Decay forms

Because the path of the s process is blocked by isotopes that undergo rapid beta decay, it cannot produce neutron-rich isotopes or elements beyond Bi, the heaviest stable element. These elements can be created by the r process, which is believed to occur in cataclysmic stellar explosions such as supemovae. In the r process the neutron flux is so high that the interaction hme between nuclei and neutrons is shorter that the beta decay lifetime of the isotopes of interest. The s process chain stops at the first unstable isotope of an element because there is time for the isotope to decay, forming a new element. In the r process, the reaction rate with neutrons is shorter than beta decay times and very neutron-rich and highly unstable isotopes are created that ultimately beta decay to form stable elements. The paths of the r process are shown in Fig. 2-3. The r process can produce neutron-rich isotopes such as Xe and Xe that cannot be reached in the s process chain (Fig. 2-3). 

Solution of this equation gives the exponential decay form of the transient excited Si molecule ... 

Figure 8.3 Fission processes. The uranium nucleus can split in many ways, of which two are shown here. Since fission fragments tend to be heavier with neutrons than stable isotopes of the same element, they each begin a sequence of beta decays, forming elements from virtually every group across the periodic table, including transition elements.

For a short range potential acting on the interface due to the wall, one considers an exponentially decaying form, i.e. for the lower wall... 

In continuous lifetime analysis, a PAL spectrum is expressed in a continuous decay form [20] ... 

The formation of most of the heavy elements occurs in one of two processes of neutron capture the s-process or the r-process. These two broad divisions are distinguished on the basis of the relative lifetimes for neutron captures (Xn) and electron decays (t ). The condition that t > where Tp is a characteristic lifetime for /3-unstable nuclei near the valley of /3-stability, ensures that as captures proceed the neutron-capture path will itself remain close to the valley of /3-stability. This defines the s-process. In contrast, when it follows that successive neutron captures will proceed into the neutron-rich regions off the /3-stable valley. Following the exhaustion of the neutron flux, the capture products approach the position of the valley of /3-stability by /3-decay, forming the r-process nuclei. The s-process and r-process patterns in solar system matter are those shown in Figure 2. 

Aspartame is completely metabolized in the gut and absorbed as aspartic acid, phenylalanine, methanol, and diketopiperazine. Above 86°F, the methanol in aspartame decays forming formaldehyde and formic acid. When ingested, methanol attacks the eyes, CNS, and the GI tract and can damage the liver and kidneys. I26l Formaldehyde and formic acid are corrosive to mucous membranes and can result in liver and kidney injury and disease when ingested. I26l Formic acid is an established human toxin. Phenylalanine is believed to mediate or exacerbate hepatic encephalopathy. I44,45 ... 

This extremely heavy uranium isotope underwent radioactive decay, forming successively heavier transuranium elements, including isotopes of elements 99 and 100. 

Euncriniui/ Decay Form of ActivityReaaion Order Differential Fonn Integral Fttrm Examples... 

Since each radioactive decay forms one atom of a different element, the accumulation of the daughter product can be followed as a function of time. This build-up can be expressed by the following equation ... 

Transient bivalent gold ions and two unidentified species, possibly Au°, were prepared and stiuded in different aqueous matrices by pulse radiolysis. Their absorption spectra and rate constants of formation and decay are reported. Bivalent gold was prepared by the oxidation of Au(CN)2 in neutral chloride solutions of N20, and also by the reduction of AuClf in the presence of CH3OH. The kinetics of its decay indicates disproportionation. The reduced species of Au(CN)2 from H atoms is different from that obtained with e aq, the latter being attributed to an electron adduct. Both of these species decay, forming colloidal gold. 

Successive neutron capture in Pu (as occurs in nuclear reactors) produces isotopes of plutonium which undergo 0 -decay, forming transplutonium elements with atomic numbers 95 (americium) and 96 (curium) (Fig. 16.2). The reaction sequence is... 

The used fiiel elemmts may later be reprocessed to recover the remaining amount of fissile material as well as any fertile material or regarded as waste fertile atoms are those which can be transformed into fissile ones, i.e. " Th and U, which through neutron capture and jS-decays form fissile and Pu, respectively. The chemical reprocessing removes the fission products and actinides other than U and Pu. Some of the removed elements might be valuable enough to be isolated although this is seldom done. The mixed fission products and waste actinides are stored as radioactive waste. The recovered fissile materials may be refabricated (the U may require re-enrichment) into new elements for reuse. This "back-end" of the nuclear fuel cycle is discussed in Chapter 21. 

Table III. Products Yield in the Gas-Phase Reactions of Decay-Formed CT3CX) Ions...

Table 12.7 Expressions for mole fraction and conversion of reactant A for various decay forms (adapted from Sadana and Doraiswamy, 1971) ... 

Solutions to this equation for w = 1 and 1, as well for the other decay forms considered for the fixed-bed reactor (Sadana and Doraiswamy, 1971), are included in Table 12.7. The corresponding expressions for conversion given by... 

Excitation S(t), L(t) Decay form Decay rate s>-i- y> Emission yield Q... 

In real experiments, involving vibronic levels with unresolved rotational structure, the decay form may be modified on scanning across the vibronic band contour (BoesI et aL 1975 Howard and Schlag, 1976). The probable reason is a slight dependence of coupling constants on the rotational quantum numbers (Howard and Schlag, 1978). 

Table 9.4 Expressions for Mole Fraction and Conversion of Reactant A for Various Decay Forms...

---