Cosmics removal

Zhao J. Image curvature correction and cosmic removal for high-throughput dispersive Raman spectroscopy. Applied Spectroscopy 2003, 57, 1368-1375. 

Figure 8.34. Cosmic removal from a single spectrum of bacteriorhodopsin by smoothing routines. A is original spectrum, with asterisks indicating cosmics. B is after a conventional quadratic, 9 point Savitsky Golay smooth. C is after a similar smooth, but including the missing point routine. Adapted from Reference 30 with permission.

Consider you have forgotten to switch on multi-read 28 with your CCD detector and the raw data are full of cosmic-ray spikes. How do you remove them without spoiling the image ... 

The decay of radioactive isotopes created in the earth s atmosphere by the interaction of cosmic rays with atomic nuclei of atmospheric constituents. After such nuclei (e.g., 3H as 3HH0 or 14C as 14C02) are removed from the atmosphere, e.g., fed into a groundwater system (3H) or built into a living organism (14C), their number decreases according to the law of radioactive decay. 

The amplitude attenuation factor, 1 + (tu/Ai)2 for nuclides satisfying relation [14], for various values of Ax and T are presented in figure 9. It is obvious from figure 9 that the attenuation is minimal when Ai > u>, i.e., when the removal residence time of the nuclide from sea water is less than the period in the variation of cosmic ray intensity. 

A single channel pulse height analyser utilizes an electronic gate typically 0.1 V wide, which only accepts pulses between the preset upper and lower limits. Scintillation counters frequently employ such devices to remove small noise pulses and large pulses initiated by cosmic rays, as well... 

In addition to cosmic ray spallation also produces many other radioactive nuclides. °Be is another example. Once cosmogenically produced, atoms of °Be are rapidly removed from the atmosphere by meteoric precipitation, and are absorbed onto surfaces of solid particles such as clay minerals. Hence, newly formed marine sediment contains some initial concentration of °Be. After removal from the atmosphere, the concentration of °Be in sediment decays away by p-decay to °B with a half-life of 1.51 million years (and a decay constant of 4.59 X 10 yr ). 

In Chapter 1 and again above, we introduced the cosmochemical classification of elements based on their relative volatilities in a system of cosmic (solar) composition. In a cooling solar gas, elements condense in a certain order, depending on their volatility (Table 7.1). Condensation and evaporation partition elements between coexisting gas and solid (or liquid) phases, and the removal of one or the other of these phases can fractionate element abundances of the system as a whole from their original cosmic relative proportions. 

In INAA, a rock or mineral sample is irradiated in the reactor. The irradiated sample is removed from the reactor, and the dangerous radioactivities are allowed to decay. Then the sample is placed into a counter and the y-rays emitted by each element in the sample are counted. A variety of counters are used, including scintillation counters, gas ionization counters, or semi-conductor counters. For the most precise results, background counts in the detectors produced by electronic noise, cosmic rays, and other radioactive decays must be eliminated. The technique is very sensitive, and samples as small as a few tens of milligrams can be measured. 

Cosmic rays hit the CCD array at random times with arbitrary intensity, resulting in spikes at individual pixels. When the array is summed and processed, sharp spectral features of arbitrary intensities may appear in the Raman spectra. These artifacts are typically removed before multivariate calibration. 

Calcium-aluminum-rich inclusions (CAIs) After removing the progressive mass-dependent fractionation that occurs in the measuring process and in the formation process for the samples, isotopic anomalies for 7°Zn are observed in certain types of CAIs ( FUN inclusions). Only one detection exists to date, a deficit of 2 parts per thousand for 7°Zn in one FUN inclusion. An excess of 1.7 parts per thousand for 66Zn exists in that same CAI. Some form of cosmic chemical memory (see Glossary) is probably involved. 

---