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The element yield distributionsσ(Z) of intermediate mass fragments from proton, helium, and heavy-ion induced reactions exhibit a universal behaviour as a function of the bombarding energy. The power law parameterτ, obtained from fits withσ(Z)∝σ -τ, falls monotonically with increasing projectile energy Elab and reaches a saturation valueτ≃2.0 atE lab≃2GeV. It is suggested that the behaviour at low bombarding energies is caused by a dynamical hindrance of the fragment emission at low angular momentum.

Inclusive cross sections of intermediate mass fragments from the reaction84Kr+197Au atE/A=35 MeV were measured over the range 8°≦Θlab≦70° with a low detection threshold. A moving-source parameterization was used to fit the double-differential cross sections. The integrated cross section for fragment production exceeds the total reaction cross section thus indicating a large probability for multi-fragment processes. The deduced large temperature parameters can be explained by assuming emission from a rotating source. From the comparison to reactions with12C and40Ar projectiles at E/A=30 MeV a systematics of inclusive fragment production as a function of the projectile mass is obtained.

Proton-proton correlations at small relative momenta were measured for [sup 40]Ar+[sup 197]Au reactions at [ital E]/[ital A]=200 MeV. Comparing the correlation functions to predictions based on single-particle phase space distributions from microscopic Boltzmann-Uehling-Uhlenbeck and quantum-molecular-dynamics (QMD) simulations, no satisfactory agreement could be established. Calculations utilizing two-particle emission probabilities predicted by the QMD model differ significantly from the single-particle calculations and are much closer to the experimental observations at [ital E]/[ital A]=200 MeV, potentially signaling the importance of the two-particle density for the proton-proton correlation function.

We have studied the fragmentation of Au projectiles interacting with targets of C, Al, Cu and Pb at an incident energy of E/A = 600 MeV. The experiment was performed with the ALADiN forward spectrometer at SIS. The employed inverse kinemantics allowed nearly complete detection of projectile fragments with charge Z ≥ 2. In addition, the number of light particles for each collision was measured. We compare different observables characterizing the event and investigate the impact parameter dependence of the fragmentation process. It is found that the correlation between the mean multiplicity of intermediate mass fragments 〈Mimf〉 and Zbound, the sum charges of all projectile fragments with Z≥2, is independent of the target nucleus. This universal behavior is consistent with an - at least partial - equilibration of the projectile fragment prior to its decay. Finally we compare to two classes of statistical models, the sequential decay code GEMINI and statistical multifragmentation models.

The mean multiplicity of intermediate mass fragments (IMF) {l angle}{ital M}{sub IMF}{r angle} produced by fragmentation of Au projectiles interacting with targets of C, Al, Cu, and Pb at an incident energy of {ital E}/{ital A}=600 MeV is compared to predictions of statistical multifragmentation and sequential evaporation models. The initial conditions for the calculations were provided by Boltzmann-Uehling-Uhlenbeck simulations. In the high excitation energy regime where the IMF multiplicity reaches its maximum the observed universal correlation between {l angle}{ital M}{sub IMF}{r angle} and the total charge {ital Z}{sub bound} of projectile fragments with charges {ital Z}{ge}2 cannot be reproduced by a sequential evaporation code. In this regime the data are better described by statistical decay calculations which assume the formation of an expanded nuclear system and a rather fast breakup.

We have studied the transition from the evaporation to the vaporization regime in 197Au induced reactions on C, Al, and Cu targets at a beam energy of 600 MeV per nucleon. The experiment was performed with the ALADIN forward spectrometer at SIS. We find that with increasing violence of the collision the mean multiplicity of intermediate mass fragments first increases to a maximum ⋍ 3.5 and then decreases again. Calculations using the BUU model suggest that the fragmentation is governed by the energy Edep deposited into the Au nucleus and that the maximum of is reached around Edep = 8 MeV/nucleon.

Apparent emission temperatures of 4 He and 5 Li fragments were deduced for the reaction 40 Ar+ 197 Au at E / A =200 MeV from the relative population of excited states. Compared to previous measurements at E / A =60 MeV, the average emission temperatures increases by less than 2 MeV to a value of about 6 MeV. QMD calculations indicate that the momentum distribution of the nucleons forming a fragment is determined at a point where the system is still close to normal nuclear density and that they do not reflect the local momentum distribution of the surrounding nucleons. The simulations suggest that the observed low emission temperatures are a consequence of the dynamics of the fragment formation process.

Inclusive cross sections of intermediate mass fragments from the reaction {sup 40}Ar+{sup 197}Au at {ital E}/{ital A}=30 and 220 MeV were measured with a low threshold and over a large range of angles. The integrated cross sections are about 2 b at both energies but the emission characteristics change considerably. The increased isotropy of the angular distributions and the strongly reduced Coulomb repulsion at the higher bombarding energy suggest that the emission process evolves towards fragmentation of excited spectator matter in central ion-ion collisions.

We have studied the fragmentation of Au projectiles interacting with targets of C, Al and Cu at an incident energy ofE/A=600 MeV. The employed inverse kinematics allowed a nearly complete detection of projectile fragments with chargeZ≧2. The recorded fragmentation events were sorted according to three observables, the multiplicityMlp of light charged particles, the largest atomic numberZmax within an event, and a new observable,Zbound, representing the sum of the atomic numbersZ of all fragments withZ≧2. Using these observables, the impact parameter dependence of the fragmentation process was investigated. For all three targets, a maximum mean multiplicity of 3 to 4 intermediate mass fragments (IMFs) is observed. The corresponding impact parameters range from central collisions for theC target to increasingly peripheral collisions for the heavier targets. It is found that the correlation between the IMF multiplicity andZbound, extending from evaporation type processes (largeZbound) to the total disassembly of the projectile (smallZbound), is independent of the target nucleus. This universal behaviour may suggest an — at least partial — equilibration of the projectile fragment prior to its decay.

With the ALADiN forward spectrometer the fragmentation of gold nuclei at 600 MeV per nucleon after interaction with carbon, aluminum, copper and lead targets has been investigated. The results are compared to Quantum Molecular Dynamics calculations using soft and hard equations of state.

Momenta and masses of heavy projectile fragments (Z >= 8), produced in collisions of 197Au with C, Al, Cu and Pb targets at E/A = 600 MeV, were determined with the ALADIN magnetic spectrometer at SIS. An analysis of kinematic correlations between the two and three heaviest projectile fragments in their rest frame was performed. The sensitivity of these correlations to the conditions at breakup was verified within the schematic SOS-model. The data were compared to calculations with statistical multifragmentation models and to classical three-body calculations. Classical trajectory calculations reproduce the dynamical observables. The deduced breakup parameters, however, differ considerably from those assumed in the statistical multifragmentation models which describe the charge correlations. If, on the other hand, the analysis of kinematic and charge correlations is performed for events with two and three heavy fragments produced by statistical multifragmentation codes, a good agreement with the data is found with the exception that the fluctuation widths of the intrinsic fragment energies are significantly underestimated. A new version of the multifragmentation code MCFRAG was therefore used to investigate the potential role of angular momentum at the breakup stage. If a mean angular momentum of 0.75$\hbar$/nucleon is added to the system, the energy fluctuations can be reproduced, but at the same time the charge partitions are modified and deviate from the data. PACS numbers: 25.70.Mn, 25.70.Pq, 25.75.Ld, 25.75.-q, 38 pages, RevTeX with 21 included figures; Also available from http://www-kp3.gsi.de/www/kp3/aladin_publications.html

We have studied multi-fragment decays of Au projectiles after collisions with C, Al, Cu and Pb targets at a bombarding energy of 600 MeV/nucleon. We examine the correlations between the charges emitted in these reactions. These correlations are given as a function of the total charge in bound fragments, Z bound , at forward angles, which is a measure of the violence of the collision and can be related to the impact parameter. The charge distributions have been fitted by a power law and the extracted τ parameter exhibits a minimum as a function of Z bound . We observe a strong reduction in the maximum charge, Z max , of the event with decreasing Z bound . For those events where Z max is less than half Z bound , the relative sizes of the two largest charges within the event cover the full spectrum of possibilities. The charge-Dalitz plots indicate that the multi-fragmentation events are not an extension of symmetric fission reactions. The event-by-event charge moments are examined to measure the size of the charge fluctuations. All of the charge correlations are independent of the target when plotted as a function of Z bound . The results are compared to both nuclear statistical and percolation calculations. The model predictions differ from each other, establishing that the observables are sensitive to how the available phase space is populated. The sequential nuclear model predicts too asymmetric a decay, while the simultaneous model predicts too symmetric a break-up. The percolation model, which was adjusted to reproduce the size of Z max , correctly predicts the mean behaviour and the fluctuations of the lighter fragments.

We review the recent results on the multi-fragment decay of heated nuclear systems that are formed in asymmetric heavy-ion collisions. Particular emphasis is placed on those observables that are sensitive to the fluctuations in the decaying system and their possible role in extracting the physics of phase transitions in nuclear systems.

We have studied multifragment decays of Au projectiles after collisions with C, Al, and Cu targets at a bombarding energy of 600 MeV nucleon. We find that with increasing violence of the collision, measured via the multiplicity of light particles, the mean multiplicity of intermediate-mass fragments originating from the projectile first increases to a maximum {l angle}{ital M}{sub IMF}{r angle}{congruent}3 and then decreases again. Calculations using the Boltzmann-Uehling-Uhlenbeck model suggest that the fragmentation is governed by the energy {ital E}{sub dep} deposited into the projectile spectator and that {l angle}{ital M}{sub IMF}{r angle} reaches its maximum around {ital E}{sub dep}{congruent}8 MeV/nucleon.

The experimental systematics of the excitation energy of mixed symmetric J π = 1 + states in 46,48 Ti, 110 Pd, 154 Sm, 154,156,158 Gd, 164 Dy, 168 Er, 174 Yb, 232 Th and 238 U is compared with theoretical predictions. The emphasis is placed on a unified description in terms of the interacting boson model (IBM-2). The Majorana force parameter changes in a systematic way as a function of the product of active neutrons and protons participating in the collective motion. The systematics of the M1 strength distribution in the rare earth nuclei is also discussed. So far only the IBM-2 description using an F -spin invariant Majorana force is able to account for the trend of the data.

An electron scattering experiment on 110 Pd has been performed at fairly small momentum transfers q , searching for mixed symmetry J π = 1 + and 2 + states predicted by the interacting boson model (IBM). Only some rather weakly excited candidates have been found and used to derive limits for the transition strength of the mixed symmetry states. While the Ml strength is compatible with the IBM predictions there is less E2 strength than expected by the model.

In a large range of nuclei low lying Jπ=1+ states have been found that are excited predominantly by a new M1 mode. Four properties of the new mode will be discussed in detail. Firstly, from the excitation energy systematics observed the strength of the Majorana force of the interacting boson model (IBA) is deduced. Secondly, through the comparison of electron scattering and proton scattering experiments it is shown that the new mode is largely due to the orbital motion of protons with respect to neutrons. Thirdly, taking the nucleus 164Dy as an example, g-factors and effective boson charges of the M1-, E2- and M3 IBA transition operators, respectively, are studied. The F-scalar magnetic octupol g-factor ΩS is derived for the first time. Finally, the distribution of M1 strength in 156Gd will be discussed in the light of recent theoretical calculations.