Intermediate-rapidity fragments with A= 1-14 emitted from 42-137-MeP/nucleon Ar + Au have been measured. Evidence i s presented that these fragments a r i s e from a common moving source. Entropy values a r e extracted from the mass distributions by use of quantum statistical and Hauser-Feshbach theories. The extracted entropy values of S / A F= 2-2.4 a r e much smaller than the values expected from measured deuteron-to-proton ratios, but a r e still considerably higher than theoretically predicted values.PACS numbers: 25.70.NpWe report the f i r s t systematic measurements of complex nuclear fragments emitted a t intermediate rapidities f r o m reactions of A r with Au a t 42, 92, and 137 MeV/nucleon, an eilergy r egion where only s p a r s e measurements exist.'-The observed fragments with A= 1-14 a r e explained by emission from a common thermal source and the m a s s distributions a r e analyzed by u s e of quantum statistica14 and Hauser-Feshbach5 theories to deduce the entropy created in the collision. Because i t stays constant during the expansion, the extracted entropy may give information about the hot, compressed stage of the ~y s t e m .~*~-~~ The entropy may provide information on the nuclear equation of state and phase transitions in nuclear matter.7v ''-l3 It has been proposed that the entropy can be deduced f r o m the ratio of deuterons to p r~t o n s ,~ but m o r e recent calculations indicate that heavier fragments must be included in the a n a l y~i s .~ Indeed our values a r e considerably Jolver than those deduced from a prescription based only on deuterons and protons, but they differ f r o m current theoretical e x p e c t a t i~n s ,~ The measurements were carried out a t the Lawrence Berkeley Laboratory Bevalac using 40Ar beams of 42, 92, and 137 MeV/nucleon with typical beam intensities of 1 X 107 particles/sec, and targets of 80 and 200 mg/cm2 Au. Heavy fragments were measured with two stacks of silicon detectors (0.1, 0.3, 5.0 mrn and 0.8, 0.8, 5.0, 5.0, 5.0 mm). Light particles ( P , d , t , 'He, 4He, and 6He) w e r e measured simultaneously with a telescope consisting of two silicon A E detectors (0.4 and 5 m m ) and a 10-cm Na1 E detectoa., A l l telescopes covered an angular range of 30" to 130" in 20" steps, with isotope resolution f o r hydrogen through carbon fragments. The energy spectra of the light particles w e r e corrected for reaction losses in the Na1 detector, and the heavy-fragment spectra were corrected for energy loss in the target. The relative normalization between different angles i s accurate to 5 % , whereas the absolute normalization is known to 20%.Measured energy spectra of ''Be a r e shown in Fig. 1. These spectra a r e typical of fragments with A> 6; the complete results will b e published elsewhere. The e r r o r b a r s reflect statistical e r r o r s only. The solid lines a r e f i t s to the spect r a assuming particle emission f r o m a single moving source.I4 The source temperature and velocity and the fragment Cross section a r e obtained by fittin...