New experimental data on the multifragmentation of carbon nuclei that is initiated by the photoproduction of neutral pions and eta mesons are discussed. The novelty is associated with the exclusive ...character of the processes being studied, in which case a determination of partial meson-photoproduction reactions is followed by an analysis of complementary particles for coincidence. The experiment being discussed was performed by the GRAAL (GRenoble Accelerateur Anneau Laser) Collaboration in a beam of 500- to 1500-MeV Compton photons. The possibility of performing new experiments within the BGO-OD Collaboration (Bonn, Germany) is considered. A new method for studying the interaction of short-lived mesons with nuclei on the basis of detecting cascade recoil nucleons is proposed.
The transparency of the carbon nucleus with respect to eta mesons of energy 25 to 95 MeV was measured. Mesons of this energy originated from the photoproduction on quasifree protons of the carbon ...nucleus (
) under the effect of photons with energies between 720 and 770 MeV. The inelastic cross sections for
interaction in nuclear matter are determined from the measured transparency of the nucleus. The absence of nucleon resonances in the measured cross section—in particular, the
resonance, which is usually associated with the assumption of the existence of eta-meson nuclei—is discussed.
An experiment to study total nuclear photoabsorption cross sections at the linear electron accelerator LUE-8-5 (INR, RAS) in the photon energy region of 5–10 MeV called the pygmy resonance is ...simulated. The motivation for the experiment is new experimental data on photoexcitation of spin isomers of medium-heavy nuclei, which indirectly indicate a change in multipolarity of near-threshold photoabsorption of nuclei. The experiment implies direct investigation of the observed effects by measuring total photoabsorption cross sections in the photon beam. The simulation is performed using the GEANT-4 code. The parameters of the facility are optimized, and the choice of the detectors for the measurements is substantiated.
The authors discuss problems of studying the yields of the reactions
13
C(γ,
p
)
12
B,
14
N(γ, 2
p
)
12
B, and
14
N(γ, 2
n
)
12
N with (
12
B,
12
N) activity measured by the telescopes of Δ
E
...detectors in the intervals between electron accelerator pulses. The fluxes and spectra of irradiating bremsstrahlung γ-quanta are found for chosen radiators and targets. The effect the parameters of targets and telescopes of Δ
E
detectors have on the production of (
12
B,
12
N) nuclei and the registration of their decay is estimated.
A procedure for measuring photonuclear-reaction cross sections by employing the method of quasimonochromatization of the bremsstrahlung photon spectrum is developed. This procedure permits ...determining reaction cross sections via measuring the reaction yield at three fixed values of the electron energy. The procedure is equivalent to measuring the cross section in question for quasimonochromatic photons. Bremsstrahlung-photon spectra are obtained using state-of-the-art simulation means involving the GEANT4 code as applied to a specific experiment with allowance for its geometry, target thicknesses, electron-beam parameters, etc. The results obtained by simulating quasimonochromatic distributions of bremsstrahlung photons are presented for experiments at the LUE-8-5 linear electron accelerator of Institute for Nuclear Research (Moscow, Russian Academy of Sciences). These results are found to be in good agreement with the experimental energy distribution of the cross section for the reaction
111
Cd(
γ
,
γ'
) in the energy range between 5 and 8 MeV.
The possibilities of studying the reaction yields of
C
B,
N
B, and
N
N through measurements of induced (
B,
N) activities with thin
detector telescopes in temporal intervals between electron ...accelerator pulses have been analyzed. Estimates for the production of (
B,
N) nuclei and registration of their decay are provided, taking into account the parameters of the electron beam, Ta radiator, irradiated targets made of graphite or NH
NO
, and telescopes of plastic scintillation
detectors.
The possibility of studying photonuclear reactions near the threshold by means of powerful femtosecond lasers is explored by considering the example of deuteron photodisintegration. The respective ...experiment was performed by employing the terawatt femtosecond laser facility of the International Laser Center at Moscow State University. The radiation from this facility is characterized by a pulse energy of up to 50 mJ, a duration of 50 fs, a repetition rate of 10 Hz, and a wavelength of 805 nm. This provides a power above 10
18
W/cm
2
. Intense relativistic-electron and photon beams of energy up to 10 MeV were obtained after the optimization of relevant experimental parameters, including the focus of the laser beam, its time structure, and the choice of target. The use of these beams made it possible to study neutron generation in heavy water, to measure the time of neutron moderation, and to determine the detection efficiency. The experimental data obtained in this way are in qualitative agreement with the results of simulations based on the GEANT-4 and LOENТ code packages and indicate that it is possible to create a neutron source on the basis of the aforementioned laser. The cross section measured for deuteron photodisintegration complies with theoretical estimates available in the literature.
Experimental results on the excitation of isomeric nuclear states in the reactions 111Cd(γ, γ′)111mCd, 113In(γ, γ′)113mIn, and 115In(γ, γ′)115mIn studied by the activation method at photon energies ...of up to 8 MeV are presented. The respective experiments were performed at the LUE-8 linear electron accelerator of the Institute for Nuclear Research (INR, Moscow). A method for calculating cross sections per equivalent photon was developed with the aid of a simulation on the basis of the GEANT-4 code. The data obtained in this way are discussed from the point of view of the possibility of studying collective nuclear excitations of various multipolarity near the threshold.
The $\Sigma$ beam asymmetry in $\eta^{\prime}$ photoproduction off the proton was measured at the GrAAL polarized photon beam with incoming photon energies of 1.461 and 1.480 GeV. For both energies ...the asymmetry as a function of the meson emission angle shows a clear structure, more pronounced at the lowest one, with a change of sign around 90$^o$. The results are compared to the existing theories that fail to account for the data.
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