Target Mass Dependence Research Articles

Target mass dependence of photoneutron spectrum for 16.6 MeV photons on medium-heavy mass targets

We measured neutron energy spectra for the photonuclear reactions of 16.6 MeV linearly polarized photons on Pb, Au, Sn, Cu, Fe and Ti. The spectra for each target show dependence on the target mass, as well as on the angle between the directions of neutron emission and polarization. The components show angular dependence were extracted from the spectra for each target and compare with the excited levels of residual nuclei. Based on the data, we discuss a plan for further experiments to clearly observe the features of the spectra.

Erratum — Cascade exciton model analysis of energetic pion-induced fission of heavy nuclei: Target mass and projectile energy dependence

Erratum — Cascade exciton model analysis of energetic pion-induced fission of heavy nuclei: Target mass and projectile energy dependence

A systematics for negative pion induced nuclear fission cross-sections: Experimental data fitting and cascade exciton model validation

The developed fission systematics depicts the projectile energy and the target mass dependence of fission cross-sections of heavy nuclei. The developed model is fitted using experimental fission cross-section data of 500–1665 MeV negative pion induced fission in [Formula: see text]Sn, [Formula: see text]Au and [Formula: see text]Bi. The same systematics is further fitted using the cascade exciton model (CEM) calculations of the above-mentioned fission reactions. Parameterization of the model is performed by calculating its parameters and uncertainties in them. A comparison of the systematics predictions with experimental data and CEM calculations is made. Validation of the systematics using new target nuclei [Formula: see text]Eu, [Formula: see text]Ta, [Formula: see text]Hg and [Formula: see text]At (not included in the systematics development) over an extended range of pion energies, from 80 MeV to 2500 MeV, builds trust in it. The systematics is not valid for [Formula: see text]Th and [Formula: see text]U. The systematics is found to be valid for target nuclei from [Formula: see text]Sn to [Formula: see text]At and for incident negative pion energies from 80 MeV to 2500 MeV. Results are discussed in detail. Merits and demerits of the developed systematics have been concisely described. Valid conclusions and future perspectives are also given.

Cascade exciton model analysis of energetic pion-induced fission of heavy nuclei: Target mass and projectile energy dependence

A data bank of negative and positive (80–1665[Formula: see text]MeV) pion-induced experimental fission cross-sections of heavy nuclei from 119Sn to 238U is compiled using present results and published data from the literature. Corresponding calculations of fission cross-sections, using the cascade exciton model (CEM) are also included in the compilation. Fission cross-sections compiled in the data bank are examined critically. Mass and energy dependences of fission cross-sections are analyzed. Fission cross-sections of 238U targets are the highest and scale down approximately, for other targets studied, with fissility, [Formula: see text]. In the fissility expression, [Formula: see text] and [Formula: see text] are atomic and mass numbers of the target while [Formula: see text] refer to positive and negative pion projectiles. The presented data bank is of interest for students and researchers involved in the investigation of energetic light particle-induced fission of heavy nuclei. Nuclear fission of heavy nuclei has been classified into three regimes. Phenomenological discussion of the fission process is also given.

Semimicroscopic analysis of Li6 elastic scattering at 40 MeV/nucleon

Analysis of the differential cross sections for $^{6}\mathrm{Li}$ elastic scattering from $^{24}\mathrm{Mg}$, $^{28}\mathrm{Si}$, $^{40}\mathrm{Ca}$, $^{48}\mathrm{Ca}$, $^{58}\mathrm{Ni}$, $^{90}\mathrm{Zr}$, and $^{116}\mathrm{Sn}$ at 40 MeV/nucleon is performed within the framework of the optical double folding model. Simple phenomenological effective nucleon-nucleon interaction represented by a density-independent single Yukawa term is utilized to generate the real optical potential part. The derived potentials in conjunction with imaginary parts expressed in phenomenological volume Woods-Saxon forms have been successfully used to reproduce the seven sets of data. For the sake of comparison, the same measurements are reanalyzed using folded potentials based upon the density-independent M3Y effective interaction. Furthermore, reasonably successful reproduction of the data is obtained by Woods-Saxon-type optical model potentials. The radial sensitivity of the derived real potentials to the calculating elastic-scattering angular distributions has been investigated using the notch perturbation technique. The target mass dependence in real and imaginary volume integrals as well as total reaction cross sections are also investigated.

Systematic analysis of elastic α scattering on [formula omitted] nuclei around the Coulomb barrier

Alpha elastic scattering angular distributions on target nuclei 118, 124Sn and 120-130Te at energies near the Coulomb barrier are analyzed. We used three versions of the nuclear optical model potentials (OMP) to analyze twenty-nine data sets. JLM and the density and energy-dependent DDM3Y1 with finite range exchange term effective interactions were used to generate these potentials. Two real folded potentials based on JLM and DDM3Y1 effective interactions supplied with the conventional Wood–Saxon (WS) imaginary potential are used in the cross sections calculations. These potentials are denoted as JLM-R and DDM3Y1-FR, respectively. In addition, we used the full complex folded OMP, denoted as JLM-RI, to analyze the same data. These potentials successfully predict the cross section of the systems under study. We found that the JLM-R and DDM3Y1-FR could reproduce the measured cross sections over the full angular range very well compared to microscopic JLM-RI potential. Our calculated potentials have a clear energy dependence and in addition a weak target mass dependence. The total reaction cross section and volume integral are investigated in comparison to previous studies. The derived potentials are very promising for the construction of a new global α-nucleus potential and provide new parameters of α–induced reactions and scattering at the energy range 17–27 MeV.

Target mass effects in parton quasi-distributions

We study the impact of non-zero (and apparently large) value of the nucleon mass M on the shape of parton quasi-distributions Q(y,p3), in particular on its change with the change of the nucleon momentum p3. We observe that the usual target-mass corrections induced by the M-dependence of the twist-2 operators are rather small. Moreover, we show that within the framework based on parametrizations by transverse momentum dependent distribution functions (TMDs) these corrections are canceled by higher-twist contributions. We identify a novel source of kinematic target-mass dependence of TMDs and build models corrected for such dependence. We find that resulting changes may be safely neglected for p3≳2M.

Photon emission in neutral-current interactions at intermediate energies

Neutral current photon emission reactions with nucleons and nuclei are studied. These processes are important backgrounds for nu_mu to nu_e (bar(nu)_mu to bar(nu)_e) appearance oscillation experiments where electromagnetic showers instigated by electrons (positrons) and photons are not distinguishable. At intermediate energies, these reactions are dominated by the weak excitation of the Delta(1232) resonance and its subsequent decay into Ngamma There are also non-resonant contributions that, close to threshold, are fully determined by the effective chiral Lagrangian of strong interactions. In addition, we have also included mechanisms mediated by nucleon excitations (N*) from the second resonance region above the Delta(1232). From these states, the contribution of the D13 N*(1520) turns out to be sizable for (anti)neutrino energies above 1.5 GeV. We have extended the model to nuclear targets taking, into account Pauli blocking, Fermi motion and the in-medium Delta resonance broadening. We present our predictions for both the incoherent and coherent channels, showing the relevance of the nuclear corrections. We also discuss the target mass dependence of the cross sections. This study is important in order to reduce systematic effects in neutrino oscillation experiments.

Charmonium production inp̄-induced reactions on nuclei

The production of charmonia in the antiproton-nucleus reactions at plab = 3 − 10 GeV/c is studied within the Glauber model and the generalized eikonal approximation. The main reaction channel is charmonium formation in an antiproton-proton collision. The target mass dependence of the charmonium transparency ratio allows to determine the charmonium-nucleon cross section. The polarization effects in the production of χc2 states are evaluated.

A COMPARATIVE STUDY OF THE EXPERIMENTAL AND SIMULATED VALUES OF MULTIFRACTAL SPECIFIC HEAT IN 14.5A GeV/c HEAVY-ION COLLISION

An attempt is made to study multifractal specific heat from Fq, modified Gq and Takagi moments, which can provide some interesting information about event-by-event fluctuations in heavy-ion collisions at high energies. It is an established fact that constancy of the specific heat (CSH) of solids and gases helps explain thermodynamical behavior of intermittency and multifractality in A–A collisions at different projectile energies. It is worthmentioning that the present paper deals with multifractal specific heat, c, extracted from Fq, modified Gq and Takagi moments for the experimental as well as FRITIOF generated data on 14.5A GeV /c28 Si -nucleus interactions. The results obtained using the three approaches are compared for both the data sets. The observed power law behavior reflects self-similar property of the multiparticle production process. The common feature of the multifractal specific heat obtained using the three approaches is that there is no systematic variation in its value for different orders of the moments. Furthermore, the value of c is found to be different for both the data sets and no strong target mass dependence is observed in any of the cases. A noteworthy observation is that a non-zero finite value of the multifractal specific heat may be considered a good signal for the presence of multifractality in the relativistic charged particle multiplicity distribution.

Measurement of the in-medium ϕ-meson width in proton–nucleus collisions

The production of ϕ mesons in the collisions of 2.83 GeV protons with C, Cu, Ag, and Au at forward angles has been measured via the ϕ→K+K− decay using the COSY-ANKE magnetic spectrometer. The ϕ meson production cross section follows a target mass dependence of A0.56±0.03 in the momentum region of 0.6–1.6 GeV/c. The comparison of the data with model calculations suggests that the in-medium ϕ width is about an order of magnitude larger than its free value.

Determining the WIMP mass from a single direct detection experiment; a more detailedstudy

The energy spectrum of nuclear recoils in weakly interacting massive particle (WIMP)direct detection experiments depends on the underlying WIMP mass. We studyhow the accuracy with which the WIMP mass could be determined by a singledirect detection experiment depends on the detector configuration and the WIMPproperties. We investigate the effects of varying the underlying WIMP mass andcross-section, the detector target nucleus, exposure, energy threshold and maximumenergy, the local circular speed and the background event rate and spectrum. Thenumber of events observed is directly proportional to both the exposure and thecross-section; therefore these quantities have the greatest bearing on the accuracy of theWIMP mass determination. The relative capabilities of different detectors fordetermining the WIMP mass depend not only on the WIMP and target masses, butalso on their energy thresholds. The WIMP and target mass dependence of thecharacteristic energy scale of the recoil spectrum suggests that heavy targets will beable to measure the mass of a heavy WIMP more accurately. We find, however,that the rapid decrease of the nuclear form factor with increasing momentumtransfer which occurs for heavy nuclei means that this is in fact not the case.Uncertainty in the local circular speed and non-negligible background would bothlead to systematic errors in the WIMP mass determination. For deviations of ± 20 km s−1 in the underlying value of the circular speed the systematic error is of order10%, increasing with increasing WIMP mass. This error can be reduced by also fitting for thecircular speed. With a single detector it will be difficult to disentangle a WIMP signal (andthe WIMP mass) from background if the background spectrum has a similar shape to theWIMP spectrum (i.e. exponential background, or flat background and a heavyWIMP).

Scaling and interference in the dissociation of halo nuclei

The dissociation of halo nuclei through their collision with light and heavy targets is considered within the Continuum Discretized Coupled Channels theory. We study the one-proton halo nucleus $^8$B and the one-neutron halo nucleus $^{11}$Be, as well as the more normal $^7$Be. The procedure previously employed to extract the Coulomb dissociation cross section by subtracting the nuclear one is critically assessed, and the scaling law usually assumed for the target mass dependence of the nuclear breakup cross section is also tested. It is found that the nuclear breakup cross section for these very loosely bound nuclei does indeed behave as $a+bA^{1/3}$. However, it does not have the geometrically inspired form of a circular ring which seems to be the case for normal nuclei such as $^{7}$Be. We find further that we cannot ignore Coulomb-nuclear interference effects, which may be constructive or destructive in nature, and so the errors in previously extracted B(E1) using the subtraction procedure are almost certainly underestimated.

Target dependence of beryllium fragment production in neutron- and alpha-induced nuclear reactions at intermediate energies

SummaryThe yields of7Be fromnatC,27Al,natCu,natAg and197Au targets and10Be fromnatCu,natAg and197Au targets in alpha- (400 MeV) and neutron- (maximum end-point energy,E0= 500 MeV) induced reactions were measured in order to compare them with the photonuclear-reaction yields atE0= 1000 MeV. The target-mass dependences of the yields of7Be and10Be showed very similar trends among alpha-, neutron-, and photon-induced reactions. The fragmentation yields of7Be decreased more slowly, and those of10Be increased gradually with an increase in the target mass; both yields intersected at an approximate target mass of 125. The exponential increase in the fragmentation-yield ratios of10Be to7Be with an increase in the neutron-to-proton ratio of the targets suggests that pre-formation of the fragments inside the excited nuclei is strongly influenced by the target properties, such asN/Z. Furthermore, the effect of the incident particle was clearly observed in the yield ratios of10Be to7Be from the Cu and Ag targets.

Calculations of K ± and ϕ Production in Near-Threshold Proton–Nucleus Collisions

K± and ϕ meson production in proton-nucleus (pA) collisions has been calculated within a BUU transport model. It is shown that the nucleon-hyperon strangeness transfer channel is essential. The role of three-body reactions has been investigated within the medium. The target mass dependence of ϕ production is predicted to give important information on the in-medium properties of all three mesons.

Target mass number dependence of subthreshold antiproton production in proton-, deuteron- and alpha-particle-induced reactions

Data from KEK on subthreshold as well as on π± and K± production in proton-, deuteron- and α-induced reactions at energies between 2.0 and 12.0 A GeV for C, Cu and Pb targets are described within a unified approach. We use a model which considers a nuclear reaction as an incoherent sum over collisions of varying numbers of projectile and target nucleons. It samples complete events and thus allows for the simultaneous consideration of all final particles including the decay products of the nuclear residues. The enormous enhancement of the cross section, as well as the moderate increase of meson production in deuteron and α induced compared to proton-induced reactions, is well reproduced for all target nuclei. In our approach, the observed enhancement near the production threshold is mainly due to the contributions from the interactions of few-nucleon clusters by simultaneously considering fragmentation processes of the nuclear residues. The ability of the model to reproduce the target mass dependence may be considered as a further proof of the validity of the cluster concept.

LOW ENERGY DOUBLE-PION PHOTOPRODUCTION IN NUCLEI

We have investigated π0π0 and π±π0 photoproduction off complex nuclei. Simulations have been performed by means of a semi-classical BUU transport model including a full coupled-channel treatment of the final state interactions. We show that the target mass dependence of the π0π0 invariant mass spectrum as measured by the TAPS collaboration can be explained without introducing medium effects beyond absorption and quasi-elastic scattering of the final state particles. On the other hand, we find considerable discrepancies with the data in the π±π0 channel, which are not understood.

Inclusive K+-meson production in proton-nucleus interactions

The production of K^+ mesons in pA (A = D, C, Cu, Ag, Au) collisions has been investigated at the COoler SYnchrotron COSY-J\"ulich for beam energies T_p = 1.0 - 2.3 GeV. Double differential inclusive pC cross sections at forward angles theta < 12 degrees as well as the target-mass dependence of the K^+ momentum spectra have been measured with the ANKE spectrometer. Far below the free NN threshold at T_{NN}=1.58 GeV the spectra reveal a high degree of collectivity in the target nucleus. From the target-mass dependence of the cross sections at higher energies, the repulsive in-medium potential of K^+ mesons can be deduced. Using pN cross-section parameterisations from literature and our measured pD data we derive a cross-section ratio of sigma(pn -> K^+ X) / sigma(pp -> K^+ X) ~ (3-4).

Low-energy ππ photoproduction off nuclei

In the present Letter we investigate π0π0 and π±π0 photoproduction off complex nuclei at incident beam energies of 400–460 MeV. Simulations of two pion photoproduction on protons and nuclei are performed by means of a semi-classical BUU transport model including a full coupled-channel treatment of the final state interactions. Elastic scattering of the final state pions with the nucleons in the surrounding nuclear medium is found to yield a downward shift of the ππ invariant mass distribution. We show that the target mass dependence of the π0π0 invariant mass spectrum as measured by the TAPS Collaboration can be explained without introducing medium effects beyond absorption and quasi-elastic scattering of the final state particles. On the other hand, we find considerable discrepancies with the data in the π±π0 channel, which are not understood.

Yield measurements for 7Be and 10Be productions from natCu, natAg and 197Au by bremsstrahlung irradiation at E0=200 MeV

The yields of 7Be and 10Be produced by bremsstrahlung having a maximum energy (E0) of 200 MeV in natCu, natAg and 197Au targets were investigated by the AMS technique at MALT of the University of Tokyo. It was found that the yields at E0=200 MeV were much lower than those at E0⩾250 MeV, obtained in our previous works. A change in the yields of the fragmentation component in the target-mass dependence was observed at E0=200 MeV when compared with those at E0⩾250 MeV. However, the ratios of the fragmentation yield of 10Be to that of 7Be remained unchanged throughout the concerned E0.