Neutron high-energy, bombardment

In the second type of analysis, high-energy bombardment of soils with neutrons, on the other hand, leads to what is called neutron activation. Reemission of radiation from neutron-activated soil allows for the identification of the elements present. This type of analysis typically requires a source of high-energy neutrons and so requires special equipment [8],... 

The effects of high-energy bombardment of solids have been studied intensively in the last decade by many investigators (/). Large changes in the physical properties of materials are observed particularly upon fast massive particle irradiation, for example, by fast neutrons in a nuclear reactor, which results in the displacement of the atoms from their normal lattice positions. 

Activation analysis has become an important technique for the environmental biologist as well as for others. By means of bombardment with neutrons, high-energy photons, or charged particles, stable elements can be transformed to radionuclides. These radionuclides can be measured relatively easily, and the results can be interpreted in terms of die type and quantity of stable elements present in the sample of interest. Although several types of bombardment may be used to transform stable elements to radionuclides, slow neutrons are usually employed. Details concerning the procedure are described in many sources (e.g., Schulze, 1969 Hendee, 1973b). In addition, publications of direct interest to the environmental scientist are fairly numerous (Leddicotte, 1969 Byrne et aL, 1971 Pillay and Thomas, 1971 Filby and Shah, 1974). 

High-energy radiation may be classified into photon and particulate radiation. Gamma radiation is utilized for fundamental studies and for low-dose rate irradiations with deep penetration. Radioactive isotopes, particularly cobalt-60, produced by neutron irradiation of naturally occurring cobalt-59 in a nuclear reactor, and caesium-137, which is a fission product of uranium-235, are the main sources of gamma radiation. X-radiation, of lower energy, is produced by electron bombardment of suitable metal targets with electron beams, or in a... 

Americium does not exist in nature. All of its isotopes are man-made and radioactive. Americium-241 is produced by bombarding plutonium-239 with high-energy neutrons, resulting in the isotope plutonium-240 that again is bombarded with neutrons and results in the formation of plutonium-241, which in turn finally decays into americium-241 by the process of beta decay. Both americium-241 and americium-243 are produced within nuclear reactors. The reaction is as follows Pu + (neutron and X gamma rays) —> " Pu + (neutron and X gamma rays) —> Pu—> Am + beta minus ([ -) followed by " Am—> jNp-237 + Hej (helium nuclei). 

Because such small amounts of berkehum have been produced, not many uses for it have been found. One use is as a source for producing the element californium by bombarding isotopes of berkehum with high-energy neutrons in nuclear reactors. Berkelium is also used in some laboratory research. 

Man-made radioactive atoms are produced either as a by-product of fission of uranium atoms in a nuclear reactor or by bombarding stable atoms with particles, such as neutrons, directed at the stable atoms with high velocity. These artificially produced radioactive elements usually decay by emission of particles, such as positive or negative beta particles and one or more high energy photons (gamma rays). Unstable (radioactive) atoms of any element can be produced. 

Only about 300 of the more than 3600 known isotopes occur naturally. The remainder have been made by nuclear transmutation, the change of one element into another. Such transmutation is often brought about by bombardment of an atom with a high-energy particle such as a proton, neutron, or a particle. In the ensuing collision between particle and atom, an unstable nucleus is momentarily... 

Studies of the effect of neutron irradiation are divided into three groups slow or thermal neutrons, fission products and reactor neutrons. The slow neutrons are obtained from a radioactive source or high energy neutrons that are produced by deuterium bombardment of a beryllium target in a cyclotron and slowed down passing thru a thick paraffin wax block. The fission products in one case are produced when a desired sample is mixed or coated with uranium oxide and subsequently irradiated with slow neutrons. The capture of neutrons by U23S leads... 

Spallation occurs in a particle accelerator when a high-energy proton bombards a heavy atomic nucleus, resulting in some neutrons being knocked out or spalled . 

Tritium is formed in the upper atmosphere by bombardment of nitrogen, oxygen and carbon by high energy protons and by capture of cosmic-ray generated neutrons by nitrogen... 

Neutron activation analysis is based upon the production of radioisotopes by nuclear reactions resulting from neutron bombardment, followed by identification and measurement of the different radioisotopes formed. Element activation can also be carried out by bombardment with high-energy charged particles, X-rays or gamma rays (5). 

Carboranes in Boron Neutron Capture Therapy of Cancer (B7YC2). The stable isotope of boron, B (19.8% natural abundance), is very effective as a neutron capture agent with the effective nuclear cross section of 3837 bams, while the "B nucleus is incapable of undergoing a BNC reaction. Therefore, the B-emiched carborane and borane-substituted biomolecules and dmgs are selectively dehvered to the cancer cells in the human body and then the tumor-localized B nucleii are bombarded with either thermal or epithermal neutrons that results in a fission reaction producing the high energy alpha (a) particles as shown in equation (2). 

Both high amounts of mass and high velocity can be used experimentally (artificially) to contrive releases of large amounts of energy such as neutron activation by bombarding an atom. 

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