Intermediate Mass Fragment Emission Research Articles

Complex fragment emission sources characterized by linear momentum transfer measurements

Triple coincidences between intermediate mass fragments (IMFs) and anglecorrelated fission fragments were measured in E/A = 35 MeV14N + 232ThandEA = 90 MeV3He + 232Th reactions. These measurements indicate that fragments emitted at backward angles are associated with more central collisions than those detected in the forward hemisphere. In the 3He-induced reaction the longitudinal orientation of the missing momentum is indicative of non-equilibrium emission prior to IMF emission; the average number of IMFs per fragmentation event was deduced to be close to unity.

Source properties of intermediate mass fragments emitted in the 270 MeV 3He + 232Th reaction

Triple coincidences between intermediate mass fragments (IMFs) and angle-correlated fission fragments were measured in the 270 MeV 3He + 232Th reaction. These measurements demonstrate that on the average IMF emission occurs prior to fission from a source which carriers 75–80% of the beam momentum. It was deduced that the average number of IMFs per fragmentation event is close to unity. The dependence of the fission probability on the IMF emission angle and atomic number suggests that fragments emitted at forward angles come from more peripheral collisions than those emitted at very backward angles.

Systematics of spontaneous emission of intermediate mass fragments from heavy nuclei.

We have used polycarbonate track-recording films to confirm the rare decay mode of $^{226}\mathrm{Ra}$ by $^{14}\mathrm{C}$ emission and to set stringent upper limits on $^{14}\mathrm{emission}$ rates of $^{221}\mathrm{Fr}$, $^{221}\mathrm{Ra}$, and $^{225}\mathrm{Ac}$. The $^{14}\mathrm{emission}$ rate exhibits a pronounced odd-even effect. For Ra isotopes the hindrance factor for odd-even parents relative to even-even parents is at least 10 times higher for $^{14}\mathrm{C}$ emission than for \ensuremath{\alpha} emission.

Experimental signature ambiguities in nuclear liquid-gas phase transitions

Characteristics of intermediate mass fragment emission data advanced as experimental evidence of a hadronic gas to liquid phase transition are reviewed. Ambiguities in the interpretation of these characteristics are presented. The necessity of large $Z$ fragments to tunnel through a large Coulomb barrier is shown to make extraction of a phase transition signature difficult.

Experimental Evidence for a Liquid-Gas Phase Transition in Nuclear Systems

At certain combinations of temperature and density, nuclear matter may exist as a liquid-gas mixture exhibiting phase instabilities, a characteristic signature of which may be found in the emission of intermediate-mass fragments in nuclear collisions. The present analysis of fragment distributions from proton- and heavy-ion-induced reactions, in the framework of a theory of condensation, is suggestive of the occurrence of such phase transitions with a critical exponent $k\ensuremath{\sim}1.7$ and a critical temperature ${T}_{c}\ensuremath{\sim}12$ MeV.