Heavy Targets Research Articles

Threshold behavior of interaction potential for the system 7Li + 64Ni: Comparison with 6Li + 64Ni

The elastic scattering angular distributions for the system 7Li + 64Ni were measured in the bombarding energy range of 12 MeV≤Elab≤26.4 MeV. A phenomenological optical model analysis was performed for the measured data. The strengths of the fitted potential components at the surface were estimated to extract their variation with energy. Further analyses of the measured angular distributions were performed with a hybrid potential composed of a renormalized folded real and a phenomenological imaginary potential. Both the model potentials predict similar energy dependent behavior for the effective interaction potential around the barrier. Unlike the heavy targets, 7Li + 64Ni does not show a normal threshold behavior. It also does not clearly exhibit a behavior similar to 6Li + 64Ni. The real potential for 7Li + 64Ni does not exhibit any significant energy dependence and the imaginary potential strength remains almost independent of energy above the Coulomb barrier (∼14 MeV). However, at energies below the barrier, a sudden drop in the imaginary potential strength is observed.

Asymptotic and near-target direct breakup ofLi6andLi7

Background: $^{6,7}\mathrm{Li}$ and $^{9}\mathrm{Be}$ are weakly bound against breakup into their cluster constituents. Breakup location is important for determining the role of breakup in above-barrier complete fusion suppression. Recent works have pointed out that experimental observables can be used to separate near-target and asymptotic breakup.Purpose: Our purpose is to distinguish near-target and asymptotic direct breakup of $^{6,7}\mathrm{Li}$ in reactions with nuclei in different mass regions.Method: Charged particle coincidence measurements are carried out with pulsed $^{6,7}\mathrm{Li}$ beams on $^{58}\mathrm{Ni}$ and $^{64}\mathrm{Zn}$ targets at sub-barrier energies and compared with previous measurements using $^{208}\mathrm{Pb}$ and $^{209}\mathrm{Bi}$ targets. A detector array providing a large angular coverage is used, along with time-of-flight information to give definitive particle identification of the direct breakup fragments.Results: In interactions of $^{6}\mathrm{Li}$ with $^{58}\mathrm{Ni}$ and $^{64}\mathrm{Zn}$, direct breakup occurs only asymptotically far away from the target. However, in interactions with $^{208}\mathrm{Pb}$ and $^{209}\mathrm{Bi}$, near-target breakup occurs in addition to asymptotic breakup. Direct breakup of $^{7}\mathrm{Li}$ into $\ensuremath{\alpha}\ensuremath{-}t$ is not observed in interactions with $^{58}\mathrm{Ni}$ and $^{64}\mathrm{Zn}$. However, near-target dominated direct breakup was observed in measurements with $^{208}\mathrm{Pb}$ and $^{209}\mathrm{Bi}$. A modified version of the Monte Carlo classical trajectory model code platypus, which explicitly takes into account lifetimes associated with unbound states, is used to simulate sub-barrier breakup reactions.Conclusions: Near-target breakup in interactions with $^{6,7}\mathrm{Li}$ is an important mechanism only for the heavy targets $^{208}\mathrm{Pb}$ and $^{209}\mathrm{Bi}$. There is insignificant near-target direct breakup of $^{6}\mathrm{Li}$ and no direct breakup of $^{7}\mathrm{Li}$ in reactions with $^{58}\mathrm{Ni}$ and $^{64}\mathrm{Zn}$. Therefore, direct breakup is unlikely to suppress the above-barrier fusion cross section in reactions of $^{6,7}\mathrm{Li}$ with $^{58}\mathrm{Ni}$ and $^{64}\mathrm{Zn}$ nuclei.

Analysis of 6Li Scattering at 240 MeV Using Different Nuclear Potentials

Angular distributions of the elastic and inelastic scattering cross sections of 6Li projectile on different heavy ion target nuclei including the 24Mg, 28Si, 48Ca, 58Ni, 90Zr, and 116Sn at energy of 240 MeV have been analyzed by using two different folded potentials based on the CDM3Y6 and Sao Paulo potentials for the real part of the optical potential, while the imaginary parts have a phenomenological Woods-Saxon shape. Coupled channel calculations for the low-lying 2+ state at 1.369, 1.779, 3.832, 1.454, 2.186, and 1.29 MeV for 24Mg, 28Si, 48Ca, 58Ni, 90Zr, and 116Sn, respectively, have been carried out, and the best fit values for B(EL) with the above models have been extracted by fitting the inelastic scattering cross section and compared with the values of previous works. The total reaction cross section and real and imaginary volume integrals have also been investigated.

Simulation of neutron production in heavy metal targets using Geant4 software

Inelastic hadronic interactions in heavy targets have been simulated using Geant4 and compared with experimental data for thin and thick lead and uranium targets. Special attention is paid to neutron and fission fragment production. Good agreement in the description of proton-beam interaction with thick targets is demonstrated, which is important for the simulation of experiments aimed at the development of subcritical reactors.

Disintegration locations inLi7→Be8transfer-triggered breakup at near-barrier energies

Background: At above-barrier energies, complete fusion cross sections in collisions of light weakly bound nuclei with heavy target nuclei are suppressed when compared to well-bound nuclei. Breakup of the projectilelike nucleus was proposed to be the cause. In addition to direct breakup, breakup following transfer was shown to be substantial.

Explicit inclusion of nonlocality in(d,p)transfer reactions

Background: Traditionally, nucleon-nucleus optical potentials are made local for convenience. In recent work we studied the effects of including nonlocal interactions explicitly in the final state for (d,p) reactions, within the distorted wave Born approximation. Purpose: Our goal in this work is to develop an improved formalism for nonlocal interactions that includes deuteron breakup and to use it to study the effects of including nonlocal interactions in transfer (d,p) reactions, in both the deuteron and the proton channel. Method: We extend the finite-range adiabatic distorted wave approximation to include nonlocal nucleon optical potentials. We apply our method to (d,p) reactions on 16O, 40Ca, 48Ca, 126Sn, 132Sn, and 208Pb at 10, 20 and 50 MeV. Results: We find that nonlocality in the deuteron scattering state reduces the amplitude of the wave function in the nuclear interior, and shifts the wave function outward. In many cases, this has the effect of increasing the transfer cross section at the first peak of the angular distributions. This increase was most significant for heavy targets and for reactions at high energies. Conclusions: Our systematic study shows that, if only local optical potentials are used in the analysis of experimental (d,p) transfer cross sections, the extracted spectroscopic factors may be incorrect by up to 40% due to the local approximation.

SHiP: a new multipurpose beam-dump experiment at the SPS

SHiP is an experiment to look for very weakly interacting particles at a new to be constructed beam-dump facility at the CERN SPS. The SHiP Technical Proposal has been submitted to the CERN SPS Committee in April 2015. The 400 GeV/c proton beam extracted from the SPS will be dumped on a heavy target with the aim of integrat- ing 2× 10 20 proton on target in five years. A detector located downstream of the targe t, based on a long vacuum tank followed by a spectrometer and particle identifi cation de- tectors, will allow probing a variety of models with light long-lived exotic partic les and masses below a few GeV/c 2 . The main focus will be the physics of the so-called Hid- den Portals, i.e. search for Dark Photons, Light scalars and pseudo-scalars, and Heavy Neutral Leptons (HNL). The sensitivity to HNL will allow for the first time to pr obe, in the mass range between the kaon and the charm meson mass, a coupling range for which Baryogenesis and active neutrino masses could also be explained. Integrated in SHiP is an Emulsion Cloud Chamber, already used in the OPERA experiment, which will allow to study active neutrino cross-sections and angular distributions. In par ticular SHiP can distinguish betweeno? and ¯ o?, and their deep inelastic scattering cross sections will be measured with statistics three orders of magnitude larger than currently available.

Four- and three-body channel coupling effects on6Li elastic scattering with CDCC

We investigate breakup dynamics in 6 Li elastic scattering on heavy targets (T = 209 Bi or 208 Pb) near the Coulomb barrier energy. Since the subsystem of 6 Li has a bound state as deuteron (n + p = d ), a four-body channel (6 Li + T → n + p + α + T) and a three-body channel (6 Li + T → d + α + T) get entangled during scattering as a breakup channel. Both channels are precisely treated with the four-body version of the continuum-discretized coupled-channels method (four-body CDCC). Four-body CDCC well reproduces measured elastic cross sections with no adjustable parameter. We then estimate the channel coupling effects by dividing the breakup channel into fourand three-body channels. It is found that 6 Li breakup is mainly induced by a three-body channel.

Prospects of heavy and superheavy element production via inelastic nucleus-nucleus collisions – from238U+238U to18O+254Es

Multi-nucleon transfer reactions, frequently termed deep-inelastic, between heavy-ion projectiles and actinide targets provide prospects to synthesize unknown isotopes of heavy actinides and superheavy elements with neutron numbers beyond present limits. The 238 U on 238 U reaction, which revealed essential aspects of those nuclear reactions leading to surviving heavy nuclides, mainly produced in 3 n and 4 n evaporation channels, is discussed in detail. Positions and widths of isotope distributions are compared. It is shown, as a general rule, that cross sections peak at irradiation energies about 10% above the Coulomb barrier. Heavy target nuclei are essential for maximizing cross sections. Experimental results from the 238 U on 248 Cm reaction, including empirical extrapolations, are compared with theoretical model calculations predicting relatively high cross sections for neutron-rich nuclei. Experiments to test the validity of such predictions are proposed. Comparisons between rather symmetric heavy-ion reactions like 238 U on 248 Cm (or heavier targets up to 254 Es) with very asymmetric ones like 18 O on 254 Es reveal that the ones with 238 U as a projectile have the highest potential in the superheavy element region while the latter ones can be advantageous for the synthesis of heavy actinide isotopes. Concepts for highly efficient recoil separators designed for transfer products are presented.

Transfer to the continuum calculations of quasifree (p,pn) and (p,2p) reactions

Nucleon removal ( p, pn ) and ( p, 2 p ) reactions at intermediate energies have gained renewed attention in recent years as a tool to extract information from exotic nuclei. The information obtained from these experiments is expected to be sensitive to deeper portions of the wave function of the removed nucleon than knockout reactions with heavier targets. In this contribution, we present calculations for ( p, 2 p ) and ( p, pn ) reactions performed within the so-called transfer to the continuum method (TR*). Results for stable and unstable nuclei are presented, and compared with experimental data, when available.

Understanding the effect of channel coupling on fusion of6Li+64Ni

The effect of inelastic excitation and single particle transfer reactions on fusion have been investigated for the system 6 Li+ 64 Ni at near barrier energies. The calculations show that a simultaneous coupling to the inelastic excitation of projectile and target along with positive Q-value 1n- and 1p-stripping channels, describes the experimental CF cross sections reasonably well in the below barrier region. Exploring the interplay of different reaction channels in the collision of weakly bound systems is a subject of interest, both experimentally and theoretically, over the past several years [1–4]. In a recent work [5], the effect of coupling to inelastic excitations and single particle transfer channels on the back angle quasi-elastic excitation function had been reported for the system 6 Li+ 64 Ni. To investigate the effect of these couplings on fusion excitation function, a complementary experimental observable, for 6 Li+ 64 Ni is the primary motivation of the present work. Unlike the heavy targets, for the lower medium mass targets like 64 Ni the measured fusion cross sections with weakly bound projectiles provide total fusion (TF) cross sections instead of the cross sections for complete fusion (CF) of the whole projectile. The TF cross section for 6 Li+ 64 Ni system includes along with CF cross section the contributions from incomplete

Complete Destruction of Ag Br Emulsion Nuclei BY<sup>28</sup>Si Ions with 4.5 GeV/Nucleon Energy

The main experimental characteristics (multiplicity characteristics) of secondary particles have been investigated in interactions of 28Si with emulsion at 4.5 GeV/c per nucleon at rest of emulsion, nuclei. The complete destruction of the heavy target nuclei (Ag, Br) has been studied. The average of shower particles s > is weakly dependent on the target mass whereas the average multiplicity of grey particles g > is strongly dependent on it. The correlations between the multiplicities of the charged secondaries at different mass number of the projectile and center-of-mass-available energy are investigated.

Transverse and Longitudinal Lambda Polarization in Lepton Scattering by Unpolarized Nucleons at HERMES

Transverse and longitudinal polarization of [Formula: see text] hyperons has been studied. The transfere of polarization from high-energy positron to [Formula: see text] hyperon has been measured. The longitudinal spin transverse coefficient is found to be [Formula: see text] = [Formula: see text]. The transverse polarization of [Formula: see text] and [Formula: see text] hyperons has been measured in inclusive quasireal photoproduction process for various target nuclei. The polarization observed is positive for light target nuclei and compartaible with zero for heavy target nuclei.

Dynamic Isovector Reorientation of Deuteron as a Probe to Nuclear Symmetry Energy.

We present the calculations on a novel reorientation effect of deuteron attributed to isovector interaction in the nuclear field of heavy target nuclei. The correlation angle determined by the relative momentum vector of the proton and the neutron originating from the breakup deuteron, which is experimentally detectable, exhibits significant dependence on the isovector nuclear potential but is robust against the variation of the isoscaler sector. In terms of sensitivity and cleanness, the breakup reactions induced by the polarized deuteron beam at about 100 MeV/u provide a more stringent constraint to the symmetry energy at subsaturation densities.

Be9elastic scattering onPb208andAl27within a four-body reaction framework

We investigate the low-energy $^9$Be elastic scattering on two different targets (heavy, light) within a four-body framework using the Continuum-Discretized Coupled-Channels (CDCC) method. The $^9$Be projectile is described in a $\alpha + \alpha + n$ three-body model using the analytical transformed harmonic oscillator (THO) basis in hyperspherical coordinates. We show that continuum couplings are important to describe the elastic cross section, especially at low energies and on heavy targets. The dipolar contribution to the elastic cross section at energies around the Coulomb barrier is important but small compared to the case of halo nuclei. The effect of the projectile low-energy resonances is also relevant. The agreement with the available experimental data supports the reliability of the method to describe reactions induced by three-body projectiles including more than one charged particle.

Systematics of the breakup probability function for 6Li and 7Li projectiles

Experimental non-capture breakup cross sections can be used to determine the probability of projectile and ejectile fragmentation in nuclear reactions involving weakly bound nuclei. Recently, the probability of both type of dissociations has been analyzed in nuclear reactions involving 9Be projectiles onto various heavy targets at sub-barrier energies. In the present work we extend this kind of systematic analysis to the case of 6Li and 7Li projectiles with the purpose of investigating general features of projectile-like breakup probabilities for reactions induced by stable weakly bound nuclei. For that purpose we have obtained the probabilities of projectile and ejectile breakup for a large number of systems, starting from a compilation of the corresponding reported non-capture breakup cross sections. We parametrize the results in accordance with the previous studies for the case of beryllium projectiles, and we discuss their systematic behavior as a function of the projectile, the target mass and the reaction Q-value.

Forward–backward emission of target evaporated fragments in high energy nucleus–nucleus collisions**Supported by National Science Foundation of China (11075100), Natural Science Foundation of Shanxi Province (2011011001-2) and the Shanxi Provincial Foundation for Returned Overseas Chinese Scholars, (2011-058)

The multiplicity distribution, multiplicity moment, scaled variance, entropy and reduced entropy of target evaporated fragments emitted in forward and backward hemispheres in 12 A GeV 4He, 3.7 A GeV 16O, 60 A GeV 16O, 1.7 A GeV 84Kr and 10.7 A GeV 197Au -induced emulsion heavy target (AgBr) interactions are investigated. It is found that the multiplicity distribution of target evaporated fragments emitted in both forward and backward hemispheres can be fitted by a Gaussian distribution. The multiplicity moments of target evaporated particles emitted in the forward and backward hemispheres increase with the order of the moment q, and the second-order multiplicity moment is energy independent over the entire energy range for all the interactions in the forward and backward hemisphere. The scaled variance, a direct measure of multiplicity fluctuations, is close to one for all the interactions, which indicate a correlation among the produced particles. The entropy of target evaporated fragments emitted in both forward and backward hemispheres are the same within experimental errors.

Microscopic calculations based on chiral two- and three-nucleon forces for proton- andHe4-nucleus scattering

We investigate the effects of chiral three-nucleon force (3NF) on proton scattering at 65 MeV and $^{4}$He scattering at 72 MeV/nucleon from heavier targets, using the standard microscopic framework composed of the Brueckner-Hartree-Fock (BHF) method and the $g$-matrix folding model. For nuclear matter, the $g$ matrix is evaluated from chiral two-nucleon force (2NF) of N$^{3}$LO and chiral 3NF of NNLO by using the BHF method. Since the $g$ matrix thus obtained is numerical and nonlocal, an optimum local form is determined from the on-shell and near-on-shell components of $g$ matrix that are important for elastic scattering. For elastic scattering, the optical potentials are calculated by folding the local chiral $g$ matrix with projectile and target densities. This microscopic framework reproduces the experimental data without introducing any adjustable parameter. Chiral-3NF effects are small for proton scattering, but sizable for $^{4}$He scattering at middle angles where the data are available. Chiral 3NF, mainly in the 2$\pi$-exchange diagram, makes the folding potential less attractive and more absorptive for all the scattering.

Neutrino Physics with SNO+

SNO+ is the successor to the Sudbury Neutrino Observatory (SNO) for which SNO's heavy water target is replaced by approximately 780 T of liquid scintillator (LAB). The combination of the 2 km underground location, the use of ultra-clean materials and the high light-yield of the liquid scintillator means that a low background level and a low energy threshold can be achieved. This creates a new multipurpose neutrino detector with the potential to address a diverse set of physics goals, including the detection of reactor, solar, geo- and supernova neutrinos. The main physics goal of SNO+ is the search for neutrinoless double beta decay. By loading the liquid scintillator with 0.3% of natural Tellurium, resulting in about 800 kg of 130Te (isotopic abundance is slightly over 34%), a competitive sensitivity to the effective neutrino mass can be reached.

Elastic Scattering of Neutron Halo Projectiles

Elastic scattering angular distributions of 6He on light, medium and heavy mass targets have been analysed using a simple diffractive model for the S-matrix. The results show that a very large diffuseness in the angular momentum space is necessary to reproduce the data in the case of scattering on heavy targets.