A structural configuration and parameters of a modernized source of electrons and gamma quanta with energy of 4–10 MeV are presented. The source is designed on the basis of electron linac LUE-8-5 RV ...(INR RAS) and can be used for detector calibration and other practical applications.
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.
γ
p
→
K
+
Λ
differential cross sections and recoil polarisation data from threshold for extremely forward angles are presented. The measurements were performed at the BGOOD experiment at ELSA, ...utilising the high angular and momentum resolution forward spectrometer for charged particle identification. The high statistics and forward angle acceptance enables the extraction of the cross section as the minimum momentum transfer to the recoiling hyperon is approached.
K+Λ(1405) photoproduction has been studied at the BGOOD experiment via the all neutral decay, Λ(1405)→Σ0π0. The unique BGOOD experimental setup allows both the cross section and Λ(1405) invariant ...mass distribution (line shape) to be measured over a broad K+ polar angle range, extending to extreme forward K+ angles unattainable at previous experiments.
Evidence is provided for the role of a triangle singularity driven by the N⁎(2030) resonance, which appears to contribute significantly to K+Λ(1405) photoproduction. This is observed in the integrated cross section which was determined with unprecedented energy resolution and supported by the angular distributions. The measured line shape is also in agreement with the previous results of CLAS and ANKE, and is consistent with two poles derived in χPT based models.
The coherent reaction, γd→π0π0d was studied with the BGOOD experiment at ELSA from threshold to a centre-of-mass energy of 2850MeV. A full kinematic reconstruction was made, with final state ...deuterons identified in the forward spectrometer and π0 decays in the central BGO Rugby Ball. The strength of the differential cross section exceeds what can be described by models of coherent photoproduction and instead supports the three isoscalar dibaryon candidates reported by the ELPH collaboration at 2.38, 2.47 and 2.63GeV/c2. A low mass enhancement in the π0π0 invariant mass is also observed at the d⁎(2380) centre-of-mass energy which is consistent with the ABC effect. At higher centre-of-mass energies, a narrow peak in the π0d invariant mass at 2114MeV/c2 with a width of 20MeV/c2 supports a sequential two-dibaryon decay mechanism.
In addition to the current BGO-OD experimental program we propose to study nuclear media effects in photoproduction of mesons using a new experimental method based on measuring a recoil nucleon as a ...tagger of the selected partial channel. The principal goal is to learn how unstable mesons (
π
o
, π
+
,
π
−
,
η, ρ, ω
, etc.) interact with nuclear media. This approach continues previous GRAAL experiments to study nuclear excitation dynamics, including multifragmentation of nuclei by intermediate energy photons.
The γp→K+Σ0 differential cross section at extremely forward angles was measured at the BGOOD experiment. A three-quarter drop in strength over a narrow range in energy and a strong dependence on the ...polar angle of the K+ in the centre-of-mass of the reaction is observed at a centre-of-mass energy of 1900 MeV. Residing close to multiple open and hidden strangeness thresholds, the structure appears consistent with meson-baryon threshold effects which may contribute to the reaction mechanism.
Nuclear Photonics Nedorezov, V. G.; Savel’ev-Trofimov, A. B.
Physics of atomic nuclei,
12/2017, Letnik:
80, Številka:
9
Journal Article
Recenzirano
A review of works performed at the Institute for Nuclear Research of the Russian Academy of Sciences and at the International Laser Center of the Moscow State University in the context of the new ...research area called “nuclear photonics” is presented. Nuclear photonics is based on creation of the new-generation gamma-ray sources which make it possible to solve a number of fundamental and applied problems, including research of low-energy photonuclear reactions, namely, investigation of collective excitations of nuclei near the threshold (pygmy resonances); nuclear safety assurance; production of low-energy positron beams; and phase-contrast X-ray imaging.
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