We describe the observation of the isospin violating and charge symmetry breaking reaction dd -> alpha pi(0) just above threshold. Measurements using a magnetic channel (gated by two photons) of the He-4 scattering angle and momentum (from time of flight) permitted reconstruction of the pi(0) "missing mass," the quantity used to separate distributions of He-4 + pi(0) events from a continuum containing He-4 + gamma + gamma and He-4 + pi(0 )+ gamma events. A review has been completed of the apparatus, relevant GEANT simulations, various corrections, and the d + p scattering cross section used as a luminosity calibration. The new values of the total cross section for neutral pion production are 14.3 +/- 2.2 (stat) +/- 1.6 (sys) pb at 228.5 MeV and 17.3 +/- 3.4 (stat) +/- 2.4 (sys) pb at 231.8 MeV. The uncertainty remains dominated by statistical errors. These cross sections arise from the down-up quark mass difference and quark electromagnetic effects.

We have studied the energy dependence of the reaction mechanism of the T(t,2n)He-4 reaction at stellar energies and of its charge symmetric analog reaction He-3(He-3,(2)p)He-4 at energies up 10 MeV. We find that the reaction mechanism changes dramatically over this energy range in part due to the interference of the two identical fermions in the three-body final state.

We have studied the energy dependence of the reaction mechanism of the T(t,2n)4He reaction at stellar energies and of its charge symmetric analog reaction 3He(3He,2p)4He at energies up 10 MeV. We find that the reaction mechanism changes dramatically over this energy range in part due to the interference of the two identical fermions in the three-body final state.

An R-matrix model for three-body final states is presented and applied to a recent measurement of the neutron energy spectrum from the H-3 + H-3 -> 2n + alpha reaction. The calculation includes the n alpha and nn interactions in the final state, angular momentum conservation, antisymmetrization, and the interference between different channels. A good fit to the measured spectrum is obtained, where clear evidence for the He-5 ground state is observed. The model is also used to predict the alpha-particle spectrum from H-3 + H-3 as well as particle spectra from He-3 + He-3. The R-matrix approach presented here is very general and can be adapted to a wide variety of problems with three-body final states.

We have studied spin observables in the three-body break-up reaction in deuteron–deuteron scattering in the phase-space regime that corresponds to the quasi-free deuteron–proton scattering process with the neutron as spectator. The data are compared to measurements of the elastic deuteron–proton scattering process and state-of-the-art Faddeev calculations. The results for iT11 and T22 for the quasi-free scattering data agree very well with previously published elastic-scattering data. A significant discrepancy is found for T20, which could point to a break-down of the quasi-free assumption.

A new technique that uses inertial confinement implosions for measuring low-energy nuclear reactions important to nuclear astrophysics is described. Simultaneous measurements of n–D and n–T elastic scattering at 14.1 MeV using deuterium–tritium gas-filled capsules provide a proof of principle for this technique. Measurements have been made of D(d,p)T (dd) and T(t,2n) 4 He (tt) reaction yields relative to the D(t,n) 4 He (dt) reaction yield for deuterium–tritium mixtures with f T / f D between 0.62 and 0.75 and for a wide range of ion temperatures to test our understanding of the implosion processes. Measurements of the shape of the neutron spectrum from the T(t,2n) 4 He reaction have been made for each of these target configurations.

Neutron time-of-flight spectra from inertial confinement fusion experiments with tritium-filled targets have been measured at the National Ignition Facility. These spectra represent a significant improvement in energy resolution and statistics over previous measurements, and afford the first definitive observation of a peak resulting from sequential decay through the ground state of (5)He at low reaction energies E(c.m.) 100 </~ keV. To describe the spectrum, we have developed an R-matrix model that accounts for interferences from fermion symmetry and intermediate states, and show these effects to be non-negligible. We also find the spectrum can be described by sequential decay through ℓ=1 states in (5)He, which differs from previous interpretations.

Measurements of the D(d,p)T (dd) and T(t,2n)(4)He (tt) reaction yields have been compared with those of the D(t,n)(4)He (dt) reaction yield, using deuterium-tritium gas-filled inertial confinement fusion capsule implosions. In these experiments, carried out on the OMEGA laser, absolute spectral measurements of dd protons and tt neutrons were obtained. From these measurements, it was concluded that the dd yield is anomalously low and the tt yield is anomalously high relative to the dt yield, an observation that we conjecture to be caused by a stratification of the fuel in the implosion core. This effect may be present in ignition experiments planned on the National Ignition Facility.

The Gamow-Teller transition strengths, $B$(GT), in $pf$-shell nuclei are of interest in nuclear physics as well as in nuclear astrophysics. A high-resolution (${}^{3}\mathrm{He},t$) charge-exchange (CE) reaction was performed on the ${T}_{z}=+1$ nucleus ${}^{54}$Fe at 0${}^{\ensuremath{\circ}}$ and at an intermediate incident energy of 140 MeV/nucleon for the study of precise GT transition strengths to the final ${T}_{z}=0$ nucleus ${}^{54}$Co. By applying dispersion matching techniques for a high-quality ${}^{3}$He beam at RCNP, an energy resolution of 21 keV and an angular resolution of 5 mr were realized. The bumplike structure of the GT resonance observed in low-resolution CE reactions at around the excitation energy (${E}_{x}$) of 10 MeV was resolved in individual $L$ $=$ 0, GT states. Excitation strengths were obtained for these GT states. If the ${R}^{2}$ value that is defined by the ratio between GT and Fermi unit cross sections is known, the $B$(GT) values can be determined from the excitation strengths. For the derivation of the ${R}^{2}$ value, the ``merged analysis'' combining the GT strength distribution from the ${}^{54}$Fe(${}^{3}\mathrm{He},t$)${}^{54}$Co study and the half-life from a ${}^{54}$Ni $\ensuremath{\beta}$ decay was used, where $T=1$ isospin symmetry for $A=54$ isobars was assumed. The GT strengths were compared with a shell-model calculation using the GXPF1 interaction. The final GT states can have the isospin values $T$ $=$ 0, 1, and 2. The isospin $T$ of each GT state observed in the $8.3\ensuremath{\le}{E}_{x}\ensuremath{\le}12.0$ MeV region of the ${}^{54}$Fe(${}^{3}\mathrm{He},t$)${}^{54}$Co spectrum was identified by comparing the excitation strength with that of corresponding $M1$ state observed in a ${}^{54}$Fe($p,{p}^{\ensuremath{'}}$)${}^{54}$Fe experiment. The $B$(GT) values of the states identified to have $T=2$, in particular, are of importance for the calculation of the electron capture rates at the core-collapse stage of presupernovae. The $B$(GT) strengths were further compared with $B(M1)$ strengths measured in the ${}^{54}$Fe($e,{e}^{\ensuremath{'}}$)${}^{54}$Fe reaction. In the $M1$ excitation using an electromagnetic probe, isoscalar (IS) and isovector (IV) orbital type operators are active in addition to the IV spin type operator that mediates the GT transitions. The contributions of the IS and IV orbital terms were studied by calculating the ratio of the strengths of analogous $M1$ and GT transitions.

Measurements of the neutron spectrum from the T(t,2n)4He (tt) reaction have been conducted using inertial confinement fusion implosions at the OMEGA laser facility. In these experiments, deuterium-tritium (DT) gas-filled capsules were imploded to study the tt reaction in thermonuclear plasmas at low reactant center-of-mass (c.m.) energies. In contrast to accelerator experiments at higher c.m. energies (above 100 keV), these results indicate a negligible n + 5He reaction channel at a c.m. energy of 23 keV.

The Gamow-Teller transition strengths, B(GT), in pf-shell nuclei are of interest in nuclear physics as well as in nuclear astrophysics. A high-resolution (He-3, t) charge-exchange (CE) reaction was performed on the T-z = +1 nucleus Fe-54 at 0 degrees and at an intermediate incident energy of 140 MeV/nucleon for the study of precise GT transition strengths to the final T-z = 0 nucleus Co-54. By applying dispersion matching techniques for a high-quality He-3 beam at RCNP, an energy resolution of 21 keV and an angular resolution of 5 mr were realized. The bumplike structure of the GT resonance observed in low-resolution CE reactions at around the excitation energy (E-x) of 10MeV was resolved in individual L = 0, GT states. Excitation strengths were obtained for these GT states. If the R-2 value that is defined by the ratio between GT and Fermi unit cross sections is known, the B(GT) values can be determined from the excitation strengths. For the derivation of the R-2 value, the "merged analysis" combining the GT strength distribution from the Fe-54(He-3, t)Co-54 study and the half-life from a Ni-54 beta decay was used, where T = 1 isospin symmetry for A = 54 isobars was assumed. The GT strengths were compared with a shell-model calculation using the GXPF1 interaction. The final GT states can have the isospin values T = 0, 1, and 2. The isospin T of each GT state observed in the 8.3 <= E-x <= 12.0 MeV region of the Fe-54(He-3, t)Co-54 spectrum was identified by comparing the excitation strength with that of corresponding M1 state observed in a Fe-54(p, p')Fe-54 experiment. The B(GT) values of the states identified to have T = 2, in particular, are of importance for the calculation of the electron capture rates at the core-collapse stage of presupernovae. The B(GT) strengths were further compared with B(M1) strengths measured in the Fe-54(e, e')Fe-54 reaction. In the M1 excitation using an electromagnetic probe, isoscalar (IS) and isovector (IV) orbital type operators are active in addition to the IV spin type operator that mediates the GT transitions. The contributions of the IS and IV orbital terms were studied by calculating the ratio of the strengths of analogous M1 and GT transitions.

We successfully identified several multibody final states in deuteron-deuteron scattering at 65 MeV/nucleon at KVI using a unique and advanced detection system called BINA. This facility enabled us to perform cross sections and polarization measurements with an improved statistical and systematic precision. The analysis procedure and a part of the results of the three-body break-up channel in the deuteron-deuteron scattering at 65 MeV/nucleon are presented.

The 'V(d, a) Ti reaction has been studied with 79.4-MeV vector polarized deuterons. Angular distributions of the differential cross section and vector analyzing power have been measured for strongly-populated states up to an excitation energy of 5 MeV. Two-particle —one-hole states of the [(trf7/i) (vf7/i) '] configuration were identified from the characteristic L =6 shapes of the differential cross section and J=7 patterns of the vector analyzing power. These states lie at 0.00, 1.54, 1.62, 2.26, 2.72, 2.98, 3.05, 3.29, 3.46, 3.97, 4.22, and 4.39 MeV in Ti. The relative (f7/i )J —7 pickup strength to these states is compared to predictions of the (f7/i )" model of Kutschera, Brown, and Ogawa. The identification in this work of [(trf7/7) (vf7/1) ] configuration states at 4.39 and 3.97 MeV tends to confirm the suggestion that states found at 4.4 and 4.0 Me& in the

This paper discusses some of the recent results obtained in a deuteron-deuteron scattering experiment using a polarized beam of deuterons with an incident energy of 130 MeV. A 4π detection system allowed to measure cross sections and spin observables for various final-state configurations. Here, we discuss the quasi-free elastic deuteron-proton scattering process in deuteron-deuteron scattering which has been observed by analyzing kinematical configurations for which the target neutron acts as a spectator particle. This part of the data can be compared directly to three-nucleon calculations and with existing data for the elastic deuteron-proton scattering process. The results for the polarization observables iT11 and T22 agree well with elastic scattering data published so-far and measured concurrently using a proton target. Surprisingly, the tensor observable T20 shows significant discrepancies with data taken using a proton target.