M. B. Greenfield

Determination of the Gamow–Teller quenching factor from charge exchange reactions on 90Zr

Abstract Double differential cross sections between 0°–12° were measured for the 90 Zr(n, p) reaction at 293 MeV over a wide excitation energy range of 0–70 MeV. A multipole decomposition technique was applied to the present data as well as the previously obtained 90 Zr(p, n) data to extract the Gamow–Teller (GT) component from the continuum. The GT quenching factor Q was derived by using the obtained total GT strengths. The result is Q = 0.88 ± 0.06 , not including an overall normalization uncertainty in the GT unit cross section of 16%.

Performance of the neutron polarimeter NPOL2 for (p,n) polarization transfer measurements

A high performance neutron polarimeter NPOL2 has been constructed to measure polarization transfer observables Dij for neutron kinetic energies of Tn = 150–400 MeV. The NPOL2 system consists of 6 planes of two-dimensional position-sensitive neutron detectors with a size of 1 × 1 × 0.1 m3. Neutron polarization is determined from the azimuthal distribution of the elastic n + p scattering in the scintillator material. The effective analyzing powers (Ay;eff) of NPOL2 have been calibrated by using the polarized neutrons from the 0° 2H(p,n)pp reaction at Tp = 146, 228, 296, 346 and 392 MeV as well as by using the polarized neutrons from the 0° 6Li(p,n)6Be(g.s.) reaction at Tp = 228 MeV. The Ay;eff values of NPOL2 have reasonable values, typically 0.223 ± 0.012 and 0.132 ± 0.004 for (n,n) and (n,p) channels, respectively, at Tn = 291 MeV. The figure-of-merit value defined as eD.S.(Ay;eff)2 is over 4 × 10−4 for the wide neutron kinetic energy region of Tn = 200–400 MeV, where eD.S. is the double scattering efficiency.

Spin-isospin resonances in nuclei

Spin-isospin excitations in nuclei have been investigated via the (He-3,t) reaction at 450 MeV. The volume integrals of the effective interactions J(sigma tau) and J(tau) for the (He-3,t) reaction at 450 MeV have been empirically determined to be 172+/-17 MeV-fm(3) and 53+/-5 MeV-fm(3), respectively. These values are consistent with those obtained for the (p,n) reaction at the same bombarding energy per nucleon. The Gamow-Teller strength can be deduced with the same reliability as the (p,n) reaction at the bombarding energy above 100 MeV. The neutrino absorption cross sections by Ga-71 is obtained on basis of the present (He-3,t) measurement. The new SNU value obtained for Ga-71 is 130.3+/-1.6(stat.)+/-16.8(syst.). The spin-isospin responses for the Sn isotopes, Cd-116 and Mo-100 are presented and are discussed in relation with double beta-decay. A measurement of decay protons from the spin-isospin resonances in N-13 is presented. A new possibility of studying the spin-isospin responses on the beta(+) side via the (t,He-3) reaction using a dispersion matching technique is discussed.

NON-SPIN-FLIP (HE-3, T) CHARGE-EXCHANGE AND ISOBARIC ANALOG STATES OF ACTINIDE NUCLEI STUDIED AT THETA=0-DEGREES, E(HE-3)=76 MEV AND 200 MEV

The (He-3, t) charge-exchange reaction has been studied at theta = 0-degree-C and bombarding energies of E(He-3) = 76.5 MeV and 200 MeV. Spectra were measured using magnetic analysis for target nuclei of C-12, C-13, O-16, F-19, Si-28, Si-29, Si-30, Zr-90, Sn-117, Sn-120, (nat)Ta, (nat)W, Au-197, Pb-208, Th-230, Th-232, U-234, U-236, U-238 and Pu-244. The measurements at 76.5 MeV concentrated on the isobaric analog states of several actinide nuclei, particularly on their widths and the branching ratios for proton decay. Cross sections, Q-values and total widths were determined for the transitions to the isobaric analog states. Coulomb displacement energies derived from the measured Q-values display the influence of deformed nuclear shapes. Escape widths GAMMA-up and spreding widths GAMMA-down of the isobaric analog states in five actinide nuclei were deduced from the measured proton-decay branching ratios. They were found to be in agreement with predictions which postulate isospin mixing via the Coulomb force with the (T0-1)-component of the isovector giant monopole resonance. The measurements at 200 MeV were concerned with transitions to isobaric analog states in both light and heavy nuclei, including several actinide nuclei, but Gamow-Teller resonances and transitions to numerous other states were also observed. The measured cross sections for several transitions to isobaric analog states from Si-30 to Pb-208 were used to extract the effective interaction V(tau) for non-spin-flip (He-3, t) charge exchange at E(He-3) almost-equal-to 200 MeV. The interaction strength V(tau) decreases by a factor 0.6 when compared to previously measured values for the energy range E(He-3) = 65 to 90 MeV. An angular distribution from theta(t) = 0-degree to 16-degrees for the transition to the isobaric analog state in Sb-120 measured at E(He-3) = 200 MeV was found to be in very good agreement with microscopic calculations.

(3He,t) Charge-Exchange Reactions at E(3He) = 450 MeV, θ = 0°

Spin-isospin excitations in nuclei have been studied by means of the (3He,t) reactions at 450 MeV on the targets sBe, natC, *%ii, 58Ni, 62Ni, seZr, l18Sn, **OSn, 124Sn, and 154Sm. The new spectrometer “Grand Raiden” was employed for the (3He,t) study for the first time. Observed (3He,t) spectra at 0’ show remarkable similarity with those from the (p,n) results at intermediate energies, suggesting a simple direct reaction mechanism for the (3He,t) reaction at 450 MeV. The GamowTeller (GT) resonances and the spin-flip AL=1 resonances are excited very strongly. A fine structure of the GT resonances in medium-heavy nuclei is observed with an energy resolution of 210 keV. It is demonstrated that the (3He,t) reaction at 450 MeV is a powerful tool to study the spin-isospin excitations in nuclei.

Neutrino studies in 100Mo and MOON - Mo Observatory of neutrinos

Abstract The MOON (Molybdenum Observatory Of Neutrinos) project is a hybrid ββ and solar ν experiment with 100 Mo. It aims at high sensitive studies of ββ decays with a sensitivity of m ν > ∼ 0.03 eV and real-time studies of pp and 7 Be solar νs. The double β rays from 100 Mo are measured in prompt coincidence for the 0νββ studies, and the inverse β rays from solar-ν captures of 100 Mo are measured in delayed coincidence with the subsequent β decay of 100 Tc. Measurements with good position resolution enable one to select true signals by spatial and time correlations.

Strength observed in Gamow-Teller resonance plus continuum in the reaction at 295 MeV

Abstract The double differential cross sections for θlab between 0.0° and 14.7° and the polarization transfer coefficient DNN(0°) for the 27 Al ( p → , n → ) reaction have been measured at a bombarding energy of 295 MeV. A multipole decomposition technique is applied for the cross section data to extract L = 0, 1, 2, and 3 contributions. The Gamow-Teller (GT) strength B(GT) deduced from the L = 0 contribution is compared with the B(GT) values calculated in a full sd shell-model space. The sum of B(GT) values up to 20 MeV excitation is Sβ− = 4.0 ± 0.1 ± 0.1. A fairly large L = 0 contribution is observed in the continuum region up to 50 MeV, which could be in part ascribed to the quenched GT strength. A limit on the effect that the Δ(1232)-isobar nucleon-hole admixture has upon the GT strength is estimated.

Spin-isospin Responses of ^{71}Ga for Solar Neutrinos Studied by ^{71}Ga(^{3}He,t

Abstract The charge-exchange 71Ga(3He,tγ)71Ge reaction was used to study the spin-isospin (Gamow Teller: GT) excitations relevant to the axial-vector charged-weak response for solar neutrinos. High-lying GT states in 71Ge with excitation energies up to one MeV above the neutron threshold were found to have finite γ-decay branches to low-lying states. The GT strengths for relevant states and absorption rates of solar neutrinos through the 71Ga(ν, e)71Ge and 71Ga(ν,eγ)71Ge reactions were derived.

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Abstract Spin-isospin excitations in nuclei have been studied by means of the ( 3 He,t) reactions at 450 MeV. The Gamow-Teller (GT) resonances are found to be strongly excited. A fine structure of the giant Gamow Teller resonances in medium-heavy nuclei is observed with an energy resolution of 130 keV. The volume integrals of the effective interactions J στ and J τ have been determined experimentally. The importance of high resolution observation of the ( 3 He,t) reactions at intermediate energies, both, to study the double β decay processes and to measure the detection sensitivities for solar neutrino experiments is discussed.

)^{71}Ge Reaction

Abstract The microscopic structure of the Gamow-Teller resonance at E x = 15.6 MeV in 208 Bi has been investigated by observing its direct proton decay to the neutron-hole states in 207 Pb following its excitation via the 208 Pb( 3 He,t) reaction at E( 3 He ) = 450 MeV and θ = 0°. The total width of the resonance as well as total and partial escape widths, associated with proton decay, have been determined. The total escape width was found to be only 4.9 ± 1.3%. A re-examination of several recent theoretical estimates becomes desirable in view of the limited agreement with this value.