Two-body Photodisintegration Research Articles

Two-body photodisintegration of the deuteron from 100 to 800 MeV

Abstract The total and the differential cross sections for the D(γ,p)n reaction have been measured over the photon energy range 100-800 MeV at the 855 MeV MAMI Microtron in Mainz. Using the large acceptance detector DAPHNE in conjunction with the Glasgow tagging spectrometer, high precision results with small systematic errors were obtained. The data are presented in the form of thirty-five angular distributions at c.m. proton angles between 30°–160° in 10° intervals and at photon energies in steps of 20 MeV. Previous experimental work is reassessed in the light of the present results and comparison with some recent theoretical calculations.

Reaction mechanisms in two-body photodisintegration and electrodisintegration of 4He

One- and two-body mechanisms alone cannot reproduce the experimental values of the 4He( γ,p)T reaction cross-section in the Δ region. Meson double scattering is shown to account for the major part of these discrepancies. All together these mechanisms account for the near equality of the cross-section of the 4He( γ,p)T and 4He( γ,n) 3He channels. Consequences on the 4He(e,e′p)T and the 4He(e,e′n) 3He channels are investigated, with a special emphasis on the determination of the 4He wave function and the study of the behavior of bound nucleon form factors. The sensitivity of spin observables, to various interaction effects, is investigated.

Two-body photodisintegration of 3He between 200 and 800 MeV

Differential cross sections for the 3He(γ,pd) reaction at photon energies between 200 and 800 MeV at all proton c.m. angles between 35° and 145° have been measured using the tagged photon beam facility of the 855 MeV MAMI accelerator in Mainz. Reaction products were detected using the large acceptance detector DAPHNE. The results confirm the rapid decrease of forward-angle cross sections with increasing E γ whilst at backward angles, aided by the high precision of the measurement, we can see a clear enhancement in the angular distribution which is a possible signature of three-body mechanisms.

Simultaneous measurement of the ( gamma,p)/( gamma,n) cross-section ratio in 4He as a test of charge symmetry.

We have measured (\ensuremath{\gamma},p) and (\ensuremath{\gamma},n) differential yields at 90\ifmmode^\circ\else\textdegree\fi{} for the two-body photodisintegration of $^{4}\mathrm{He}$ using tagged photons of energy ${\mathit{E}}_{\ensuremath{\gamma}}$=25--60 MeV. Data for both channels were obtained simultaneously using windowless \ensuremath{\Delta}E-E telescopes to detect the $^{3}\mathrm{He}$ and $^{3}\mathrm{H}$ recoils. The ration of our angle-integrated yields, which is insensitive to systematic uncertainies due to the simultaneity of the measurements, agrees with calculations employing only charge-symmetric nuclear interactions. Thus, within the present errors, our data show no evidence of a significant charge-symmetry violation in $^{4}\mathrm{He}$ in this energy range.

3He(n, gamma )4He cross section and the photodisintegration of 4He.

The absolute cross section of the $^{3}\mathrm{He}$(n,\ensuremath{\gamma}${)}^{4}$He reaction was measured at five energies between ${\mathit{E}}_{\mathit{n}}$=0.14--2.0 MeV to an accuracy of \ensuremath{\sim}\ifmmode\pm\else\textpm\fi{}10%. The \ensuremath{\sim}21 MeV gamma rays produced in a $^{3}\mathrm{He}$ gas target were detected at 90\ifmmode^\circ\else\textdegree\fi{} with respect to the beam direction. The results are discussed in light of previous measurements of the two-body photodisintegration of $^{4}\mathrm{He}$.

Two-body photodisintegration of 3H and 3He near the giant resonance : (I). Plane-wave approximation

A concise survey of the current status of two-body photodisintegration of the trinucleons in the region of the giant resonance is presented. Calculations neglecting both final-state interactions (FSI) and M1 transitions are presented using the Reid soft-core, Paris and Bonn potentials. D-wave contributions to these reactions are not in agreement in the literature. The present results indicate that approximately (10±4)% of the cross section is due to constructive transitions involving the D-waves. Furthermore, E2 contributions at a photon excitation energy of ∼ 12.5 MeV are found to be approximately 2% for 3He(γ,p)d and 0.1% for 3H(γ,n)d. In addition, fore-aft asymmetry calculations indicate markedly different contributions from E1–E2 interference in a comparison of the 3He and 3H systems.

Three-body exchange mechanisms in the 3He( gamma,p)2H reaction.

The role of three-body exchange currents is investigated in the two-body photodisintegration of $^{3}\mathrm{He}$.

Two-body photodisintegration ofHe3between 150 and 350 MeV

Differential cross sections for /sup 3/He(..gamma..,d)/sup 1/H for incident energies between 150 and 350 MeV at center-of-mass proton angles near 60/sup 0/ and 90/sup 0/ have been measured with an absolute uncertainty of less than 6%. The experiment used a single-arm spectrometer, a gas target, and an uncollimated bremsstrahlung beam. The results are in good agreement with new measurements of the time-reversed reaction, /sup 2/H(p,/sup 3/He)..gamma.., giving no evidence for a violation of time-reversal invariance. The differential cross sections decrease smoothly with energy and show only a small contribution from the ..delta..(1232) resonance.

Two-body photodisintegration of 3He

The two-body photodisintegration cross section on 3He has been measured at excitation energies between 21 and 32 MeV and at several angles, using the inverse 2H(p, γ 0) 3He reaction. The angular distribution coefficients seem to be dependent on the 4D and 2S' components of the three-body ground-state wave function.

Two-body photodisintegration of 3He with realistic bound-state wave functions

Total and differential cross sections for two-body photodisintegration of 3He have been recalculated using realistic bound-state wave functions. Contrary to previous calculations we find neither any unusual structure in the energy distributions nor any distinct signature of D-state components in the bound-state wave functions for photon energies ω ≦ 35 MeV. Final-state interactions and, possibly, meson exchange currents increase the total cross section substantially, but decrease the E2 contribution from 1 % to 0.5 %. After subtraction of spurious non-orthogonal components in the wave function, the M1 contribution decreases by about one order of magnitude to a value of 1.5 % in agreement with the experimental data.

Measurement of the two-body photodisintegration of3He in the?(1236) resonance region

The3He(γ, p)d reaction has been measured in the photon energy region between 200 MeV and 450 MeV at proton c.m. angles between 20° and 150°.

Quasiparticle effects in the two-body photodisintegration of 4He

The total cross sections for the reactions 4He(γ, n) 3He and 4He(γ, p) 3H are calculated for photon energies between 50 MeV and 150 MeV in a quasiparticle formalism, leading to a simple interpretation for the γ-absorption mechanism. Results are compared with shell model calculations.

Photodisintegration ofH3

Measurements of the two-body and three-body photodisintegration cross sections for tritium are reported. The measurements were done with monoenergetic photons, high-pressure gas samples, and neutron-multiplicity detection. Presently available theoretical calculations are not adequate to explain the results.

Suppression of the isospin-½, three-body photodisintegration ofHe3

The suppression of the isospin-1/2, three-body photodisintegration of /sup 3/He is shown to result from two facts: (1) For the S = 1/2, I = 1/2 states of three nucleons, the spin-isospin symmetries lead to integral equations dominated by a single effective interaction V/sup +/, which is the average of the NN s-wave spin-singlet and spin-triplet interactions and (2) This V/sup +/ supports a bound state due to the nature of the NN effective-range parameters. In the approximation that the (1/2,1/2) states are generated from V/sup +/ alone, it is clear that a fraction of the isospin-1/2 bremsstrahlung-weighted sum rule must come from two-body photodisintegration with a corresponding reduction of the three-body channel contribution, since the total isospin-1/2 sum rule is fixed. The substantial reduction of the actual physical isospin-1/2, three-body photodisintegration is directly related to the strength of V/sup +/.

Proton-deuteron radiative capture and the two-body photodisintegration of 3He

We investigate the two-body photodisintegration of 3He and its inverse, radiative p-d capture using bound-state functions corresponding to the N-N interaction being given by the Reid soft-core potential. For the two-body photodisintegration of 3He Coulomb effects and the final-state interactions between the proton and deuteron are not included. At low energy the shape of the angular distribution agrees well with experiment, but the 90° cross section exhibits an anomalous peak at 15 MeV due to electric dipole transitions connecting the deuteron and 3He D-states. The low-energy cross section is 25–40 % too small. The intermediate-energy angular distribution peaks too near the forward direction, and, contrary to experiment, has a minimum at 100°. At higher energy the 90° cross section in the center-of-momentum frame is at least an order of magnitude too small, but does display the correct energy dependence. This energy dependence is related to the properties of the bound-state wave functions and it is plausible that it will persist in an improved treatment (e.g. one which includes exchange currents) which properly accounts for the magnitude of the cross section. Contributions from the 3He S-states are negligible for photon energies between 100 and 150 MeV, but are dominant outside this energy region.

Two-Body Photodisintegration ofHe3and a New Test of Time-Reversal Invariance in the Electromagnetic Interaction

We have measured the two-body photodisintegration process $\ensuremath{\gamma}^{3}\mathrm{He}\ensuremath{\rightarrow}\mathrm{pd}$ in the energy region sensitive to intermediate photoexcitation of one nucleon to the isobar $\ensuremath{\Delta}(1238)$. We present angular distributions at center-of-mass angles from 30\ifmmode^\circ\else\textdegree\fi{} to 150\ifmmode^\circ\else\textdegree\fi{} for incoming photon energies 200-600 MeV. Magnetic dipole excitation appears to be suppressed.

Two-body photodisintegration of 3He and 4He in the Δ(1236) region

Differential cross sections for the reactions 3He(γ, p)d and 4He(γ, p)t were measured at proton c.m. angles of 60° and 90° for photon energies ranging from 150–450 MeV with an average resolution of 8 MeV. Bremsstrahlung was used as the photon source; deuterons/tritons were analyzed in a magnetic spectrometer whereas coincident protons were detected in a plastic scintillator telescope. The experimental method includes a calibration by means of 1H(γ, π0)p differential cross section measurement at 90° c.m. in the same photon energy range. The 3He and 4He two-body photodisintegration differential cross sections show a monotonically decreasing variation with photon energy. In addition, partial data on the differential cross section of the reaction 4He(γ, n)τ at 90° and 120° neutron c.m. angle are given.

Two-body photodisintegration ofHe3andH3

Cross sections for two-body photodisintegration of $^{3}\mathrm{He}$ and $^{3}\mathrm{H}$ are calculated in electric-dipole approximation. The calculation is performed within the context of exact three-body theory with the two-nucleon interactions represented by $s$-wave spin-dependent separable potentials fitted to the low-energy nucleon-nucleon scattering data. The two-body photo-disintegration amplitude is expressed in terms of the half-off-shell nucleon plus correlated-pair amplitudes, a method applicable to any weak-process disintegration amplitude. The numerical results indicate: (1) The $^{3}\mathrm{He}$ and $^{3}\mathrm{H}$ 90\ifmmode^\circ\else\textdegree\fi{} photodisintegration cross sections are essentially identical in shape, being only slightly displaced at low energy due to the different thresholds, when both initial and final states are treated consistently. (2) The $^{3}\mathrm{He}(\ensuremath{\gamma}, d)p$ 90\ifmmode^\circ\else\textdegree\fi{} differential cross section has a peak value of approximately 95 \ensuremath{\mu}b/sr.NUCLEAR REACTIONS Photodisintegration of $^{3}\mathrm{He}$ and $^{3}\mathrm{H}$; exact three-body calculation; separable potentials; charge-dependent interactions.

The two-body photodisintegration of 3He

The differential cross section for the reaction 3He(γ,d) 1 1H has been measured for proton energies 11–65 MeV. The results are compared with previous measurements and with a recent theoretical calculation.

The two-body photodisintegration of the 3He nucleus

The two-body photodisintegration of 3He is calculated using 3He and proton-deuteron wave functions obtained by assuming a separable interaction for the two-nucleon t-matrix. We show that the isotropic component of the cross section is unlikely to yield useful information on the D-state probability densities of the deuteron and 3He. A detailed comparison is made with the data on the cross section at 90°. The separable approximation can account for some of the experimental results, but other experiments suggest that a more sophisticated treatment of the nuclear interactions and wave functions is necessary.