Photodisintegration Cross Section Research Articles

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.

Photoproton cross section and isospin components of the giant resonance in 64Zn

The absolute cross section for the reaction 64Zn(γ, p) 63Cu using a thin target of 99.6 % isotopically pure 64Zn has been measured at four angles using bremsstrahlung from the Los Alamos Electron Prototype Accelerator. The results are compared with the previously measured 64Zn(γ, n) 63Zn cross section to clearly show the two isospin components of the giant dipole resonance. The measured photoproton cross section is combined with previously measured (γ, n), (γ, 2n) and (γ, np) results to obtain a “total” photodisintegration cross section for 64Zn.

The dependence of the photodisintegration cross section on the off-shell T-matrix

Nucleon-nucleon scattering phase shifts determine the diagonal element of the transition matrix. The off-diagonal elements are not completely arbitrary but have conditions imposed on them by the range and the tail of the potential. Electromagnetic interaction can also be used to place restrictions on the off-diagonal elements. We find that the cross section of the deuteron photodisintegration is sensitive to the off-shell transition matrix. The integrated cross section can be varied by as much as 30 % or more, and the matrix element for the El transition by a factor of 2. While the matrix element for the photodisintegration depends on the off-shell elements of the T-matrix, it cannot be used to discriminate between alternative off-shell T-matrices. We have constructed classes of different off-shell T-matrices, which produce identical photo-disintegration cross sections and other two-body scattering and bound-state properties.

Two-Body Photodisintegration ofHe3Between 40 and 150 MeV

In an experiment with semiconductor and scintillation counter telescopes we have measured the photodisintegration cross section of ${\mathrm{He}}^{3}$ at photon energies from 40 to 150 MeV and proton laboratory angles of 30, 60, 90, 120, and 135\ifmmode^\circ\else\textdegree\fi{}.

Sum Rule Photo-Disintegration Cross Sections for the Deuteron with Velocity-Dependent and Hard-Core Potentials

We apply the sum rules of Levinger and Bethe to calculate the integrated cross section[Formula: see text]and the bremsstrahlung-weighted cross section[Formula: see text]for the deuteron in the dipole approximation. In our calculations we use (i) Nestor's velocity-dependent potential and (ii) Reid's hard-core potential. Our results for σint and σb obtained with the velocity-dependent potential of Nestor and the hard-core potential of Reid agree well with experiments.

Differentieller Wirkungsquerschnitt für die Photospaltung des Deuterons zwischen 20 und 35 MeV

The differential cross section of the deuteron photodisintegration was determined in the photon energy range 20 to 35 MeV at the angle of 90 degrees in the laboratory system. The experimental points were fitted in this range by a parabola $$d\sigma _D (90^\circ )/d\Omega = 140.6 - 5.41{\rm E}_\gamma + 0.0621E_\gamma ^2 $$ withE in MeV anddσD/dΩ in 10−30 cm2/sr.

Two-particle (γ, n) photodisintegration of the triton

The two-particle (γ, n) photodisintegration of the triton is studied using a modified Irving wave function for the triton and including the final-state interaction. The parameters of the triton wave function are given by the variational calculations of the binding energy of the system using a central velocity-dependent potential, and those of the n-d interaction are obtained from the p-wave scattering phase shifts. The n-d interaction is found to be important and it is possible to obtain a satisfactory agreement to the observed energy variation of the photodisintegration cross section.

Study of the photodisintegration of 4He

Results on measurements of differential and total photodisintegration cross sections for 4He below 85 MeV are presented. The asymmetry in the angular distribution suggests possible dynamic correlations in the ground state.

Determination of photodisintegration cross sections independent of detector efficiency and photon spectrum

For a nucleus of mass number A whose binding energy for a particle of mass X exceeds that of the nucleus with mass S≈2 X, the differential cross section σ A(γ, X) can be obtained at one photon energy when neither the detector efficiency nor the photon energy spectrum is known, provided that the cross section σ S(γ, X) is known. For example, if X is a nucleon, S is the deuteron, and if X is a triton, S is 6Li. At one specific energy the detector efficiencies and photon fluxes will cancel in the ration of the counting rates. If the relative detector efficiency and spectral shape of the photon beam are known, the comparison sets the absolute cross section scale over an extended energy region. Where efficiency and number of photons per interval are both thought to be known absolutely, the comparison point allows a check on self-consistency. When the spectral shape has been obtained from deuteron photodisintegration, secondary standards can be used if the detector efficiency is known. Alternatively the efficiency function can be checked by comparing several different nuclei. The method is applicable to photoneutron time-of-flight measurements.

Photodisintegration of 4He

The cross section for two-body photodisintegration of 4He into deuterons has been calculated using wave functions which give the correct binding energy and the radius of 4He. The results we obtain are compared with the previous theoretical calculations as well as with the recent experiment of Del Bianco and Poutissou. We find that our theoretical results are in good agreement with the experimental results.

Direct Photodisintegration of 13C below 17 MeV. Reaction 13C(γ,n) 12C

A nuclear model where the single-particle states of the valence neutron are vector coupled to the ground (0+) and first excited (2+) 12C-core states, is considered. The model is applied to calculate total photodisintegration cross sections of the reaction 13C(γ, n)12C for energies below the Giant dipole resonance. The radial wavefunctions in initial- as well as final states are of the Saxon-Woods type.

Isospin Sum Rules and the Photodisintegration of theA=3Nuclei

Three sum rules for the electric dipole photodisintegration cross section of the $A=3$ nuclei are split into their final-state isospin components. The isospin doublet contribution to the three-nucleon breakup mode is estimated to be of the order of 10-20% and originates primarily in the high-energy region.

Cross section for the reaction 16O(γ,n0)15O at giant resonance energies

The cross section for that photoneutron reaction in 16O which leaves 15O in its ground state has been measured for photon energies ranging from 17 to 30 MeV, i.e. at energies corresponding to giant resonance excitations in 16O. Time-of-flight methods, yielding resolutions equal to 100 keV at a neutron energy of 6 MeV, were used to measure neutron spectra emitted at an angle of 98° when targets of ordinary and heavy water were irradiated with pulsed bremsstrahlung. The differential cross section at 22.3 MeV excitation was found to be 1.00 ±.05 mb/sr, assuming a photodisintegration cross section at 98° equal to 55.3 μb/sr (laboratory system) for deuterium, this latter value having been derived from calculations which have been substantiated experimentally to within ± 10%. The results are discussed with reference to other photodisintegration experiments and to recent theoretical work.

A new model for trinucleons

The binding energy, the bare form factor and the photodisintegration, bremsstrahlung-weighted and integrated cross sections of the trinucleons (3H and 3He) have been calculated earlier by using a modified Feshbach wave function and a velocity- dependent potential. These properties of trinucleons are recalculated with a modified Irving wave function but using the same velocity-dependent potential giving a better agreement with experiments. This shows that the present model for the trinucleons is much more satisfactory than the earlier model using a modified Feshbach wave function.

Sum-rule photodisintegration cross sections for the three-nucleon system with the Hamada-Johnston potential

A sum-rule calculation of the three-body photodisintegration cross sections ( σ in† and σ b ) is performed using the Hamada-Johnston potential. This is the first calculation of the E1 transition with a realistic potential, and the results show the importance of the tensor force in obtaining agreement with experiment. The contributions of the parity dependent linear LS and quadratic LS forces are negligible. The quantity σ b is closely related to the charge radius of 3H and thus allows an estimation of the Coulomb energy. This estimation gives E C = 0.60 ± 0.03 MeV, which is in accordance with our previous calculation.

Muon-Capture and Photon-Absorption Calculations in a Configuration-Mixing Model forO16

The utility of multiparticle, multihole configuration mixing as a mechanism for resolving certain theoretical-experimental discrepancies for muon capture and photodisintegration on ${\mathrm{O}}^{16}$ is considered. An ${\mathrm{O}}^{16}$ ground state containing a two-particle, two-hole (2p-2h) component is assumed. The usual particle-hole odd-parity states are amended to contain three-particle, three-hole configuration admixtures consistent with the choice of the more complicated ground state. The results of the calculations indicate that the configuration-mixing model can appreciably lower the partial muon-capture rates to the lowest ${0}^{\ensuremath{-}}$, ${1}^{\ensuremath{-}}$, and ${2}^{\ensuremath{-}}$ states. Moreover, a shift in the energy distribution of the transition strength, obtained in the model calculations, lowers the capture rate and photodisintegration cross section in and below the giant-resonance region. However, correction terms, arising mainly from ${0}^{+}$ \ensuremath{\rightarrow} ${1}^{+}$ (2p-2h) allowed Gamow-Teller transitions, seem to preclude a lowering of the total capture rate.

Calculation of the photodisintegration cross section of 4He

Calculation of the photodisintegration cross section of 4He

The photodisintegration cross section of 4He

The integrated cross section σ int for the photodisintegration of helium ( 4He) is calculated by applying the sum rules of Levinger and Bethe and using a two-parameter Irving wave function. the two-body interactions are assumed to be that obtained from our modification of the central velocity-dependent potential of Srivastava and the Rarita-Present potential. Our results give considerably better agreement with the experimental results of Gorbunov and Spiridonov than do those of other authors and indicate that Serber and Biel force mixtures are more suitable forms of interaction.

Two-Body Photodisintegration ofHe3

A discussion and comparison of the two forms of interaction, A\ifmmode\cdot\else\textperiodcentered\fi{}p and E\ifmmode\cdot\else\textperiodcentered\fi{}r, is given for two-body photodisintegration of ${\mathrm{He}}^{3}$. It is shown that in general the E\ifmmode\cdot\else\textperiodcentered\fi{}r results are much better than the A\ifmmode\cdot\else\textperiodcentered\fi{}p results. Calculations are carried out to 140 MeV to compare with recent data. The Gunn-Irving wave function gives a good fit to the total cross section at all energies, but fails to account for the ground-state matter form factor. A simple three-nucleon ground-state wave function is suggested which adequately reproduces the Coulomb energy, rms radius, and matter form factor (for ${q}^{2}\ensuremath{\lesssim}3.5$ ${\mathrm{F}}^{\ensuremath{-}2}$) of ${\mathrm{He}}^{3}$, but predicts a photodisintegration cross section which is 20% small at the peak, assuming no final-state interactions. The spin magnetic-moment interaction, which Verde has shown is forbidden in the dipole approximation for transitions from a spatially symmetric ground state, is computed without this approximation and is shown to contribute only 1-10% of the total cross section, the larger amount only at high energies.

Trinucleon three-body photodisintegration

Corrections to the three-body photodisintegration cross section due to (i) the use of an S-state containing a soft core and the inclusion of admixed states of the S′ and D type in the ground state and (ii) final-state interactions between nucleons in relative s-states are calculated. A satisfactory fit to the data is obtained for energies up to the peak cross section.