Beta stabilizers

However, a more realistic model for the phase transition between baryonic and quark phase inside the star is the Glendenning construction [16], which determines the range of baryon density where both phases coexist. The essential point of this procedure is that both the hadron and the quark phase are allowed to be separately charged, still preserving the total charge neutrality. This implies that neutron star matter can be treated as a two-component system, and therefore can be parametrized by two chemical potentials like electron and baryon chemical potentials [if. and iin. The pressure is the same in the two phases to ensure mechanical stability, while the chemical potentials of the different species are related to each other satisfying chemical and beta stability. The Gibbs condition for mechanical and chemical equilibrium at zero temperature between both phases reads... 

Primary fission products, secondary Sl deexcited fission fragments in their V ground state. These nuclei are far removed from beta stability and are radioactive. 

A continuing effort among experimentalists who study nuclei far from beta stability is the measurement of the atomic mass surface As a manifestation of the nuclear force and the nuclear many body system, atomic masses signal important features of nuclear structure on both a macroscopic and microscopic scale It has thus been a challenge to nuclear theorists to devise models which can reproduce the measured mass surface and to predict successfully the masses of new isotopes Both the measured mass surface and that beyond it which can be predicted by these models serve as important input to a variety of fundamental and applied problems, e g, nucleosynthesis calculations, predictions of decay modes of exotic nuclei far from stability, nuclear de-excitation by particle evaporation, decay heat simulations, etc ... 

Well determined masses of nuclei which lie far from beta stability can provide very sensitive tests of atomic mass models While a single new mass measurement from one previously uncharacterized isotope carries with it only limited information about the quality of mass predictions from the models, important trends frequently become evident across isotopic sequences or when global comparisons of many new masses are made against the various mass models It is in this context that a comprehensive and critical assessment of the predictive properties of atomic mass models is presented with the aim of identifying both the successes and failures in the models A summary of a portion of this effort has been published earlier [HAU84] ... 

Hyperfine structure measurements using on-line atomic-beam techniques are of great importance in the systematic study of spins and moments of nuclei far from beta-stability. We will discuss the atomic-beam magnetic resonance (ABMR) method, and laser spectroscopy methods based on crossed-beam geometry with a collimated thermal atomic-beam and collinear geometry with a fast atomic-beam. Selected results from the extensive measurements at the ISOLDE facility at CERN will be presented. 

SF = spontaneous fission. Fission fragments are rich in neutrons and decay toward beta stability from the neutron-rich side. Fission produces... 

Where possible, the r-process flow follows the magic neutron numbers. At these points, the nuclei present lie closer to beta stability than elsewhere in the flow. This means that the beta-decay rates decrease, which causes a traffic jam in the upward flow in nuclear mass thus, there is an abundance build up for these nuclei. When the flux of neufrons ceases, the r-process nuclei decay back to stability. Because the r-process flow encounters the magic neutron numbers at nuclear masses less than die s-process flow, the resulting r-process abundance peaks lie lower in nuclear mass than the corresponding s-process peaks. 

Alloys with compositions less than the point where the a transus meets the composition axis are termed a alloys. The CP alloy discussed in this chapter is an example of an a alloy. Those with compositions greater than the point where the 3 transus meets the axis are termed 3 alloys. Those with compositions in between have a microstructure of a and 3 phases at ambient temperature under equilibrium conditions. Two types of these alloys can be identified. One type has composition limits between the a transus and the Mj curve and can be described by the term a-P alloy. The T1-6A1-4V alloy discussed later in this chapter is a common a-p alloy. The second type is given the name metastable p alloy. Composition limits for metastable p alloys fall between the and the p transus. Metastable beta alloys can best be described as alpha-beta alloys that contain an appreciable level of beta stabilizers. The low difhisivity of the beta stabilizers promotes complete retention of beta phase to room temperature at moderate cooling rates. The Ti-15V-3Cr-3Al-3Sn and Beta 21-S alloys are common metastable beta alloys. 

Figure 19.1. The line of beta stability. Each point corresponds to a stable isotope. 

Industrial grades of pure titanium have relatively low tensile strength in comparison to alpha-beta stabilized alloys such as Ti6A14V. Therefore, the majority of industrial uses for titanium incorporate the alpha-beta alloys and as such these are the focus of most adhesion studies.As with other metals, there is a large range of pre-treatments available for titanium and its alloys, as indicated in Table 1. 

In heavy-ion reactions, the more general term quasielastic scatteringis frequently applied to reactions at the nuclear surface. This more inclusive definition covers not only the above mechanisms, but also multiple-nucleon-traws r reactions. In these events, two or more nucleons may be transferred, producing a more diverse array of reaction products. The multiple-nucleon-transfer mechanism can produce nuclei relatively far away from the line of beta stability. Consider the example,... 

Alpha-titanium alloys. These alloys range in yield tensile strength from 173 to 483 MPa. Variations are generally achieved by alloy selection and not heat treatment. They usually contain alpha stabilizers and have the lowest strengths. However, they are formable and weldable. Some contain beta stabilizers to improve strength. Alpha-titanium alloys are generally in the annealed or stress-relieved condition. They are considered fully annealed after... 

Timetal 62S Ti-6Al-2Fe-0.1Si Properties and processing characteristics equivalent to or better than Timetal 6-4, but with significantly higher Young s modulus. Due to the use of iron as the beta stabilizer, the alloy has lower formulation costs than Timetal 6-4. The combination of reasonable cost and excellent mechanical properties makes it a practical substitute for many engineering materials. 

Craighead, C. M., Leiming, G. A., and Jaffe, R. I., Hydrogen Embrittlement of Beta-Stabilized Titaniirm Alloys, Transactions of the Metallurgical Society of AIME, August 1956, p. 923. 

Figure 1.2 The beta stability valley at low Z. Adapted from a figure published by New Scientist, and reproduced with permission...

Luh70 ] Luhman, T.S., Taggart, R., and Polo-nis, D.H., The Effects of Step Quenching and Aging on the Superconducting Transition in Beta Stabilized Ti-Cr Alloys, Scr. Metall, Vol 4, 1970, p. 611-615... 

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