Emission temperatures from widely separated states in−14andinduced

Abstract

Charged-particle correlations were measured for the reactions N+ Au and N+ Al at E/A = 75 MeV and for Xe+ Al and Xe+ Sn at E/A = 31 MeV. Relative populations of widely separated states in He, Li, and Be, only weakly a8'ected by side feeding, indicate emission temperatures of T=4 -5 MeV for the ¹induced reactions and values about 1 MeV lower for the Xe-induced reactions. PACS number(s): 25.70.Mn, 25.70.Gh I. INTR. ODUCTION Highly excited nuclear matter can be formed in intermediate-energy heavy-ion reactions. To address questions concerning the statistical properties of hot nuclei, it is important to determine their temperature. Experimental investigations have found evidence for a saturation in emission temperatures for fragments of T=4-6 MeV [1 -27] and evidence for a possible limitation on excitation energy of targetlike residues [28 -42]. However, it is not clear if this saturation of excitation energy arises from an instability of bulk nuclear matter which may be related to a phase transition or from dynamical limitations which may govern the energy dissipation into internal degrees of freedom. Both statistical [43,44] and dynamical [45,46] models predict that nuclear matter at suKciently high temperatures expands due to the action of thermal pressure. The rate of this expansion and the *Present address:

Liquid-Gas Phase Transition in Nuclear Multifragmentation

“…However, the other light charged particles, d and t, exhibit similar trends, namely, the kinetic energy temperature increases rapidly with the incident energy. A collection of the T ∆E ( 5 Li) over a range of incident energies from 30 to 200 AMeV are plotted as solid points in Fig.11 [59,71,73]. Contrary to the kinetic temperature, there is only a slight increase from 3 to 5.5 MeV, in the excited state temperature as a function of the incident energy spanning over one order of magnitude.…”

“…They behave more like the excited state temperature. [76] Experimentally, temperatures extracted from excited states or yield ratios involving carbon isotopes are around 4-5 MeV [77,59,73,69,63]. Around 4 MeV emission temperatures, the secondary decay effects are small and can be corrected with current models incorporating sequential decays.…”

“…To minimize the influence of sequential decays, nuclei with levels that are widely separated are often chosen [59]. One of the most commonly used nuclei is the unstable 5 Li isotope.…”

Excited state populations for equilibrium and preequilibrium emission

“…The Nal(Tl) detectors were 3.4 MeV) which dominates at backward angles. Other investigations [15] have reported OCR Output MeV) which dominates at forward angles and an isotropic equilibrated source (yielding T from fits to the IMF energy spectra[2], assuming a preequilibrium source (yielding 'l'= 8…”

Temperatures of Exploding Nuclei

“…The presented interpretation of the observed qualitative difference between the isotope and excited-state temperatures seems rather attractive. It implies that isotope yields may be used to probe the early stages of the fragment formation process, and it may explain the saturation of the excited-state temperatures that characterizes a wide variety of measurements at intermediate and relatiistic energies [13,15]. This interpretation, therefore, should be confirmed by further work which may aim at a quantitative interpretation of the internal fragment excitation but also address current open questions such as the role of initial correlations (see, e.g., [21,24,36,37]) and of quantum effects in the fragment formation process [38][39][40][41] …”