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The elastic-scattering, neutron transfer and projectile break-up channels have been studied for the reaction 6 He + 64 Zn at energies around the Coulomb barrier. The results show a very large break-up and transfer cross-section corresponding to the largest fraction of the total reaction cross-section. No evidence of threshold anomaly emerged from the elasticscattering optical-model analysis.

We h a ve searched all even{even nuclei with Z 20, N 20 to nd examples which display c haracteristics of X(5) critical point b e h a vior. On the basis of the yrast state energies and yrast intraband transition strengths, the best candidates are 126 Ba, 130 Ce, and the previously suggested examples of the N=90 isotones of Nd, Sm, Gd, and Dy.PACS numbers: 21.60.-n 21.10.-k Typeset using REVT E X 1 Notable benchmarks of collective n uclear behavior are the harmonic vibrator 1], the symmetrically deformed rotor 2], and the triaxially soft rotor 3]. While nuclei may display behavior near these idealized limits, many lie in transitional regions between them. Recently, it has been suggested that a useful approach is to apply the ideas of a phase transition of the nuclear shape and to try to de ne critical points of the shape change as new benchmarks against which n uclear properties can be compared 4,5]. In particular, the transition from a spherical harmonic vibrator to an axially deformed rotor has been described analytically 5] by i n troducing a dynamic symmetry, denoted as X(5), which arises when the potential in the Bohr Hamiltonian 2] is decoupled into two components { an in nite square well potential for the quadrupole deformation parameter, , and a harmonic potential well for the triaxiality deformation parameter, .Several empirical examples of nuclei that may be close to an X(5) critical point h a ve been suggested. These include 150 Nd (Z=60, N=90) 6], 152 Sm (Z=62, N=90) 7], and 104 Mo (Z=42, N=62) 8]. For the N=90 isotones a recent paper 9] has shown that the properties of these nuclei, especially the intersequence transition strengths, are not reproduced by the X(5) description. An alternative picture involving simple couplings between rotational bands (and microscopically justi ed by the Pairing{Plus{Quadrupole model 10]) fares better. In the case of 104 Mo, the reduced transition strengths, derived from recent lifetime measurements of states in the yrast sequence 11,12], were used to demonstrate that this nucleus does not display X ( 5 ) b e h a vior 12].If the X(5) description is to be taken as a benchmark for describing shape transitional behavior, then it is important t o n d n uclei which follow the predicted behavior more closely than the examples discussed above. Motivated by such considerations we h a ve searched all known even{even nuclei with Z 20, N 20.The experimental signatures for X(5) behavior are: a) the ratios of the energies of the yrast states, E(I spacings than the yrast sequence e) the B(E2 I!I-2) values for intrasequence transitions should be lower for the non{yrast sequence relative to those of the yrast sequence (these latter two p o i n ts re ect the fact that the non{yrast states have a l o wer expectation value of deformation than the states in the yrast sequence) f) intersequence B(E2) values should show a c haracteristic pattern. We shall use all of the above points in our search for nuclei displaying behavior similar to the X(5) predictions.As a rst step we used...

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