Neutron-proton Radiative Capture Research Articles

Low-energy photodisintegration of the deuteron and Big-Bang nucleosynthesis

The photon analyzing power for the photodisintegration of the deuteron was measured for seven gamma-ray energies between 2.39 and 4.05 MeV using the linearly polarized gamma-ray beam of the high-intensity gamma-ray source at the Duke Free-Electron Laser Laboratory. The data provide a stringent test of theoretical calculations for the inverse reaction, the neutron–proton radiative capture reaction at energies important for Big-Bang nucleosynthesis. Our data are in excellent agreement with potential model and effective field theory calculations. Therefore, the uncertainty in the baryon density ΩBh2 obtained from Big-Bang Nucleosynthesis can be reduced at least by 20%.

Parity-violating gamma-ray asymmetry in the neutron-proton capture

An experiment to measure γ-ray asymmetry A γ with a high precision in neutron-proton radiative capture is under construction at LANSCE. The experiment will determine the weak pion-nucleon coupling constant H π 1,, 30% of its predicted value.

ANALYZING POWER FOR THE PHOTODISINTEGRATION OF THE DEUTERON BETWEEN Eγ = 2.4 AND 4.0 MEV

The photon analyzing power for the photodisintegration of the deuteron was measured for seven gamma-ray energies between 2.39 and 4.05 MeV using the linearly polarized gamma-ray beam of the High-Intensity Gamma-ray Source at the Duke Free-Electron Laser Laboratory. The data provide a stringent test of theoretical calculations for the inverse reaction, the neutron-proton radiative capture reaction at energies important for Big-Bang nucleosynthesis. Our data are in excellent agreement with potential model and effective field theory calculations.

Dynamics of low-energy nuclear forces for electromagnetic and weak reactions with the deuteron in the Nambu-Jona-Lasinio model of light nuclei

A dynamics of low-energy nuclear forces is investigated for low-energy electromagnetic and weak nuclear reactions with the deuteron in the Nambu-Jona-Lasinio model of light nuclei by example of the neutron-proton radiative capture (M1-capture) n + p → D + γ, the photomagnetic disintegration of the deuteron γ + D → n + p and weak reactions of astrophysical interest. These are the solar proton burning p + p → D + e+ + ν e, the pep-process p + e− + p → D + ν e and the neutrino and antineutrino disintegration of the deuteron caused by charged ν e + D → e− + p + p, \(\bar \nu _e \) + D → e+ + n + n and neutral ν e(\(\bar \nu _e \)) + D → ν e(\(\bar \nu _e \)) + n + p weak currents.

Measurement of the analyzing power Ay in neutron-proton radiative capture at En = 68 MeV

The vector analyzing power A y for the reaction 1 H( n , γ) 2 H has been measured at five angles between 60° and 140° in the lab at an incident neutron energy of 67.7 MeV. The measurement is of a presision never before acheived ( ΔA y ⩽ 0.01, statistical) for this observable. This precision makes possible a quantitative comparison with meson-exchange theories, thus enhancing our understanding of the role of non-nucleonic degrees of freedom.

Spin correlation and analyzing power measurements for neutron-proton radiative capture at Tn=183 MeV.

We have measured the spin correlation coefficient (${\mathit{C}}_{\mathit{N}\mathit{N}}$) and the neutron and proton analyzing powers (${\mathit{A}}_{\mathit{n}}$ and ${\mathit{A}}_{\mathit{p}}$) for the n\ensuremath{\rightarrow}p\ensuremath{\rightarrow}\ensuremath{\rightarrow}d\ensuremath{\gamma} reaction at a neutron beam energy of 183 MeV. Calculations of the spin correlation are particularly sensitive to the treatment of mesonic and isobaric currents. Predictions that include both explicit photon couplings to exchanged mesons and intermediate isobar states, and relativistic correction terms in the Hamiltonian, agree well with our data, thus demonstrating the quantitative accuracy of present treatments of meson-exchange currents at moderate momentum transfer (q\ensuremath{\sim}1-2 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$).

Spin correlation coefficients for neutron-proton radiative capture

Abstract We use a theoretical model for deuteron photodisintegration below the pion production threshold, which has previously been used to calculate the observables for which experimental data is available, in order to calculate the spin correlation coefficients for radiative capture of a polarized neutron beam by a polarized proton target. We give results for the coefficients whose measurement is possible in the near future and explain how such experimental results could improve our understanding of the reaction mechanism. We also comment on exciting measurements of the neutron analyzing power at very low energies.

Neutron-proton radiative capture cross section at Tn

The differential cross section for the reaction p(n,d)..gamma.. has been measured for center-of-mass angles between 0/sup 0/ and 65/sup 0/ at a neutron kinetic energy T/sub n/ = 185 MeV. Assuming time-reversal invariance, our result is in essential agreement with the deuteron photodisintegration measurement at theta/sub p/ = 0/sup 0/ performed by Hughes et al. at Mainz. In addition to this confirmation of the absolute magnitude, our results, for the first time, provide information on the shape of the cross section distribution near 0/sup 0/, i.e., the region where existing theories show the largest differences. This paper contains a detailed account of the experiment and a comparison with relevant experimental information. A discussion of some theoretical implications is also included. The best agreement with our data is obtained from these theories where relativistic corrections to the charge density are taken into account.

Recent studies of radiative capture and photodisintegration in few-nucleon systems

A recent measurement of the neutron–proton radiative capture cross section at Tn = 185 MeV is discussed in the context of previous data and current theories. The method used to obtain an absolute normalization of the data is outlined. Recent data on proton–deuteron capture are also presented and discussed. Future plans are indicated.

Neutron-proton radiative capture at medium energies

The differential cross section of the neutron-proton radiative capture process, n + p → d + γ, has been measured in the energy interval from 190 MeV to 590 MeV for deutron angles θ d cm < 65°. The results are compared to experiments and theoretical predictions of the inverse reaction, i.e. the photodisintegration of the deuteron.

The meson exchange current effect in radiative np capture

The pion exchange current contribution to the thermal neutron proton radiative capture cross section is calculated on the basis of potential theory by extracting a local “absorptive exchange potential” from the corresponding fourth order Feynman diagram with the deuteron nucleon vertex on the mass shell. Taking into account that the repulsive core of nucleon interaction leads to modifications not only of the wave functions (which include off-mass shell properties of the deuteron nucleon vertex) but also of this absorptive OPE potential a result is obtained which explains the main part (⋍ 2 3 ) of the well-known 10%-discrepancy between experiment and impulse approximation.

Neutron-proton radiative capture at 14.4 MeV

The energy spectrum of deuterons from the H(n, d)γ reaction at 14.4 MeV was measured with a counter telescope. The c.m. differential cross section of this reaction was deduced from the deuteron energy distribution. A least-squares fit yielded a total cross section of σ = 30.6±1.8 μb, which is about 10% larger than the theoretical prediction. The isotropy ratio a b was found to be 0.08±0.06 and the asymmetry parameter was determined to be d b = 0.12±0.09 .

Polarization phenomena in neutron-proton radiative capture

An analysis of the polarization phenomena in the an evaluation of the resulting fiuctuations and the neutron-proton radiative capture and the photodisintegration of the deuteron is given. The usefulness of some polarization experiments is indicated. (auth)