Cross bombardment

Assignment of an atomic number to a new radioactive nuclide is generally simpler than assignment of a mass number. The latter is sometimes accomplished by the method of cross bombardments, illustrated in Exercise 14. 

The bombardment of natural zinc (isotopes 64. 66. 67, 68, and 70) with slow neutrons yields 3 different radioactive isotopes of zinc, which we may designate as A, B, and C. These are identified by the method of cross bombardment as follows ... 

Other reactions with charged particles may be discussed in a similar way. In reactions with y-ray photons the compound nuclei are excited states of the target nuclei and may give off their excitation energy by emission of particles. It is evident from Fig. 8.11 that the same nuclides can be produced by application of various nuclear reactions, and by the method of cross bombardment radionuclides can be identified. 

Indirect methods such as half-life systematics, excitation functions for the production reactions, and cross bombardments have been used to reinforce this information. In order to positively identify the atomic number of a spontaneously fissioning nuclide from detection of the fragments, the atomic numbers of both primary fragments from the same SF event must be determined in coincidence and added together to determine the Z of the new, unknown fissioning nuclide. Detection of only SF decay has resulted in much controversy concerning discovery and identification of the transactinide elements. 

The strategy of the Dubna group is to build up a region of nuclides in an internally consistent manner where descendants appearing in decay chains are, in addition, directly synthesized by the complete fusion of heavy ions including using the technique of cross bombardments (O Fig. 19.5). Thus, if one nuclide in this region is safely identified, the whole island is fixed. This process explains the importance of the recent experiment (Hofmann... 

Also in 1974, Oganesyan and co-workers of JINR, Dubna, reported the production of spontaneously fissioning nuclei with a half-life of several milliseconds in bombardments of Pb and Pb with Cr ions [96]. On the basis of their new understanding of spontaneous-fission systematics derived from studies on elements 100-104 and from the results of cross-bombardments of targets of different Pb and Bi isotopes with V, Cr, and Cr ions, the Dubna... 

In early 1941, 0.5 )-lg of Pu was produced (eqs. 3 and 4) and subjected to neutron bombardment (9) demonstrating that plutonium undergoes thermal neutron-induced fission with a cross section greater than that of U. In 1942, a self-sustaining chain reaction was induced by fissioning 235u... 

Imagine an emulsion formed of suspended particles all exactly alike, and contained in a vertical cylinder of unit cross-section. The state of a horizontal slice contained between the levels h and h - - dh would not be changed if we enclosed it between two semipermeable pistons which allow the molecules of water to pass, but stop those of the gamboge. Each piston experiences an osmotic pressure, by reason of its bombardment by gamboge particles, and if there are n particles per unit volume at height h... 

In charge exchange collisions the cross-section depends upon the energetics of the reaction. To compute the energy defect, the initial and final states of the colliding particles must be specified. This can be done easily for the bombarded neutral molecule, which usually can be assumed to be in the ground state before the collision, but not for the incident ion which is often in one of its metastable states. 

The use of ionizing radiation to induce cross-linking is another important technique for producing hydrogels from linear water-soluble polymers. When such polymers are bombarded by ionizing radiation, either in the bulk state or in solu-... 

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