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Record 1 2010-02-10


Subject field(s)
  • Analytical Chemistry
  • Radiological Physics (Theory and Application)

NIST [National Institute of Standards and Technology] researchers have implemented a novel approach to cavity ring-down spectroscopy (CRDS) using pulsed lasers. The ring-down method exploits the finite lifetime of light within an optical resonator, which is manifest as an exponential decay of the photon flux exiting the cavity. This lifetime measurement can be used to determine the presence of trace quantities of gaseous molecules, because the photon lifetime decreases as a result of light absorption within the cavity.


Lifetime measurement. The activity (in decays per second) of some radioactive samples varies in time in a particularly simple way. If the activity (R) in decays per second of a sample is proportional to the amount of radioactive material (R [alpha] N, where N is the number of radioactive nuclei), then the activity must decrease in time exponentially …


  • Chimie analytique
  • Physique radiologique et applications

Dans la mesure du temps de vie avec un faisceau de positons lents, plusieurs méthodes sont utilisées pour générer un signal qui marque l’entrée du positon dans le solide. Par exemple, la détection des électrons secondaires émis lors de l’entrée du positon dans le solide permet d’obtenir une résolution en temps de l’ordre de 500 ps [picosecondes]. Cette résolution est suffisante pour l’étude des polymères mais reste insuffisante pour les métaux ou les semi-conducteurs, matériaux pour lesquels les temps de vie du positon sont de l’ordre de 100 ps à 250 ps.


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