Intense bombardment

With arcs, intense bombardment by ions and electrons and the heat produced at the electrodes cause sample molecules to be vaporized and broken down into their constituent elements. These sources are used particularly for analysis or isotope studies when the samples involved are inorganic, nonvolatile, and thermally very stable. 

Silvery white, artificial element that is also generated by intensive bombardment of plutonium with neutrons. It is a strong ("hot") neutron emitter and is used in microgram quantities in nuclear medicine. This reliable neutron source is also used in industry and science (for activation analysis). 

All the early work on plutonium was done with unweighable amounts on a tracer scale. When it became apparent that large amounts would be needed for the atomic bomb, it was necessary to have a more detailed knowledge of the chemical properties of this element. Intensive bombardment of hundreds of pounds of uranium was therefore begun in the cyclotrons at Berkeley and at Washington University in St. Louis. Sepa-ration of plutonium from neptunium was based on the fact that neptunium is oxidized by bromate while plutonium is not, and that reduced fluorides of the two metals are carried down by precipitation of rare earth fluorides, while the fluorides of the oxidized states of the two elements are not. Therefore a separation results by repeated bromate oxidations and precipitations with rare earth fluorides. 

Hartmann, W. K., Ryder, G., Dones, L. and Grinspoon, D. (2000) The time-dependent intense bombardment of the primordial Earth/Moon system. In Origin of the Earth and Moon, eds. Canup, R. M. and Righter, K. Tucson University of Arizona Press, pp. 493-512. 

We have little evidence of what such a crust might have looked Uke. Unlike on the Moon and Mars, Earth appears to have no rock preserved that is more than 4.0 Gyr old. There was intense bombardment of the Moon until —3.9 Gyr ago (WetheriU, 1975b Hartmann et al., 2000 Ryder et al., 2000). Earth s earlier crust may therefore have been decimated by concomitant impacts. 

Sample discoloration may occur and is usually due to ionisation, (whereas overheating causes physical deformation). It affects only sensitive specimens under intense bombardment. The sensitivity depends inversely on the beam diameter. Some effects must be taken into account, such as the charging of insulating components, and the sputter removal of some components, which prevents repeat investigations. Image contrast may also arise from chemical or topographic rather than isotopic differences. 

Our solar system and the Earth are thought to be about 4.6 Ga (4.6 billion or 4.6 x 10 years) old (Fig. 1). Meteorite bombardment made the surface of our planet a rather inhospitable place during the first few hundred years after its formation, however, isotopic patterns in sediments from Greenland indicate that life already existed as early as 3.8 Ga ago. The upper limit for the emergence of life is set by the intense bombardment of the Earth between 3.9-4.1 Ga ago, which without doubt sterilized it, e.g., by boiling off the oceans. " destroying the prebiotic matter... 

---