Narrow Results

A model-independent irreducible tensor approach is presented for the np fusion reaction. Appropriate spin-observables are identified to determine empirically the initial spin singlet and triplet contributions to the differential cross-section, in view of the recent experimental interest in studying radiative capture of polarized neutrons by polarized protons.

We made again an experiment of pd radiative capture at , and obtained A_xx, A_yy and A_zz (= -A_xx - A_yy) data using a newly-developed data-analysis method of high detection efficiency. Re-analysis of previous data on A_xx and A_yy was also made using a new method. All the new and previous data at 197 MeV agree to each other, and A_xx anomaly has been confirmed.

Direct searches for dark matter lead to serious problems for simple models with stable neutral Weakly Interacting Massive Particles (WIMPs) as candidates for dark matter. A possibility is discussed that new stable quarks and charged leptons exist and are hidden from detection, being bound in neutral dark atoms of composite dark matter. Stable -2 charged particles O^-- are bound with primordial helium in O-helium (OHe) atoms, being specific nuclear interacting form of composite Warmer than Cold dark matter. Slowed down in the terrestrial matter, OHe is elusive for direct methods of underground dark matter detection based on the search for effects of nuclear recoil in WIMP-nucleus collisions. The positive results of DAMA experiments can be explained as annual modulation of radiative capture of O-helium by nuclei. In the framework of this approach, test of DAMA results in detectors with other chemical content becomes a nontrivial task, while the experimental search of stable charged particles at LHC or in cosmic rays acquires a meaning of direct test for composite dark matter scenario.

In the framework of the modified potential cluster model (PCM), the possibility of describing the available experimental data for the total cross-sections for n¹¹B radiative capture at thermal and astrophysical energies were considered with taking into account the 21 keV and 430 keV resonances.

Among dark atom scenarios, the simplest and most predictive one is that of O-helium (OHe) dark atoms, in which a leptonlike doubly charged particle O^–– is bound to a primordial helium nucleus, and is the main constituent of dark matter. The OHe cosmology has several successes: it leads to a warmer-than-cold-dark matter scenario for large-scale-structure formation, it can provide an explanation for the excess in positron annihilation line in the galactic bulge and it may explain the results of direct dark matter searches. This model liberates the physics of dark atoms from many unknown features of new physics, but it is still not free from astrophysical uncertainties. It also demands a deeper understanding of the details of known nuclear and atomic physics, which are still somewhat unclear in the case of nuclear interacting “atomic” shells. These potential problems of the OHe scenario are also discussed.

Electric dipole strength below the particle emission threshold both in stable nuclei and short-lived isotopes has received increasing interest due to its astrophysical impact. In analogy to the giant dipole resonance, this strength is commonly referred to as pygmy resonance. Coulomb dissociation of neutron-rich unstable isotopes and nuclear resonance fluorescence photon scattering have begun to provide systematic data on electric dipole strength in various isotope chains. We review the present state of the art of theoretical approaches and point out some open problems. We emphasize the necessity of a simultaneous theoretical treatment of the nucleon separation energies and the energetically low-lying dipole strength because the presently available data do not exclude a non-collective nature of the pygmy strength.

Astrophysical S-factors of radiative capture reactions on light nuclei have been calculated in a two-cluster potential model, taking into account the separation of orbital states by the use of Young schemes. The local two-body potentials describing the interaction of the clusters were determined by fitting scattering data and properties of bound states. The many-body character of the problem is approximatively accounted for by Pauli forbidden states. An important feature of the approach is the consideration of the dependence of the interaction potential between the clusters on the orbital Young schemes, which determine the permutation symmetry of the nucleon system. Proton capture on ²H, ⁶Li, ⁷Li, ¹²C and ¹³C was analyzed in this approach. Experimental data at low energies were described reasonably well when the phase shifts for cluster–cluster scattering, extracted from precise data, were used. This shows that decreasing the experimental error on differential elastic scattering cross-sections of light nuclei at astrophysical energies is very important also to allow a more accurate phase shift analysis. A future increase in precision will allow more definite conclusions regarding the reaction mechanisms and astrophysical conditions of thermonuclear reactions.

The total cross-sections of the radiative neutron capture processes on ⁹Be, ¹⁴C, ¹⁴N, ¹⁵N and ¹⁶O are described in the framework of the modified potential cluster model with the classification of orbital states according to Young tableaux. The continued interest in the study of these reactions is due, on the one hand, to the important role played by this process in the analysis of many fundamental properties of nuclei and nuclear reactions, and, on the other hand, to the wide use of the capture cross-section data in the various applications of nuclear physics and nuclear astrophysics, and, also, to the importance of the analysis of primordial nucleosynthesis in the Universe. This article is devoted to the description of results for the processes of the radiative neutron capture on certain light atomic nuclei at thermal and astrophysical energies. The considered capture reactions are not part of stellar thermonuclear cycles, but involve in the reaction chains of inhomogeneous Big Bang models.

We have studied the neutron-capture reactions ^10,11B(n, γ) and the role of the ¹¹B(n, γ) reaction in seeding r-process nucleosynthesis. The possibility of the description of the available experimental data for cross-sections of the neutron capture reaction on ¹⁰B at thermal and astrophysical energies, taking into account the resonance at 475 keV, was considered within the framework of the modified potential cluster model (MPCM) with forbidden states (FS) and accounting for the resonance behavior of the scattering phase shifts. In the framework of the same model, the possibility of describing the available experimental data for the total cross-sections of the neutron radiative capture on ¹¹B at thermal and astrophysical energies were considered with taking into account the 21 and 430 keV resonances. Description of the available experimental data on the total cross-sections and astrophysical S-factor of the radiative proton capture on ¹¹B to the GS of ¹²C was treated at astrophysical energies. The possibility of description of the experimental data for the astrophysical S-factor of the radiative proton capture on ¹⁴C to the GS of ¹⁵N at astrophysical energies, and the radiative proton capture on ¹⁵N at the energies from 50 to 1500 keV was considered in the framework of the MPCM with the classification of the orbital states according to Young tableaux. It was shown that, on the basis of the M1 and the E1 transitions from different states of the p¹⁵N scattering to the GS of ¹⁶O in the p¹⁵N channel, it is quite succeed to explain general behavior of the S-factor in the considered energy range in the presence of two resonances.

We have studied the neutron-capture reactions ⁸Li($n,\gamma {)}^9$Li and its role in the primordial nucleosynthesis. The $n{+}^8\mathrm{\text{Li}}{\to }^9\mathrm{\text{Li}}+\gamma$ reaction has a significant astrophysical interest because it includes one of the variants of chain of primordial nucleosynthesis processes of the Universe and thermonuclear reactions in type II supernovae. Furthermore, we consider the ${}^9\mathrm{\text{Be}}{(p,\gamma )}^{10}\mathrm{\text{B}}$ reaction in the astrophysical energy range in the modified potential cluster model (MPCM) with splitting of orbital states according to Young tableaux and, in some cases, with forbidden states (FS). The reaction ${}^9\mathrm{\text{Be}}{(p,\gamma )}^{10}\mathrm{\text{B}}$ plays an important role in primordial and stellar nucleosynthesis of light elements in the $p$ shell. Hydrogen burning in second-generation stars occurs via the proton–proton (pp) chain and CNO cycle, with the ${}^9\mathrm{\text{Be}}{(p,\gamma )}^{10}\mathrm{\text{B}}$ reaction serving as an intermediate link between these cycles. Furthermore, the possibility of describing available experimental data for the total reaction cross-sections of neutron radiative capture on ${}^{10}$Be at thermal and astrophysical energies has been shown. This reaction is a part of one of the variants of the chain of primordial nucleosynthesis of the Universe due to which the elements with a mass of $A>11\text{–}12$ may be formed. The results in the field of study of thermonuclear proton-capture reaction on ${}^{10}\mathrm{\text{B}}$ at ultralow, i.e., astrophysical energies will be presented further. The possibility of description of the experimental data for the astrophysical $S$-factor of the proton radiative capture on ${}^{16}$O to the ground state (GS) of ${}^{17}$F was considered in the frame of the MPCM with FS and classification of the states according to Young tableaux. It was shown that on the basis of the $E1$ transitions from the states of $p^{16}$O scattering to the GS of ${}^{17}$F in the $p^{16}$O channel generally succeed to explain the value of measured cross-sections at astrophysical energies.

In this article we review the recent progress in radiative reaction calculations in halo effective field theory. We look at radiative capture and breakup processes that involve a halo nucleus with a single valence neutron or proton. Looking at ${}^7\mathrm{\text{Li}}(n,\gamma )$${}^8\mathrm{\text{Li}}$,${}^{14}\mathrm{\text{C}}($n$,\gamma {)}^{15}\mathrm{\text{C}}$ and related reactions, the dominant source of theoretical uncertainty in $s$- and $p$-wave halo nuclei reaction calculations is quantified in a model-independent framework. The analysis for neutron halos is extended to proton halo systems. The effective field theory results quantify which observable parameters of the strong interaction at low energy need to be determined more precisely for accurate cross-section calculations.

We have studied the proton capture reaction ${}^3\mathrm{\text{H}}{(p,\gamma )}^4\mathrm{\text{He}}$. It plays a role in the nucleosynthesis of primordial elements in the early Universe leading to the prestellar formation of ${}^4\mathrm{\text{He}}$ nuclei. All results of our researches and more new data from works show that the contribution of the ${}^3\mathrm{\text{H}}{(p,\gamma )}^4\mathrm{\text{He}}$ capture reaction into the processes of primordial nucleosynthesis is relatively small. However, it makes sense to consider this process for making the picture complete for the formation of prestellar ${}^4\mathrm{\text{He}}$ and clearing of mechanisms of this reaction. Furthermore, we have considered the ${}^3\mathrm{\text{He}}{{(}^2\mathrm{\text{H}},\gamma )}^5\mathrm{\text{Li}}$ reaction in the low energy. This reaction also forms part of the nucleosynthesis chain of the processes occurring in the early stages of formation of stable stars. They are possible candidates for overcoming the well-known problem of the $A=5$ gap in the synthesis of light elements in the primordial Universe. Continuing the study, we have considered the radiative capture ${}^4\mathrm{\text{He}}{{(}^3\mathrm{\text{He}},\gamma )}^7\mathrm{\text{Be}}$ at superlow energies, which has a undeniable interest for nuclear astrophysics, since it takes part in the proton–proton fusion chain, and new experimental data on the astrophysical $S$-factors of this process at energies down to 90 and 23keV and data on the radiative capture reaction ${}^4\mathrm{\text{He}}{{(}^3\mathrm{\text{H}},\gamma )}^7\mathrm{\text{Li}}$ down to 50keV appeared recently. Moreover, radiative capture reactions ${}^4\mathrm{\text{He}}{{(}^3\mathrm{\text{He}},\gamma )}^7\mathrm{\text{Be}}$ and ${}^4\mathrm{\text{He}}{{(}^2\mathrm{\text{H}},\gamma )}^6\mathrm{\text{Li}}$ may have played a certain role in prestellar nucleosynthesis after the Big Bang, when the temperature of the Universe decreased to the value of $0.3T_9$.

Review of calculation results for astrophysical $S$-factor of the ${}^{14}$N${(p,\gamma )}^{15}$O capture reaction in the $p^{14}$N channel of ${}^{15}$O was presented. It was carried out in the frame of the modified potential cluster model (MPCM) taking into account resonances in the ${}^{15}$O spectrum up to 3.2MeV at energy of incident protons varying of 30keV to 5MeV. It is possible to describe experimental data for the astrophysical $S$-factors of the radiative proton capture on ${}^{14}$N to five excited states of ${}^{15}$O at excitation energies of 5.18MeV to 6.86MeV, only under assumption, that all five resonances are $D$ scattering waves. Quality new physical interpretation of the capture mechanism is discussed in this channel to the ground state of ${}^{15}$O. We assumed that the ground state of ${}^{15}$O is determined by the $p^{14}$N${}^{\ast }$ channel with excited ${}^{14}$N${}^{\ast }$ cluster, which immediately allowed us to correctly describe order of values of the experimental $S$-factor for capture to this state. Taking into account these results, the total $S$-factor of the proton capture on ${}^{14}$N and the reaction rates to the ground and five excited states of ${}^{15}$O were determined at temperatures of 0.01$T_9$ to 10$T_9$. The parametrization of the total reaction rate with a simple form is performed, which allows as to obtain ${\chi }^2$ equal to 0.06 with 5% errors of the calculated rate.

Based on the framework of the modified potential cluster model (MPCM), with orbital states classified using Young diagrams, we consider the possibility of prediction absentee of experimental data for the total cross-sections of the radiative neutron capture on ${}^{11}$B to the first excited state of ${}^{12}$B at 0.95314MeV (2${}^{+}$), to the second excited state of ${}^{12}$B at 1.67365MeV (2⁻), and prediction absentee of experimental data for the total cross-sections to the third and fourth excited states of ${}^{12}$B at 2.6208MeV (1⁻) and 2.723MeV (0${}^{+}$), for a reaction energy of 10meV to 7MeV. We calculate the reaction rate for a temperature range of 0.01–10.0 $T_9$ on the basis of the obtained cross-sections, which take into account resonances up to 5MeV. We then demonstrate that low-lying resonances have a significant impact on the reaction rate of capture. An approximation for the calculated reaction rate is derived based on an analytical formula.

The isotope ${}^{16}\mathrm{\text{O}}$ is one of the most abundant light isotopes, and therefore the process ${}^{16}\mathrm{\text{O}}{(n,\gamma )}^{17}\mathrm{\text{O}}$ reaction plays a critical role in stellar nucleosynthesis. Reaction cross-sections and rates for neutron capture by ${}^{16}\mathrm{\text{O}}$ at astrophysical energies have been calculated with special attention to low-lying, narrow resonances while implementing $R$-matrix formalism during integration.

Some accelerator technologies are already used for commercial ${}^{99}$Mo-^99mTc production, as the economic criteria are considered representative of the main differences between diverse technologies including accelerators and reactors. This study has provided a review of known and potential ${}^{99}$Mo production using conventional medical facilities. Accelerator-based method in ^99mTc production via ($p$, $2n$) direct reaction on ${}^{100}$Mo was simulated using 18MeV proton beam. Meanwhile, a conceptual design for indirect ${}^{99}$Mo production via ${}^{100}$Mo($\gamma ,n$)${}^{99}$Mo and ${}^{100}$Mo(n,2n)${}^{99}$Mo reactions was investigated when an electron source of 35MeV by accelerator is used. These indirect reactions were explored via inserted ${}^{100}$Mo samples at different positions inside the lead region. Furthermore, Adiabatic Resonance Crossing (ARC) method based on proton accelerator via transmutation in ${}^{98}$Mo($n,\gamma {)}^{99}$Mo was examined when the 30MeV proton beam is used. Saturation activity and yield were investigated using alternative proposed methods. The potential proliferation risk associated with accelerator technetium production is minimal. While accelerators could be turned into neutron sources which could in turn be used to irradiate ${}^{238}$U to breed plutonium, and centrifuges used to enrich ${}^{100}$Mo for targets could conceivably be turned to enriching uranium, this would result in very tiny global production capability particularly compared with research or power reactors. The potential of the fresh methods could provide a replacement or complement over current reactor-based supply sources in various radioisotopes production purposes.

The reaction rates of the direct astrophysical capture processes ${}^3\mathrm{\text{He}}{(\alpha ,\gamma )}^7\mathrm{\text{Be}}$ and ${}^3\mathrm{\text{H}}{(\alpha ,\gamma )}^7\mathrm{\text{Li}}$, as well as the abundance of the ${}^7\mathrm{\text{Li}}$ element are estimated in the framework of a two-body potential model. The estimated ${}^7\mathrm{\text{Li/H}}$ abundance ratio of ${}^7\mathrm{\text{Li/H}}=(5.07\pm 0.14)\times 10^{-10}$ is in a very good agreement with the recent measurement ${}^7\mathrm{\text{Li/H}}=(5.0\pm 0.3)\times 10^{-10}$ of the LUNA collaboration.

The DANCE¹ (Detector for Advanced Neutron Capture Experiments) array at LANSCE spallation neutron source in Los Alamos has been used to obtain the neutron radiative capture cross sections for ¹⁷⁵Lu and ¹⁷⁶Lu with neutron energies from thermal up to 100 keV. Both isotopes are of current interest for the nucleosynthesis s-process.^2,3 Three targets were used to perform these measurements. One was natural Lu foil of 31 mg/cm² and the other two were isotope-enriched targets of ¹⁷⁵Lu and ¹⁷⁶Lu. Firstly, the cross sections were obtained by normalizing yield to a well-known cross section at the thermal neutron energy. Now, we want to obtain absolute cross sections of radiative capture through a precise neutron flux determination, an accurate target mass measurement and an efficiency determination of the DANCE array.