Total Photonuclear Cross Section Research Articles

Understanding the relationship between electric dipole polarizability and photonuclear (-2) moment in odd-A actinide nuclei

The nuclear electric dipole (E1) polarizability (α E1) is mainly dominated by the dynamics of the giant dipole resonance (GDR). α E1 is proportional to the (-2) moment of the total photo nuclear cross-section (σ −2). This research investigates the relationship between α E1 and σ −2, along with the effects of the Pygmy Dipole Resonance (PDR) and GDR in odd-mass actinide nuclei. For the first time, α E1 and σ −2 values have been calculated using the Translational and Galilean Invariant Quasiparticle Phonon Nuclear Model (TGI-QPNM) approach for odd-A actinide nuclei. According to TGI-QPNM results, E1 dipole transitions in the GDR region significantly contribute to σ −2 due to the energy weighting factor. Below the neutron separation threshold, the PDR in neutron-rich nuclei shows a contribution of about 5% to σ −2 values. In this region, E1 polarizability can reach values of 20%–25%. The α E1 values indicate the presence of PDR in these nuclei. Additionally, the Adaptive Neuro-Fuzzy Inference System (ANFIS), a new machine learning method, has been performed to analyze the relationship between α E1 and σ −2. The ANFIS results have been compared with those from the TGI-QPNM and experimental data. The TGI-QPNM model achieves an R2 of 0.85–0.95, while the ANFIS model achieves an R2 of 0.99. Moreover, the study suggests that the ANFIS model, consistent with TGI-QPNM results, could be an effective tool for estimating σ −2 in odd-A actinide nuclei.

Integrated photonuclear cross sections in the giant dipole resonance of odd-mass actinide nuclei

This study explores the integrated total photonuclear cross section (σ0) within the context of the giant dipole resonance (GDR) in odd-mass actinide nuclei. Using artificial neural networks (ANNs) and adaptive neuro-fuzzy ınference system (ANFIS) machine learning algorithms, we analyze the GDR behaviors associated with the σ0 values in these nuclei. The modeling results obtained from ANFIS and ANN are compared among themselves and with the Translational Galilean Invariant Quasiparticle Phonon Nuclear Model (TGI-QPNM) and experimental data. Machine learning analysis and TGI-QPNM results provide valuable insights into the GDR characteristics of odd-mass actinides, shedding light on their photonuclear properties. The ANFIS model has achieved an R2 value of 0.98 and an RMSE of 0.19, while the ANN model (LM) has yielded an R2 value of 0.95 and an RMSE of 0.24. These findings deepen our understanding of nuclear physics, underscoring the role of artificial intelligence techniques in deciphering complex phenomena within nuclear structures. In conclusion, our study suggests that the ANFIS model, in agreement with TGI-QPNM results, generally outperforms the ANN (LM) method and could be a more effective tool for estimating the energy-weighted sum rule for GDR.

Study of giant dipole resonances for neodymium isotopes with an exciton model

The partial photonuclear [Formula: see text], pn) and [Formula: see text] and the total photonuclear cross-sections (the giant dipole resonance (GDR)) have been investigated theoretically for neodymium isotopes, namely [Formula: see text]Nd, using framework of the EMPIRE 3.2.2 code. The energy, width and cross-section parameters of the GDR used in our calculations have been investigated in this paper depending on the deformation parameters of nuclei. The calculated results have been compared with the experimental data and with those calculated using Lorentzian fitting parameters. Our calculations show a good agreement for all isotopes under study and give better results than the results calculated with Lorentzian parameters. Furthermore, the neutron number dependence of the total and partial photonuclear cross-sections has also been discussed. The results appear that the EMPIRE code used is a perfect tool for reproducing the splitting in the GDR for deformed [Formula: see text]Nd isotope in two distinct dipole modes which are perfectly consistent with the experimental results. It has also been shown that the present parameters are suitable parameters for reproducing the GDR for spherical, or nearly spherical, and the deformed ([Formula: see text]Nd) neodymium isotopes. The parameters have been indicating the small deformation in [Formula: see text]Nd, which cannot be shown by the Lorentzian fitting parameters.

SU‐GG‐T‐343: Comparison of MCNP and GEANT4 Monte Carlo Codes On Photo‐Neutron Generation in High Energy X‐Ray Beams

Purpose: Photo‐neutrons generated in high‐energy X‐ray beams are of increasing interest. Secondary neutrons introduce concerns such as neutron shielding and additional dose to patients. The Monte Carlo method is an appropriate choice for studying photo‐neutron production and transport. However, unlike interactions of photons with orbital electrons, photonuclear reactions suffer from the incompleteness and inconsistence of the cross section data. The purpose of this investigation is to compare two major Monte Carlo codes MCNP and GEANT4 in implementing the photonuclear process. Method and Materials: Cross section data (total photonuclear cross section, neutron production yield, and neutron energy/angular distribution data) were extracted from the respective external cross section files (MCNP) or from the code (GEANT4) directly for the major materials/elements in linear accelerator and human body. The Varian linear accelerator with multi‐leaf collimator (MLC) was modeled identically with MCNP and GEANT4. Neutron generation in major components in the linear accelerator was simulated and compared. Results: MCNP and GEANT4 implemented the photonuclear process in very different manners. Significant differences in cross section data between MCNP and GEANT4 were discovered. Several institutions provided the cross section data used in MCNP, and the cross section data for the same isotope from different providers may also present large discrepancies. The results of photo‐neutron production in linear accelerator components simulated with the two Monte Carlo codes can be quite different. Although neutrons were not transported in our simulations, appreciable differences in neutron fluence or neutron dose can be expected. Conclusion: MCNP and GEANT4 are two major Monte Carlo codes, capable of simulating photon‐neutron generation and transport. The discrepancies between the two codes indicate the lack of comprehensive understanding in physics of the photonuclear process. The investigators who worked with either code should be aware of the potential uncertainties in their results regarding to secondary photo‐neutrons.

Test of J-matrix inverse scattering potentials on photonuclear reactions of A=2,3,4 nuclei

This contribution reports on a recent calculation of the total photonuclear cross sections of 2 H, 3 H, 3 He and 4 He performed with the Lorentz Integral Transform (LIT) method [V.D. Efros, W. Leidemann, and G. Orlandini, Phys. Lett. B 338 (1994) 130], using J-matrix inverse scattering potentials (JISP) [A.M. Shirokov et al. , Phys. Lett. B 68 (2003) 041001(R); A.M. Shirokov, J.P. Vary, A.I. Mazur, T.A. Weber, ArXiv.org:nucl-th/0512105 ]. The results are compared with those obtained with traditional realistic potentials, also including three-nucleon forces, and with the Unitary Correlation Operator Method potential (UCOM) of Ref. [R. Roth, T. Neff, H. Hergert and H. Feldmeier, Nucl. Phys. A 745 (2004) 3]. The aim is to investigate the underlying degrees of freedom of those potentials which reproduce the binding energies of light systems without the need of a three-nucleon force.

Super High Resolution Measurement of Fine Structure in the Total Photonuclear Cross Section of 13C

KEYWORDS: photonuclear reactionscross sections fine structurephoton absorptioncarbon 13resolutionhigh energy photonphoton spectrometerlaser Compton scattering photonexperimentgamma radiation width

Super High Resolution Measurement of Fine Structure in the Total Photonuclear Cross Section of 13C.

Super High Resolution Measurement of Fine Structure in the Total Photonuclear Cross Section of 13C.

Phenomenological approach to baryon resonance damping in nuclei

We analyse the total photonuclear cross section in the energy range from 0.2 to 1.2 GeV, recently measured in Frascati on C, Be and U. By employing a simple resonance-hole model for the various baryonic resonances, which exist in the above range, we find that the experimental cross sections can be fairly well reproduced if one assumes that the nuclear medium strongly increases the width of all resonances above the Δ.

Deeply bound pionic atoms with resonant Compton scattering

We study the contribution to ordinary Compton nuclear scattering of the resonant channel γ + A → (A′ π −) → γ + A with the π − bound in the nucleus. We show that the interference of this resonant channel with background amplitudes produces significant peaks in the elastic backward differential cross section as a function of the incoming photon energy for light and medium-size nuclei. We also find that for light nuclei the signals in forward Compton scattering or in the total photonuclear cross section are big enough to be observed, provided there is a good resolution in the photon beam. The reaction is particularly suited to find deeply bound pionic states in medium-size nuclei, or ordinary levels in unstable light nuclei.

Total photonuclear cross section in the nucleon resonance region

We present the results of measurements of the total photonuclear absorption in light, medium-heavy and heavy nuclei carried on at Frascati with 200–1200 MeV monochromatic photons, to obtain information on the behavior of baryon resonances in nuclei and on the possible onset of the shadowing effect. Preliminary results obtained from Be and C, using the transmission technique, and from U using the photofission method show no evidence of baryon resonances at about 700 and about 1000 MeV seen in the photon absorption on the proton and the deuteron.

Behavior of the Be and C total photonuclear cross section in the nucleon resonance region

We present the total photonuclear cross section for Be and C measured between 200 and 1100 MeV, with the aim of clarifying the existence of a resonant behavior in the region above the \ensuremath{\Delta}. We used a tagged photon beam and the transmission technique. The results show no evidence of baryon resonances that are clearly seen at \ensuremath{\approxeq}700 and \ensuremath{\approxeq}1000 MeV in photon absorption on the proton and the deuteron.

Interaction of real photons with nuclei from 100 to 500 MeV

Starting from the basic interactions between photons, pions, nucleons and isobars we reconstruct a standard model providing an adequate description of the γN→ πN reaction. With this, and the ph, Δh effective interactions used with success in the pion-nuclear reactions, we develop a systematic many-body expansion in the number of ph excitations in the nucleus up to 3p3h excitations in a single step, where convergence was found in the related pion-nuclear problem. We evaluate total photonuclear cross sections in different nuclei which compare rather favorably with experiment. The method allows for a separation of the γ absorption and the ( γ, π) cross sections and they are also evaluated here.

Molecular effects on the cross section for pair production and their importance in the evaluation of the total photonuclear cross section of 16O in the Δ-resonance region

The screening correction to the coherent pair-production cross section on the oxygen molecule has been calculated using self-consistent relativistic wave functions for the one-center and two-center Coulomb potentials. It is shown that the modification of the wave function due to molecular binding and the interference between contributions from the two atoms have both sizeable effects on the screening correction. The so-obtained coherent pair-production cross section which makes up the largest part of the total atomic cross section was used to evaluate the total nuclear absorption cross section from photon attenuation measurements on liquid oxygen. The result agrees with cross sections for other nuclei if A-scaling is assumed. The molecular effect on the pair cross section amounts to 15% of the nuclear cross section in the Δ-resonance region.

Microscopic Studies of Electric Dipole Resonances in 1p Shell Nuclei

Recent data on total and partial photonuclear cross sections in the GDR region of the nuclei 6Li to 16O are compared with theoretical predictions, mostly from shell model and continum shell model studies. The influence of the size of the configuration space, of the adopted residual interaction and of the continuous spectrum on the isovector E1 response is discussed to some detail. The observed trends of the localization, the shape and width, the isospin and the configurational structure of the GDR with increasing 1p shell occupation are related to the microscopic structure of the nuclear ground state. Particular attention is given to the partial (γ, Ni) disintegration channels. Complex-particle emission and isospin mixing in the nuclear states are discussed for a few cases. An attempt is made to bring some systematics also in the evidence on excited-state giant resonances through the 1p shell region. The photonuclear GDR is compared with other giant multipole excitations, mostly for the example of the 14C nucleus.

Photofission and photoneutron cross sections and photofission neutron multiplicities for 233U, 234U, 237Np, and 239Pu.

The photonuclear cross sections for $^{233}\mathrm{U}$, $^{234}\mathrm{U}$, $^{237}\mathrm{Np}$, and $^{239}\mathrm{Pu}$ have been measured from threshold up to 18 MeV. The source of radiation was the monoenergetic photon beam from the annihilation in flight of fast positrons. The branching among the neutron-producing reaction channels was determined by measuring the photofission prompt neutron multiplicities \ensuremath{\nu}${\ifmmode\bar\else\textasciimacron\fi{}}_{p}$. One interesting result is the complete absence of any (\ensuremath{\gamma},2n) cross section for $^{233}\mathrm{U}$ and $^{234}\mathrm{U}$. The values of \ensuremath{\nu}${\ifmmode\bar\else\textasciimacron\fi{}}_{p}$(E) for $^{234}\mathrm{U}$ agree with those measured with neutrons incident on $^{233}\mathrm{U}$. The parameters of the giant dipole resonance deduced from the total photonuclear cross sections show that these nuclei have large static deformations, as expected. The integrated photofission cross sections are large (as are the absolute fission probabilities), and account for 60% to 80% of the total photonuclear absorption strength.

Measurement of the total photonuclear cross section for16O in the region of the giant dipole resonance

Using a gamma -ray spectrometer consisting of a liquid deuterium target and a photoneutron time-of-flight detector, the total absorption cross section of 16O was measured in the energy range from the 3 to 38 MeV. The total photonuclear component of the cross section integrated from 10 to 30 MeV was found to be (182+or-16) MeV mb, or (0.76+or-0.07) TRK sum-rule units. This result is compared with previous measurements, and its significance to the theory of meson-exchange currents is discussed.

Recent experimental studies of the total photonuclear cross-sections between 30 and 140 MeV

Recent experimental data concerning the total photonuclear cross-section from 30 to 140 MeV have recently been obtained at the ALS linac of Saclay by means of quasi-monochromatic photons produced by in-flight annihilation of positrons. This total photonuclear cross-section was obtained in the case of heavy nuclei as the sum of all the measured cross-sections for the partial photoneutron decay channels. The integrated cross-section, integrated up to 140 MeV, shows an enhancement factorK≈0.76 above the classicalE1 sum rule. This largeK value is well explained by the effect of the tensor force and the tensor correlations. The dependence of σ(γ, tot;Eγ) upon the energyEγ agrees well with the new quasi-deuteron models.

Photonuclear reactions at intermediate energies

The interaction mechanism between an intermediate-energy photon and a nucleus is discussed with special attention given to Siegert’s theorem and the role of exchange currents. In particular, the relative contributions of (γ, p), (γ, n), (γ, pp), (γ, nn) and (γ, pn) cross-sections for16O to the total photonuclear cross-section are studied in the region of photon energies between 40 and 140 MeV, and comparison with recent measurements is made. Numerical results for (γ, p) and (γ, n) reactions in light nuclei are discussed for photon energies extending from 40 MeV up to the Δ region.

Dynamical correlations in finite nuclei: A simple method to study tensor effects

Dynamical correlations are introduced in finite nuclei by changing the two-body density through a phenomenological method. The role of tensor and short-range correlations in nuclear momentum distribution, electric form factor and two-body density of 4He is investigated. The importance of induced tensor correlations in the total photonuclear cross section is reinvestigated providing a successful test of the method proposed here.

Total Photonuclear Cross Section in the 3,3 Resonance Region

The quasi-Δ33 doorway state model, previously developed for describing pion-nucleus scattering, is used to obtain the resonant part of the photo-nucleus scattering amplitude. An investigation of the photo-excitation of Δ(1232) states in nuclei provides information about the properties of nuclear Δ-hole excitations complementary, to that obtained from pion-induced processes..