380 research outputs found
Prompt Gamma Activation Analysis (PGAA): Technique of choice for nondestructive bulk analysis of returned comet samples
Prompt gamma activation analysis (PGAA) is a well-developed analytical technique. The technique involves irradiation of samples in an external neutron beam from a nuclear reactor, with simultaneous counting of gamma rays produced in the sample by neutron capture. Capture of neutrons leads to excited nuclei which decay immediately with the emission of energetic gamma rays to the ground state. PGAA has several advantages over other techniques for the analysis of cometary materials: (1) It is nondestructive; (2) It can be used to determine abundances of a wide variety of elements, including most major and minor elements (Na, Mg, Al, Si, P, K, Ca, Ti, Cr, Mn, Fe, Co, Ni), volatiles (H, C, N, F, Cl, S), and some trace elements (those with high neutron capture cross sections, including B, Cd, Nd, Sm, and Gd); and (3) It is a true bulk analysis technique. Recent developments should improve the technique's sensitivity and accuracy considerably
A hybrid, asymmetric, linear Higgs factory based on plasma-wakefield and radio-frequency acceleration
The construction of an electron--positron collider "Higgs factory" has been
stalled for a decade, not because of feasibility but because of the cost of
conventional radio-frequency (RF) acceleration. Plasma-wakefield acceleration
promises to alleviate this problem via significant cost reduction based on its
orders-of-magnitude higher accelerating gradients. However, plasma-based
acceleration of positrons is much more difficult than for electrons. We propose
a collider scheme that avoids positron acceleration in plasma, using a mixture
of beam-driven plasma-wakefield acceleration to high energy for the electrons
and conventional RF acceleration to low energy for the positrons. We emphasise
the benefits of asymmetric energies, asymmetric bunch charges and asymmetric
transverse emittances. The implications for luminosity and experimentation at
such an asymmetric facility are explored and found to be comparable to
conventional facilities; the cost is found to be much lower.Comment: 13 pages, 3 figures, 3 table
Dead Time, Pileup, and Accurate Gamma-Ray Spectrometry
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58611/1/R&R.pd
The half-life of 76 As
In the course of making high-accuracy measurements of arsenic, we found that the most recently published and compiled half-life of 76 As did not agree with our data as well as the earlier accepted value. To redetermine this parameter, 76 As sources were measured on four Ge gamma detector systems, and an exponential function was fitted to the decay data by two different nonlinear least-squares methods. We obtained T 1/2 = 1.09379 days with a standard uncertainty of 0.00045 days. This result is 1.5% higher than the most recent value, but is in agreement with the older, less precise, consensus value.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43130/1/10967_2004_Article_5117002.pd
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