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On the basis of objective physics criteria, it is shown that the cross sections determined for partial photoneutron reactions on $${}^{51}$$ V nucleus by the method of photoneutron multiplicity sorting, primarily at Livermore (USA) and Saclay (France), are not reliable because of large systematic uncertainties in them. New cross sections evaluated for such reactions by the experimental–theoretical method are found to satisfy the data reliability criteria. The discrepancies between the evaluated and experimental reaction cross sections are analyzed in detail. It is found that, in the case of the $${}^{51}$$ V nucleus, which is relatively light, the disregard of the contribution from the ( $$\gamma$$ , 1 $$n$$ 1 $$p$$ ) reaction is the main reason of sizable systematic uncertainties in the procedure used at Livermore to identify neutrons from the ( $$\gamma$$ , 1 $$n$$ ), ( $$\gamma$$ , 1 $$n$$ 1 $$p$$ ), and ( $$\gamma$$ , 2 $$n$$ ) reactions.

Experimental studies and theoretical calculations of photonuclear reactions on a natural mixture of palladium isotopes have been performed. The yields of photonuclear reactions on a natural mixture of Pd isotopes were measured for bremsstrahlung $$\gamma$$ radiation with a maximum energy of 55 MeV. The results are compared with calculations using the combined model of photonuclear reactions.

The electromagnetic dissociation of ultrarelativistic nuclei has a substantial impact on the lifetime of beams in the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC), and secondary nuclei produced upon this dissociation may have an adverse effect on collider components. At the same time, the detection of neutrons originating from the electromagnetic dissociation process makes it possible to monitor the luminosity of colliders. In order to calculate the total and partial cross sections for the electromagnetic dissociation process by the Weizsacker–Williams method, one needs reliable photonuclear reaction models preliminarily tested via a comparison of the results that they produce with available experimental data. Since the commissioning of the LHC, attention has been given primarily to $${}^{208}$$Pb–$${}^{208}$$Pb collisions. A run involving $${}^{129}$$Xe nuclei was also performed. In contrast to the case of $${}^{208}$$Pb nuclei, for which the photonuclear reaction and electromagnetic dissociation cross sections have been measured at various laboratories, there are no data for $${}^{129}$$Xe. By employing the experimental–theoretical method, the ($$\gamma,1n$$), ($$\gamma,2n$$), ($$\gamma,3n$$), and ($$\gamma$$, abs) cross sections for the $${}^{129}$$Xe nucleus are evaluated on the basis of available data for the neighboring nucleus of $${}^{127}$$I and the combined photonuclear reaction model (CPNRM). It is found that the results of CPNRM calculations performed for $${}^{129}$$Xe at photon energies up to 40 MeV by employing the TENDL-2017 library compiled by means of the TALYS code are close to one another and are in fairly good agreement with data obtained at the Saclay laboratory for $${}^{127}$$I. These new evaluated data, the TENDL-2017 library, and approximations of the total photoabsorption cross sections above the pion production threshold are used to calculate the electromagnetic dissociation cross section for $${}^{129}$$Xe at the LHC and at the FCC-hh collider being designed. The results of these calculations are compared with their counterparts obtained on the basis of the RELDIS model.

New cross sections of the partial ( $$\gamma ,1n)$$ , ( $$\gamma ,2n)$$ , and ( $$\gamma $$ , 3n) and total ( $$\gamma $$ , Sn), and ( $$\gamma $$ , tot) photoneutron reactions for $$^{{206,207}}$$ Pb were evaluated using the experimental-theoretical method. The evaluation procedure was based on the comparison in detail of $$^{{206,207}}$$ Pb data obtained only at Livermore (USA) with $$^{{208}}$$ Pb data obtained at Livermore, Saclay (France) and also in other experiments. It was found that in the cases of all $$^{{206,207,208}}$$ Pb isotopes clear disagreements between Livermore data and new evaluated data can be explained by the assumption of loss of many neutrons in experimental ( $$\gamma $$ , 1n) reaction cross sections. It was shown that Livermore experimental data for $$^{{206,207,208}}$$ Pb as well as for $$^{{75}}$$ As, $$^{{127}}$$ I, and $$^{{181}}$$ Ta investigated before are not reliable.

There is well-known problem of significant systematic disagreements between data for reactions (γ, 1n), (γ, 2n), obtained at Livermore (USA) and Saclay (France) using the method of photoneutron multiplicity sorting. The averaged ratios RS/Lint of integrated cross sections obtained at Saclay and Livermore for 19 nuclei from 51V to 239U are equal to 0.84 for (γ, 2n) and 1.07 for (γ, 1n) reactions. For 75As RS/Lint ratios for both partial reactions are very close (1.22 and 1.21) but for 181Ta - are quite different (0.89 and 1.25). Using the objective physical data reliability criteria it was found that there are serious doubts in reliability of Saclay and Livermore data. The newly evaluated reliable cross sections disagree with experimental data. In addition to unreliable sorting of many neutrons between both partial reactions many neutrons were lost - on the case of 181Ta in 1n channel, in the case of 75As in both 1n and 2n channels.

Photonuclear reactions on a natural mixture of tin isotopes are studied by means of gamma activation. The experiment is performed using the bremsstrahlung γ-beam of an RTM55 racetrack microtron with a maximum electron energy of 55.6 MeV. The measured yields of photoproton and photoneutron reactions are compared to results from other experimental studies, and to calculations using the TALYS code and the combined model of photonucleon reactions (CMPR).

With the aid of the results obtained by evaluating cross sections of partial photoneutron reactions on the isotope 116Sn and the energy spectra of neutrons originating from these reactions, the possible reasons for the well-known discrepancies between the results of different photonuclear experiments were studied on the basis of a combinedmodel of photonuclear reactions. On the basis of physical criteria of data reliability and an experimental–theoretical method for evaluating cross sections of partial reactions, it was found that these discrepancies were due to unreliably redistributing neutrons between (γ, 1n), (γ, 2n), and (γ, 3n) reactions because of nontrivial correlations between the experimentally measured energy of neutrons and their multiplicity.

Using objective physical criteria for data reliability, cross sections of partial photoneutron reactions (γ, 1n), (γ, 2n) and (γ, 3n) that are free of the shortcomings of neutron multiplicity sorting methods used on beams of quasimonoenergetic annihilation photons are obtained for 141Pr and 186W nuclei. Evaluation is performed using the experimental–theoretical method (ETM), based on the experimental cross section of neutron yield reaction σexp(γ, xn) = σexp(γ, 1n) + 2 σexp(γ, 2n) + 3 σexp(γ, 3n) + … and ratios F i theor= σtheor(γ, in)/σtheor(γ, xn) calculated within the combined model (CM) of photonuclear reactions, which stipulates that σeval(γ, in) = F i theor σexp(γ, xn). It is found that for 141Pr and 186W, ratios F exp i do not contradict the data reliability criteria only at energies up to ~21 and ~22 MeV, respectively. At the same time, there are notable discrepancies between F i theor and F exp i, and thus between the evaluated and experimental cross sections of reactions. It is shown that the discrepancies between the evaluated and experimental cross sections are due to the assumed unreliable experimental distribution of neutrons in the channels with multiplicities 1, 2, and 3.

Experimental photonuclear reaction cross sections obtained in experiments using quasimonoenergetic annihilation, monoenergetic tagged photons, and bremsstrahlung γ-radiation are analyzed using physical criteria for the reliability of data on the 89Y nucleus. It is found that the reliability of data on the cross sections of partial reactions (γ, 1n) and (γ, 2n), obtained by means of photoneutron multiplicity sorting, is highly doubtful. Reliable cross sections of reactions (γ, 1n) and (γ, 2n) are obtained using the experimental–theoretical method (ETM) for evaluating using both experimental cross sections of neutron yield reaction σexp(γ, xn) that are free of neutron multiplicity problems, and theoretically calculated F i theor ratios of the cross sections of definite (i) partial reactions to cross section σtheor(γ, xn). It is shown that the evaluated cross sections differ noticeably from the experimental data.

The well-known significant systematic disagreements between data on partial photoneutron reaction cross sections obtained in experiments using quasimonoenergetic annihilation photons and bremsstrahlung were investigated using objective physical criteria of data reliability. It was shown that many data are not reliable because of significant systematic uncertainties of the photoneutron multiplicity sorting methods used. The experimental–theoretical method for evaluation of reliable partial reaction cross sections was proposed and many new data were obtained.

Basic methods for determining cross sections for photoneutron partial reactions are examined. They are obtained directly in experiments with quasimonoeneregetic annihilation photons or from the cross section for the (γ, xn) = (γ, 1n) + 2(γ, 2n) + 3(γ, 3n) +... neutron-yield reaction in experiments with bremsstrahlung photons by introducing corrections based on statistical nuclear-reaction theory. The difference in the conditions of these experiments, which leads to discrepancies between their results because of sizable systematic errors, is analyzed. Physical criteria are used to study the reliability of data on the photodisintegration of 133Cs, 138Ba, and 209Bi nuclei. The cross sections for partial and total reactions satisfying the reliability criteria are evaluated within the experimental–theoretical method (σ eval(γ, in) = F i theor × σ expt(γ, xn)) on the basis of the experimental cross sections σ expt(γ, xn) and the results of the calculations within the combined model of photonuclear reactions.

The dependence of the properties of low-lying states of Mo isotopes on the mass number A = 83–117 is studied based on the collective and shell models of atomic nuclei. The variation of the nuclear shape with an increasing number of neutrons influences strongly the properties of excited states of Mo isotopes. Decay channels of isovector giant dipole resonance with emission of protons and neutrons are studied in the framework of the combined model. The basic mechanisms of the production of stable Mo isotopes in astrophysical nuclear reactions are described.

The well-known problem of noticeable disagreements between photoneutron cross sections from various experiments was discussed in detail for 209Bi. Data for partial photoneutron reactions cross sections obtained at Livermore (USA) using quasimonoenergetic annihilation photons and the method of neutron multiplicity sorting were analyzed using the objective physical criteria and the experimental-theoretical method for evaluation. Because of significant systematic uncertainties involved in the method for determining the neutron multiplicity, experimental data do not satisfy the criteria of reliability and differ noticeably from the evaluated data. The new experimental data for 209Bi (γ, in) reactions with i = 1–4 were obtained using quasimonochromatic laser Compton-scattering (LCS) γ-ray beams at the NewSUBARU synchrotron radiation facility and the novel technique of direct neutron-multiplicity sorting with a flat-efficiency detector. It was found that new σ(γ, 1n), σ (γ, 2n), and σ (γ, 3n) contradict noticeably to the Livermore data. It was shown that at the same time the new 209Bi photoneutron cross-sections are in good agreement with data evaluated using experimental-theoretical method and assuring the reliability of those.

The experimental data for photoneutron reaction cross sections for 127I obtained using beams of quasimonoenergetic annihilation photons and the method of neutron multiplicity-sorting at Livermore (USA) and Saclay (France) were analyzed using objective physical data reliability criteria. It was found that data of both laboratories contain significant systematic uncertainties and therefore are not reliable. New data for partial and total photoneutron reactions cross sections for 127I satisfied physical criteria of data reliability were evaluated using experimental-theoretical method based on both experimental neutron yield reaction cross-section and results of calculation in the combined photonucleon reaction model (CPNRM). The neutron yield reaction cross-section obtained at Saclay (France) was used in evaluation procedure. The newly evaluated cross sections for partial (γ, 1n), (γ, 2n) and (γ, 3n) reactions for 127I were used for discussion in detail the problems of significant disagreements between experimental data for many nuclei obtained at Saclay and Livermore. It was found that systematic uncertainties of experimental data for the (γ, 1n), (γ, 2n), and (γ, 3n) reactions cross sections for 127I obtained at both laboratories are of different nature. One of the reasons of noticeable systematic uncertainties of cross sections obtained are the shortcomings of the procedures used to separate counts into 1n, 2n, and 3n events. At the same time it was shown that the main reason of significant disagreements between new evaluated data and data obtained at Livermore experiment for 127I is the loss of many neutrons from the (γ, 1n) reaction. This situation is analogous to those in Livermore experiments for 75As and 181Ta.

Data on partial photoneutron reaction cross sections $(\gamma,1n)$ and $(\gamma,2n)$ for 90,91,92,94Zr obtained at Livermore (USA) and for 90Zr obtained at Saclay (France) were analyzed. Experimental data were obtained using quasimonoenergetic photon beams from the annihilation in flight of relativistic positrons. The method of photoneutron multiplicity sorting based on the neutron energy measuring was used to separate partial reactions. The research carried out is based on the objective of using the physical criteria of data reliability. The large systematic uncertainties were found in partial cross sections, since they do not satisfy those criteria. To obtain the reliable cross sections of the partial $(\gamma,1n)$ and $(\gamma,2n)$ and total $(\gamma,1n)$ + $(\gamma,2n)$ reactions on 90,91,92,94Zr and $(\gamma,3n)$ reaction on 94Zr, the experimental-theoretical method was used. It is based on the experimental data for neutron yield cross section rather independent from the neutron multiplicity and theoretical equations of the combined photonucleon reaction model (CPNRM). Newly evaluated data are compared with experimental ones. The reasons of noticeable disagreements between those are discussed.

A refined version of the combined photonucleon-reaction model is described. This version makes it possible to take into account the effect of structural features of the doorway dipole state on photonucleon reactions in the energy range of E γ ≤ 30 MeV. In relation to the previous version of the model, the treatment of isospin effects at the preequilibrium and evaporation reaction stages is refined; in addition, the description of the semidirect effect caused by nucleon emission from the doorway dipole state is improved. The model in question is used to study photonucleon reactions on the isotopes 35-56Ca and 102-134Sn in the energy range indicated above.

The photodisintegration of titanium isotopes in the giant-dipole-resonance energy region is studied by the photon-activation method. Bremsstrahlung photons whose spectrum has the endpoint energy of 55 MeV is used. The yields and integrated cross sections are determined for photoproton reactions on the titanium isotopes 47,48,49,50Ti. The respective experimental results are compared with their counterparts calculated on the basis of the TALYS code and a combined photonucleon-reaction model. The TALYS code disregards the isospin structure of the giant dipole resonance and is therefore unable to describe the yield of photoproton reactions on the heavy titanium isotopes 49,50Ti.

Among key problems in nuclear astrophysics, that of obtaining deeper insight into the mechanism of synthesis of chemical elements is of paramount importance. The majority of heavy elements existing in nature are produced in stars via radiative neutron capture in so-called s- and r processes, which are, respectively, slow and fast, in relation to competing β−-decay processes. At the same time, we know 35 neutron-deficient so-called bypassed p-nuclei that lie between 74Se and 196Hg and which cannot originate from the aforementioned s- and r-processes. Their production is possible in (γ, n), (γ, p), or (γ, α) photonuclear reactions. In view of this, data on photoneutron reactions play an important role in predicting and describing processes leading to the production of p-nuclei. Interest in determining cross sections for photoneutron reactions in the threshold energy region, which is of particular importance for astrophysics, has grown substantially in recent years. The use of modern sources of quasimonoenergetic photons obtained in processes of inverse Compton laser-radiation scattering on relativistic electronsmakes it possible to reveal rather interesting special features of respective cross sections, manifestations of pygmy E1 and M1 resonances, or the production of nuclei in isomeric states, on one hand, and to revisit the problem of systematic discrepancies between data on reaction cross sections from experiments of different types, on the other hand. Data obtained on the basis of our new experimental-theoretical approach to evaluating cross sections for partial photoneutron reactions are invoked in considering these problems.

There is a serious well-known problem of noticeable disagreements between the partial photoneutron cross sections obtained in various experiments. Such data were mainly determined using quasimonoenergetic annihilation photon beams and the method of neutron multiplicity sorting at Lawrence Livermore National Laboratory (USA) and Centre d'Etudes Nucleaires of Saclay (France). The analysis of experimental cross sections employing new objective physical data reliability criteria has shown that many of those are not reliable. The IAEA Coordinated Research Project (CRP) on photonuclear data evaluation was approved. The experimental and previously evaluated cross sections of the partial photoneutron reactions $(\ensuremath{\gamma},1n)$ and $(\ensuremath{\gamma},2n)$ on $^{197}\mathrm{Au}$ were analyzed using the new data reliability criteria. The data evaluated using the new experimental-theoretical method noticeably differ from both experimental data and data previously evaluated using nuclear modeling codes gnash, gunf, alice-f, and others. These discrepancies needed to be resolved.

Photoneutron cross sections were measured in the $^{209}\mathrm{Bi}$($\ensuremath{\gamma}, xn$) reaction with $x=1--4$ at energies from the neutron threshold to 40 MeV using quasimonochromatic laser Compton-scattering $\ensuremath{\gamma}$-ray beams. A novel technique of direct neutron-multiplicity sorting with a flat-efficiency detector was used. Results are compared with the positron in-flight annihilation data of Livermore and Saclay as well as with bremsstrahlung data. The present neutron yields are consistent with the latest photoactivation measurement with bremsstrahlung. The giant dipole resonance component of the total photoneutron cross section is reasonably reproduced by model calculations of the Hartree-Fock Bogoliubov plus quasiparticle random phase approximation based on the Gogny D1M interaction for both E1 and M1 components. In contrast, the quasideuteron component of the total photoneutron cross section requires a factor of $\ensuremath{\sim}3$ enhancement of the Levinger parameter. Furthermore, a survival of large $(\ensuremath{\gamma},n)$ cross sections above 20 MeV may indicate the surface effect on the two-component particle-hole state density. The threshold behavior of photoneutron emission is discussed in terms of the average neutron kinetic energy.

The majority of photonuclear reaction cross sections important for many fields of science and technology and various data files (EXFOR, RIPL, ENDF, etc.) supported by the IAEA were obtained in experiments using quasimonoenergetic annihilation photons. There are well–known systematic discrepancies between the partial photoneutron reactions (γ, 1n), (γ, 2n), (γ, 3n). For analysis of the data reliability the objective physical criteria were proposed. It was found out that the experimental data for many nuclei are not reliable because of large systematic uncertainties of the neutron multiplicity sorting method used. The experimentally–theoretical method was proposed for evaluating the reaction cross sections data satisfying the reliability criteria. The partial and total reaction cross sections were evaluated for many nuclei. In many cases evaluated data differ noticeably from both the experimental data and the data evaluated before for the IAEA Photonuclear Data Library. Therefore it became evident that the IAEA Library needs to be revised and updated.

The yields of photonucleon reactions having various multiplicities and occurring on a natural mixture of cadmium isotopes were measured. Bremsstrahlung whose spectrum had an endpoint energy of 55 MeV was used as a gamma-ray source. The reaction yields were determined with the aid of the induced-activity method. The yields of photonuclear reactions for several channels of decay of excited states of cadmium isotopes in the energy region extending up to 55MeV were obtained for the first time. A comparison of the results obtained experimentallywith the results of theoretical calculations reveals that, in the case of heavy cadmium isotopes, it is possible to obtain a reasonably good description of experimental data. In the case of the light isotope 106Cd, however, the results of the theoretical calculations are at odds with experimental data, and this is likely to be due to special features of the shell structure of the isotope 106Cd, which lies near the beta-stability boundary.

The process of photodisintegration of molybdenum isotopes was studied using the induced activity method. The yields of isotopes produced as a result of photonuclear reactions on a natural mixture of molybdenum isotopes were determined at an electron accelerator energy of 67.7 MeV. A comparison of the experimental results with the theoretical calculation carried out using the combined model of photonucleon reactions shows that the model gives a fair description of the experimental yields of photonucleon reactions on all molybdenum isotopes except for 92Mo. The high yields of the proton channels of photonuclear reactions on the 92Mo isotope and low yields of the corresponding neutron channels are interpreted based on the shell structure of molybdenum isotopes.

Systematic discrepancies between the results of various experiments devoted to determining cross sections for total and partial photoneutron reactions are analyzed by using objective criteria of reliability of data in terms of the transitional photoneutron-multiplicity function F i = σ(γ, in)/σ(γ, xn), whose values for i = 1, 2, 3, ... cannot exceed by definition 1.00, 0.50, 0.33, ..., respectively. It was found that the majority of experimental data on the cross sections obtained for (γ, n), (γ, 2n), and (γ, 3n) reactions with the aid of methods of photoneutron multiplicity sorting do not meet objective criteria (in particular, F 2 > 0.50 for a vast body of data). New data on the cross sections for partial reactions on 181Ta and 208Pb nuclei were obtained within a new experimental-theoretical method that was proposed for the evaluation of cross sections for partial reactions and in which the experimental neutron yield cross section σ expt(γ, xn) = σ(γ, n) + 2σ(γ, 2n) + 3σ(γ, 3n) + ..., which is free from problems associated with determining neutron multiplicities, is used simultaneously with the functions F theor calculated within a combined model of photonuclear reactions.

The results obtained by measuring the yields of photodisintegration of the isotope 116Cd irradiated with bremsstrahlung photons whose spectrum had an endpoint energy of 55 MeV are presented and compared with the results of theoretical calculations.

A joint analysis of the experimental data on cross sections of total and partial photoneutron reac� tions is performed for the 115 In isotope. The data are obtained by using the quasimonoenergetic photons gen� erated upon the annihilation of relativistic positrons. Wellknown systematic discrepancies between the results of various experiments are analyzed using objective absolute criteria of data reliability and authenticity. Methods for taking these discrepancies into account are considered. New reliable and authentic evaluations for cross sections of the σ(γ, n), σ(γ2n), and σ(γ, 3n) reactions are obtained using the data on the cross section of the reaction of photoneutron total yields σ(γ,xn) in the context of a new experimentaltheoretical approach to evaluating the cross sections of partial reactions. These data are free from the shortcomings of experimental methods for the photoneuron multiplicity sorting.

The effect of the isovector giant quadrupole resonance and an overtone of the isovector giant dipole resonance on the photodisintegration of medium-mass and heavy nuclei in the energy range of 20–40 MeV is studied on the basis of a combined model of photonucleon reactions. Basic features of these resonances are evaluated within a semimicroscopic approach. Their deformation spitting is described on the basis of the model of polarization vibrations of a two-component nuclear liquid.

The presence of substantial systematic discrepancies between the results of different experiments devoted to determining cross sections for partial photoneutron reactions—first of all, (γ, n), (γ, 2n), and (γ, 3n) reactions—is a strong motivation for studying the reliability and authenticity of these data and for developing methods for taking into account and removing the discrepancies in question. In order to solve the first problem, we introduce objective absolute criteria involving transitional photoneutron-multiplicity functions F 1, F 2, F 3, …; by definition, their values cannot exceed 1.0, 0.5, 0.33, …, respectively. With the aim of solving the second problem, we propose a new experimental-theoretical approach. In this approach, reaction cross sections are evaluated by simultaneously employing experimental data on the cross section for the total photoneutron yield, σ expt(γ, xn) = σ expt(γ, n) + 2σ expt(γ, 2n) + 3σ expt(γ, 3n) + …, which are free from drawbacks plaguing experimental methods for sorting neutrons in multiplicity, and the results obtained by calculating the functions F theor 1 , F theor 2 , F theor 3 , … on the basis of the modern model of photonuclear reactions. The reliability and authenticity of data on the cross sections for (γ, n), (γ, 2n), and (γ, 3n) partial reactions—σ eval(γ, in) = F theor σ expt(γ, xn)—were evaluated for the 90Zr, 115In, 112,114,116,117,118,119,120,122,124Sn, 159Tb, and 197Au nuclei.

The yields of photonucleon reactions on the isotope 181Ta that are induced by bremsstrahlung photons whose endpoint energy is 67.7 MeV are measured by the residual-activity method. The cross sections for photonucleon reactions on the isotope 181Ta are calculated on the basis of the TALYS code and a combined model. The measured reaction yields are compared with their counterparts rescaled from cross sections obtained in experiments that employed beams of quasimonochromatic and bremsstrahlung photons. The spectra of neutrons emitted from 181Ta nuclei after the absorption of photons having various energies are calculated within the TALYS code and the combined model in question.

The perspectives for photonuclear experiments at the new Extreme Light Infrastructure - Nuclear Physics (ELI-NP) facility are discussed in view of the need to accumulate novel and more precise nuclear data. The parameters of the ELI-NP gamma beam system are presented. The emerging experimental program, which will be realized at ELI-NP, is presented. Examples of day-one experiments with the nuclear resonance fluorescence technique, photonuclear reaction measurements, photofission experiments and studies of nuclear collective excitation modes and competition between various decay channels are discussed. The advantages which ELI-NP provides for all these experiments compared to the existing facilities are discussed.

Experimental data on yields of multi-particle photonuclear reactions (involving the emission of up to seven neutrons from the nucleus involved) on 197 Au, 203;205 Tl, and 209 Bi nuclei in the region extending from the giant dipole resonance to an energy of 67.7 MeV are presented. These data are compared with the results of modern theoretical calculations that take into account both the excitation of a giant dipole resonance (GDR) in a nucleus and the photodisintegration of quasideutrons (QD) in it. By and large, experimental data conrm the results of theoretical calculations { that is, only upon taking simultaneously into account both alternative photodisintegration mechanisms (GDR excitation and QD photodisintegration) can one describe these experimental data. The contribution of QD photodisintegration grows with increasing photon energy and neutron multiplicity and becomes dominant for reactions with the emission of not less than ve neutrons from the nucleus being considered.

The induced-activity method is used to measure yields of photonuclear reactions induced in stable mercury isotopes by beams of bremsstrahlung photons whose spectra have the endpoint energies of 19.5 and 29.1 MeV. On the basis of a collective model, the partial cross sections and yields are calculated for photoproton and photoneutron reactions on these isotopes. The yields calculated theoretically are compared with their measured counterparts. The possibility for the production in photonuclear reactions of the bypassed nucleus 196Hg, which cannot be formed in astrophysical r and s processes, is analyzed.

Yields of photonucleon reactions of different multiplicity of natural isotopic mixture of Pb were measured on a bremsstrahlung photon beam with a maximum energy of 67.7 MeV using gamma-activation methods. Cross-sections of photonucleon reactions of different multiplicity were calculated on stable Pb isotopes within the bounds of the combined model. The calculated cross sections are compared to those measured in experiments on quasimonochromatic photon beams. They are also used to split the measured yields into yields of particular photonucleon reactions.

A combination of the semimicroscopic, exciton, and evaporation models is used to describe photonucleon reactions induced in medium-mass and heavy nuclei by photons of energy below the mesonproduction threshold. Two mechanisms of the photoexcitation of nuclei are considered. These are the formation of a giant dipole resonance (GDR) at energies in the range E γ ≲ 30 MeV and quasideuteron photoabsorption, which is dominant at energies in the region E γ ≳ 40 MeV. The densities of particle-hole states appearing in the exciton model are calculated on the basis of the Fermi gas model. Our combined model takes into account the multiparticle emission of preequilibrium particles. The influence of isospin conservation and collective phenomena on photonucleon emission by giant dipole resonances is considered. The combined model is used to describe cross sections for photonucleon reactions proceeding on the 40,48Ca, 90Zr, 139La, 142Nd, and 181Ta nuclei, as well as difference (E γmax = 85–55 MeV) bremsstrahlung photoneutron spectra for the 63Cu, 115In, 118Sn, 181Ta, 207Pb, 209Bi, and 235U nuclei and bremsstrahlung photoproton spectra for the 90Zr nucleus at the energies of E γmax = 22, 25, and 34 MeV.

Yields of photonuclear reactions of several Hg isotopes are measured on a bremsstrahlung photon beam with a maximal energy of 19.5 MeV using a gamma-activation analysis. Cross sections of photonuclear reactions on stable Hg isotopes are calculated within bonds of the collective model taking isospin splitting of giant dipole resonance into account. The experimental results are compared with the results of theoretical calculations and earlier experimental studies.

A combined analysis of experimental data on total and partial photoneutron reaction cross sections, obtained using bremsstrahlung γ-radiation and quasi-monoenergetic annihilation photon beams, was performed for nine Sn isotopes. The partial reactions σeval(γ, nX) and σeval(γ, 2nX) cross sections were evaluated using an approach free of the shortcomings of experimental neutron multiplicity sorting methods. This approach involves calculations within the photonuclear reaction model, based on Fermi gas densities and considering the effects of nucleus deformation, the isospin splitting of its giant dipole resonance (GDR), and experimental data on the total photoneutron cross sections σexp(γ, xn) = σexp(γ, nX) + 2σexp(γ, 2nX) = σexp(γ, n) + σexp(γ, np) + … + 2σexp(γ, 2n) + 2σexp(γ, 2np) + …. The evaluated σeval(γ, nX) and σeval(γ, 2nX) reactions cross sections were obtained using the introduced transition multiplicity functions Ftheor = σtheor(γ, 2nX)/σtheor(γ, xn) = σtheor(γ, 2nX)/[σtheor(γ, nX) + 2σtheor(γ, 2nX) + …]; and σeval.(γ, 2nX) = Ftheor.σexp.(γ, xn) = σeval(γ, nX) = (1 − 2Ftheor)σexp(γ, xn). The evaluated partial reaction cross sections were used to assess the total photoneutron reaction cross sections σeval(γ, sn) = σeval(γ, nX) + σeval(γ, 2nX) + … as functions of the mass number A. The GDR features of 112, 114, 116, 117, 118, 119, 120, 122, 124Sn isotopes were studied and are discussed here.

A modified model of preequilibrium decay is considered. This model makes it possible to calculate cross sections for multiparticle photonucleon reactions with allowance for the impact of collective isospin effects. Features of the photodisintegration of 101 ≤ A ≤ 135 tin isotopes in the energy range 2 ≤ Eγ ≤ 140 MeV are studied on the basis of this model.

A combination of the exciton and evaporation models is used to describe photonuclear reactions induced in light, medium-mass, and heavy nuclei by photons of energy in the range 7 ≤ Eγ ≤ 140 MeV. Two mechanisms of the photoexcitation of nuclei are considered. These are the formation of a giant dipole resonance at energies in the range Eγ ≲ 30 MeV and quasideuteron photoabsorption, which is dominant at energies in the region Eγ ≳ 40 MeV. The density of particle-hole states, which appears in the exciton model, is calculated on the basis of the Fermi gas model. The emission of two preequilibrium particles is taken into account in describing the quasideuteron reaction channel. The effect of isospin conservation on giant-dipole-resonance decay accompanied by photonucleon emission is examined. The model in question is used to describe cross sections for photon-induced reactions on 26Mg, 54Fe, 112,118,119,124Sn, and 181Ta nuclei.

An experiment in which the gold isotope 197Au was irradiated with a beam of bremsstrahlung photons having an endpoint energy of Eγm = 67.7 MeV and originating from the RTM-70 racetrack microtron of the Institute of Nuclear Physics at Moscow State University was performed. The gammaray spectra of the residual beta activity of an irradiated sample were measured. Multinucleon photonuclear reactions on 197Au nuclei were observed in the experiment. Photonuclear reactions on a 197Au nucleus that involve the emission of up to seven neutrons were recorded for the first time. The experimental results in question suggest the important role of the quasideuteron photodisintegration mechanism in the energy region behind the giant dipole resonance.

A combination of the exciton and evaporation models is used to describe photonucleon reactions induced in heavy and medium-mass nuclei by photons of energy in the range 7 ≤ Eγ ≤ 140 MeV. The formation of a giant dipole resonance and quasideuteron absorption are considered as two mechanisms that are responsible for the photoexcitation of a nucleus in the energy regions Eγ ≲ 20 MeV and Eγ ≳ 40 MeV, respectively. As is well known, the densities of particle-hole states are employed in the exciton model, and these quantities are calculated on the basis of the Fermi gas model. This makes it possible to take into account the effect of the energy dependence of single-particle and single-hole densities of states on the rate of emission and intranuclear processes. The model in question is applied to describing partial photonucleon cross sections for 119Sn, 140Ce, 181Ta, and 208Pb nuclei.

Based on the new Chart (database) of deformations of atomic nuclei, a systematic comparative analysis of quadrupole deformation parameters obtained by different methods for a large number of even-even nuclei is performed. It is shown that all nuclides whose quadrupole deformation parameters are deduced from the data on quadrupole moments (Q-type data) and on the reduced probability B(E2)↑ of quadrupole electric transitions 0+ → 21+ (B-type data) are clearly divided into two groups. In one of them, the data of both types show good agreement (within experimental errors) and in the other the B-type deformations are systematically (sometimes greatly) larger than the Q-type deformations. It is shown that this relationship among the data from different sources may be explained by assuming that a deformation parameter depends upon vibrations of the nuclear surface in the ground state. In this case, the B-type data, unlike the Q-type data, are believed to allow for these nuclear surface vibrations. In other words, the B-type data take into account not only static deformation, i.e., the “shape” of the nucleus, but also dynamic deformation resulting from vibrations of the nuclear surface in the ground state. The assumption that the nuclear dynamic deformation affects the nuclear shape allows one to assess “rigidity” of nuclei dividing them into two groups: “rigid” and “nonrigid”, i.e., “loose”. A comparison of the static and total deformations may yield data on nuclear properties, e.g., estimates of relationships between mass parameters and rigidity parameters.

A simple semimicroscopic model providing the possibility of taking into account the influence of deformation, configuration, and isospin effects on the structure of giant dipole resonance is formulated. This model is applied for the description of global specific features of photoabsorption cross sections for spherical, deformed, and transition nuclei in the mass region 10 ≲ A ≲ 240.