Quasifragments: hot nuclei embedded in a nucleon vapor Page: 4 of 4
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
Thus, the density of single-particle states for the total system is decomposed as g(!) = gapor(e) +
gA(e), where the part associated with the nucleon vapor is gvpor(e) = g>(e)+#A(e). The partition func-
tion Z for the total system then factories correspondingly, Z = Z.aporZA, where ZA is given by eq. (1)
and Zapw is given analogously in terms of gwapor(e). It should be noted that the total partition function
Z is independent of the particular way in which the partition of g(e) is made, as long as the single-
particle idealization is maintained. However, the partition of g(e) is significant when the transition-state
approximation is invoked in order to describe the disassembly of the system into distinct, real fragments.
The figure tl!ustrates the result of the proposed reflection-coefficient prescription. The use of the
reflection coefficient to truncate the level density leads to a natural A-dependence: a larger nucleus
(having a smaller surface-to-volume ratio) holds more energy per nucleon at a given temperature, until
this behavior saturates in the limit A - oo. It is interesting to note that for the relatively adundant
lighter nuclei the limiting temperature comes out to be around 8 MeV, so for the practical applications
the relatively complicated (but parameter-free) reflection-coefficient prescription can he well approxi-
mated by e.g. an exponential cutoff with m a 8 MeV.
The present study is motivated by our interest in the description of hot nuclear matter at subsatura-
tion densities, as may be produced in nuclear collisions at medium energies. At the high temperatures
of interest, for which the excitation of the system is comparable to its binding energy, the metastable
fragmented must be considered in conjunction with a surrounding nucleon vapor. (Similar scenarios occur
in astrophysical systems, albeit typically at temperatures and densities that are considerably lower, and
the proper inclusion of the vapor in those situations have been discussed.[6,7]) The statistical treatment
of such systems is conveniently formulated in terms of excitable quasifragments embedded in a nucleon
vapor. We have formulated a conceptually simple, parameter-free method for making the formal split of
the partition function into a factor associated with the vapor and one factor for each quasifragment. The
method can be characterized roughly by saying that a particular nucleon, situated within the interior
of a fragment, is considered as part of that fragment if it is reflected back into the fragment's interior
when reaching its surface. This prescription yields a masw-dependent limiting nuclear temperature,
decreasing from 10-12 MeV for heavy nuclei to around 8 MeV for A s 10.
We wish to acknowledge instructive discussions with S.E. Koonin, S. Pratt, and P.J. Siemens. One
of us (GF) is on leave of absence from Department of Physics, Kent State University, Kent, Ohio 44242.
This work was supported by the Director, Office of Energy Research, Division of Nuclear Physics of
the Office of High-Energy and Nuclear Physics of the U.S. Department of Energy under Contract
DE-AC03-76SF00098 and Grant DE-FG02-86ER40251.
References
[1] G. Fai and J. Randrup, Nucl. Phys. A404 (1983) 551; Comp. Phys. Comm. 42 (1986) 385
[2] S.E. Koonin and J. Randrup, Nucl. Phys. A474 (1987) 183
[3] H.A. Weidenmiller, Ann. of Phys. 28 (1964) 60
[4] S. Pratt, P.J. Siemens, and Q.N. Usmani, Phys. Lett. 189B (1987) 1
[5] N. Levinson, Kgl. Danske Videnskab. Selskab. 25 (1949) 9
(6] D.L. Tubbs and S.E. Koonin, Astrophys. J. 232 (1979) L59
[7] T.J. Masurek, J.M. Lattimer, and G.E. Brown, Astrophys. J. 229 (1979) 7134
Search Inside
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Fai, G. & Randrup, J. Quasifragments: hot nuclei embedded in a nucleon vapor, article, March 1, 1988; California. (https://digital.library.unt.edu/ark:/67531/metadc1198788/m1/4/: accessed April 27, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.