Np Reaction Research Articles

Novel Interpretation of the “Θ+(1540)Pentaquark” Peak

We use a theoretical model of the γd→K+ K- np reaction adapted to the experiment done at LEPS where a peak was observed and associated with the Θ+ (1540) pentaquark. The study shows that the method used in the experiment to assign momenta to the undetected proton and neutron, together with the chosen cuts, necessarily creates an artificial broad peak in the assumed K+ n invariant mass in the region of the claimed Θ+ (1540), such that the remaining strength seen for the experimental peak is compatible with a fluctuation of 2σ significance.

DYNAMIC-STATISTICAL APPROACH TO THE DESCRIPTION OF THE INDUCED FISSION IN WIDE EXCITATION ENERGY RANGE

It is developed a new approach to analyze the induced fission of heavy nuclei, which takes into account the nuclear dissipation phenomenon and the shell structure of nuclei in determination of fission barriers. The approach is based on the combined dynamical and statistical simulations. In the framework of this approach the method of calculation the fission fragment angular distributions in a wide energy range is discussed. The ability of the method is demonstrated in the simultaneous description of the experimental data of the fission probabilities on the Am and Pu nuclei, yields of the spontaneous fission of isomers for the α + 238 U reaction at E α = (20 - 32) MeV and the d + 242,240 Pu reactions at E d = (20 - 30) MeV , the fission times for the α + 238 U reaction and angular distribution of fission fragments for the α + 238 U , 237 Np reactions at E α = (20 - 100) MeV . A further information on the value of the nuclear dissipation at low excitation energies is obtained. In addition, it is demonstrated that the influence of the shell effects on the deformation potential energy holds up to excitation energies of about (50 - 60) MeV.

The study of the negative pion production in neutron-proton collisions at beam momenta below 1.8 GeV/c

A detailed investigation of the reaction np $ \rightarrow$ pp $ \pi^{{-}}_{}$ has been carried out using the data obtained with the continuous neutron beam produced by charge exchange scattering of protons off the deuterium target. Partial-wave event-by-event analysis based on the maximum likelihood method was applied to determine contributions of different partial waves to the pion production process. A combined analysis of the np $ \rightarrow$ pp $ \pi^{{-}}_{}$ and pp $ \rightarrow$ pp $ \pi^{{0}}_{}$ data measured in the same energy region allows us to determine the contribution of isoscalar partial waves (I = 0 in the momentum range from 1.1 up to 1.8GeV/c . The decay of isoscalar partial waves into the (1 S 0)pp $ \pi$ channel provides us with a good tool for the determination of the pp S -wave scalar scattering length in the final state which was found to be a pp = - 7.5±0.3 fm.

Measurement of the spectrum of neutrons produced in pd collisions at an angle of θ = 0° at a proton-beam energy of 1 GeV

The energy spectrum of a neutron beam produced in a thin-wall liquid-deuterium target by a proton beam of energy 1 GeV was measured in a hydrogen bubble chamber by detecting events of the reaction np → ppπ −.

Measurements of the magnetic field map of the analyzing magnet of the Delta-Sigma setup spectrometer

One of the basic tasks of the Delta-Sigma Experiment project is to measure the energy dependences in the GeV region of the neutron beam of spin dependent NN observables A 00kk (np), A 00nn (np), and R dp . These observables are determined by measuring proton yields in the charge-exchange reaction np → pn at an angle of 0° using the magnetic spectrometer of the Delta-Sigma setup. The magnetic field map of the analyzing magnet of the setup spectrometer was measured in order to precisely determine the charge exchange proton momenta. The Delta-Sigma setup is situated in building 205 of the Laboratory of High Energies of the Joint Institute for Nuclear Research. The spectrometer magnet 2-SP-94 in 1V channel has external dimensions of 2.95 × 2.12 × 1.62 m and an aperture (occupied by the beam) of 0.30 × 0.09 m. A three-component Hall probe was used to measure the magnetic field. The volume of measurements was 0.33 × 0.0645 × 1.02 m. In this paper, the measuring equipment, measurement procedure, and results used in processing and analyzing the physical data obtained are described.

Helicity dependence and contribution to the Gerasimov-Drell-Hearn sum rule of theγ→d→→πNNreaction channels in the energy region from threshold up to theΔ(1232)resonance

The helicity dependence of the {gamma}-vectord-vector{yields}{pi}{sup -}pp,{gamma}-vectord-vector{yields}{pi}{sup +}nn, and {gamma}-vectord-vector{yields}{pi}{sup 0}np reaction channels is studied for incident photon energies from threshold up to the {delta}(1232) resonance with inclusion of leading {pi}NN effects. The doubly polarized total and differential cross sections for parallel and antiparallel helicity states are predicted. Then the contribution of various channels to the deuteron spin asymmetry and the double polarization E asymmetry is calculated. In addition, the contribution to the Gerasimov-Drell-Hearn (GDH) integral from separate channels is evaluated by explicit integration up to a photon lab energy of 350 MeV. Sizeable effects from final-state interactions, specially for {pi}{sup 0} production, are found. The sensitivity of the results to the elementary pion photoproduction operator is also investigated. Considerable dependence of the results on the elementary amplitude is found. We expect that these results may be useful to interpret the recent measurements from LEGS-BNL, A2, and GDH-MAMI Collaborations.

The reaction np→ppπ- from threshold up to 570 MeV

The reaction ${n} {p} \to {p} {p} \pi^{-}$ has been studied in a kinematically complete measurement with a large acceptance time-of-flight spectrometer for incident neutron energies between threshold and 570 MeV. The proton-proton invariant mass distributions show a strong enhancement due to the pp($^{1}{S}_{0}$) final state interaction. A large anisotropy was found in the pion angular distributions in contrast to the reaction ${p}{p} \to {p}{p} \pi^{0}$. At small energies, a large forward/backward asymmetry has been observed. From the measured integrated cross section $\sigma({n}{p} \to {\rm p}{p} \pi^{-})$, the isoscalar cross section $\sigma_{01}$ has been extracted. Its energy dependence indicates that mainly partial waves with Sp final states contribute. Note: Due to a coding error, the differential cross sections ${d \sigma}/{d M_{pp}}$ as shown in Fig. 9 are too small by a factor of two, and inn Table 3 the differential cross sections ${d \sigma}/{d \Omega_{\pi}^{*}}$ are too large by a factor of $10/2\pi$. The integrated cross sections and all conclusions remain unchanged. A corresponding erratum has been submitted and accepted by European Physics Journal.

Study of spectator tagging in the reaction np → ppπwith a deuteron beam

The reaction \(dp \ensuremath \rightarrow ppp \pi^-\) has been studied in a kinematically complete experiment at a single beam momentum \(\ensuremath p_{d}=1.85\)GeV/c (T = 759MeV). All four ejectiles have been detected in the large-acceptance time-of-flight spectrometer COSY-TOF. We analyzed the data along the lines of the spectator model as a means to isolate the quasi-free \(\ensuremath np\rightarrow pp\pi^-\) reaction. The spectator proton was identified by its momentum and flight direction thus yielding access to the associated Fermi motion of the bound neutron. A comparison is carried out with Monte Carlo simulations based on two different parameterizations of the deuteron wave function. Up to a Fermi momentum of roughly 150MeV/c no significant deviations between experimental and simulated data of various observables were found from which we conclude that the deuteron can indeed be taken as a valid substitute for the neutron.

Energy efficiency of neptunium redox battery in comparison with vanadium battery

A neptunium ion possesses two isostructural and reversible redox couples (Np 3+/Np 4+ and NpO 2 +/NpO 2 2+) and is therefore suitable as an active material for a redox-flow battery. Since the plastic formed carbon (PFC) is known to show the largest k 0 values for Np(IV)/Np(III) and Np(V)/Np(VI) reactions among various carbon electrodes, a cell was constructed by using the PFC, with the circulation induced by bubbling gas through the electrolyte. In discharge experiments with a neptunium and a vanadium battery using the cell, the former showed a lower voltage loss which suggests a smaller reaction overvoltage. Because of the high radioactivity of the neptunium, it was difficult to obtain sufficient circulation required for the redox-flow battery, therefore a model for evaluating the energy efficiency of the redox-flow battery was developed. By using the known k 0 values for neptunium and vanadium electrode reactions at PFC electrodes, the energy efficiency of the neptunium battery was calculated to be 99.1% at 70 mA cm −2, which exceeds that of the vanadium battery by ca. 16%.

First measurement of the cross-section ratioR dp(0) in charge-exchange (np) reactions on H2/D2 at 0o andT n = 1 GeV Dubna “Delta-Sigma experiment”

The first results of the measurement of 0o of the cross-section ratioR dp=0.50±0.02 in charge-exchange (np) reaction on H2/D2 targets at the neutron beam kinetic energie 1.0 GeV are presented. As a result the value of the ratio of non spin-flip to spin-flip contribution innp→pn charge-exchange at 0o r np→pn /nf/fl =0.33±0.03 was obtained.

Attachment of 31Cl and 39Cl induced by high-energy neutrons to coexisted aerosols

In order to confirm the effects of physicochemical properties such as liquid or solid of coexisted aerosol on radioactive aerosol formation, the number size and activity size distributions of 38C1 and 39C1 aerosols (just use Cl aerosols to protect confusion) generated by irradiation of argon (Ar) gas containing liquid dioctyl-phthalate (DOP) or solid NaCl aerosols with 45 MeV quasi-monoenergetic neutrons were measured. In the case of DOP aerosol, the 38C1 and 39C1 respectively formed from the (n, 2np) and (n, np) reactions of 40Ar were observed. It was found that the activity size distribution curve shifted toward larger particle diameter, compared to the number size distribution. The measured activity size distribution of Cl aerosols was in good agreement with the calculated activity size distribution assuming the surface attachment of 38C1 and 39C1 to DOP aerosol. In the case of NaCl aerosol, the Cl aerosol formation could be also explained by the same attachment model in the case of DOP. These findings suggest that the formation mechanism of Cl aerosols is not affected by the physicochemical properties such as liquid or solid coexisted aerosols.

Kinetics and Mechanism of RedOx Reactions of Np and Pu Ions with Several Organic Reductants

The paper discusses specific features pertaining to reactions of single electron oxidants of Np(VI) and Pu(IV) with organic nitrogen containing reductants such as substitution derivatives of hydrazine and hydroxylamine, nitriles, guanidines, oximes and aziridines. The oxidation rates of derivatives of hydrazine as well as hydrazine nitrite in HNO3 solutions obey the first order equations in relation to oxidation and reduction while the reaction order relative to H** ions is equal or close to minus 1. The reactions of this type are limited by the slow stage of the interaction between the uncharged molecule of a reductant and ions of NpO22+ or Pu4+. The oxidation mechanism of derivatives of hydroxylamine depends on the types of oxidants and reductants. The key specific features of the reactions of Pu(IV) are its second order relative to Pu(IV) and retardation by its product Pu(III) ions. These specific features find explanation in the mechanism of the reactions. As distinct from reactions of Pu(IV) reactions of Np(VI) are of the first order in relation to each reagent. General mechanisms of those reactions are also typical of Np(VI) and Pu(IV) reactions with acetaldoxime, diaziridine and aminoguanidine. The reactions of Np(VI) and Pu(IV) with the studied nitrogen containing organic reductants obey the isokinetic ratio: the activation enthalpy of those reactions increases in proportion to the activation enthropy.

The reaction np $\rightarrow$ pp $\pi^-$ from threshold up to 570 MeV

The reaction np\(\rightarrow\) pp\(\pi^-}\) has been studied in a kinematically complete measurement with a large acceptance time-of-flight spectrometer for incident neutron energies between threshold and 570 MeV. The proton-proton invariant mass distributions show a strong enhancement due to the pp(\(^1{\rm S}_0\)) final state interaction. A large anisotropy was found in the pion angular distributions in contrast to the reaction pp\(\rightarrow\)pp\(\pi^0\). At small energies, a large forward/backward asymmetry has been observed. From the measured integrated cross section \(\sigma({{\rm n}{\rm p} \rightarrow{\rm p}{\rm p} \pi^-})\), the isoscalar cross section \(\sigma_{01}\) has been extracted. Its energy dependence indicates that mainly partial waves with Sp final states contribute.

Performance of the multiple target He/PbI 2 aerosol jet system for mass separation of neutron-deficient actinide isotopes

A multiple target He/PbI 2 aerosol jet system coupled with a thermal ion source was installed in the isotope separator on line (JAERI-ISOL) at the JAERI tandem accelerator facility. The neutron-deficient americium and curium isotopes produced in the 233,235 U( 6 Li, xn) and 237 Np( 6 Li, xn) reactions were successfully mass-separated and the overall efficiency including the ionization of Am atoms was evaluated to be 0.3–0.4%. The identification of a new isotope 237 Cm with the present system is reported.

Radioactivity Sputtered from Cooling-Pipe Materials into Coolant in the ITER Cooling System

The radioactivity induced by D-T neutron sputtering from piping materials to the coolant is described. The sputtering yields were calculated based on the systematics for (n,p), (n,α), (n,2n), and (n,np) reactions. Four candidate piping materials of AISI Types 316L and 304 stainless steel, Incoloy 800, and V-4 Cr-4 Ti alloy were investigated to estimate their radioactivity sputtered to the coolant. The investigation shows that radioactivity of ~1500 to 2000 Ci sputtered into the coolant at 1000-s plasma burn time of ITER, and after 1-day cooling, a few curies of gamma activity remain in the coolant, which will accumulate in the heat exchanger.

Apparatus for a measurement of charge symmetry breaking in np→dπ 0

TRIUMF experiment E704 is a study of Charge Symmetry Breaking in the reaction np→dπ 0. The observable is the forward–backward asymmetry in the centre-of-mass differential cross-section, predicted to be −0.0035 at 5 MeV above threshold. As a check on the understanding of certain systematic effects the reaction pp→dπ +, which cannot have an asymmetry, is measured also. Similarly, neutron–proton elastic scattering is used to verify spectrometer acceptance. We describe the beams, target, and detectors developed for this experiment.

Seeking and investigating isospin-two narrow dibaryon resonances in neutron-proton interactions at P n =5.20±0.13 Gev/c

The results are presented that are obtained from searches for and an investigation of isospin-two narrow resonances in the effective-mass spectrum of ppπ+ combinations originating from the reaction np → ppπ+π−π− induced by P n =5.20±0.13 GeV/c neutrons. Data subjected to our analysis come from the 1-m hydrogen bubble chamber installed at the Laboratory for High Energies, Joint Institute for Nuclear Research (Dubna), and exposed to a beam of quasimonochromatic neutrons. Narrow structures in the effective-mass spectrum of ppπ+ combinations are found at 2175, 2221, 2321, 2398, 2471, 2525, 2596, and 2709 MeV/c 2. The experimental widths of the resonances are determined primarily by the instrumental resolution. The branching fractions for various channels through which the 2596-MeV/c 2 resonance decays are determined to be (83±23)% for the Δ 33 ++ p channel, (10±3)% for the (BB) 2095 ++ π+ channel, and (7 −7 +15 for the ppπ+ channel; here, (BB) 2095 ++ is a dibaryon in the two-proton system with a mass around 2095 MeV/c 2. A qualitative analysis of the spins of the 2596-and 2709-MeV/c 2 resonances is performed.

Charge symmetry breaking in the reaction np → d π0

Charge symmetry breaking in the reaction np → d π0

Synthesis of phosphonates by nucleophilic substitution at phosphorus: The S NP(V) reaction

Synthesis of phosphonates by nucleophilic substitution at phosphorus: The S NP(V) reaction

Critical review of [formula omitted] scattering

Nucleon-antinucleon scattering experiments carried out at LEAR are briefly reviewed. Differential cross-section data of high accuracy are now available at many energies, and for the first time also analysing power data and some data on spin correlation parameters. Excellent fits to the N N data base have been performed by the Nijmegen group, both with a phase-shift analysis and with a coupled-channel potential model. The high precision cross section data from experiment PS206 have allowed a determination of the charged pion-nucleon coupling constant by a simple extrapolation to the pion pole. A phenomenological analysis of the line-reversed reaction np → pn and p p → n n data is ongoing, to single out the basic dynamical features of the long-range part of the interaction and possibly experimental manifestations of the G-parity rule.