Energy Spectrum Of Photoprotons Research Articles

Photo-proton emission from halo nuclei in the presence of a linearly polarized laser field

We investigate the emission of protons from halo nuclei which are subject to the combined electromagnetic fields of a γ-ray photon and an intense laser beam of linear polarization. Photo-proton energy spectra resulting from this laser-assisted nuclear photoeffect are calculated within an S-matrix approach based on the strong-field approximation. We analyze the influence of the applied γ-ray energy, laser field polarization and nuclear isotope on the proton emission spectra. The process represents an example from the field of laser-assisted photo-nuclear physics which may be explored at the upcoming Extreme Light Infrastructure.

Laser-assisted nuclear photoeffect

Proton emission from nuclei via the nuclear photoeffect in the combined electromagnetic fields of a $\ensuremath{\gamma}$-ray photon and an intense laser wave is studied. An $S$-matrix approach to the process is developed by utilizing methods known from the theory of nonperturbative laser-atom interactions. As a specific example, photo-proton ejection from halo nuclei is considered. We show that, due to the presence of the laser field, rich sideband structures arise in the photo-proton energy spectra. Their dependence on the parameters and relative orientation of the photon fields is discussed.

Photoproton energy spectra and isospin effects in the decay of highly excited states of Ni isotopes

The technique of the difference proton spectra is used to study the decay properties of highly excited states of the 58Ni and 60Ni isotopes in the energy region of the giant dipole resonance. The proton transition strengths to specific final states from particular initial states have been extracted. Experimental data are interpreted in terms of isospin splitting of the giant dipole resonance.

Yield curves for photo-proton emission from carbon and beryllium

The yields of photo-protons at laboratory angles of 40° and 70° from carbon irradiated with bremsstrahlung of end-point energies between 125 and 1000 MeV are given. From these data and a more limited set for beryllium, the shapes of the cross-sections for photo-proton emission by monochromatic photons are deduced. From a separate series of measurements on carbon at 70° lab with bremsstrahlung of end-point energies 380 and 420 MeV, the energy spectrum of photo-protons emitted by photons of energies 400±20 MeV has been derived.

90,91Zr photoproton spectra and the core-excitation model

Photoproton energy spectra have been measured for the 90,91Zr(γ,P) 89,90Y reactions at an E γ endpoint energy of 30 MeV, and for the 90,91Zr,(e, e'p) 89,90Y reactions at a number of different electron beam energies around E e = 21 MeV. Isotopically enriched target foils of metallic 90Zr(97.65%) and 91Zr(89.2%) were used, and the proton spectra measured at 90°. Prominent proton groups are observed in the 91Zr spectra, particularly around E p ≈ 11 MeV, which closely resemble groups produced in the 90Zr photoreactions. Moreover, the correlating non-ground state proton groups are being produced in transitions leaving the corresponding 89Y, 90Y residual nuclei in excited levels which also correlate in energy. These photoproton groups from 90Zr have previously been identified as representing T > strength. A qualitative explanation is proposed in terms of the core-excitation model, in which the structure in the 91Zr proton spectrum is described as representing dipole T > (T = 13 2 ) strength formed by coupling the 2d 5 2 neutron to dipole T > ( T = 6) excitations of a 90Zr core.

The Al 27(γ, n)Al 26m cross section

The yield curve of the reaction Al 27( γ, n)Al 26 m has been determined by measuring the short-lived positon activity from the first excited state of Al 26. Analysis of the yield curve by the least structure method reveals a cross section consistent with, but with more detail than, previous measurements, there being at least 14 resonances between threshold and 23 MeV. Consistency is shown to exist between the energies of these peaks and the energies of those found in photoneutron and photoproton energy spectra from Al 27 reported from other laboratories. The reaction threshold is found to be 13.27±0.05 MeV. The integrated cross section from threshold to 25 MeV is found to be 31±5 MeV ṡ mb. Interpretation of the cross section is discussed.

Photoprotons from Fluorine and Carbon

The (γ, p ) reactions in fluorine and carbon were studied with bremsstrahlung X-rays of energies up to 24 MeV. Photoprotons were observed by using nuclear plates. Energy spectrum of photoprotons from fluorine exhibits peaks at 3.8, 4.6, and 7.4 MeV which are in good accord with those observed previously by Forkman and Wahlstrom, and Dodge and Barber. In addition to these we found peaks at 1.9 and 2.8 and a somewhat uncertain peak at 6.1 MeV. Angular distributions of photoprotons from fluorine showed an asymmetry around 90° with respect to the direction of incident photons, which suggests interference between absorbed photons of different parities. In the case of carbon, a main peak at proton energy of 6.0 MeV was observed along with slight humps at 4.5 and 5.2 MeV. The observed structure is in good agreement with those reported previously.

Photoneutron Reaction of S32

The photoneutron cross section of S/sup 32/ was observed up to 22 Mev with good energy resolution, together with the photoneutron spectrum using a stilbene scintillation spectrometer. Fine structures were observed in either of the two measurements. Taking into account the threshold energy and the excitation energies of the residual nucleus, these structures were shown to be consistently related with each other. Experimental results were discussed using the statistical model calculation, assuming that the emitted particles were only p-wave and f-wave particles. The integrated cross section ratio for S/sup 32/ ( gamma ,n) to P/sup 31/ ( gamma ,n) reaction and the same ratio for S/sup 32/ ( gamma ,p) to S/sup 32/ ( gamma ,n) reaction were well explained by the calculations. The difference between the energy spectrum of the photoprotons from P/sup 31/ and that from Si/sup 28/ also seemed to be well explained qualitatively. In the appendix, the contributions of the f-wave protons for the energy spectrum of photoprotons were shown. The photodisintegration of nuclei in these mass number region was concluded to occur mainly through the compound process in the giant resonance energy region. (auth)

The Energy Spectrum of Photoprotonas from Ne20

The energy spectrum of photoprotons from Ne20 at 23.5 Mev was detected by Sakura NR-M1 emulsions which were placed in a scattering gas chamber parallel to the x-ray beam. The gas chamber was filled with natural neon gas at a pressure of 3.09 atm. The number of observed proton tracks was 4345 in the scanned area of 3.59 cm.

Photoprotons from Potassium

The energy spectrum of photoprotons from K 39 induced by 24 Mev bremsstrahlung was observed using nuclear emulsions. The observed spectrum does not agree so well with the calculated one using Weisskopf level density and classical Coulomb barrier height. The choice of a much lower Coulomb barrier height seems to give better agreement with the experimental result. Structures are observed in the energy spectrum. These are discussed using various reaction mechanisms.

Energy Spectrum of Photoprotons from Al27

The energy spectrum of photoprotons from Al27, induced by 24-Mev bremsstrahlung, was detected in emulsions using previous methods and apparatus (K. Shoda, et al., J. Phys. Soc. Japan, 16: 1807(1961)). Spectral types differ between odd and even Z nuclei. Data are presented in graphical form.

Fine Structures of Photoprotons from Si28

The energy spectrum of photoprotons from silicon-28 is investigated using 24 Mev bremsstrahlung. The energy loss is about 30% for 3 Mev and about 10% for 6 Mev protons. The number of detected tracks is 4366 for a scanned area of 1.6 cm². The energy spectrum is deduced by the statistical model with the level density omega given by omega = Cexp (E/2.8)Mev⁻¹. The many fine structures may be explained by a resonating group model. The cross section of Si²⁸( gamma ,p)Al²⁷ is compared with that for Al²⁷(p, gamma )Si²⁸ and the shapes coincide fairly well. (N.W.R.)

Photodisintegration ofLi6

The photodisintegration of ${\mathrm{Li}}^{6}$ by bremsstrahlung radiation of 17.3-Mev peak energy was investigated by use of coincidence techniques to detect neutron-proton coincidences and by measurement of the photo-proton energy spectra. The ${\mathrm{Li}}^{6}(\ensuremath{\gamma}, n){\mathrm{Li}}^{5}$ reaction is found to be responsible for 0.58\ifmmode\pm\else\textpm\fi{}0.13 of the photoneutron yield measured by Romanowski while the ${\mathrm{Li}}^{6}(\ensuremath{\gamma}, p){\mathrm{He}}^{5}$ reaction contributes 0.31\ifmmode\pm\else\textpm\fi{}0.04 of the yield. No angularly correlated neutron-proton coincidences were detected which would support a deuteron-alpha-particle model for the ${\mathrm{Li}}^{6}(\ensuremath{\gamma}, np){\mathrm{He}}^{4}$ reaction; however, the possible existence of this reaction is not eliminated.

Photodisintegration of Sodium by7Li(p, ) Radiation

A small thin NaI(Tl) scintillator has been used as both source and detector of photoprotons produced in sodium by 7Li(p, γ) radiation. This technique provides photoproton energy spectra of good resolution and high statistical precision. Spectra were obtained with both resonance and non-resonance radiation from the 7Li(p, γ) reaction which permit identification of protons produced by the 17.6 MeV component of the incident radiation. These protons correspond to transitions to states in 22Ne at energies of 0 (0.31 mbn), 13 (2.5mbn), 3.3 (0.6 mbn), 4.4 (0.9 mbn), 5.4 and 5.7 MeV (approximately 2mbn for both). This experiment establishes the existence of 22Ne levels at the three highest energies. Previous evidence for a level between 4 and 5 MeV is discussed and is found to be compatible with the present results.

Bremsstrahlung Spectrum from the Internal Target of a 22-Mev Betatron

The intensity and energy distribution of the bremsstrahlung photons produced in a betatron operating at 22 Mev have been determined by measurement of the energy spectrum of photoprotons ejected from deuterium. The protons were detected using a 0.15 cm thick NaI crystal followed by a 100-channel pulse-height analyzer. The photon beam was highly collimated in the forward direction. If one assumes the energy dependence of the cross section for the photodisintegration of deuterium as given by Hulth\'en, the computed bremsstrahlung energy distribution is in excellent agreement with the theoretical thin-target spectrum. The observed total intensity is that indicated by monitoring using an "$R$" thimble imbedded in 3.9 cm of Lucite.