54 research outputs found
Imaging SIMS with an accelerator (and biomedical applications)
No full textThe combination of a scanning secondary ion source and an accelerator mass spectrometer is a powerful tool for performing imaging secondary ion mass spectrometry, offering various fundamental and operational advantages over conventional high performance magnetic sector instruments. Not only are lower concentrations detectable by AMS, but even at conventionally measurable levels the analysis of desirable surface areas (even greater than can be achieved conventionally with dynamic emittance matching) can be simpler, more sensitive and/or faster by AMS. This is principally a consequence of the large and constant spectrometer acceptance. These benefits are being explored with developments of the Oxford 14C-AMS system. This method is ideally suited to quantitative imaging of radiocarbon labels widely employed in biomédical research to tag specific molecules, is capable of the most sensitive detection and submicron resolution and potentially offers considerable advantages over traditional radiographic imaging
Microbeam PIXE analysis using wavelength dispersive spectrometry
No full textWavelength dispersive X-ray spectrometry (WDS) offers significant advantages over energy dispersive X-ray spectrometry for PIXE analysis in some situations. Compared with energy dispersive Si(Li) detectors, the better energy resolution of WDS results in better separation of closely spaced adjacent X-ray peaks and enhanced signal to background ratios. These can result in greater accuracy in quantitative analysis, and increased sensitivity for trace element analysis. In addition, it is possible to analyze elements from beryllium upwards (Z ≥ 4). We have installed a commercial WDS detector on a nuclear microprobe system located at Lawrence Livermore National Laboratory. Advantages and limitations of wavelength dispersive spectrometry and considerations for calibration and operation are discussed. Representative results are presented for micro-PIXE analysis
The design of a radiocarbon muprobe for tracer mapping in biological specimens
No full textBiological scientists use radioisotopes to label and subsequently monitor specific molecules within living systems. We aim to improve on conventional methods of imaging 14C tracers, in both sensitivity and resolution, by combining a new scanning-beam ion source generating C− secondary ions with our AMS system.
Our measurements, including that of the generation of sufficient C− ions to the quantity of tissue sputtered, demonstrate that the radiocarbon muprobe is feasible, and we expect its sensitivity to be 1 14C label atom in 2000.
We have employed the negative ion production enhancing effect of surface caesiation, investigating the potential of a Cs vapour spray for this purpose. As suitable Cs+ ion sources are unavailable, the muprobe will feature a Cs spray to compensate for the lack of primary beam surface caesiation, in conjunction with a 0.2 μm spot Ga+ beam
Imaging AMS
No full textThe benefits of simultaneous high effective mass resolution and large spectrometer acceptance that accelerator mass spectrometry has afforded the bulk analysis of material samples by secondary ion mass spectrometry may also be applied to imaging SIMS. We are exploring imaging AMS with the addition to the Oxford 14C-AMS system of a scanning secondary ion source. It employs a sub-micron probe and separate apparatus for caesiating sample surfaces to further increase the useful ion yield. The source has been accommodated on the system by directly injecting sputtered ions into the accelerator without mass analysis. They are detected with a range of devices including new Si detectors. Qualitative mass spectra may be easily generated by varying only the post-accelerator analysis magnet. Selected ion signals may be used for imaging. In developing the instrument for bioscience research we are establishing its capability for measuring the lighter elements prevalent in biological tissue. Importantly, the machine can map the distributions of radiocarbon labeled compounds with an efficiency of about 1‰. A background due to misidentification of non-14C ions as a result of the reduced ion mass filtering is too small to hinder high magnification microscopy
Single-stage accelerator mass spectrometer radiocarbon-interference identification and positive-ionisation characterisation
No full textA single-stageaccelerator mass spectrometer (SSAMS) is a good alternative to conventional spectrometers based on tandem electrostatic acceleration for radiocarbon measurement and permits experimentation with both negative and positive carbon ions. However, such <sup>14</sup>C AMS of either polarity ions is limited by an interference. In the case of anion acceleration we have newly determined this to be summed <sup>13</sup>C and <sup>16</sup>O by improvising an additional Wien filter on our SSAMS deck. Also, <sup>14</sup>C AMS might be improved by removing its dependency on negative-ionisation in a sputter ion source. This requires negative-ionisation of sample atoms elsewhere to suppress the <sup>14</sup>N interference, which we accomplish by transmitting initially positive ions through a thin membrane. The ionisation dependence on ion-energy is found to be consistent with previous experimentation with vapours and thicker foils
Cl can interfere with Al<sup>3+</sup> AMS but B need not matter to Be measurement
No full textAl AMS can be subject to particle detector ion interference despite effective <sup>26</sup>Mg suppression and molecule digestion. Using our thinnest-yet 30 nm SiN membrane detector window to best separate four signals close to the 16 MeV <sup>26</sup>Al<sup>3+</sup> ions we identify <sup>35</sup>Cl<sup>4+</sup> interference consistent with molecular-dissociation before the accelerator, in addition to <sup>9</sup>Be<sup>1+</sup> and <sup>17</sup>O<sup>2+</sup> ions. The problem is likely generic and possibly applies to other charge-states too.
Separately we have measured highly borated beryl <sup>10</sup>Be blank samples to confirm the insensitivity to <sup>10</sup>B<sup>3+</sup> interference of our two different detector arrangement for <sup>10</sup>Be<sup>3+</sup> AMS. Be AMS correction for B is unnecessary, and is also invariant of <sup>9</sup>Be beam current
Positive ion AMS with single stage accelerator and RF-plasma ion source at SUERC
No full textThe new single-stageaccelerator mass spectrometer at SUERC can also accept positiveions. Potential benefits of positiveion measurement with suitable ionsources are more convenient sample form, smaller sample size, a variety of available charge states and maybe new applications. We have begun with oxygen isotope analyses to demonstrate destruction of interfering molecules
Cosmogenic <sup>10</sup>Be and <sup>26</sup>Al ages of Holocene moraines in southern Norway I: testing the method and confirmation of the date of the Erdalen Event (<i>c</i>. 10 ka) at its type-site
No full textCosmogenic nuclide dating (10Be and 26Al) is applied to boulders on two moraine ridges at the type-site of the early-Holocene Erdalen Event, southern Norway, dated previously using radiocarbon. Quartz-rich rock samples yielded 10Be age estimates between 9.8 ± 1.2 and 10.1 ± 1.1ka (external uncertainties, ±1σ), with an average of 9.95 ka. These age estimates are statistically indistinguishable from the independent radiocarbon age estimate. 26Al age estimates, which ranged from 9.4 ± 1.1 to 11.2 ± 1.3 ka, provided useful corroboration of the 10Be results. Although current levels of precision and accuracy are insufficient to distinguish between the ages of younger inner and older outer moraines, the results demonstrate the potential of the method at suitable sites where radiocarbon dating is not possible. Several environmental factors, including effective glacial erosion, stability of moraine sloes, snow cover of sufficiently shallow depth and short duration, and the absence of colluvial contamination, appear to have been instrumental in the success of applying the method at this site. The results confirm the timing and extent of the Erdalen Event in southern Norway with implications for Holocene glacier chronology and millennial-scale climatic variability
Improved 10Be and 26Al AMS with a 5 MV spectrometer
No full textDetector and ion source changes have increased Be and Al count rates and reduced measurement background at SUERC. Low energy 16 MeV 26Al3+ ions can be separated from interferences by adopting thin silicon nitride membrane detector windows. In contrast, a thick Havar detector window is used to preferentially slow boron ions for simplified 10Be vs. 10B separation without an additional gas cell
Performance of the new single stage accelerator mass spectrometer at the SUERC
No full textA NEC 250 kV single stage accelerator mass spectrometer (SSAMS) has been installed along-side our five year old 5 MV spectrometer. The new instrument is intended to take over routine radiocarbon measurement, thereby providing more capacity for our rapidly growing cosmogenic nuclide programme. Initial tests show that although flawed the SSAMS sufficiently mimics the good performance of the first machine; high-precision 14C/13C measurement is being achieved with a background limited by sample preparation
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