Spin-Isospin Excitations and Muon Capture by Nuclei

By analyzing the energy-weighted moments of the strength function calculated in RPA and beyond it is shown that the explanation of the effect of missing strength of Gamow-Teller transitions requires that residual interaction produce high-excited $1^{+}$ particle-hole collective states. The example of this interaction is presented. The manifestations of spin-isospin nuclear response in nuclear muon capture are discussed.Comment: 16 pages, 5 figures, 2 tables. The talk at the XVI International School on Nuclear Physics, Neutron Physics and Nuclear Energy, September 19-26, Varna, Bulgari

Peripheral elastic and inelastic scattering of O 17 , 18 on light targets at 12 MeV/nucleon

A study of interaction of neutron rich oxygen isotopes $^{17,18}$O with light targets has been undertaken in order to determine the optical potentials needed for the transfer reaction $^{13}$C($^{17}$O,$^{18}$O)$^{12}$C. Optical potentials in both incoming and outgoing channels have been determined in a single experiment. This transfer reaction was used to infer the direct capture rate to the $^{17}$F(p,$\gamma$)$^{18}$Ne which is essential to estimate the production of $^{18}$F at stellar energies in ONe novae. The success of the asymptotic normalization coefficient (ANC) as indirect method for astrophysics is guaranteed if the reaction mechanism is peripheral and the DWBA cross section calculations are warranted and stable against OMP used. We demonstrate the stability of the ANC method and OMP results using good quality elastic and inelastic scattering data with stable beams before extending the procedures to rare ion beams. The peripherality of our reaction is inferred from a semiclassical decomposition of the total scattering amplitude into barrier and internal barrier components. Comparison between elastic scattering of $^{17}$O, $^{18}$O and $^{16}$O projectiles is made.Comment: 14 pages, 19 figure

Experiments and simulations on interactions between 2,3-bis(hydroxymethyl)-2,3-dinitro-1,4-butanediol tetranitrate (DNTN) with some energetic components and inert materials

Abstract In order to survey the application prospects of 2,3-bis(hydroxymethyl)-2,3-dinitro-1,4-butanediol tetranitrate (DNTN, NEST-1, SMX) in high - energy solid rocket propellants and explosives, the interactionsbetween DNTN with some energetic components and inert materials were investigated by means of differential scanning calorimetry (DSC) and molecular dynamic (MD) methods, where glycidyl azide polymer (GAP), cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitroamine (HMX), lead 3-nitro-1,2,4-triazol-5-onate (NTO-Pb), hexanitrohexaazaisowurtzitane (CL-20), aluminum powder (Al) and magnesium powder (Mg), 3,4-dinitrofurzanfuroxan (DNTF), N-guanylurea-dinitramide (GUDN), N-butyl-N-(2-nitroxy-ethyl)nitramine (Bu-NENA), bis(2,2-dinitropropyl) acetal (BDNPA)/bis(2,2-dinitropropyl) formal (BDNPF) mixture (A3), nitrocellulose - nitroglycerine (NC-NG) and ammonium dinitramide (ADN) were used as energetic components and hydroxyl terminated polybutadiene (HTPB), polyoxytetram ethylene-co- oxyethylene (PET), addition product of hexamethylene diisocyanate and water (N-100), 2,4-toluene diisocyanate (TDI), 1,3-dimethyl-1,3-diphenyl urea (C2), carbon black (C.B.), aluminum oxide (Al2O3), lead phthalate (φ-Pb), N-nitro-dihydroxyethylamine dinitrate (DINA), cupric 2,4-dihydroxy-benzoate (β-Cu) were used as inert materials. The impact and friction sensitivities of DNTN and DNTN in combination with energetic materials were obtained. . It was concluded that the binary systems of DNTN with RDX, HMX, NTO-Pb, Al, Mg, ADN, NC-NG, HTPB, PET, C2, C.B., β-Cu and Al2O3 are compatible, whereas systems of DNTN with GAP, CL-20, A3, N-100, TDI and DINA are slightly sensitive, and those containing DNTF and GUDN are incompatible. It is demonstrated that no consequential trend between sensitivity and compatibility is found. The mechanical properties and safety performance of GAP mixtures plasticized with three plasticizers decrease in the following order: [BTTN] > [TMETN] > [Bu-NENA]

Effect of amide-based compounds on the combustion characteristics of composite solid rocket propellants

Oxamide (OXA) and azodicarbonamide (ADA) are among the known burning rate suppressants used in composite solid rocket propellants. Much research has been carried out to understand mechanism of suppression but literature about the action of OXA and ADA on the combustion characteristics of propellant is still scarce. Here, a systematic study on coolant-based propellants has been undertaken spanning from thermal analyses of ingredients to a variety of burning processes of the corresponding propellants. Thermal gravimetric analysis and differential thermal analysis on individual coolants are carried out to study their behaviour with temperature. It was noticed that the thermal decomposition of OXA exhibits only endothermic effects, whereas that of ADA presents both endothermic and exothermic effects. Successive experiments on solid propellant looking at burning rate characterization, condensed combustion product collection and visualization, pressure deflagration limit and thermochemical analysis gave a greater insight and enabled better understanding of the action of coolants during combustion. It is proposed that OXA and ADA are acting on both the condensed and gas phases. Also, the nature of coolant is a key parameter, which affects the burning rate pressure index. Increase of agglomerate size and of pressure deflagration limit was obtained in the coolant-based propellants, confirming the trend given in the literature. Keywords: Composite propellant, Ammonium perchlorate, Burning rate suppressant, Combustion characteristic

Asymptotic normalization coefficients for 8B->7Be+p from a study of 8Li->7Li+n

Asymptotic normalization coefficients (ANCs) for 8Li->7Li+n have been extracted from the neutron transfer reaction 13C(7Li,8Li)12C at 63 MeV. These are related to the ANCs in 8B->7Be+p using charge symmetry. We extract ANCs for 8B that are in very good agreement with those inferred from proton transfer and breakup experiments. We have also separated the contributions from the p_1/2 and p_3/2 components in the transfer. We find the astrophysical factor for the 7Be(p,gamma)8B reaction to be S_17(0)=17.6+/-1.7 eVb. This is the first time that the rate of a direct capture reaction of astrophysical interest has been determined through a measurement of the ANCs in the mirror system.Comment: 5 pages, 3 figures, 2 table

Three-body decay of 6^{6}Be

Three-body correlations for the ground-state decay of the lightest two-proton emitter $^{6}$Be are studied both theoretically and experimentally. Theoretical studies are performed in a three-body hyperspherical-harmonics cluster model. In the experimental studies, the ground state of $^{6}$Be was formed following the $\alpha$ decay of a $^{10}$C beam inelastically excited through interactions with Be and C targets. Excellent agreement between theory and experiment is obtained demonstrating the existence of complicated correlation patterns which can elucidate the structure of $^{6}$Be and, possibly, of the A=6 isobar.Comment: 17 pages, 21 figures, 5 table

Astrophysical S factor for the radiative capture 12N(p,gamma)13O determined from the 14N(12N,13O)13C proton transfer reaction

The cross section of the radiative proton capture reaction on the drip line nucleus 12N was investigated using the Asymptotic Normalization Coefficient (ANC) method. We have used the 14N(12N,13O)13C proton transfer reaction at 12 MeV/nucleon to extract the ANC for 13O -> 12N + p and calculate from it the direct component of the astrophysical S factor of the 12N(p,gamma)13O reaction. The optical potentials used and the DWBA analysis of the proton transfer reaction are discussed. For the entrance channel, the optical potential was inferred from an elastic scattering measurement carried out at the same time with the transfer measurement. From the transfer, we determined the square of the ANC, C^2(13Og.s.) = 2.53 +/- 0.30 fm-1, and hence a value of 0.33(4) keVb was obtained for the direct astrophysical S factor at zero energy. Constructive interference at low energies between the direct and resonant captures leads to an enhancement of Stotal(0) = 0.42(5) keVb. The 12N(p,gamma)13O reaction was investigated in relation to the evolution of hydrogen-rich massive Population III stars, for the role that it may play in the hot pp-chain nuclear burning processes, possibly occurring in such objects.Comment: 15 pages, 10 figures, 3 tables submitted to Phys. Rev.

Asymptotic normalization coefficient of ^{8}B from breakup reactions and the S_{17} astrophysical factor

We show that asymptotic normalization coefficients (ANC) can be extracted from one nucleon breakup reactions of loosely bound nuclei at 30-300 MeV/u. In particular, the breakup of ^{8}B is described in terms of an extended Glauber model. The 8B ANC extracted for the ground state of this nucleus from breakup data at several energies and on different targets, C^2 = 0.450+/-0.039} fm^-1, leads to the astrophysical factor S_{17}(0)= 17.4+/-1.5 eVb for the key reaction for solar neutrino production 7Be(p,gamma)8B. The procedure described here is more general, providing an indirect method to determine reaction rates of astrophysical interest with beams of loosely bound radioactive nuclei.Comment: 4 pages, RevTex, 3 figures revised version to appear in Phys Rev Let

Sliding and abrasive wear behaviour of HVOF- and HVAF-sprayed Cr3C2-NiCr hardmetal coatings

This paper provides a comprehensive characterisation of HVOF- and HVAF-sprayed Cr3C2-25 wt.% NiCr hardmetal coatings. One commercial powder composition with two different particle size distributions was processed using five HVOF and HVAF thermal spray systems. All coatings contain less Cr3C2 than the feedstock powder, possibly due to the rebound of some Cr3C2-rich particles during high-velocity impact onto the substrate. Dry sand-rubber wheel abrasive wear testing causes both grooving and pull-out of splat fragments. Mass losses depend on inter- and intra-lamellar cohesion, being higher (≥70 mg after a wear distance of 5904 m) for the coatings deposited with the coarser feedstock powder or with one type of HVAF torch. Sliding wear at room temperature against alumina involves shallower abrasive grooving, small-scale delamination and carbide pull-outs, and it is controlled by intra-lamellar cohesion. The coatings obtained from the fine feedstock powder exhibit the lowest wear rates (≈5×10-6 mm3/(Nm)). At 400 °C, abrasive grooving dominates the sliding wear behaviour; wear rates increase by one order of magnitude but friction coefficients decrease from ≈0.7 to ≈0.5. The thermal expansion coefficient of the coatings (11.08×10-6 °C-1 in the 30-400 °C range) is sufficiently close to that of the steel substrate (14.23×10-6 °C-1) to avoid macro-cracking

Tests of Transfer Reaction Determinations of Astrophysical S-Factors

The ${}^{16}O ({}^{3}He,d) {}^{17}F$ reaction has been used to determine asymptotic normalization coefficients for transitions to the ground and first excited states of ${}^{17}F$. The coefficients provide the normalization for the tails of the overlap functions for ${}^{17}F \to{}^{16}O + p$ and allow us to calculate the S-factors for ${}^{16}O (p,\gamma){}^{17}F$ at astrophysical energies. The calculated S-factors are compared to measurements and found to be in very good agreement. This provides the first test of this indirect method to determine astrophysical direct capture rates using transfer reactions. In addition, our results yield S(0) for capture to the ground and first excited states in $^{17}F$, without the uncertainty associated with extrapolation from higher energies.Comment: 6 pages, 2 figure