LIGHT AND MEDIUM–HEAVY NUCLEI PHOTONEUTRON REACTION CROSS-SECTIONS IN BREMSSTRAHLUNG BEAM EXPERIMENTS

2 Jul 2024, 16:00
10m
Second floor Hall (BLTP)

Second floor Hall

BLTP

second floor, Chairman: Nesterenko V.

Speaker

Aleksandr Davydov

Description

In cases for many (~50) nuclei from $^{51}$V to $^{209}$Bi the experimental data on photoneutron partial reactions ($\gamma$,1n), ($\gamma$,2n), ($\gamma$,3n) cross sections directly obtained using beams of quasimonoenergetic annihilation photons [1] do not satisfy objective physical criteria of data reliability [2–5]. The reasons are systematic uncertainties of experimental photoneutron multiplicity sorting method basing on partial reactions separation via measurement of neutron energies. Therefore, the experimental-theoretical method for partial reaction cross-section evaluation basing on physical criteria was used for analysis of reliability of data obtained using quite different method on the beams of bremsstrahlung [6]. Partial reaction cross sections are separated and determined in such kind experiment using statistical theory corrections to the neutron yield cross section $\sigma$($\gamma$,xn) = $\sigma$($\gamma$,1n)+2$\sigma$($\gamma$,2n)+3$\sigma$($\gamma$,3n)+… measured at first. Experimental cross sections of the reactions ($\gamma$,1n) and ($\gamma$,2n) are definitely unreliable in the cases of $^{51}$V, $^{52}$Cr, $^{59}$Co, but enough reliable in the case of $^{90}$Zr. The reason is that the role of two-nucleon reaction ($\gamma$,1n1p) was not taken into account, though this reaction competes with also two-nucleon reaction ($\gamma$,2n). It was shown via the results of calculation in the frame of the Combined photonuclear reaction model [5] that energy positions and amplitudes of cross sections of ($\gamma$,1n1p) and ($\gamma$,2n) reactions are very close to each other in the cases of $^{51}$V, $^{52}$Cr, $^{59}$Co, but in the case of $^{90}$Zr the value of ($\gamma$,1n1p) reaction cross section is very small and could be negligible. This conclusion is analogous to that of the preliminary investigation of the cases of $^{127}$I, $^{165}$Ho, $^{181}$Ta [7]. It means that in the cases of relatively light nuclei $^{51}$V, $^{52}$Cr, $^{59}$Co, as well as $^{58,60}$Ni [8] the reaction ($\gamma$,1n1p) plays important role in nucleus photodisintegration but its contribution is not correctly described by statistical theory corrections.

  1. IAEA Nuclear Data Section database “EXFOR. Experimental nuclear reaction data”, http://www-nds.iaea.org/exfor.
  2. V.V.Varlamov et al. // Phys. Atom. Nucl. 2017. V. 80. P.957.
  3. V.V.Varlamov // Phys. Part. Nucl. 2019. V. 50. P.637.
  4. V.V.Varlamov et al. // Moscow University Physics Bulletin. 2023. V. 78. N. 3. P. 303.
  5. B.S.Ishkhanov et al. // Phys. Atom. Nucl. 2008. V.71. P.493.
  6. A.V.Varlamov et al. Atlas of Giant Dipole Resonances. Parameters and Graphs of Photonuclear Reaction Cross Sections. // INDC(NDS) –394, IAEA NDS, Vienna, Austria, 1999.
  7. V.V.Varlamov et al. // Bull. Rus. Acad. Sci. Phys., 2023. V. 87. N. 8. P. 1188.
  8. V.V.Varlamov et al. // Bull. Rus. Acad. Sci. Phys., 2023. V. 87. N. 8. P. 1179.
Section Experimental and theoretical studies of nuclear reactions

Primary authors

Aleksandr Davydov Ivan Mostakov (Physics Faxculty of Lomonosov Moscow State University) Vadim Orlin (Skobeltsyn Institute of Nuclear Physics of Lomonosov Moscow State University) Vladimir Varlamov (Skobeltsyn Institute of Nuclear Physics of Lomonosov Moscow State University)

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