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Phys. Rev. C 75, 014601 (2007) [7 pages]

Experimental determination of the symmetry energy of a low density nuclear gas

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S. Kowalski*, J. B. Natowitz, S. Shlomo, R. Wada, K. Hagel, J. Wang†, T. Materna, Z. Chen, Y. G. Ma‡, L. Qin, and A. S. Botvina§
Cyclotron Institute, Texas A&M University, College Station, Texas 77843, USA

D. Fabris, M. Lunardon, S. Moretto, G. Nebbia, S. Pesente, V. Rizzi, and G. Viesti
INFN and Dipartimento di Fisica dell’ Universitá di Padova, I-35131 Padova, Italy

M. Cinausero and G. Prete
INFN, Laboratori Nazionali di Legnaro, I-35020 Legnaro, Italy

T. Keutgen and Y. El Masri
FNRS and IPN, Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium

Z. Majka
Jagellonian University, M Smoluchowski Institute of Physics, PL-30059, Krakow, Poland

A. Ono
Department of Physics, Tohoku University, Sendai, Japan

Received 28 February 2006; published 3 January 2007

Experimental analyses of moderate-temperature nuclear gases produced in the violent collisions of 35 MeV/nucleon 64Zn projectiles with 92Mo and 197Au target nuclei reveal a large degree of α particle clustering at low densities. For these gases, temperature- and density-dependent symmetry energy coefficients have been derived from isoscaling analyses of the yields of nuclei with A⩽4. At densities of 0.01 to 0.05 times the ground-state density of symmetric nuclear matter, the temperature- and density-dependent symmetry energies range from 9.03 to 13.6 MeV. This is much larger than those obtained in mean-field calculations and reflects the clusterization of low-density nuclear matter. The results are in quite reasonable agreement with calculated values obtained with a recently proposed virial equation of state calculation.

© 2007 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevC.75.014601
DOI:
10.1103/PhysRevC.75.014601
PACS:
24.10.-i, 21.30.Fe, 25.70.Gh

*Now at Institute of Physics, Silesia University, Katowice, Poland.

†Now at Institute of Modern Physics Chinese Academy of Science, Lanzhou 73, People's Republic of China.

‡Now at Shanghai Institute of Nuclear Research, Chinese Academy of Sciences, Shanghai 201800, China.

§Now at Institute for Nuclear Research, Russian Academy of Sciences, RU-117312 Moscow, Russia.

 
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