope Ratio Studies Using Mass Spectrometry. Reproduced with permission from Science Photo Library. 

When a suitable depth of sampling is reached, a lump containing sufficient material for the radiocarbon dating must be identified. Where an Accelerator Mass Spectrometer (AMS) is used in the radiocarbon dating, at least 20 milligrams of calcium carbonate will be required. 

Mass Spectrometer. The mass spectrometer is the principal analytical tool of direct process control for the estimation of tritium. Gas samples are taken from several process points and analy2ed rapidly and continually to ensure proper operation of the system. Mass spectrometry is particularly useful in the detection of diatomic hydrogen species such as HD, HT, and DT. Mass spectrometric detection of helium-3 formed by radioactive decay of tritium is still another way to detect low levels of tritium (65). Accelerator mass spectroscopy (ams) has also been used for the detection of tritium and carbon-14 at extremely low levels. The principal appHcation of ams as of this writing has been in archeology and the geosciences, but this technique is expected to faciUtate the use of tritium in biomedical research, various clinical appHcations, and in environmental investigations (66). 

A more recently developed technique, known as the accelerator mass spectrometry (AMS) radiocarbon dating technique, based on counting, in a mass spectrometer, the relative amount of radiocarbon to stable carbon isotopes in a sample (see Textbox 10). 

Analysis time is typically of the order of minutes to hours depending on the sample. Normally the time spent in actual AMS analysis is not the constraining factor, but rather sample purification prior to the spectrometric analysis. Accelerator mass spectrometers are space demanding facilities that typically occupy hundreds of square meters. Normally, dedicated personnel operate the device. Considerable effort is directed into refining the methods to allow operation by smaller, less costly facilities. 

AMS) measurement of atoms (which provides concentrations). The development of linear accelerator mass spectrometer has significantly increased the sensitivity of measurements, leading to an increase of the limit of ages to be dated, but more significantly to a decrease of sample size to be measured and the measurement time. 

Acceleration mass spectrometry (AMS) - The precise measurement of isotopic ratios for very low abundance isotopes is beyond the capability of conventional mass spectrometers. In these cases of isotopes at minute trace levels, some 50 mass spectrometers exist worldwide. The tendetrons used for these types of analyses are derived from Van de Graaff-type particle accelerators. These instruments are based on tandem mass spectrometry. 

Figure 2.9. Accelerator mass spectrometer used for bioanalytical analysis at Xceleron (formely CBAMS). Pharmaceutical companies have not adopted AMS as an in-house technique because of cost and size of instrumentation (compare the scale of the instrument to the kitchen in the lower left). Samples are outsourced to companies that specialize in the technique.

AMS directly measures the number of 14C atoms, and the ratio of 14C to 13C and/ or 12C, using a high-energy accelerator as an inlet to a mass spectrometer. The key characteristics of 14C-AMS are the electron stripping and ion acceleration, which allow 14C to be distinguished from isobars and molecules that would confuse a standard mass spectrometer. AMS requires only a fairly small sample of lOOpg to 1 mg of C. In addition, the measurement only takes minutes per sample. 

At the three laboratories, samples were cleaned and treated following standard procednres to remove contaminants. The cloth samples were then combusted to gas and their radiocarbon content was measured in an Accelerator Mass Spectrometer. The almost identical AMS measurements at the three laboratories provided a calendar age range of ad 1260-1390 with at least 95% confidence (Fig. 5.17). The results from the three control samples agree with previous radiocarbon measurements and/or historical dates. The AMS dating provides conclusive evidence that the linen of the Shroud of Turin is medieval. 

Accelerator mass spectrometry (AMS) - precise measurement of the isotopic ratios of the long-lived radionuclides that occur naturally in our environment are beyond the ability of conventional mass spectrometers. For isotopes that exist as infinitesimal traces (a single atom in the presence of 1x10 stable atoms) there exist worldwide, a network of around 50 mass spectrometers, each derived from Van de Graaff accelerators, which are used for these analyses (Figure 16.28). 

In VoL 2 of this handbook, the origin of elements has been discussed in detail. Therefore, the present authors will exclude that part, except for some comments on the importance of particular radionucKdes. In this chapter, the principles and instrumentation of accelerator mass spectrometry (AMS), the key player for detection of cosmological radionucKdes in ultra trace scale, will be discussed in detail. Detailed discussion of all the research works carried out to date with cosmogenic radionuclides is out of scope. Only the detection of million-year half-life radionucKdes in ultra trace concentration will be touched, followed by concise description of the required chemistry. Rather than giving a general description, a few of them have been chosen and described in separate sections. Inductively coupled plasma-mass spectrometry (ICP-MS), thermal ionization mass spectrometry (TIMS), secondary ion mass spectrometry (SIMS), or resonant laser ionization mass spectrometer (RIMS), etc. have also been used for detection of cosmogenic radionucKdes. However, these techniques have much lower sensitivity compared to AMS. Brief discussions on these instruments have been appended at the end of this chapter. This chapter ends with a conclusion. 

Fig. 15.19. AMS facility of CBAMS. The instrument is typical for its kind. Note the scale bar for 1 m. CBAMS, founded in 1997, is the first private company in the world to offer a fully commercial analytical service using an accelerator mass spectrometer. Reproduced from Ref. [13] withpermission. John Wiley Sons, Ltd., 1999.

Figure 2 Schematic of the accelerator mass spectrometer at the Centre for AMS at Lawrence Livermore National Laboratory. Negative ions from a muiti-sampie ion source are separated by a low-energy mass spectrometer, accelerated to 6 MeV in an electrostatic accelerator, converted to positive ions by passage through a foil stripper, and accelerated again. Quadruply charged carbon atomic ions (30 MeV kinetic energy) are focused by quadrupole lenses and resolved by high-energy mass spectrometers, followed by velocity selection and identification of charge state in an ionization detector.

Accelerator mass spectrometry (AMS) Method of direct or ion counting of isotopes using particle accelerators as mass spectrometers. 

Wood and bone samples, chosen from each site, were radiocarbon dated using the technique of AMS in The Poznan Radiocarbon Laboratory. The laboratory is equip>p)ed with a accelerator mass spectrometer type 1,5 SDH-Pelletron, Model Compact Carbon AMS". 

Hopfgartner, G., Chernushevich, I. V., Covey, T., Plomley, J. B., and Bonner, R. (1999). Exact mass measurement of product ions for the structural elucidation of dmg metabolites with a tandem quadmpole orthogonal-acceleration time-of-flight mass spectrometer. J. Am. Soc. 

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