PubMed · 13628972
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H ATKINS. 1959. Ionizing radiations and the surgeon.. https://doi.org/10.1259/0007-1285-32-374-72
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The spatial response of an 8 x 4 block detector made up of 5.6-mm-wide, 12.9-mm-high, 30-mm-thick individual detector crystals to a collimated line source of 511 keV annihilation photons was examined. The response of each crystal showed a spread around the average positioning values and distributions from adjacent crystals overlapped as the collimated source scanned the individual detectors. This leads to possible errors in the event assignment. The implementation of double differentiation or the second derivative method was proposed for the removal of scattered photons so as to reduce the overlap and, hence, avoid mis-positioning. This method is a mathematical solution implemented when analysing the results. A curve in a spatial spectrum could be considered to be a function f(x), where x is the position. When double differentiation of f(x) is carried out, then the normalized curve d2f(x) appears with some reduction in the wings. It was shown that a reduction of the scattering contribution in the tails without overestimating the contribution of scattered events could be achieved by implementing a double-differentiation process.
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Improving Keszthelyi's simple model the evolutionary appearance of concentration difference of enanthiomeric compounds due to their differential decomposition by beta-rays is investigated taking into account the racemization as well. It is shown that if the difference in the cross sections is very small then the resulting concentration difference will never exceed the statistical fluctuations, while in the case of a sufficiently large difference in the cross sections the concentration difference can overgrow the statistical fluctuations in an evolutionary reasonable period of time. The relative difference of the concentrations, however, will be generally much smaller than that of the cross sections. Therefore some other, amplifying mechanism must be postulated in order to explain the optical purity of living beings.