Radioactive stability

Figure 10.2 The radioactive stability of the elements. The x axis is proton number (up to Z = 83, bismuth), the y axis the neutron number (N). Stable isotopes are shown in black and radioactive isotopes in grey, indicating the relative excess of radioactive isotopes over stable isotopes in nature, and the fact that as proton number increases, the neutron number has to increase faster to maintain stability. The basic data for this figure are given in Appendix VI.

To clarify the purity, labeling site, specific radioactivity, stability, the guidance on repeated dose tissue distribution studies is to be referred in the Notification No. 442 of the PAB in July 1996. 

Atoms with the same number of protons but a different number of neutrons are called isotopes. To identify an isotope we use the symbol E, where E is the element s atomic symbol, Z is the element s atomic number (which is the number of protons), and A is the element s atomic mass number (which is the sum of the number of protons and neutrons). Although isotopes of a given element have the same chemical properties, their nuclear properties are different. The most important difference between isotopes is their stability. The nuclear configuration of a stable isotope remains constant with time. Unstable isotopes, however, spontaneously disintegrate, emitting radioactive particles as they transform into a more stable form. 

Sulfur polymer cement shows promise as an encapsulation and stabilization agent for use with low level radioactive and mixed wastes. Use of SPC allows accommodation of larger percentages of waste than PCC. As of this writing (1997), SPC-treated waste forms have met requirements of both the Nuclear Regulatory Commission (NRC) and the Environmental Protection Agency (EPA). 

Applicability Limitation Vitrification was originally tested as a means of solidification/immobilization of low level radioactive materials. It may also be useful for forming barrier walls. This latter use needs testing and evaluation to determine how uniform the wall would be and to evaluate the stability of the material over a period of time. 

Applicability Most hazardous waste slurried in water can be mixed directly with cement, and the suspended solids will be incorporated into the rigid matrices of the hardened concrete. This process is especially effective for waste with high levels of toxic metals since at the pH of the cement mixture, most multivalent cations are converted into insoluble hydroxides or carbonates. Metal ions also may be incorporated into the crystalline structure of the cement minerals that form. Materials in the waste (such as sulfides, asbestos, latex and solid plastic wastes) may actually increase the strength and stability of the waste concrete. It is also effective for high-volume, low-toxic, radioactive wastes. 

Deactivation and D D actions can range from stabilization of multiple hazards at a single site or facilities containing chemical or radioactive contamination, or both, to routine asbestos and lead abatement in a nonindustrial structure. Strategies include programs that meet compliance objectives, protect workers, and make certain that productivity and cost-effectiveness are maintained. The content and extent of health and safety-related programs should be proportionate to the types and degrees of hazards and risks associated with specific operations. 

Waste management is a field that involves tlie reduction, stabilization, and ultimate disposal of waste. Waste reduction is tlie practice of minimizing file amount of material tliat requires disposal. Some of the common ways in which waste reduction is accomplished are incineration, compaction, and dewatering. The object of waste disposal is to isolate tlie material from tlie biosphere, and in the case of radioactive wtiste, allow it time to decay to sufficiently safe levels. 

Since the radioactive half-lives of the known transuranium elements and their resistance to spontaneous fission decrease with increase in atomic number, the outlook for the synthesis of further elements might appear increasingly bleak. However, theoretical calculations of nuclear stabilities, based on the concept of closed nucleon shells (p. 13) suggest the existence of an island of stability around Z= 114 and N= 184. Attention has therefore been directed towards the synthesis of element 114 (a congenor of Pb in Group 14 and adjacent superheavy elements, by bombardment of heavy nuclides with a wide range of heavy ions, but so far without success. 

The ratios of stable isotopes (red dots) fall within a narrow range, referred to as the "belt of stability." For light isotopes of small atomic number the stable ratio is 1 1. For heavier isotopes the ratio gradually increases to about 1.5 1. Isotopes outside the band of stability are unstable and radioactive. There are no stable isotopes for elements of atomic number greater than 83 (Bi). 

Radioactivity The ability possessed by some natural and synthetic isotopes to undergo nuclear transformation to other isotopes, 513 applications, 516-518 biological effects, 528-529 bombardment reactions, 514-516 diagnostic uses, 516t discovery of, 517 modes of decay, 513-514 nuclear stability and, 29-30 rate of decay, 518-520,531q Radium, 521-522 Radon, 528 Ramsay, William, 190 Random polymer 613-614 Randomness factor, 452-453 Raoult s law A relation between the vapor pressure (P) of a component of a solution and that of the pure component (P°) at the same temperature P — XP°, where X is the mole fraction, 268... 

There are three common ways by which nuclei can approach the region of stability (1) loss of alpha particles (a-decay) (2) loss of beta particles (/3-decay) (3) capture of an orbital electron. We have already encountered the first type of radioactivity, a-decay, in equation (/0). Emission of a helium nucleus, or alpha particle, is a common form of radioactivity among nuclei with charge greater than 82, since it provides a mechanism by which these nuclei can be converted to new nuclei of lower charge and mass which lie in the belt of stability. The actinides, in particular, are very likely to decay in this way. 

Principal advantages of 7-rays over polychromatic x-rays- (1) Greater source stability (radioactive isotopes as compared with x-ray tubes) (2) simpler equipment (3) greater compactness of source (4) beams more nearly monochromatic (5) wider energy range available, 2(IQ4) to 2(107) ev (6) lower cost ... 

We can use Fig. 17.13 to predict the type of disintegration that a radioactive nuclide is likely to undergo. Nuclei that lie above the band of stability are neutron rich they have a high proportion of neutrons. These nuclei tend to decay in such a way that the final n/p ratio is closer to that found in the band of stability. For example, a l4C nucleus can reach a more stable state by ejecting a (3 particle, which reduces the n/p ratio as a result of the conversion of a neutron into a proton (Fig. 17.15) ... 

The pattern of nuclear stability can be used to predict the likely mode of radioactive decay neutron-rich nuclei tend to reduce their neutron count proton-rich nuclei tend to reduce their proton count. In general, only heavy nuclides emit a particles. 

Use the band of stability to predict the types of decay that a given radioactive nucleus is likely to undergo (Self-Test 17.3). 

The other numbers are 0 (absence of secondary danger), 2 (gas), 3 (flammable liquid already seen), 6 (toxic material), 7 (radioactive material), 8 (corrosive materials). When different figures are put together it leads to more or less complicated risk clauses. Thus 265 refers to oxidising toxic gases. The code is a stability as well as a reactivity one, as can be seen. 

---