Spallation process

The above models are all rather unsatisfactory, because they involve somewhat arbitrary assumptions about the time-dependence of the cosmic-ray flux and spectrum and because they predict a secondary-like behaviour for Be and B abundances, whereas the overall trend indicated by the data is more like a primary one and there are the energetic difficulties pointed out above. In the case of nB, there is a possible primary mechanism for stellar production in supemovae by neutrino spallation processes (Woosley et al. 1990 Woosley Weaver 1995), but the primary-like behaviour of beryllium in metal-poor stars, combined with a constant B/Be ratio of about 20 fully consistent with cosmic-ray spallation (Garcia Lopez et al. 1998) in the absence of any known similar process for Be, indicates that this does not solve the problem unless a primary process can be found for Be as well. Indeed,... 

Feasibility studies have shown that a He-jet activity transport line, with a target chamber placed in the LAMPF main beam line, will provide access to short-lived isotopes of a number of elements that cannot be extracted efficiently for study at any other type of on-line facility. The He-jet technique requires targets thin enough to allow a large fraction of the reaction products to recoil out of the target foils hence, a very intense incident beam current, such as that uniquely available at LAMPF, is needed to produce yields of individual radioisotopes sufficient for detailed nuclear studies. We present the results of feasibility experiments on He-jet transport efficiency and timing. We also present estimates on availability of nuclei far from stability from both fission and spallation processes. Areas of interest for study of nuclear properties far from stability will be outlined. 

In the early stages of dating by nuclear methods, the measurement of He formed by a decay in the natural decay series (9, 6 and 7 He atoms in the uranium series, the thorium series and the actinium series, respectively) has been applied. The preferred method was the U/He method which allows dating of samples with very low concentrations of U of the order of 1 mg/kg. Helium produced by a decay is driven out by heating and measured by sensitive methods, e.g. by MS. However, it is difficult to ensure the prerequisites of dating by the U/He method neither " He nor a-emitting members of the decay series must be lost and no " He atoms must be produced by other processes such as decay of Th and spallation processes in meteorites. 

At present, the Be versus O and the Be versus Mg relations for metal-poor stars appear to be quasi-linear King (2002) gives indices of about 1.1 for both Be and B when Mg is adopted. Recent determinations of the O abundance seem likely to confirm this near-linear trend. All interpretations assume that spallation processes are the sole source of the Be but not necessarily of the B (see below). Ingredients of the modelling other than the mode of synthesis are varied to fit the Be vs O (or Mg) relations. 

During the Big Bang the light elements (D, 3He, AHe and 7Li) were produced. On the other hand, all the elements heavier than 7Li, with the exception of Be and B, are produced inside stars. The light elements 6Li, Be and B are instead manufactured by spallation processes in the ISM due to the interaction between cosmic rays and interstellar atoms. 

Big Bang —> light elements H, D, 3He, 4 He, 7Li. Deuterium is only destroyed inside stars to form 3He. 3He is also mainly destroyed. The only stars producing some 3//e are those with masses < 2.5Mq. Recent prescriptions for the yields of 3He are from Forestini Charbonnel (1997) and Sackmann Boothroyd (1999). Lithium 7Li is produced during the Big Bang but also in stars massive AGB stars, SNe II, carbon-stars and novae. Some 7Li should also be produced in spallation processes by galactic cosmic rays (see Romano et al. 2001). 

X-ray beams can be generated by anode or synchrotron sources, while neutron beams are obtained from nuclear processes using either an atomic reactor or by spallation processes. 

The radionuclide Cu emits P -particles of ideally suitable energy. It is occasionally produced via the spallation process, but more commonly via the Zn(p,2p) Cu reaction with protons of energies above 50 MeV. (Mirzadeh et al. 1986 Schwarzbach et al. 1995 Stoll et al. 2002). A recently reported method of production makes use of the Zn(p,a) Cu reaction over the energy range of 12 to 21 MeV. If highly enriched target material is used, the resulting Cu is very pure (Kastleiner et al. 1999). 

Yu A, Gupta V (1998) Measurement of in situ fiber/ matrix interface strength in graphite/epoxy composites. Comp Sci Tech 58 1827-1837 Yuan J, Gupta V (1993) Measurement of interface strength by the modified laser spallation technique. I.Experiment and simulation of the spallation process. J Appl Phys 74 2388-2397... 

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