Beryllium nuclides

Self-Test 17.2A Identify the nuclide produced and write the nuclear equation for (a) electron capture by beryllium-7 (b) positron emission by sodium-22. 

An important reaction used quite widely for this purpose is irradiation by neutrons and measurement of die energies of radiations emitted. The source of the neutrons may be a nuclear reactor, a particle accelerator, or an isotopic source, that is, a sealed container in which neutrons are produced by alpha rays emitted by a source such as radium, sodium-24(24Na), yttrium-88f8sY), etc., and arranged so that the alpha rays react-with a substance such as beryllium which in turn emits neutrons. The neutrons react with stable nuclides in the sample to produce radioactive ones. Thus... 

This reaction liberated 17.3 MeV, the mass afterwards being 0.0186 AMU less than before. Beryllium, fluorine, sodium and magnesium provide nuclides which undergo proton-induced reactions. Nitrogen-14 yields carbon-11, a positron-emitter with a half-life of twenty minutes. 

The development of more sensitive ways to measure levels of radioactive substances has allowed scientists to take advantage of the decay of nuclides other than carbon-14. For example, chlorine-36 can be used to date ground water, marine sediments can be dated by measuring levels of beryllium-11 and aluminum-26, and krypton-81 has been used to estimate the age of glacial ice. 

The nuclide gCf emits neutrons through spontaneous fission in 3% of all decays, the rest being a-decays. All the other neutron sources listed involve a radioactive nuclide whose decay causes a nuclear reaction in a secondary substance which produces neutrons. For example, ffSb produces neutrons in beryllium powder or metal as a result of the initial emission of 7-rays, in which case there is no coulomb barrier to penetrate. Radium, polonium, plutonium, and americium produce neutrons by nuclear reactions induced in beryllium by the a-particles from their radioactive decay. For the neutrons produced either by spontaneous fission in californium or by the a-particle reaction with beryllium, the... 

The first photonuclear activation for analytical purposes was performed with radionuclides as the activating radiation source. These applications were reported in the early 1950s, although apparently the first beryllium determinations by photodisintegration were performed in the late 1930s in the Soviet Union. The analytical detection power of photon activation analysis using radionuclide sources is poor and restricted to the analysis of deuterium, beryllium, several fissile nuclides, and a few nuclides that have low-lying isomeric states. Nonetheless, nuclide excitation is still in use. 

The light and fragile elements lithium, beryllium, and boron (LiBeB) are not primarily produced in primordial or stellar nucleosynthesis. In fact, the abundance curve in O Fig. 12.13 shows a huge dip (almost a gap, actually) for the mass numbers 8-11, reflecting the scarcity of LiBeB-nuclei in the solar system. Only the nuclide Li can be produced both in primordial (see Sect. 12.3) and in stellar nucleosynthesis (see Sect. 12.4.2), whereas the nuclides Li, Be, B, and B are almost pure spallation products of heavier elements. 

Not all routines accurately correct for coincidence summing with X-rays. This may be important, especially for heavy nuclides, but it is difficult to accurately correct because it varies greatly with detector window thickness and sample thickness. For this reason, detectors with thin beryllium windows should not be used with fco blAA unless samples are counted at distances of 10 cm or more. None of the routines correct for coincidence summing with beta rays. This maybe important for some short-lived light nuclides that emit high-energy betas in coincidence with gamma rays. In these cases, a 4 mm thick plastic absorber should be placed between sample and detector. 

Several actinide nuclides have found other applications. Heat sources made from kilogram amounts of Pu have been used to drive thermoelectric power units in space vehicles. In medicine, Pu was applied as a long-lived compact power unit to provide energy for cardiac pacemakers and artificial organs. Am has been used in neutron sources of various sizes on the basis of the (a,n) reaction on beryllium. The monoenergetic 59-keV y radiation of Am is used in a multitude of density and thickness determinations and in ionization smoke detectors. Cf decays by both a emission and spontaneous fission. One gram of Cf emits 2.4 10 neutrons per second. "Cf thus provides an intense and compact neutron source. Neutron sources based on Cf are applied in nuclear reactor start-up operations and in neutron activation analysis. 

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