Search

Detailed assessments of the ability of recent theoretical approaches to modeling existing experimental data for ternary fission confirm earlier indications that the dominant mode of cluster formation in ternary fission is clusterization in very neutron rich, very low density, essentially chemically equilibrated, nucleonic matter. An extended study and comparison of these approaches applied to ternary fission yields in the thermal neutron induced reaction $^{241}$Pu($n_{\rm th}$,f) has been undertaken to refine the characterization of the source matter. The resonance gas approximation has been improved taking in-medium effects on the binding energies into account. A temperature of 1.29 MeV, density of $6.7 \times 10^{-5}$ nucleons/fm$^3$ and proton fraction $Y_p$ = 0.035 are found to provide a good representation of yields of the ternary emitted light particles and clusters. In particular, results for $Z= 1$ and 2 isotopes are presented. Isotopes with larger $Z$ are discussed, and the roles of medium and continuum effects, even at very low density are illustrated., 19 pages, 5 figures

The mass dependence of the transverse flow for $Z=1$--5 fragments from the collisions of $^{40}\mathrm{Ar}+^{27}\mathrm{Al}, ^{40}\mathrm{Ar}+^{48}\mathrm{Ti}$, and $^{40}\mathrm{Ar}+^{58}\mathrm{Ni}$ at 47 MeV/nucleon is investigated experimentally in this article. The transverse flow values are determined using the in-plane components of the fragment transverse momenta, where three conventional methods, i.e., the kinetic flow tensor method, the transverse momentum analysis method, and the azimuthal correlation method, are applied to reconstruct the reaction plane in an event-by-event basis. It is demonstrated from the comparison of the present experimental mass dependent flow measurements and the model simulations using an improved antisymmetrized molecular dynamics model that the experimentally observed abnormal $\ensuremath{\alpha}$ transverse flow enhancement is closely related to the reaction plane reconstruction procedure in the flow extraction. We further investigate the physical existence of the abnormal $\ensuremath{\alpha}$ flow behavior using a two-particle azimuthal correlation method, which allows us to provide the relative flow magnitude information with an identification of fragment charge number without the knowledge of the reaction plane differing from the three conventional methods. It is found that the relative flow magnitudes deduced from the two-particle azimuthal correlation functions with an identification of $Z$, with the correction for the recoil effect imposed by the momentum conservation, show a monotonically increasing trend as a function of fragment charge number, with no exception of the $\ensuremath{\alpha}$ flow enhancement. These results, in addition to those from the improved antisymmetrized molecular dynamics model simulations, definitely provide experimental evidences for the inexistence of the abnormal $\ensuremath{\alpha}$ flow behavior in the heavy-ion collisions at the present incident energy region in nature.

Albergo thermometers with double isotope, isotone, and isobar yield ratio pairs with one proton and/or neutron difference are investigated. Without any extra sequential decay correction, a real temperature value of $4.9\ifmmode\pm\else\textpm\fi{}0.5$ MeV is deduced from the yields of the experimentally reconstructed primary hot intermediate mass fragments (IMFs) from $^{64}\mathrm{Zn}+^{112}\mathrm{Sn}$ collisions at 40 MeV/nucleon using the Albergo thermometer for the first time. An experimental sequential decay correction from the apparent temperatures to the real ones for 12 other reaction systems with different neutron-proton ($N/Z$) asymmetries in the same experiment, $^{70}\mathrm{Zn}$, $^{64}\mathrm{Ni}$ on $^{112,124}\mathrm{Sn}$, $^{58,64}\mathrm{Ni}$, $^{197}\mathrm{Au}$, and $^{232}\mathrm{Th}$ at 40 MeV/nucleon, is performed using an empirical correction factor approach of Tsang et al. [Phys. Rev. Lett. 78, 3836 (1997)] with the deduced 4.9-MeV temperature value. The dependence of nuclear temperature on the source $N/Z$ asymmetry is further investigated using these deduced real source temperature values from the present 13 systems. It is found that the deduced real source temperatures at the present source $N/Z$ range show a rather weak dependence on the source $N/Z$ asymmetry. By comparison between our previous results and those from other independent experiments, a consistent description for the $N/Z$ asymmetry dependence of nuclear temperature is addressed.

The $^{12}\mathrm{C}+^{12}\mathrm{C}$ sub-barrier fusion cross section is calculated within the framework of a time-dependent Hartree-Fock-based classical model using the Feynman path-integral method. The modified astrophysical ${S}^{*}$ factor is compared to direct and indirect experimental results. A good agreement with the direct data is found. In the lower-energy region where recent analyses of experimental data obtained with the Trojan horse method (THM) lead to contrasting results, the model predicts a nonresonant ${S}^{*}$ factor half-way between those results. Low-energy resonances revealed in the THM data are added to the calculation, and the relative reaction rate in the Gamow region is calculated. In particular, including ${0}^{+}$ resonances result in some agreement with the THM data. The role of different resonances is discussed in detail, and their influence on the reaction rate at temperatures relevant to stellar evolution is investigated.

The yields of light elements ($Z=1,2$) obtained from spontaneous ternary fission of $^{252}$Cf are treated within a nonequilibrium approach, and the contribution of unstable nuclei and excited bound states is taken into account. These light cluster yields may be used to probe dense matter, and to infer in-medium corrections. Continuum correlations are calculated from scattering phase shifts using the Beth-Uhlenbeck formula, and the effect of medium modification is estimated. The relevant distribution is reconstructed from the measured yields of isotopes. This describes the state of the nucleon system at scission and cluster formation, using only three Lagrange parameters which are the nonequilibrium counterparts of the temperature and chemical potentials, as defined in thermodynamic equilibrium. We concluded that a simple nuclear statistical equilibrium model neglecting continuum correlations and medium effects is not able to describe the measured distribution of H and He isotopes. Moreover, the freeze-out concept may serve as an important ingredient to the nonequilibrium approach using the relevant statistical operator concept., 13 pages, 1 figure

We present a dedicated experimental setup that has been built in Institute of Physics of the Jagiellonian University and is currently used to search long lived super heavy elements (LLSHE) that could be produced in the reaction between heavy ions and then deposited in the active catcher (AC) scintillation material. The collisions between heavy nuclei $^{197}Au$ (7.5 A.MeV) and $^{232}Th$ have been performed during our experiment at the Cyclotron Institute, Texas A&M in 2015. An innovative apparatus, which consists of ΔE–E detectors, enables the registration and identification of spontaneous decays (α or fission - SF) of heavy products, which were deposited in the scintillation material of the AC. Unique feature of the apparatus is that the AC scintillators are at the same time ΔE part of each of ΔE–E detector. The other part, E part, is a silicon detector. This construction largely eliminates background events in the region where alpha particles emitted by decaying reaction products are expected. Our measurements should be sensitive to search for super heavy elements (SHE) which could be deposited in irradiated scintillators and which have lifetimes of a year till over a dozen of years. Some results of the continuous measurement that already lasts 1.5 year will be shown.

X. G. Cao, E. J. Kim, K. Hagel, M. Barbui, J. Gauthier, S. Wuenschel, G. Giuliani, M. R. D. Rodriguez, H. Zheng, M. Huang, A. Bonasera, R. Wada, N. Blando, G. Q. Zhang, C. Y. Wong A. Staszczak, Z. X. Ren, Y. K. Wang, S. Q. Zhang, J. Meng, J. B. Natowitz, Exclusive measurements for α and α conjugate exit channels are carried out for 35 MeV/nucleon 28Si induced reactions. Systematic analyses of these channels reveal high energy resonance structures in 7 de-excitation channels. The resonances are compared with results of several recent theoretical calculations for toroidal high-spin isomers. The possible underlying physics of these observations are discussed.

Ternary fission of actinides probes the state of the nucleus at scission. Light clusters are produced in space and time very close to the scission point. Within the nonequilibrium statistical operator method, a generalized Gibbs distribution is constructed from the information given by the observed yields of isotopes. Using this relevant statistical operator, yields are calculated taking excited states and continuum correlations into account, in accordance with the virial expansion of the equation of state. Clusters with mass number $A \le 10$ are well described using the nonequilibrium generalizations of temperature and chemical potentials. Improving the virial expansion, in-medium effects may become of importance in determining the contribution of weakly bound states and continuum correlations to the intrinsic partition function. Yields of larger clusters, which fail to reach this quasi-equilibrium form of the relevant distribution, are described by nucleation kinetics, and a saddle-to-scission relaxation time of about 7000 fm/c is inferred. Light charged particle emission, described by reaction kinetics and virial expansions, may therefore be regarded as a very important tool to probe the nonequilibrium time evolution of actinide nuclei during fission., Comment: 5 pages, 1 figure

Yields of equatorially emitted light isotopes, $1\le Z\le 14$, observed in ternary fission in the reaction $^{241}$Pu($n_{\rm th}$,f) are employed to determine apparent chemical equilibrium constants for low-temperature and low-density nuclear matter. The degree of liberation and role of medium modifications are probed through a comparison of experimentally derived reaction quotients with equilibrium constants calculated using a relativistic mean-field model employing a universal medium modification correction for the attractive $\sigma$ meson coupling. The results of these comparisons indicate that equilibrium is achieved for the lighter ternary fission isotopes. For the heavier isotopes experimental reaction quotients are well below calculated equilibrium constants. This is attributed to a dynamical limitation reflecting insufficient time for full equilibrium to develop. The role of medium effects leading to yield reductions is discussed as is the apparent enhancement of yields for $^8$He and other very neutron rich exotic nuclei., Comment: 8 pages, 2 figures

The dependence of the nuclear temperature on the source neutron-proton ($N/Z$) asymmetry has been experimentally investigated with the light charged particles (LCPs) generated from 13 reaction systems with different $N/Z$ asymmetries, $^{64}\mathrm{Zn}$ on $^{112}\mathrm{Sn}$, and $^{70}\mathrm{Zn}$, $^{64}\mathrm{Ni}$ on $^{112,124}\mathrm{Sn}$, $^{58,64}\mathrm{Ni}$, $^{197}\mathrm{Au}$, and $^{232}\mathrm{Th}$ at 40 MeV/u. A rather weak $N/Z$ asymmetry dependence of the source temperature has been qualitatively inferred from the extracted $N/Z$ asymmetry dependence of the apparent temperature and that of the relative temperature change by the sequential decay effects with the help of the theoretical simulations. Comparing the present result with those from our previous work and other available experimental results, a weak $N/Z$ asymmetry dependence of nuclear temperature is commonly observed in different independent experiments and with different thermometers, except for the result reported by McIntosh et al. [Phys. Lett. B 719, 337 (2013)]. The origin of the difference between the conclusion of the former group and that of McIntosh et al. is addressed, using statistical multifragmentation model (SMM) simulations.

The dependence of the nuclear temperature on the source neutron-proton ($N/Z$) asymmetry is experimentally investigated with the intermediate mass fragments (IMFs) generated from thirteen reaction systems with different $N/Z$ asymmetries, $^{64}\mathrm{Zn}$ on $^{112}\mathrm{Sn}$ and $^{70}\mathrm{Zn}, ^{64}\mathrm{Ni}$ on $^{112,124}\mathrm{Sn}, ^{58,64}\mathrm{Ni}, ^{197}\mathrm{Au}, ^{232}\mathrm{Th}$ at 40 MeV/nucleon. The apparent source temperatures for these systems are determined from the measured IMF yields from the intermediate velocity sources using eight carbon-related double isotope ratio thermometers. A rather weak $N/Z$ asymmetry dependence of the source temperature is qualitatively inferred from the extracted $N/Z$ asymmetry dependence of the apparent temperature and that of the relative temperature change by the sequential decay effects with the help of the theoretical simulations. The present result is compared with those from other available experiments.

Marc LefortIt was with great sadness that we learned of the death of Professor Marc Lefort on 16 January 2001 at the age of 98. He was the initiator of the development of heavy ion physics in Franc...

Over the last decade, the Low-Energy Nuclear Physics (LENP) and Nuclear Astrophysics (NAP) communities have increasingly organized themselves in order to take a coherent approach to resolving the challenges they face. As a result, there is a high level of optimism in view of the unprecedented opportunities for substantial progress. In preparation of the 2015 US Nuclear Science Long Range Plan (LRP), the two American Physical Society Division of Nuclear Physics town meetings on LENP and NAP were held jointly on August 21–23, 2014, at Texas A&M, College Station, in Texas. These meetings were co-organized to take advantage of the strong synergy between the two fields. The present White Paper attempts to communicate the sense of great anticipation and enthusiasm that came out of these meetings. A unanimously endorsed set of joint resolutions condensed from the individual recommendations of the two town meetings were agreed upon. The present LENP White Paper discusses the above and summarizes in detail for each of the sub-fields within low-energy nuclear physics, the major accomplishments since the last LRP, the compelling near-term and long-term scientific opportunities plus the resources needed to achieve these goals, along with the scientific impact on, and interdisciplinary connections to, other fields.

The experimental excitation function for the $7\ensuremath{\alpha}$ de-excitation of $^{28}\mathrm{Si}$ nuclei excited to high excitation energies in the collisions of 35 MeV/nucleon $^{28}\mathrm{Si}$ with $^{12}\mathrm{C}$ reveals resonance structures. The possibility that these structures may indicate the population of toroidal high-spin isomers such as those predicted by a number of recent theoretical calculations is discussed and the need for further investigations is emphasized.

We present a dedicated experimental setup which is currently used to search for long lived super heavy elements (SHE) implanted in catcher scintillators which were irradiated by reaction products of $^{197}$Au (7.5 A.MeV) projectile and $^{232}$Th target collisions during our experiment performed at Cyclotrone Institute, Texas A$\&$M University in 2015. The built-in novel measuring apparatus consists of $\Delta$E-E detector pairs which are able to register $\alpha$ or spontaneous fission (SF) decays of heavy reaction products deposited in the scintillators. Their unique feature is that the examined scintillators are at the same time $\Delta$E part of each of $\Delta$E-E detector while E part is a silicon detector. Our apparatus is dedicated to search for SHEs which have a lifetime of a year till tens of years. Results of commissioning tests of our setup are presented., Comment: 6 pages, 3 figures, presented at Zakopane Conference on Nulear Physics 2018, submitted to Acta Physica Polonica B

Identification of alpha cluster states analogous to the 12C Hoyle state in heavier alpha- conjugate nuclei can provide tests of the existence of alpha condensates in nuclei. Such states are predicted for 16O, 20Ne, 24Mg, 28Si etc. at excitation energies slightly above the multi-alpha particle decay threshold, but have not yet been experimentally identified. The Thick Target Inverse Kinematics (TTIK) technique can be used to study the breakup of excited self-conjugate nuclei into many alpha particles. The reaction 20Ne+{\alpha} was studied using a 20Ne beam at 12 MeV/nucleon from the K150 cyclotron at Texas A&M University. The TTIK method was used to study both single {\alpha}-particle emission and multiple {\alpha}-particle decays. Events with alpha multiplicity up to four were analyzed. The analysis of the three {\alpha} - particle emission data allowed the identification of the Hoyle state and other 12C excited states decaying into three alpha particles. The results are shown and compared with other data available in the literature. Although the statistics for events with alpha multiplicity four is low, the data show a structure at about 15.2 MeV that could indicate the existence in 16O of a state analogous to the 12C Hoyle state. This structure is confirmed by the re-analysis of alpha multiplicity four events from a previous experiment performed at 9.7 MeV/nucleon with a similar setup but lower granularity. Moreover, the reconstructed excitation energy of 24Mg for these events peaks at around 34 MeV, very close to the predicted excitation energy for an excited state analogous to the 12C Hoyle state in 24Mg., Comment: 22 pages, 16 figures

The production of $\ensuremath{\alpha}$-particle decaying heavy nuclei in reactions of 7.5--6.1 MeV/nucleon $^{238}\mathrm{U}$ +$^{232}\mathrm{Th}$ was explored using an in-beam detection array composed of YAP scintillators and gas ionization chamber-Si telescopes. Comparisons of $\ensuremath{\alpha}$ energies and half-lives for the observed products with those of the previously known isotopes and with theoretically predicted values indicate the observation of a number of previously unreported $\ensuremath{\alpha}$ emitters. $\ensuremath{\alpha}$-particle decay energies reaching as high as 12 MeV are observed. Many of these are expected to be from decay of previously unseen relatively neutron rich products. While the contributions of isomeric states require further exploration and specific isotope identifications need to be made, the production of heavy isotopes with quite high atomic numbers is suggested by the data.

In this article, a mistake in the formulation of the modified Fisher model (MFM) derived in the pioneering works of the Purdue group is addressed and corrected by reversing the sign of the mixing entropy term in the original formulation. The errors in the results of the previous MFM-related studies, such as isotopic yield distribution, isobaric yield ratios, isoscaling, $m$ scaling, self-consistent determination of density, symmetry energy, and temperature, and density and temperature determination related to the intermediate mass fragment (IMF) freezeout, are quantitatively analyzed. It is found that the errors originating from the mistake in sign of the mixing entropy term are generally small and even have no effect in some cases.

Resonance structures are observed in the excitation function of the 7α de-excitation of 28Si nuclei are observed in the collisions of 35 MeV/nucleon 28Si with 12C. These structures may indicate that toroidal high-spin isomers such as those predicted by recent theoretical calculations are populated.

The paper presents a novel instrumentation for rare events selection which was tested in our research of short lived super heavy elements production and detection. The instrumentation includes an active catcher multi elements system and dedicated electronics. The active catcher located in the forward hemisphere is composed of 63 scintillator detection modules. Reaction products of damped collisions between heavy ion projectiles and heavy target nuclei are implanted in the fast plastic scintillators of the active catcher modules. The acquisition system trigger delivered by logical branch of the electronics allows to record the reaction products which decay via the alpha particle emissions or spontaneous fission which take place between beam bursts. One microsecond wave form signal from FADCs contains information on heavy implanted nucleus as well as its decays., Comment: 12 pages, 5 figures, accepted for publication in Acta Physica Polonica B

Symmetry energy, temperature and density at the time of the intermediate mass fragment formation are determined in a self-consistent manner, using the experimentally reconstructed primary hot isotope yields and anti-symmetrized molecular dynamics (AMD) simulations. The yields of primary hot fragments are experimentally reconstructed for multifragmentation events in the reaction system Zn 64 + Sn 112 at 40 MeV / nucleon . Using the reconstructed hot isotope yields and an improved method, based on the modified Fisher model, symmetry energy values relative to the apparent temperature, a sym / T , are extracted. The extracted values are compared with those of the AMD simulations, extracted in the same way as those for the experiment, with the Gogny interaction with three different density-dependent symmetry energy terms. The a sym / T values change according to the density-dependent symmetry energy terms used. Using this relation, the density of the fragmenting system is extracted first. Then symmetry energy and apparent temperature are determined in a self consistent manner in the AMD model simulations. Comparing the calculated a sym / T values and those of the experimental values from the reconstructed yields, ρ / ρ 0 = 0.65 ± 0.02 , a sym = 23.1 ± 0.6 MeV and T = 5.0 ± 0.4 MeV are evaluated for the fragmenting system experimentally observed in the reaction studied.

The de-excitation of alpha-conjugate nuclei produced in reactions of 35 MeV/nucleon 40Ca with 40Ca has been investigated. Particular emphasis is placed on examining the dynamics of collisions leading to projectile-like fragment exit channels. A general exploration of the reaction systematics reveals the binary dissipative character of the collisions and a hierarchy effect similar to that seen for heavier systems. Investigation of the subset of events characterized by a total alpha-conjugate mass (alpha particles plus alpha-conjugate fragments) equal to 40 and atomic number equal to 20 reveals a dominance of alpha-conjugate exit channels. The hierarchy effect for these channels leads to the production of alpha-clustered neck structures with potentially exotic geometries and properties.

Ratios of differential chemical potential values relative to the temperature, $({\ensuremath{\mu}}_{n}\ensuremath{-}{\ensuremath{\mu}}_{p})/T$, extracted from isotope yields of 13 reaction systems at 40 MeV/nucleon are compared to those of a quantum statistical model to determine the temperature and symmetry energy values of the fragmenting system. The experimental $({\ensuremath{\mu}}_{n}\ensuremath{-}{\ensuremath{\mu}}_{p})/T$ values are extracted based on the modified Fisher model. Using the density value of $\ensuremath{\rho}/{\ensuremath{\rho}}_{0}=0.56$ from the previous analysis, the temperature and symmetry energy values of $T=4.6\ifmmode\pm\else\textpm\fi{}0.4$ MeV and ${a}_{\mathrm{sym}}=23.6\ifmmode\pm\else\textpm\fi{}2.1$ MeV are extracted in a framework of a quantum statistical model. These values agree well with those of the previous work, in which a self-consistent method was utilized with antisymmetrized molecular dynamics simulations. The extracted temperature and symmetry energies are discussed together with other experimental values published in literature.

Fermi energy heavy ion collisions provide a valuable tool to research nuclear reaction dynamics and the hot nuclear matter Equation of State (EOS) at sub/supra-normal densities. In this energy regime, multi-fragmentation becomes important and the ejected light particles and intermediate mass fragments (IMFs) with Z > 2 carry a great deal of information on the thermal and chemical evolution of the reaction system under investigation. Existing detectors [1] include those with excellent isotopic resolution with limited angular coverage or excellent geometric acceptance with moderate isotopic resolution. Much information has been extracted from experiments performed with these detectors [2–9]. Ideally, a detector array with both excellent isotopic resolution and with a nearly 4π angular coverage of discrete telescopes with a high granularity is desirable. NIMROD–ISiS at the Cyclotron Institute, TAMU, is designed for such purposes and provides a powerful detector array capable of both charged particle and neut...

The neutron detection efficiency of a DEMON detector, averaged over the whole volume, was calculated using GEANT and applied to determine neutron multiplicities in an intermediate heavy ion reaction. When a neutron source is set at a distance of about 1 m from the front surface of the detector, the average efficiency, eav , is found to be significantly lower (20-30%) than the efficiency measured at the center of the detector, e0 . In the GEANT simulation the ratio R= eav / e0 was calculated as a function of neutron energy. The experimental central efficiency multiplied by R was then used to determine the average efficiency. The results were applied to a study of the 64 Zn+ 112 Sn reaction at 40 A MeV which employed 16 DEMON detectors. The neutron multiplicity was extracted using a moving source fit. The derived multiplicities are compared well with those determined using the neutron ball in the NIMROD detector array in a separate experiment. Both are in good agreement with multiplicities predicted by a transport model calculation using an antisymmetric molecular dynamics (AMD) model code. © 2013 Elsevier B.V.

The BRAHMS collaboration has measured transverse momentum spectra of pions, kaons, protons, and antiprotons at rapidities 0 and 3 for Cu+Cu collisions at sNN=200 GeV. As the collisions become more central the collective radial flow increases while the temperature of kinetic freeze-out decreases. The temperature is lower and the radial flow weaker at forward rapidity. Pion and kaon yields with transverse momenta between 1.5 and 2.5 GeV/c are suppressed for central collisions relative to scaled p+p collisions. This suppression, which increases as the collisions become more central, is consistent with jet quenching models and is also present with comparable magnitude at forward rapidity. At such rapidities, initial state effects may also be present and persistence of the meson suppression to high rapidity may reflect a combination of jet quenching and nuclear shadowing. The ratio of protons to mesons increases as the collisions become more central and is largest at forward rapidities.

12th International Conference on Nucleus-Nucleus Collisions, NN2015, Catania, Italy, 21 Jun 2015 - 26 Jun 2015; The European physical journal / Web of Conferences 117, 07018 (2016). doi:10.1051/epjconf/201611707018, Published by EDP Sciences, Les Ulis

We will show that the Thick Target Inverse Kinematics (TTIK) technique can be used to investigate the breakup of excited selfconjugate nuclei into many alpha particles. Two test runs were performed at Cyclotron Institute of Texas A&M University to study the reaction 20 Ne+α at maximum beam energies of 10 and 12 AMeV. Due to the limited statistics, only events with alpha multiplicity up to three were analyzed. The analysis of the three α -particle emission data allowed the identification of the Hoyle state and other 12 C excited states decaying into three alpha particles. The results will be shown and compared with other data available in the literature.

In this work, we present a new and general method for measuring the astrophysical $S$ factor of nuclear reactions in laser-induced plasmas and we apply it to $^{2}\mathrm{H}(d,n)^{3}\mathrm{He}$. The experiment was performed with the Texas Petawatt Laser, which delivered 150--270 fs pulses of energy ranging from 90 to 180 J to ${\mathrm{D}}_{2}$ or ${\mathrm{CD}}_{4}$ molecular clusters (where D denotes ${}^{2}\mathrm{H})$. After removing the background noise, we used the measured time-of-flight data of energetic deuterium ions to obtain their energy distribution. We derive the $S$ factor using the measured energy distribution of the ions, the measured volume of the fusion plasma, and the measured fusion yields. This method is model independent in the sense that no assumption on the state of the system is required, but it requires an accurate measurement of the ion energy distribution, especially at high energies, and of the relevant fusion yields. In the $^{2}\mathrm{H}(d,n)^{3}\mathrm{He}$ and $^{3}\mathrm{He}(d,p)^{4}\mathrm{He}$ cases discussed here, it is very important to apply the background subtraction for the energetic ions and to measure the fusion yields with high precision. While the available data on both ion distribution and fusion yields allow us to determine with good precision the $S$ factor in the $d+d$ case (lower Gamow energies), for the $d+^{3}\mathrm{He}$ case the data are not precise enough to obtain the $S$ factor using this method. Our results agree with other experiments within the experimental error, even though smaller values of the $S$ factor were obtained. This might be due to the plasma environment differing from the beam target conditions in a conventional accelerator experiment.

The multiplicity of fragments in Fermi energy heavy-ion collisions was experimentally extracted. Compared with the results of calculation using the antisymmetrized molecular dynamics (AMD) model which accounts for the primary fragments only, the results calculated using the AMD together with a statistical decay code GEMINI to account for the deexcitation of excited primary fragments are in better agreement with those extracted from the experiment. This observation indicates that the experimental multiplicity distribution may be significantly different from those of primary fragments.

Isoscaling is derived within a recently proposed modified Fisher model where the free energy near the critical point is described by the Landau O ( m 6 ) theory. In this model m = N f − Z f A f is the order parameter, a consequence of (one of) the symmetries of the nuclear Hamiltonian. Within this framework we show that isoscaling depends mainly on this order parameter through the ‘external (conjugate) field’ H. The external field is just given by the difference in chemical potentials of the neutrons and protons of the two sources. To distinguish from previously employed isoscaling relationships, this approach is dubbed: m-scaling. We discuss the relationship between this framework and the standard isoscaling formalism and point out some substantial differences in interpretation of experimental results which might result. These should be investigated further both theoretically and experimentally.

The experimental results reveal the isospin dependence of the nuclear phase transition in terms of the Landau Free Energy description of critical phenomena. Near the critical point, different ratios of the neutron to proton concentrations lead to different critical points for the phase transition which is analogous to the phase transitions in He 4- He 3 liquid mixtures. The antisymmetrized molecular dynamics (AMD) and GEMINI models calculations were also performed and the results will be discussed as well.

Invariant p T spectra and rapidity densities covering a large rapidity range ( − 0.1 y 3.5 ) are presented for π ± and K ± mesons from central Au + Au collisions at s NN = 62.4 GeV . The mid-rapidity yields of meson particles relative to their anti-particles are found to be close to unity ( π − / π + ∼ 1 , K − / K + ∼ 0.85 ) while the anti-proton to proton ratio is p ¯ / p ∼ 0.49 . The rapidity dependence of the π − / π + ratio is consistent with a small increase towards forward rapidities while the K − / K + and p ¯ / p ratios show a steep decrease to ∼0.3 for kaons and 0.022 for protons at y ∼ 3 . It is observed that the kaon production relative to its own anti-particle as well as to pion production in wide rapidity and energy ranges shows an apparent universal behavior consistent with the baryo-chemical potential, as deduced from the p ¯ / p ratio, being the driving parameter.

A very brief summary Of Our Current research on clustering in low density matter formed in near Fermi energy heavy ion collisions is presented. At the lowest densities and temperatures large alpha mass fractions are observed. Temperature and density dependent symmetry free energies have been derived from isoscaling analyzes of the yields of nuclei with A = 4. The symmetry free energies are far above those obtained in common effective interaction calculations, reflecting cluster formation, primarily of alpha particles, not included in such calculations.

The proton-to-pion ratios measured in the BRAHMS experiment for Au + Au and p + p collisions at s N N = 62.4 and 200 GeV are presented as a function of transverse momentum and collision centrality at selected pseudorapidities in the range of 0–3.8. A strong pseudorapidity dependence of these ratios is observed. We also compare the magnitude and p T -dependence of the p / π + ratios measured in Au + Au collisions at s N N = 200 GeV and η ≈ 2.2 with the same ratio measured at s N N = 62.4 GeV and η = 0 . The great similarity found between these ratios throughout the whole p T range (up to 2.2 GeV / c ) is consistent with particle ratios in A + A collisions being described with grand-canonical distributions characterized by the baryo-chemical potential μ B . At the collision energy of 62.4 GeV, we have observed a unique point in pseudorapidity, η = 3.2 , where the p / π + ratio is independent of the collision system size in a wide p T -range of 0.3 ⩽ p T ⩽ 1.8 GeV / c .

The BigSol Superconducting Solenoid Beam Line at the Texas A&M Superconducting Cyclotron has been used to measure energy losses of 40Ar, 84Kr, 197Au and 238U ions in mylar, aluminum and isobutane at energies ranging from the Bragg peak up to several MeV/nucleon. The experimental data are compared with predictions from the SRIM code. In general experimental data for 40Ar and 84Kr are in agreement with model predictions whereas differences on the order of 10% are evidenced in some cases for 197Au and 238U ions especially at and around the Bragg peak energies.

Transverse momentum spectra of protons and anti-protons measured in the rapidity range 0 y 3.1 from 0–10% central Au + Au collisions at s N N = 62.4 GeV are presented. The rapidity densities, d N / d y , of protons, anti-protons and net-protons ( N p – N p ¯ ) have been deduced from the spectra over a rapidity range wide enough to observe the expected maximum net-baryon density. From mid-rapidity to y = 1 the net-proton yield is roughly constant ( d N / d y ∼ 10 ), but rises to d N / d y ∼ 25 at 2.3 y 3.1 . The mean rapidity loss is 2.01 ± 0.14 ± 0.12 units from beam rapidity. The measured rapidity distributions are compared to model predictions. Systematics of net-baryon distributions and rapidity loss vs. collision energy are discussed.

The upgraded NIMROD–ISiS 4 π detector array is described. The array is composed of 228 detector modules annularly arranged into 14 rings. Telescopes of Si–CsI and Si–Si–CsI provide excellent isotopic resolution throughout the detector array. To enhance event characterization, the entire charged particle array is housed inside the TAMU Neutron Ball.

Experiments with 1-3 MeV He-4 beams and 2.2-3.2 MeV proton beams have been performed in order to develop a precise and highly sensitive method for the detection and analysis of light elements in threat or drug materials using simultaneously the RBS and ERDA techniques. Commercially available plastic films have been used as samples. The 1 MeV He-4 beam has been found to be inadequate owing to the rapid destruction of the targets. Best results have been obtained using proton beams with energies higher than 3 MeV. For 3.2 MeV proton beams, ERDA has been used for the analysis of the hydrogen constituent. (c) 2009 Elsevier B.V. All rights reserved.

The detector system used at the first focus of the BigSol superconducting solenoid beam line at the Texas A & M superconducting cyclotron is presented. The system is composed of a position sensitive PPAC followed by an ionization chamber (IC) with a YAP(Ce) array in its back plane. The position sensitivity of the PPAC as well the energy resolution of the IC is investigated as a function of the counting rate. Pulse height, pulse height resolution and time resolution of the YAP(Ce) crystals are studied for a variety of heavy ion beams ranging from 20 Ne to 197 Au at energies from 15 AMeV to 40 AMeV. The pulse shape discrimination method using a Flash ADC is also explored, in order to identify decay products (alpha particles and electron/gamma) from the fragments implanted in the scintillator.

In this work we explore the possibility that the motion of the deuterium ions emitted from Coulomb cluster explosions is chaotic enough to resemble thermalization. We analyze the process of nuclear fusion reactions driven by laser-cluster interactions in experiments conducted at the Texas Petawatt laser facility using a mixture of D2+3He and CD4+3He cluster targets. When clusters explode by Coulomb repulsion, the emission of the energetic ions is nearly isotropic. In the framework of cluster Coulomb explosions, we analyze the energy distributions of the ions using a Maxwell- Boltzmann (MB) distribution, a shifted MB distribution (sMB) and the energy distribution derived from a log-normal (LN) size distribution of clusters. We show that the first two distributions reproduce well the experimentally measured ion energy distributions and the number of fusions from d-d and d-3He reactions. The LN distribution is a good representation of the ion kinetic energy distribution well up to high momenta where the noise becomes dominant, but overestimates both the neutron and the proton yields. If the parameters of the LN distributions are chosen to reproduce the fusion yields correctly, the experimentally measured high energy ion spectrum is not well represented. We conclude that the ion kinetic energy distribution is highly chaotic and practically not distinguishable from a thermalized one., Comment: 9 pages, 6 figures

Different approaches for measuring nuclear temperatures are described. The quantitative results of different thermometer approaches are often not consistent. These differences are traced back to the different basic assumptions of the applied methods. Moreover, an overview of recent theoretical investigations is given, which study the quantitative influence of dynamical aspects of the nuclear-reaction process on the extracted apparent temperatures. The status of the present experimental and theoretical knowledge is reviewed. Guidelines for future investigations, especially concerning the properties of asymmetric nuclear matter, are given.

We review the main results obtained by the BRAHMS collaboration on the properties of hot and dense hadronic and partonic matter produced in ultrarelativistic heavy ion collisions at RHIC. A particular focus of this paper is to discuss to what extent the results collected so far by BRAHMS, and by the other three experiments at RHIC, can be taken as evidence for the formation of a state of deconfined partonic matter, the so called quark-gluon-plasma (QGP). We also discuss evidence for a possible precursor state to the QGP, i.e. the proposed Color Glass Condensate., 32 pages, 18 figures

We present the results obtained by the BRAHMS experiment at the Relativistic Heavy Ion Collider (RHIC) for three colliding systems, namely: Au + Au , d + Au and p + p at [Formula: see text]. The main focus here is to give an overview of the main results on the reaction dynamics and on the properties of hot and high energy density matter produced in utra-relativistic heavy ion collisions. Measurement of particle production, particle spectra over a large rapidity interval as well as high pt measurements related to nuclear modification in Au + Au and d + Au collision are discussed. The observed number of charged particles produced per unit of rapidity at the central rapidity region indicates that a high energy density (> 5 GeV/fm3) system is created at the initial stage of the Au + Au reaction. From the particle spectra we deduced significant radial expansion (β ≈ 0.75) which is consistent with the large initial energy density. For Au + Au at η = 0 we observe the suppression of the high p T particles as compared to the elementary collisions, whereas for the d + Au reaction the Cronin type enhancement is observed. We also discuss to what extent these results can be taken as evidence for the quark gluon plasma (QGP). Finally, we present the nuclear modification effects in d + Au reaction as a function of rapidity and consider whether the observed suppression at forward rapidities constitutes sufficient evidence for a possible precursor state to the QGP, i.e. the Color Glass Condensate (CGC).

We present a measurement of π − / π + , K − / K + and p ¯ / p from p + p collisions at s = 200 GeV over the rapidity range 0 y 3.4 . For p T 2.0 GeV / c we see no significant transverse momentum dependence of the ratios. All three ratios are independent of rapidity for y ≲ 1.5 and then steadily decline from y ∼ 1.5 to y ∼ 3 . The π − / π + ratio is below unity for y > 2.0 . The p ¯ / p ratio is very similar for p + p and 20% central Au + Au collisions at all rapidities. In the fragmentation region the three ratios seem to be independent of beam energy when viewed from the rest frame of one of the protons. Theoretical models based on quark–diquark breaking mechanisms overestimate the p ¯ / p ratio up to y ≲ 3 . Including additional mechanisms for baryon number transport such as baryon junctions leads to a better description of the data.

Recent results on limiting temperatures and caloric curves are discussed with respect to the question of identifying critical behavior in the disassembly of nuclei. We suggest that the best candidates for exploring such behavior are light nuclei in which the Coulomb Energies are less disruptive.

The BRAHMS experiment at RHIC was conceived to pursue the understanding of nuclear matter under extreme conditions by detailed measurements of charged hadrons over the widest possible range of rapidity and transverse momentum. The experiment consists of two spectrometers with complementary charged hadron detection capabilities as well as a series of global detectors for event characterization. A series of tracking detectors, time-of-flight arms and Cherenkov detectors enables momentum determination and particle identification over a wide range of rapidity and transverse momentum. Technical details and performance results are presented for the various detector subsystems. The performance of the entire system working together is shown to meet the goals of the experiment.