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تسجيل مستخدم جديدLifetime measurements of Triaxial Strongly Deformed bands in $^{163}$Tm
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With the Doppler Shift Attenuation Method, quadrupole transition moments, $Q_t$, were determined for the two recently proposed Triaxial Strongly Deformed (TSD) bands in $^{163}$Tm. The measured $Q_t$ moments indicate that the deformation of these bands is larger than that of the yrast, signature partners. However, the measured values are smaller than those predicted by theory. This observation appears to be valid for TSD bands in several nuclei of the region
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Two interacting, strongly-deformed triaxial (TSD) bands have been identified in the Z = 69 nucleus ^{163}Tm. This is the first time that interacting TSD bands have been observed in an element other than the Z = 71 Lu nuclei, where wobbling bands have
been previously identified. The observed TSD bands in ^{163}Tm appear to be associated with particle-hole excitations, rather than wobbling. Tilted-Axis Cranking (TAC) calculations reproduce all experimental observables of these bands reasonably well and also provide an explanation for the presence of wobbling bands in the Lu nuclei, and their absence in the Tm isotopes.
The wobbling spectrum of $^{163}$Lu is described through a novel approach, starting from a triaxial rotor model within a semi-classical picture, and obtaining a new set of equations for all four rotational bands that have wobbling character. Redefini
ng the band structure in the present model is done by adopting the concepts of Signature Partner Bands and Parity Partner Bands. Indeed, describing a wobbling spectrum in an even-odd nucleus through signature and parity quantum numbers is an inedited interpretation of the triaxial super-deformed bands.
Lifetimes in the yrast bands of the nuclei $^{182,186}$Pt have been measured using the Doppler-shift Recoil Distance technique. The results in both cases {em viz.} a sharp increase in B(E2) values at very low spins, may be interpreted as resulting fr
om a mixing between two bands of different quadrupole deformations.
The triaxial dynamics of the quadrupole-deformed rotor model of both the rigid and the irrotational type have been investigated in detail. The results indicate that level patterns and E2 transitional characters of the two types of the model can be ma
tched with each other to the leading order of the deformation parameter $beta$. Especially, it is found that the dynamical structure of the irrotational type with most triaxial deformation ($gamma=30^circ$) is equivalent to that of the rigid type with oblate deformation ($gamma=60^circ$), and the associated spectrum can be classified into the standard rotational bands obeying the rotational $L(L+1)$-law or regrouped into a new ground- and $gamma$-band with odd-even staggering in the new $gamma$-band commonly recognized as a signature of the triaxiality. The differences between the two types of the model in this case are emphasized especially on the E2 transitional characters.
The electric quadrupole transition from the first 2+ state to the ground 0+ state in 18C was studied through lifetime measurement by an upgraded recoil shadow method applied to inelastically scattered radioactive 18C nuclei. The measured mean lifetim
e is 18.9 +/- 0.9 (stat) +/- 4.4 (syst) ps, corresponding to a B(E2;2+ -> 0+) value of 4.3 +/- 0.2 +/- 1.0 e2fm4, or about 1.5 Weisskopf units. The mean lifetime of the first 2+ state in 16C was remeasured to be 18.0 +/- 1.6 +/- 4.7 ps, about four times shorter than the value reported previously. The discrepancy between the two results was resolved by incorporating the gamma-ray angular distribution measured in this work into the previous measurement. These transition strengths are hindered compared to the empirical transition strengths, indicating that the anomalous hindrance observed in 16C persists in 18C.
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