Modern status of photonuclear data Varlamov, V. V.; Ishkhanov, B. S.
Physics of atomic nuclei,
09/2017, Letnik:
80, Številka:
5
Journal Article
Recenzirano
The reliability of experimental cross sections obtained for (γ, 1
n
), (γ, 2
n
), and (γ, 3
n
) partial photoneutron reactions using beams of quasimonoenergetic annihilation photons and ...bremsstrahlung is analyzed by employing data for a large number of medium-heavy and heavy nuclei, including those of
63,65
Cu,
80
Se,
90,91,94
Zr,
115
In,
112−124
Sn,
133
Cs,
138
Ba,
159
Tb,
181
Ta,
186−192
Os,
197
Au,
208
Pb, and
209
Bi. The ratios of the cross sections of definite partial reactions to the cross section of the neutron-yield reaction,
F
i
=
σ
(γ,
in
)/
σ
(γ,
xn
), are used as criteria of experimental-data reliability. By definition, positive values of these ratios should not exceed the upper limits of 1.00, 0.50, 0.33,... for
i
= 1, 2, 3,..., respectively. For many nuclei, unreliable values of the above ratios were found to correlate clearly in various photon-energy regions
F
i
with physically forbidden negative values of cross sections of partial reactions. On this basis, one can conclude that correspondent experimental data are unreliable. Significant systematic uncertainties of the methods used to determine photoneutron multiplicity are shown to be the main reason for this. New partial-reaction cross sections that satisfy the above data-reliability criteria were evaluated within an experimental–theoretical method
σ
eval
(γ,
in
) =
F
i
theor
(γ,
in
) ×
σ
expt
(γ,
xn
) by employing the ratios
F
i
theor
(γ,
in
) calculated on the basis of a combined photonuclear-reaction model. It was obtained that cross sections evaluated in this way deviate substantially from the results of many experiments performed via neutron-multiplicity sorting, but, at the same time, agree with the results of alternative activation experiments. Prospects of employing methods that would provide, without recourse to photoneutron-multiplicity sorting, reliable data on cross sections of partial photoneutron reactions are discussed.
There are well-known systematic disagreements in partial photoneutron reaction cross sections obtained using quasimonoenergetic annihilation photons in experiments based on neutron multiplicity ...sorting methods. Using newly proposed criteria we demonstrate that a large part of the systematic uncertainty comes from certain shortcomings of experimental methods of neutron multiplicity sorting. To develop methods of correction of data obtained in experiments a new approach to data evaluation was developed in which a combined model of photonuclear reactions is used to decompose experimental total neutron yield reaction cross sections into partial reaction contributions. Evaluated cross sections of partial photoneutron reactions obtained using this method show a good agreement with results of alternative experiments.
The electromagnetic dissociation of ultrarelativistic nuclei has a substantial impact on the lifetime of beams in the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC), and ...secondary nuclei produced upon this dissociation may have an adverse effect on collider components. At the same time, the detection of neutrons originating from the electromagnetic dissociation process makes it possible to monitor the luminosity of colliders. In order to calculate the total and partial cross sections for the electromagnetic dissociation process by the Weizsäcker–Williams method, one needs reliable photonuclear reaction models preliminarily tested via a comparison of the results that they produce with available experimental data. Since the commissioning of the LHC, attention has been given primarily to
Pb–
Pb collisions. A run involving
Xe nuclei was also performed. In contrast to the case of
Pb nuclei, for which the photonuclear reaction and electromagnetic dissociation cross sections have been measured at various laboratories, there are no data for
Xe. By employing the experimental–theoretical method, the (
), (
), (
), and (
, abs) cross sections for the
Xe nucleus are evaluated on the basis of available data for the neighboring nucleus of
I and the combined photonuclear reaction model (CPNRM). It is found that the results of CPNRM calculations performed for
Xe at photon energies up to 40 MeV by employing the TENDL-2017 library compiled by means of the TALYS code are close to one another and are in fairly good agreement with data obtained at the Saclay laboratory for
I. These new evaluated data, the TENDL-2017 library, and approximations of the total photoabsorption cross sections above the pion production threshold are used to calculate the electromagnetic dissociation cross section for
Xe at the LHC and at the FCC-hh collider being designed. The results of these calculations are compared with their counterparts obtained on the basis of the RELDIS model.
.
The perspectives for photonuclear experiments at the new Extreme Light Infrastructure - Nuclear Physics (ELI-NP) facility are discussed in view of the need to accumulate novel and more precise ...nuclear data. The parameters of the ELI-NP gamma beam system are presented. The emerging experimental program, which will be realized at ELI-NP, is presented. Examples of day-one experiments with the nuclear resonance fluorescence technique, photonuclear reaction measurements, photofission experiments and studies of nuclear collective excitation modes and competition between various decay channels are discussed. The advantages which ELI-NP provides for all these experiments compared to the existing facilities are discussed.
Studying photonuclear reactions using the activation technique Belyshev, S.S.; Ermakov, A.N.; Ishkhanov, B.S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2014, Letnik:
745
Journal Article
Recenzirano
The experimental setup that is used at the Skobeltsyn Institute of Nuclear Physics of the Moscow State University to study photonuclear reactions using the activation technique is described. The ...system is based on two modern compact race track microtrons with maximum energy of electrons of up to 55 and 67.7MeV. A low-background HPGe detector is used to measure the induced gamma activity. The data acquisition and analysis system, used to process the measured spectra, is described. The described system is used to study multiparticle photonuclear reactions and production of nuclei far from the beta stability region.
Experimental investigations and theoretical calculations were performed for the photoneutron reactions on the light palladium isotopes
and
. A target from a natural mixture palladium isotopes was ...irradiated with bremsstrahlung gamma rays generated at a racetrack microtron accelerating electrons to an energy of
MeV (RTM-55). The absolute yields of the photoneutron reactions occurring on the isotopes
and
and leading to the emission of up to three neutrons were determined. The experimental results obtained in this way are compared with their counterparts calculated by means of the TALYS code and with evaluated cross sections.
The analysis of the nine 1-fold differential cross sections for the γr,vp→π+π−p photo- and electroproduction reactions obtained with the CLAS detector at Jefferson Laboratory was carried out with the ...goal to establish the contributing resonances in the mass range from 1.6 GeV to 1.8 GeV. In order to describe the photo- and electroproduction data with Q2-independent resonance masses and hadronic decay widths in the Q2 range below 1.5 GeV2, it was found that an N′(1720)3/2+ state is required in addition to the already well-established nucleon resonances. This work demonstrates that the combined studies of π+π−p photo- and electroproduction data are vital for the observation of this resonance. The contributions from the N′(1720)3/2+ state and the already established N(1720)3/2+ state with a mass of 1.745 GeV are well separated by their different hadronic decays to the πΔ and ρp final states and the different Q2-evolution of their photo-/electroexcitation amplitudes. The N′(1720)3/2+ state is the first recently established baryon resonance for which the results on the Q2-evolution of the photo-/electrocouplings have become available. These results are important for the exploration of the nature of the “missing” baryon resonances.
The data on photo- and electroexcitation amplitudes of most nucleon resonances in the mass range up to 2.0 GeV determined from the CLAS experiments on exclusive
π
+
π
−
p
photo-electroproduction off ...protons in collaboration between the Jefferson Lab and Moscow State University are presented. The first (and, currently, the only available) data on electroexcitation amplitudes from CLAS in a wide range of photon virtualities
Q
2
<5.0 GeV
2
reveal the nucleon resonance structure as a complex interplay between the inner core of three dressed quarks and an external meson-baryon cloud. These results shed light on the strong QCD dynamics, which underlies the generation of excited nucleon states with different structural features from confined quarks and gluons. The future prospects of these studies in the new era of experiments with the CLAS 12 detector, which began in the spring of 2018, are outlined.
The problem of reliability of the cross section data obtained for partial photoneutron reactions on
76,78,80,82
Se nuclei in beams of quasimonoenergetic annihilation photons by means of neutron ...multiplicity sorting is discussed by employing objective physical criteria. It is shown that, because of substantial systematic uncertainties, experimental data on the (
γ
, 1
n
) and (
γ
, 2
n
) cross sections are unreliable. New data satisfying the reliability criteria are obtained for the partial photoneutron reaction cross sections for
76,78,82
Se nuclei by an experimental—theoretical method for evaluating such cross sections and are compared with experimental data and with data evaluated earlier for the isotope
80
Se. The evaluated integrated cross sections for the total photoneutron reactions on
76,78,80,82
Se nuclei are compared with the predictions of the Thomas-Reiche-Kuhn classical dipole sum rule.
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