Pd Radiative Capture Research Articles

Magnetic dipole transition in proton-deuteron radiative capture at BBN energies within potential model

The pd radiative capture reaction plays a vital role in Big Bang nucleosynthesis and stellar proton-proton chain. The study of the low-energy reaction is challenging in both experiments and theories. Using the framework of potential model, we analyze pd radiative capture below 1 MeV for both electric dipole (E1) and magnetic dipole (M1) transitions. The obtained astrophysical S factors agree well with recent results, especially at energies relevant to sensitive deuterium abundance. The calculated reaction rate shows good agreement, with less than a 5% difference compared to recent works. The extrapolated value for S(0) including both transitions is determined to be 0.211 ± 0.016 eV b. A comparison with experimental data using the χ 2 test reveals the sensitivity of the M1 cross section at low energies to the scattering potential depth.

MEASUREMENT AND RE-ANALYSIS OF TENSOR ANALYZING POWER OF pd RADIATIVE CAPTURE AT RCNP

We made again an experiment of pd radiative capture at [Formula: see text], and obtained Axx, Ayy and Azz (= -Axx - Ayy) data using a newly-developed data-analysis method of high detection efficiency. Re-analysis of previous data on Axx and Ayy was also made using a new method. All the new and previous data at 197 MeV agree to each other, and Axx anomaly has been confirmed.

Measurement of A zz of pd radiative capture at E d = 196 MeV

In our previous measurement of pd radiative capture at Ed = 137 and 196 MeV, we found an interesting fact that the measured tensor analyzing powers show the relation Axx ≈ Ayy, although calculated Axx and Ayy are apparently different, Axx ≠ Ayy. The measured Ayy agrees fairly well with the 3N calculations, and the measured Axx largely disagrees with calculated Axx. Similar experiments on pd capture have been made at KVI at nearly the same energies of 130–180 MeV. The KVI data also support Axx ≈ Ayy relation, but absolute values of Axx and Ayy at KVI are about half of RCNP data. Therefore, we made a new experiment of pd capture at Ed = 196 MeV. Azz was measured in three different ways, and data analysis is in progress. Preliminary data seem to support our previous data.

Tensor analyzing powers of pd radiative capture at [formula omitted

A measurement of tensor analyzing power A x x and A y y of H ( d → , He 3 ) γ reaction at E d → = 137 MeV was made at RCNP. Both the relation of A x x ≈ A y y and the discrepancy in A x x between experiment and calculations were confirmed at 137 MeV, in consistent with our previous measurement at 196 MeV. Present data are compared with KVI data at 133 MeV.

Electromagnetic structure of A=2 and 3 nuclei and the nuclear current operator

Different models for conserved two- and three-body electromagnetic currents are constructed from two- and three-nucleon interactions, using either meson-exchange mechanisms or minimal substitution in the momentum dependence of these interactions. The connection between these two different schemes is elucidated. A number of low-energy electronuclear observables, including (i) np radiative capture at thermal neutron energies and deuteron photodisintegration at low energies, (ii) nd and pd radiative capture reactions, and (iii) isoscalar and isovector magnetic form factors of $^{3}\mathrm{H}$ and $^{3}\mathrm{He}$, are calculated to make a comparative study of these models for the current operator. The realistic Argonne ${v}_{18}$ two-nucleon and Urbana IX or Tucson-Melbourne three-nucleon interactions are taken as a case study. For $A=3$ processes, the bound and continuum wave functions, both below and above deuteron breakup threshold, are obtained with the correlated hyperspherical harmonics method. Three-body currents give small but significant contributions to some of the polarization observables in the $^{2}\mathrm{H}$($p,\ensuremath{\gamma}$)$^{3}\mathrm{He}$ process and the $^{2}\mathrm{H}$($n,\ensuremath{\gamma}$)$^{3}\mathrm{H}$ cross section at thermal neutron energies. It is shown that the use of a current that did not exactly satisfy current conservation with the two- and three-nucleon interactions in the Hamiltonian was responsible for some of the discrepancies reported in previous studies between the experimental and theoretical polarization observables in pd radiative capture.

Electrodisintegration of 3He below and above deuteron breakup threshold

Recent advances in the study of electrodisintegration of 3He are presented and discussed. The pair-correlated hyperspherical harmonics method is used to calculate the initial and final state wave functions, with a realistic Hamiltonian consisting of the Argonne v18 two-nucleon and Urbana IX three-nucleon interactions. The model for the nuclear current and charge operators retains one- and many-body contributions. Particular attention is made in the construction of the two-body current operators arising from the momentum-dependent part of the two-nucleon interaction. Three-body current operators are also included so that the full current operator is strictly conserved. The present model for the nuclear current operator is tested comparing theoretical predictions and experimental data of pd radiative capture cross section and spin observables.

Photodisintegration and electrodisintegration of3Heat threshold andpdradiative capture

The present work reports results for: pd radiative capture observables measured at center-of-mass (c.m.) energies in the range 0--100 keV and at 2 MeV by the TUNL and Wisconsin groups, respectively; contributions to the Gerasimov-Drell-Hearn (GDH) integral in 3He from the two- up to the three-body breakup thresholds, compared to experimental determinations by the TUNL group in this threshold region; longitudinal, transverse, and interference response functions measured in inclusive polarized electron scattering off polarized 3He at excitation energies below the threshold for breakup into ppn, compared to unpolarized longitudinal and transverse data from the Saskatoon group. The calculations are based on a realistic Hamiltonian with two- and three-nucleon interactions and a realistic current operator, including one- and two-body components. The theoretical predictions obtained by including only one-body currents are in violent disagreement with data. These differences between theory and experiment are, to a large extent, removed when two-body currents are taken into account, although some rather large discrepancies remain in the c.m. energy range 0--100 keV, particularly for the pd differential cross section and tensor analyzing power at small angles, and contributions to the GDH integral. A rather detailed analysis indicates that these discrepancies have, in large part, a common origin, and can be traced back to an excess strength obtained in the theoretical calculation of the E1 reduced matrix element associated with the pd channel having L,S,J=1,1/2,3/2. It is suggested that this lack of E1 strength observed experimentally might have implications for the nuclear interaction at very low energies. Finally, the validity of the long-wavelength approximation for electric dipole transitions is discussed.