Skip to main content Accessibility help

We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.

Close cookie message
×
Home
  • Home

Refine search

Refine search

Access:
Content type:
Publication date:
Apply
Subject: Show more
Journals Show more
Publishers: Show more
Societies Show more
Series: Show more
Collections: Show more

Actions for selected content:

Select all | Deselect all
  • View selected items
  • Export citations
  • Download PDF (zip)
  • Send to Kindle
  • Send to Dropbox
  • Send to Google Drive

Save Search

You can save your searches here and later view and run them again in "My saved searches".

Please provide a title, maximum of 40 characters.
Cancel
×

123 results

Page 1 of 7

  • 14C AMS Measurements of <100 μG Samples with a High-Current System
  • Karl F. Von Reden, Ann P. McNichol, Ann Pearson, Robert J. Schneider
  • Journal: Radiocarbon / Volume 40 / Issue 1 / 1997
  • Published online by Cambridge University Press: 18 July 2016, pp. 247-253
  • Print publication: 1997
    • Article
    • Access
    • PDF
    • Export citation
  • View abstract

    The NOSAMS facility at Woods Hole Oceanographic Institution has started to develop and apply techniques for measuring very small samples on a standard Tandetron accelerator mass spectrometry (AMS) system with high-current hemispherical Cs sputter ion sources. Over the past year, results on samples ranging from 7 to 160 μg C showed both the feasibility of such analyses and the present limitations on reducing the size of solid carbon samples. One of the main factors affecting the AMS results is the dependence of a number of the beam optics parameters on the extracted ion beam current. The extracted currents range from 0.5 to 10 μA of 12C− for the sample sizes given above. We here discuss the setup of the AMS system and methods for reliable small-sample measurements and give the AMS-related limits to sample size and the measurement uncertainties.

  • Microscale AMS 14C Measurement at NOSAMS
  • Ann Pearson, Ann P. Mcnichol, Robert J. Schneider, Karl F. Von Reden, Yan Zheng
  • Journal: Radiocarbon / Volume 40 / Issue 1 / 1997
  • Published online by Cambridge University Press: 18 July 2016, pp. 61-75
  • Print publication: 1997
    • Article
    • Access
    • PDF
    • Export citation
  • View abstract

    Techniques for making precise and accurate radiocarbon accelerator mass spectrometry (AMS) measurements on samples containing less than a few hundred micrograms of carbon are being developed at the NOSAMS facility. A detailed examination of all aspects of the sample preparation and data analysis process shows encouraging results. Small quantities of CO2 are reduced to graphite over cobalt catalyst at an optimal temperature of 605°. Measured 14C/12C ratios of the resulting targets are affected by machine-induced isotopic fractionation, which appears directly related to the decrease in ion current generated by the smaller sample sizes. It is possible to compensate effectively for this fractionation by measuring samples relative to small standards of identical size. Examination of the various potential sources of background 14C contamination indicates that the sample combustion process is the largest contributor, adding ca. 1 μg of carbon with a less-than-modern 14C concentration.

The Grammar of Science
  • The Grammar of Science
  • Karl Pearson
  • Published online: 05 June 2015
  • Print publication: 18 December 2014
  • View description
    First published in 1892, this important work by the mathematician Karl Pearson (1857–1936) presents a thoroughly positivist account of the nature of science. Pearson claims that 'the scientific method is the sole gateway to the whole region of knowledge', rejecting additional fields of inquiry such as metaphysics. He also emphasises that science can, and should, describe only the 'how' of phenomena and never the 'why'. A scholar of King's College, Cambridge, and later a professor at King's College and University College London, Pearson made significant contributions to the philosophy of science. Including helpful chapter summaries, this book explores in detail a number of scientific concepts, such as matter, energy, space and time. The work influenced such thinkers as Albert Einstein, who considered it to be essential reading when he created his study group, the Olympia Academy, at the age of twenty-three.

Page 1 of 7