Measurement of γ detector backgrounds in the energy range of 3-8 MeV at Jinping underground laboratory for nuclear astrophysics

<正>The astrophysical reaction rate of the charged-particleinduced reaction is dominated by the cross section within the Gamow window.The total cross section σ(E)of a chargedparticle-induced reaction is known to drops steeply with decreasing energy owing to the Coulomb barrier in the entrance channel:     

Excitation of isomeric 1h 11/2 states in nuclear reactions induced by γ rays and neutrons and in beta decay

Isomeric ratios were measured for N=81 isotones (¹³⁵Xe, ¹³⁷Ba, ¹³⁹Ce, ¹⁴¹Nd, ¹⁴³Sm). In the experiment reported here, μ _ν ≤3±10^? J ^π=11/2^? isomers were excited in (n, γ) and (γ, n) reactions and in the β ⁺ decay of ¹³⁹Pr and ¹⁴¹Pm. In order to determine the reaction yields, use was made of the activation method involving measurement of the gamma-ray spectra of reaction products. It is found that, in the same reactions, isomeric ratios are different for isotones characterized by different atomic numbers Z. Isomeric ratios were calculated with the spectra of low-lying levels and radiative-transition probabilities established on the basis of the quasiparticle-phonon model. Good agreement between the experimental and calculated values of isomeric ratios is obtained for all isotopes invesigated here. The dependence of isomeric ratios on the atomic number Z of a nucleus is explained by the difference of reaction energies, which leads to different probabilities of excitation of activation levels through which the isomers being considered are populated.     

Deuteron disintegration, thermonuclear and nuclear fission reactions induced by γ-quanta in D-saturated palladium and dense deuterium gas with synthesis of new structures

The results obtained by investigating the chemical composition and structure of Pd sample sur-faces, chamber components, and a new synthesized object (NSO) are presented. The NSO is produced in the chamber with a high-pressure (about 3 kbar) deuterium gas under irradiation by γ-quanta with an energy of 8.8 MeV. The measured concentrations of chemical elements arisen from nuclear reactions initiated by γ-quanta have made it possible to develop the phenomenological approach to describing the process whereby deuterium atoms are heated by the protons and neutrons of a deuteron photofission reaction, hot D-D fusion, Oppenheimer reactions, and palladium nuclear fission. The coefficient of the process efficiency greatly exceeds unity. A new type of reactors (deuterated nuclear fission reactor) is proposed.     

Inclusive spectra of protons and α particles from reactions induced by protons with an energy of 30.0 MeV on the 209Bi nucleus

Inclusive spectra of protons and α particles resulting from the interaction between 30.0-MeV protons and the ²⁰⁹Bi nucleus are investigated. Double differential and integral cross sections for the (p,xp) and (p,xα) reactions are obtained and total partial cross sections for these reactions are subsequently determined. The experimental spectra are analyzed using a modified version of the exciton model of preequilibrium decay and the PRECO-2006 code. Contributions from the compound and direct mechanisms to the formation of integral cross sections are calculated.     

Investigation of the threshold intensity versus gas pressure in the breakdown of helium by 248 nm laser radiation

An investigation of the unexpectedly strong dependence of the threshold intensity on the gas pressure in the experimental study on the breakdown of He by short laser wavelength (Turcu et al., in Opt Commun, 134:66–68, 1997) is presented. A modified electron cascade model is applied (Evans and Gamal, in J Phys D Appl Phys, 13:1447–1458, 1980). Computations revealed reasonable agreement between the calculated thresholds and the measured ones. Moreover, the calculated electron energy distribution function and its parameters proved that multiphoton ionization of ground and excited atoms is the main source for the seed electrons, which contributes to the breakdown of helium. The effect of diffusion losses over pressures <1,000 Torr elucidated the origin of the strong dependence of the threshold intensity on the gas pressure. Collisional ionization dominates only at high pressures. No evidence for recombination losses is observed for pressures up to 3,000 Torr.     

Results of irradiating aluminum and homogeneous alloy YMn2 by 23 MeV γ-quanta in a molecular deuterium atmosphere at 2 kbar pressure

Specimens of a number of metal were placed successively along the length in a deuterium high-pressure chamber of the “finger type” (DHPC-FT). The specimens were: two aluminum rods, a copper rod, two YMn₂ alloy specimens, and stainless steel. The molecular deuterium pressure in the DHPC-FT chamber was 2 kbar. The specimens were irradiated by braking γ-quanta with boundary energy 23 MeV. After irradiation, all specimens were investigated on scanning electron microscopes (SEM) with electron probe X-ray microelement analysis (XMA). Considerable changes in the structure of the surfaces and elemental composition of the measured aluminum, destruction of the homogeneous YMn₂ alloy specimen, and the “formation of monocrystalline specimens” of the YMn₂ type and structures resembling manganese-based “crystals” were observed. A phenomenological explanation of the observed phenomena and effects based on nuclear reactions is proposed with consideration of certain new approaches, which are examined.     

Results from the irradiation of stainless steel and copper by 23 MeV γ-quanta in the atmosphere of molecular deuterium at a pressure of 2 kbar

Metal samples were arranged inside a “finger-type” high-pressure chamber (DHPC-FT) filled by deuterium. They were two aluminum rods, a copper rod, two specimens of homogeneous YMn₂ alloy, and a stainless steel wire. The pressure of molecular deuterium in DHPC-FT was about 2 kbar. The samples were irradiated by braking γ-quanta at a threshold energy of 23 MeV. All the samples were studied using scanning electron microscopy (SEM) and X-ray (roentgen) microelement probe analysis (RMPA). Considerable changes in the surface structure and elemental composition were found for the samples of copper, aluminum, YMn₂ alloy, and stainless steel. Unusual results were analyzed in detail and compared with the earlier data.     

Isomeric pair 95m,gNb in the photonuclear reactions on natMo at the bremsstrahlung end-point energy of 38–93 MeV

The ^natMo(γ,xnp)^95m,g Nb photonuclear reaction was studied using the electron beam from the NSC KIPT linear accelerator LUE-40.The experiment was performed using the activation and off-line γ-ray spectrometric technique.The experimental isomeric yield ratio(IR) was determined for the reaction products ^95m,gNb at the bremsstrahlung end-point energy E_γmax range of 38-93 MeV.The obtained values of IR are in satisfactory agreement with the results of other...     

Study of background processes with the formation of neutrons in nuclear reactions in the energy range of 26–32 kev

The nature of background processes accompanying astrophysical nuclear reactions induced by hydrogen, helium, and neon ions in deuterated targets with small cross sections has been studied in calculations and experiments. The experiments have been performed at a Hall pulsed plasma accelerator in the ion energy range of 26–32 keV. The yield of background neutrons and γ-quanta with energies below 4 MeV in the proton-induced D(p, γ)³He reaction is primarily due to the presence of a natural impurity of gaseous deuterium in gaseous hydrogen and the chain of D(D, ³He)n → (n, γ) or (n, n'γ) reactions. A small contribution comes from the chain of D(¹H, ¹H)D → D(D, ³He)n → (n, γ) or (n, n'γ) reactions. It has been shown that background neutrons and γ-quanta from the D(4He, γ)6Li reaction are entirely due to the chain of D(⁴He, ⁴He)D → D(D, ³He)n → (n, γ) or (n, n'γ) reactions. It has been shown that the yield of neutrons and γ-ray photons detected at the interaction of neon ions with deuterated targets is also entirely due to the chain of elastic- scattering reactions of neon ions on deuterons in the target and to subsequent inelastic processes of interaction of deuterons accelerated at elastic scattering with other deuterons of the target. The main contribution to the yields of background neutrons and γ-quanta comes from doubly charged neon ions. The main conclusion is that the explanation of the yield of neutrons and γ-quanta at the interaction of hydrogen, helium, and neon ions with deuterated targets does not require “exotic” theoretical models.     

Measurement of the 85Rb(γ, n)84mRb cross-section in the energy range 10-19 MeV with bremsstrahlung photons

We study the charmonium 2S states ??? and ??? _c , and the bottomonium 2S states ???? and ??? _b , using the light-front quark model and the 2S state wave function of harmonic oscillator as the approximation of the 2S quarkonium wave function. The decay constants, transition form factors and masses of these mesons are calculated and compared with experimental data. Predictions of quantities such as Br(???????? _c ) are made. The 2S wave function may help us learn more about the structure of these heavy quarkonia.     

Measurement of the yields of positively charged particles at an angle of 35° in proton interactions with nuclear targets at an energy of 50 GeV

Momentum spectra of cumulative particles in the region of high transverse momenta (P _T ) in pA → h ⁺ + X reactions were obtained for the first time. The experiment in which this was done was performed at the SPIN setup (Institute for High Energy Physics, Protvino) in a beam of 50-GeV protons interacting with C, Al, Cu, and W nuclei. Positively charged particles were detected at a laboratory angle of 35° and in the transverse-momentum range between 0.6 and 3.7 GeV/c. A strong dependence of the particle-production cross section on the atomic number was observed. A comparison with the results of calculations based on the HIJING and UrQMD models was performed in the subcumulative region.     

Fusion and transfer cross sections of 3He induced reaction on Pt and Au in energy range 10–24.5 MeV

In experiments performed by accelerated ion ³He-beam irradiated gold and platinum targets on the cyclotron U-120M of the Nuclear Physics Institute of the Czech Academy of Sciences, ?e?, reactions of complete and incomplete fusion and nucleon transfer reactions in the ³He energy range from 10 to 24.5 MeV have been investigated. To determine the yield of the nuclides resulting from the nuclear reaction, the activation technique has been used. The obtained data are analyzed using models based on statistical calculations and compared with similar results for other light stable particles. Transfer reactions with positive Q values have relatively high cross sections in the energy range below the Coulomb barrier. These cross sections continue to grow with increasing ³He energy, and, in the case of capturing neutron from target nucleus by a nucleus of ³He, the excitation functions of these reactions reach their maximum almost at the Coulomb barrier of the reactions.     

Elliptic flow in the nuclear interaction of an astroparticle with an energy of ∼10<Superscript>16</Superscript> eV

A total of 107 cascades formed by secondary particles of the nuclear interaction of an astroparticle with an energy of ～10¹⁶ eV are detected in a stratospheric emulsion chamber. Their azimuthal distribution revealed a distinct anisotropy. The elliptic flow coefficient V₂ was estimated at 0.35 ± 0.02. The average transverse momentum of cascades in the direction of the impact parameter exceeded 3 GeV/c.     

Program for Experimental Investigations of the Mechanisms for the Emission of Coherent Radiation by Relativistic Electrons with Energies of 10–500 MeV in Oriented Crystals

A program of experimental investigations of the mechanisms for the emission of coherent radiation by electrons in periodic structures is proposed. The program is aimed at developing sources of energy-tunable quasimonochromatic x radiation and radiation.     

Investigation of total cross sections for reactions induced by <Superscript>6</Superscript>He interaction with silicon nuclei at energies between 5 and 50 MeV/<Emphasis Type="Italic">А</Emphasis>

Experimental excitation functions in terms of the total cross sections for ⁶He + Si nuclear reactions are analyzed in the energy range between 5 and 50 MeV/А, and a brief survey of the procedures used to obtain experimental data is given. Particular attention is given to describing experiments performed in beams of radioactive nuclei from the accelerators of the Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research (JINR, Dubna). The experimental data in question are analyzed on the basis of a semimicroscopic optical model.     

Study of the coordinate prediction accuracy for galactic particles with an energy of 10–1000 TeV/particle using a new method for searching and tracking particles in nuclear emulsion films. (Data of the Russia–Nippon Joint Balloon (RUNJOB) experiment)

Experimental and methodological errors in the coordinate prediction for primary cosmic ray nucleons and nuclei in nuclear emulsions using a new method for searching and tracing particle tracks in emulsion films of X-ray emulsion chambers (XRECs) exposed in the stratosphere in the Russia–Nippon Joint Balloon (RUNJOB) experiment are considered in detail. The dependence of errors on the relation between angular characteristics of the sought particle and auxiliary multiply charged nuclei is analyzed. Angular selection criteria for auxiliary nuclei, at which the methodological error of the particle track coordinate prediction decreases, are found.