Long-Lived Radioactive Aluminum 26

Abstract

hydrogen events" were examined under high magnification to determine whether one or more light tracks were also associated. One example of a pair of light tracks, assumed to be electrons, was found (Fig. 1). s'~e++e +y.(2) followed by the direct decay of the neutral pion, as predicted by Dalitz4 and as observed by various authors'' CpĨ t~P rocess (1) is the charge-symmetric analog of the process which was used to explain the pairs in the negative pion beam: s. +~'+e.(3)Since there are approximately as many neutrons as protons in the emulsion the cross sections for (1) and (3) should be nearly the same, which is not inconsistent with the results reported here. The lack of a visible gap between the pair and the star is in agreement with the short lifetime reported earlier. FIG. 1. Electron pair produced by 113-Mev positive pion: u, incident pion; b, proton of 75&10 Mev or other fragment of same ionization; c1, c2 electrons of 27&9 and 56&14 Mev, respectively.The angle between the two electron tracks 8 is 5.2 1. 0' and the angle between the direction of the incident pion and the direction of the center of mass of the pair p is 62&2'. The energies of the two electrons are 27~9 Mev and 56&14 Mev. These data are consistent with the earlier results obtained on the negativepion-produced pairs' except for the angle g, which is smaller than any of the angles reported earlier and which seemed in the earlier work to have an improbably sharp distribution centered around 115' in the laboratory system. Since this is the only case in the positive beam, the significance of the occurrence of such an angle is not clear. In the area scanned for this experiment, there were (1.56+0.05)&&10' cm of pion track. ' Since the mean free path for pions at very nearly the same energy' is 33.6&17 cm, approximately 4600 interactions must have occurred. Approximately one-eighth of these would be "possible hydrogen events" as described earlier. Thus one pair was found in about 600 stars examined. There is no visible gap on this pair, and a gap would have been seen if it were as large as one micron. It is suggested that this pair can be interpreted as the result of the charge-exchange scattering of a pion on a neutron in a nucleus of the emulsion: vr++ m -+n'+ p, HERE are experimental' ' and theoretical~' indications of a state in Al" lying below the 6-second positron-emitting 0+ state. The ground state apparently4' lies 4.0 Mev above that of Mg" and is expected~to have a 5+ configuration. If the Mg' states at 1.83 and 2.97 Mev" both have 2+ configurations,Ap" should decay predominantly by positron emission to the 1.83-Mev state with a half-life estimated'' at 10' -10' years, with smaller amounts of electron capture to both states. We have sought radioactivity in aluminum carrier isolated from a target of commercial magnesium bombarded with 400 pa-hr of 15-Mev deuterons in the University of Pittsburgh cyclotron. After numerous NH4OH precipitations at pH 6, numerous NaOH precipitations of Fe(OH). -, and two 8-hydroxyquinoline precipi. tations, the a...

Short-lived nuclei in the early Solar System: Possible AGB sources

“…This is in general accord with the effects expected from first dredge-up in Red Giant stars (see Dearborn [73]). However, observations on the grains show overproduction of 17 O and much more extensive destruction of 18 O that is far outside the range to be expected for standard RGB or AGB models [71] [74].…”

“…It is thus possible to obtain destruction of 18 O with or without significant 26 Al production and substantial 26 Al production with or without 18 O destruction; however, conditions on oxide versus carbide production discussed below place further constraints on which compositions are possible in a given type of grain. 17 Fig. 4).…”

“…26 Al was then found to have been present in CAIs through a clear correlation of excess 26 Mg ( 26 Mg * ) with 27 Al in different minerals with widely varying Mg/Al ratios [13] [14]. Early suggestions by Urey [15] and Urey & Donn [16] indicated that the nuclide 26 Al, which had just then been discovered in a cyclotron target [17], was the only reasonable source for the early heating and melting of planetesimals. The authors noted that: "If the problem of producing sufficient quantities of 26 Al can be solved, this nuclide should be of considerable value in chemistry, metallurgy, and related fields" [17].…”

“…Early suggestions by Urey [15] and Urey & Donn [16] indicated that the nuclide 26 Al, which had just then been discovered in a cyclotron target [17], was the only reasonable source for the early heating and melting of planetesimals. The authors noted that: "If the problem of producing sufficient quantities of 26 Al can be solved, this nuclide should be of considerable value in chemistry, metallurgy, and related fields" [17]. As pointed out by Urey [15], the heating and melting of small planetesimals required a short-lived radioactivity of a major element as the heat source, since there would not be sufficient gravitational energy to melt them.…”

Short-Lived Nuclei in the Early Solar System: A Low Mass Stellar Source?

“…In particular, 26 Al (τ = 1.05 Myr) was found to have been present in CAIs with a clear correlation of 26 Mg * with 27 Al (Lee, Papanastassiou, & Wasserburg 1976. Early suggestions by Urey (1955) and Urey & Donn (1956) indicated that the nuclide 26 Al, which had just then been discovered (Simanton et al 1954), was the only reasonable source for the heating and melting of planetesimals.…”