Photodisintegration Cross Section Research Articles

Hyperspherical formalism for the photoeffect of the alpha particle.

In this work we employ the hyperspherical harmonics formalism to calculate the moments of the photoeffect of the alpha particle. The grand orbital quantum number is increased until well-converged results are obtained. The adiabatic approximation is used to solve the coupled differential equations. The calculations are performed for a central N-N potential with Serber exchange. Lastly, the moments are inverted to obtain the photodisintegration cross section. Comparisons with experimental observations are presented.

Theoretical calculation of the forward cross section for deuteron photodisintegration up to 120 MeV

The forward differential cross section for γd → pn in the c.m. frame is calculated for laboratory photon energies up to 120 MeV, using the Paris potential and including relativistic corrections to the impulse approximation and the effect of one-pion exchange, with and without Δ(1231) intermediate states. We give a full treatment of one-pion exchange effects and show that the correction due to them is small (except at energies below 20 MeV) and that it can be accurately calculated. We give a consistent relativistic treatment of the two-nucleon system and correct errors in the well-known work of Partovi which arise from his nonrelativistic treatment. It is shown that the calculated cross section is very sensitive to charge-dependent effects in the one-pion exchange part of the nucleon-nucleon potential and that it is possible to obtain reasonable agreement with the present experimental data when the potential used to calculate the T = 1 np wave functions has a one-pion exchange part which takes account of the masses and coupling constants of both neutral and charged pions.

Deuteron photodisintegration at 0° and 180°

The Mainz (1976) data on deuteron photodisintegration cross sections at €) , ' @ (c.m. -centre of mass) were done at six energies from E, = 20120 MeV, and have been confirmed by recent measurements at Louvain and Indiana. In view of calculations that predict a dip in the 0 cross section at E, = 10 MeV, the Mainz group are currently engaged in measurements at 0; = 0°, E, = 10 MeV. The principle of the measurement is that a bremsstrahlung beam is incident on a deuterium target and the photoprotons are detected in a magnetic spectrometer, while the rest of the beam passes through a beam intensity monitor located downstream. The beam monitor is calibrated, using the same spectrometer system, to measure the yield of Compton electrons. For both the photoproton and Compton electron measurements, the target was 0.1-mm-thick CD2, which is feasible because the beam energy is below the 16-MeV thresh-

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.

Experimental test of virtual photon theory

An isochromat of the E1 virtual photon spectrum has been measured by counting the number of ground-state protons emitted by the 16.28 MeV isobaric analog state in /sup 90/Zr as a function of incident electron energy in the range 17--105 MeV. The experimental results reproduce well the distorted wave Born approximation spectra for a point Zr nucleus for electron energies up to 30 MeV. A radiator was used for electron energies of 60--100 MeV to measure the photodisintegration plus electrodisintegration cross section. These results showed that the Davies-Bethe-Maximon bremsstrahlung cross section magnitude yields the same result as the electrodisintegration results below 30 MeV where size corrections for the finite extent of the nucleus are minimal. As E/sub 0/ increases to 105 MeV the need for such corrections becomes manifest. Several such corrections are discussed. As by-products of this study the quantity GAMMA/sub ..gamma../GAMMA0/GAMMA was determined to be 63.8 +- 1.9 eV or 66.1 +- 2.0 eV depending on the virtual photon spectrum used in analysis. The GAMMA/sub p//sub 2//GAMMA0 ratio was also determined to be 0.58 +- 0.02. Combining these results yields for GAMMA/sub ..gamma../ 100.8 +- 5.0 eV or 104.4 +- 5.2 eV.

Deuteron photodisintegration at photon energies between 200 and 700 MeV in backward direction

The differential cross section of the deuteron photodisintegration was measured at a protion c.m. angle of 180 degrees and for photon energies between 180 and 730 MeV. The protons were detected in a magnetic spectrometer. The proton energy resolution varied between 30 MeV and 50 MeV FWHM. Since these are the first data at 180 degrees in this energy range a comparison can only be done with data from other laboratories extrapolated to 180 degrees and with theoretical predictions. The agreement with existing calculations is poor. Contributions of dibaryons to the cross section seem not to improve the situation.

Virtual photons and electrodisintegration of the deuteron

The validity of the virtual photon concept in the analysis of deuteron electrodisintegration for equivalent photon energies up to 300 MeV is investigated. The deuteron and the final state interaction are described by the consistent nonrelativistic calculation of Fabian and Arenhoevel neglecting the effects of meson exchange currents and isobar configurations. We find that in well defined kinematic domains the use of the virtual photon concept is justified in extracting photodisintegration cross sections.

Relativistic and Mesonic Corrections to the Forward Cross Section ford(γ, p)n

The discrepancy between the theoretical and the experimental values of the forward deuteron photodisintegration cross section is found to be sensibly reduced by the inclusion of the relativistic corrections (Darwin-Foldy and spin-orbit terms) in the charge density. On the contrary, the pionic corrections calculated in the pseudoscalar $\ensuremath{\pi}\mathrm{NN}$ coupling are in the opposite direction.

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.

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.

Photoproton and photo-α cross sections of 19F to excited residual states

Abstract Cross sections and integrated cross sections for photodisintegration of 19F to excited residual states following emission of protons, neutrons and α-particles have been measured. The size of the photo-α cross sections appear to be too large to be explained by a semidirect reaction mechanism.

The reaction 15N(e, t0) between 20 and 25 MeV

The differential cross section for the reaction 15N(γ, t0) at θlab = 90° has been obtained for excitation energies between 20 and 25 MeV by the measurement of a triton energy spectrum from the reaction 15N(e, t0)e′12C. A virtual photon analysis was used to extract the photodisintegration cross section from the electrodisintegration data. Comparison of this cross section to the cross section at lower excitation energies shows that the 15N(γ, t0) strength is concentrated in the region between 16 and 21 MeV. Comparison of the (γ, t0) cross section with those of other photodisintegration channels suggests an isospin separation energy of 6 MeV.

Trinucleon photoeffect to isospin 3/2, using coupled hyperspherical harmonics

We extend the Fabre-Levinger calculation of the $^{3}\mathrm{He}$ photoeffect ($E1$ transition to final isospin 3/2) by including an additional grand orbital ($L=3$) in the final state wave function. The coupled differential equations between $L=1$ and $L=3$ for the final state are given. We solve for two model potentials, and find the Blatt-Biedenharn eigenphase shifts and the mixing parameter, and also the total cross section for photodisintegration. We find reasonable agreement (generally within 10%) with the cross section found for one hyperspherical harmonic. The convergence speed of the hyperspherical harmonic expansion for the outgoing channel is also examined by comparison with sum rules for the integrated cross section: We find rapid convergence for both models.[NUCLEAR REACTIONS Photodisintegration of trinucleon system, coupled hyperspherical harmonics.]

Cross sections for photodisintegration of 32S to excited residual states

Cross sections and integrated cross sections for photodisintegration of 32S to specific residual states in 31P and 31S have been measured. Comparison with spectroscopic factors for nucleon pickup reactions on 32S leading to the same residual states are made. It is concluded that the creation and decay of the dipole state in 32S is predominantly a single-nucleon interaction.

E2 strength distribution in 1s nuclei

We study the quadrupole contribution to the photodisintegration cross-section of 1s nuclei (2H,3H,3He,4He) by means of isospin sum rules. The sum rules are derived, discussed and compared with the previously obtained ones and with the available experimental data.

Giant dipole state in the deuteron in simple models

By assuming a Serber interaction and either asymptotic or Hulthen wave functions for the deuteron, we can easily obtain the mean energy of the dipole state of the deuteron. We do this in two ways: first, we construct the dipole state as a bound state in the continuum and, secondly, we use the photodisintegration cross section. The results for the bound state calculation agree with the continuum calculation.

A test of virtual photon theory

In order to extract a photodisintegration cross section in the c.m. system from an electrodisintegration cross section measured in the lab system, one has to assume that the electrons are mostly scattered forward and that the monopole contributions are negligible. To test the validity of these approximations, we assumed a square well potential for the initial and final states and calculated the photodisintegration cross section exactly within this model. These results were then compared with the results one would obtain using the virtual photon theory approximations for electron energies of 0–300 MeV and excitation energies up to 40 MeV. In comparing the two results, we are able to show how and why the virtual photon theory approximations fail in certain kinematical regions.

Theory and experiment for the reactionLi6(e,d)e′,He4

Deuterons from the reaction $^{6}\mathrm{Li}(e,d){e}^{\ensuremath{'}}$, $^{4}\mathrm{He}$ were measured at eight laboratory angles over a deuteron energy interval of approximately 2-10 MeV. The incident electron energy was chosen so that only deuterons and $\ensuremath{\alpha}$ particles were left in the final state. These data are compared to a one-resonance square-well electrodisintegration model. Extracted photodisintegration cross sections are also compared with a more sophisticated Woods-Saxon photodisintegration theory. In both comparisons the data and theory are in overall qualitative agreement.NUCLEAR REACTIONS $^{6}\mathrm{Li}(e,d){e}^{\ensuremath{'}}$, $^{4}\mathrm{He}$, measured $\ensuremath{\sigma}({E}_{d},{\ensuremath{\theta}}_{d})$, ${E}_{d}\ensuremath{\simeq}2\ensuremath{-}10$ MeV, $\ensuremath{\theta}=30\ensuremath{-}150\ifmmode^\circ\else\textdegree\fi{}$, extracted $^{6}\mathrm{Li}(\ensuremath{\gamma},d)^{4}\mathrm{He}$ for ${E}_{x}>10$ MeV.

Three-body photodisintegration ofHe3

Cross sections for three-body photodisintegration of $sup 3$He are calculated in the 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 low-energy nucleon-nucleon scattering data. The photodisintegration amplitude is expressed in terms of the fully-off-shell nucleon plus correlated-pair amplitudes, a method applicable to any weak-process disintegration amplitude. The numerical results indicate: (1) The $sup 3$He($gamma$,n)2p total cross section has a peak value of approximately 1 mb. (2) The neutron spectra for $sup 3$He($gamma$,n)2p and the proton spectra for $sup 3$He($gamma$,p) np peak sharply in the region of the strong p-p final state interaction. (AIP)

The 15N(e, p 0)e' 14C cross section between 14 and 28 MeV excitation energy

The electrodisintegration cross section for the reaction 15N(e, p 0)e' 14C was measured and converted to the corresponding photodisintegration cross section at five angles. Results for the differential and total cross sections are given for excitation energies between 14 and 28 MeV. The Legendre coefficients of the angular distributions indicate not only the dominance of the E1 excitation but also the presence of higher multipole excitations in the energy region studied. Our work is compared to older photodisintegration measurements and to more recent proton capture experiments.