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56 56
The hjalf life of m , which decays by K-capture into Co (80d) has recentlybeen
found to be 6-5 days (Shel^ne and Stoughton (1952) and Worthington (1952))-
Hence the process leading to the excessive abundance of mass 56 cannot have taken
longer than a few days«
Together "Wil^ Fe, the elements Cr, Ti, and Ca show an excessively hi^
abundance of their Isotopes with the neutron excess of I equal to ii
This
may be taken as an indication, that -'n this tihola nasa range nuclei with zero
neutron excess, i» e- (N = Z), had formed first and thereafter decayed into their
I equal to k isobars o In general nuclei with N » Z seem to show higb»r binding
energies than would correspond to a perfectly parabolic energy valley and this
2/
makes ths high original abundance apnear plausible---
That the abundance
distribution was actually established within less than a day is indicated by the
half life of Fe^^ of 7o8 hours, which decays into Cr^^o
Undoubtedly, magic nunfcer effects exist at N « 8, Ik and 20, although
the uncertainties in the abundance values and the rapid change of abundances
with mass number in this region makes the character of these effects sooewhat
obscure- The enhanced abundance of the nuclei Mg and A-'" with I equal to 2
indicates effects Srcm the shell closure at N equal to lU and 20, respectivolyo
Harkin's rule and the abxindanees of odd A nuclei
According to Mattauch's law, there is only one isobar stable at each odd
mass numbero Tta»z« exists, however, for eadi odd mass nuidber greater than 32$
also at least one unstable isobar with & half life of xaare than a day, that
is a half life loiig connparsd to the tiina in which the mass distribution was
establishedo
Cto'Tiouslr, at an odd mass number iinstable isdbars must have on the
average contributed relatively more to the abundance of the stable species tiian
2/ See Blatt and Weisskopf, Theor- Nuc- Phys- P- 2I4I ff- Theoretically the
°" "aymetry" enei^jy leads to two parabulae crossing at N » Z«