content_image/372292.jpg
<img src='content_image/372292.jpg'>

A = 11 , a s the n + α + $^{11}$C decay mode competes favorably with the α + $^{12}$C mode due to the limited number of particle-bound excited states of $^{12}$C. When all excited states are included in the calculation, all isotopic distributions have their peaks at the minimum of the valley of stability and roughly reflect the (inverted) form of the valley. 

The mean primary fragment multiplicity decreases from 2.8 for the ground-state only calculation to 2.4 for the particle-stable state one to 2.3 when all excited states are included. Neglecting the four-fragment or higher modes, which correspond to less than 1% of the cross section in all cases, these multiplicities imply that the contribution of three-fragment modes to the primary fragment distribution is about 80% in the ground-state only calculation, about 40% in the particle-stable calculation and only 25% in the calculation containing all excited states. That is, the decay tends from dominance of the three-fragment modes to dominance of the two-fragment modes as excited states are taken into account. The decrease in the primary multiplicity is easily understood, since an increasing portion of the excitation energy remains in the fragments as excited states are added, rather than being liberated as a larger number of smaller, lesser-bound fragments. The fact that the multiplicity decreases from a value close to three to one close to two is a result of the relatively low excitation energy of the calculation. At higher excitation energies, the average multiplicity is larger but follows the same trend - as more excited states are included, the average primary multiplicity decreases. We note that the excited fragments of the generalized FBM will, of course, subsequently decay and increase the net multiplicity. To be consistent, however, this subsequent decay would also be best described using the generalized version of the FBM. 

Before concluding this section, we briefly discuss the primary distributions of hydrogen and helium isotopes, shown in Fig. 2. These remain fairly stable in relative yield but 

