Angular momentum alignment in the reaction154Sm+214 MeV32S

Abstract

Angular momentum alignment in the reaction 154Sm+214MeV 328 has been investigated using discrete-line 7-ray techniques. The anisotropies of stretched E2 transitions from the target-like fragments reach approximately three at the largest energy losses, implying rather strong alignment. The results are compared with the predictions of a simple model.Studies of the angular momentum transferred in heavy-ion collisions have proved very valuable in unraveling the complex dynamics of these reactions [1,2]. Although early efforts generally concentrated on the mean spin transfer, a variety of measurements have shown the importance of fluctuations about the mean value. The bulk of the information on these fluctuations has been obtained from spin alignment studies, such as measurements of sequential fission fragment angular distributions [3][4][5][6] and the anisotropies of either continuum [-7, 8] or discrete [9,10] gamma-rays. While a variety of theoretical explanations for these fluctuations have been suggested, including vibrational modes [11,12], nucleon exchange [13][14][15][16], and the statistical excitation of collective modes [17,18], the underlying mechanism is still largely an open question. One important issue still to be resolved is the extent to which equilibrium is achieved for these fluctuations. In order to obtain further insight into the origin of angular momentum fluctuations and their degree of equilibration, we have undertaken a detailed study of the reaction 154Sm+214MeV 328 utilizing the discrete-line method. This technique avoids problems connected with the unknown 7-ray multipolarities which arise in continuum studies and provides better exit channel definition than the sequential fission method. Exit channel selectivity may prove to * Present address: Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA be important in comparison with model calculations. A t.38mg/cm 2 thick, self-supporting foil of 1548m (99% enrichment) was bombarded with 214MeV 3287+ ions accelerated by the Texas A&M variableenergy cyclotron. Projectile-like fragments emitted at 0~a b = 47 ~ were detected and indentified in Z using a pair of solid state telescopes mounted in perpendicular planes (see the top of Fig. 1). Two high-resolution Ge(Li) detectors were placed in the horizontal plane at 90 ~ and 120 ~ with respect to the beam axis. During the measurements, particle-7, particle-v-7 events and scaled-down particle singles were recorded on tape in an event-by-event format. The beam intensity was controlled to minimize accidental coincidences (<8 %) and count rate instabilities in the Ge(Li) detectors (the average instantaneous rate was about 20kHz). The resolution (FWHM) integrated over eight days of running time was 3.5-4.0keV due to doppler broadening and some small gain shifts. In related experiments the continuum 7-ray multiplicities (Mr) were studied for the same reaction using an array of eight 7.6 x 7.6 cm NaI detectors. Experimental details regarding the M r measurements are reported elsewhere...

Angular momentum transfer in the deepinelastic reaction 245 MeV32S +64Ni from neutron angular correlations

“…This is in contrast to results on the same reaction where large alignment was observed in a study of discrete y-rays [34]. The latter result agrees with recent work on the reaction 214 MeV 32S+154Nm [35] where strong alignment at the largest energy losses was found, using also the discrete-line method.…”

Discrete ?-rays in the reactions of 143 MeV32S with58Ni

“…The out-of-plane Ge provided Doppler-free reference spectra for energy determinations. For this kind of reactions the in-plane anisotropy is rather small [3,8], therefore in-plane isotropy was assumed.…”

“…Discrete-line spectroscopy offers advantages also in determining the spin alignment [2,3]: the multipolarity of ~)-lines is usually known and their emitting sources (PLF and TLF) can be discriminated.…”

Projectile-like fragments excitation and gamma-rays emission after the deep inelastic reaction of32S on58Ni

“…In this case it is clear that exit channel tagging (by energy loss and/or fragments identifi-cation) may imply the selection of classes of fragments with different structure properties and then with different gamma emission patterns. As an example it has been shown that energy integrated v-ray anisotropies measured with scintillators are lower than those associated with discrete lines [2,3]. A systematic comparison of results obtained with the two techniques has not yet been reported.…”