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Pigmy Resonance in Soft Nuclei: Measurement and Perspectives

This article explores pigmy resonances in soft nuclei through the excitation of spin isomers, with a focus on total photoabsorption cross sections and new experimental results. It also discusses the potential applications of nuclear photonics and the optical properties of nuclei.

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Pigmy Resonance in Soft Nuclei: Measurement and Perspectives

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  1. Pigmy resonance in soft nuclei measured through excitation of spin isomers. V.NedorezovINR RAS , Moscow

  2. Content Introduction. Collective nuclear excitations. Different nuclear shapes and deformations. Pygmy resonances in total photoabsorption cross sections. INR new resultsand perspectives. Spin isomer production in soft nuclei near the threshold. Additional motivation : Nuclear photonics -new generation gamma sources based on femtosecond laser technology to study photonuclear reactions near threshold. Comparison of the traditional electron accelerators with the laser-plasma facilities.

  3. Total nuclear photoabsorption near threshold.Pigmy resonances in soft nuclei [S.P. Kamerdzhiev, private communication] New physics in the Pigmy resonance region. Isoscalar nature of the pigmy resonances. M1, M2, E2 toroidal and compression modes. Deformed nuclei, scissor modes. V.Nedorezov, S.Polikanov. Experimental study of spontaneously fissioning isomers. Phys. of Elementary Particles and Nuclei. 8 (1977) 374 :: some new ideas are well-forgotten old ones

  4. Inertia moment of nuclei[from Rev. of V. Nedorezov, S.Polikanov. Experimental study of spontaneously fissioning isomers. Phys. OfElementary Particles and Nuclei. 8 (1977) 374] Experiment based on the identification of the rotation band [1] allows measurement of Inertia moment of nuclei: Superfluid nuclear model [2] predicts that at an excitation energy of 2-3 MeV, the pairing between nucleons breaks down and the superfluid nuclear state passes into the ordinary state. The moment of inertia changes by a factor of 2, since the coupled nucleons do not contribute to the total angular momentum of the nucleus.The deformation e does not change at the same time. Experiment [1] and calculation [3] show that the moment of inertia of the isomer nuclei is 2 times greater than that of the nuclei in the ground state.: On the figure: 1- hard rotator, 2 – experiment, 3 - the pairing force G is proportional to the surface of the nucleus, 4 - G = const, 5 - liquid drop. . 1. J.P.A.Sobichevski e.a. Nucl.Phys.A 202, 274, 1974. 2. V.Solovjev, Theory of complex nuclei, M., Nauka, ch. 7, 1971. 3. S.G.Nilsson. Summer school on Nucl.Phys. Vfrenna, Lund, 1974.

  5. Optical anisotropy of nuclei[from Rev. of V. Nedorezov, S.Polikanov. Experimental study of spontaneously fissioning isomers. Phys. OfElementary Particles and Nuclei. 8 (1977) 374] optical anisotropy of nuclei [1] – splitting of giant resonances in deformed nuclei in two maxima corresponding to oscillations along and across the axis of symmetry. Evaluation of the quadrupole moment Q and the quadrupole deformation b . Experiment: Total photoabsorption cross section of nuclei with b = 0 - 0.3 [2]. 1. A.M.Baldin e.a. Rus.J.Nucl.Phys. 8, 327, 1968 2. G.M.Gurevich e.a. Nucl.Phys. A351 (1981) 257-268

  6. Measurement of nuclear radius by optical spectroscopy methods [from Rev. of V. Nedorezov, S.Polikanov. Experimental study of spontaneously fissioning isomers. Phys. OfElementary Particles and Nuclei. 8 (1977) 374] Increase of nuclear deformation leads to an increase of nuclear mean-square radius which can be measured as isomeric shift in the optical range using the optical laser spectroscopy method [1]. Effect is about 20 cm-1 at b = 0.6. Bubble nuclei predicted in [2] studied experimentally [3] but the result is not confirmed. Possibilities of existence M1, M2, E2 toroidal and compression modes in deformed nuclei, scissor modesare being discussed, but the question is still open. 1. D.P.Grechukhin. Rus.J.Nucl.Phys. 21, 956, 1975 2. D.L.Hill, J.A.Wheeler. Phys.Rev. 89, 1102, 1963. 3. C.Y.Wong. Phys.Lett., 41, 451, 1972.

  7. Collective excitations of nuclei

  8. Electron LinacLUE-8-5 INR RAS The energy of accelerated electrons4 – 9.5MeV Frequency of repetitionsto 600 Hz Pulse width 3 μs The average electron current at a frequency of 50 Hz40-50 μА

  9. W - e-γ - Conversion Target Conversion W target - 0.4 mm thick 9

  10. Low-background γ-spectrometer chamber Low-background camera of a gamma spectrometer based on a detectorof High Purity Germanium with "passive" protection (protective upper part is shifted to set the sample)

  11. Experiment (2017) at electron 8.5 MeV Linac INR RASExcitation of 111mCd, 113mIn, 115mI isomeric states in (g,g’) reaction near threshold

  12. Method of measurements - Activation method The peak area of the i-th radionuclide in the gamma spectrum of the activated sample is represented asSi: σi(E) – cross-section of the nuclear reaction as a function of the energy of the incident photon Е; Φ(E) – gamma radiation flux spectral density; tа – activation time; tв – delay time after irradiation; tи – measuring time; λi – radioactive decay constant 12

  13. Quasi-monochromatization of the photon spectrum Ф8.5 Ф8 Ф7.5 Ee MeV Suppose that the three fluxes Ф8.5, Ф8 and Ф7.5 are calculated for the same integral of the electron beam. It was found that such coefficients, for example C8.5, C8 and C7.5, can be obtained, that for all energies less than 7 MeV the combination C8.5 * Ф8.5 + C7.5 * Ф7.5 - C8 * Ф8 was close to 0.

  14. Quasi-monochromatization of the photon spectrum Distributions for intermediate points can be obtained using interpolated values. At the same time, the GEANT-modeled distributions were approximated by a set of mathematical functions fitted according to the 2 method, and the dependences of the expansion coefficients on the electron energy were used to calculate with arbitrary energy. Ee MeV The figure shows the dependence of some parameters on the energy of electrons. It can be seen that the dependences on the energy are smooth, which allows us to hope for sufficient accuracy of obtaining photon spectra during interpolation. 14

  15. Quasi-monochromatization method for bremsstrahlung beam:INR simulation by GEANT-4first proposed by E.Van Camp e.a. Phys.ReV. C 24 (1981) 2499

  16. Cross section of (g,g’) 111mCd reaction,circles are V.Mazur data [ Rus.J.N.P. 56,1, 20,1999], squares – INR (2017) recalculations

  17. Radiation transition probability near neutron threshold[L.Z.Dzhilavjan e.a. Rus.J.Nucl.Phys.51(1990)336-344].dw(if) = (i/tot){Ef, Jf,f}dEf, where {Ef,Jf,f} – density of final states, iandtot – partial and total width of the initial level.150In(,')m180Hf(,')m

  18. Table of spin isomers

  19. Perspectives:Direct measurement of the total photoabsorption cross section • Subtraction of atomic photoabsorption yields • Polarization of gamma beam using crystal diamond target • Quasi-monochromatic gamma beam As the part of nuclear photonics scientific program based on the Compton back scattering technique. Can we compete using a conventional electron accelerators ?

  20. Nuclear photonics based on the Compton back scattering technique 1963 – F.Arutunyan, V.Tumanyan. JETF 44 (1963) 6, 2100. R.H.Milburn, Phys.Rev.Lett. 10 (1963) 3, 75 1964 – Moscow (Lebedev FIAN) – first experimental evidence 1976 - Frascati (LADONE - ADONE) – photonuclear physics 1984 - Novosibirsk Budker INP (ROKK – 1,2 – VEPP 3,4) nuclear fission 1988 – Brookhaven BNL (LEGS - NSLS)- meson photoproduction 1995 – Grenoble (GRAAL – ESRF ) 1998 – Osaka (LEPS - Spring-8) 2000 – Duke (HIgS - ) low energy nuclear excitations New history: FEMTOSECIND LASER DRIVEN GAMMA SOURCES

  21. Femtosecond laser facility at ILC MSUReaction chamber Wave length 800 nm, Impulse length 50 fc, Frequency 10 Hz, Pulse energy 50 mJ, Focusing diameter 4 mm. Beam intensity on the target 1019W/cm2, being equivalent to the electron quasi-temperature of ~1 МэВ.

  22. Electron spectrum measured by magnetic spectrometer

  23. Relativistic electromagnetic fields produced by femtosecond laserMourou G., Tajima T., Bulanov S.V. // Review of Modern Physics. 2006. V.78. P.309-371 Time duration — to 10-15 s (femtosecond) Wave packet length — to 10 m (10 wave lengths) Pulse energy - to 100 J, power - to 1015 Wt (petawatt). Focus on radius of 10 m provides W = 1020Wt/сm2 Electric field strength Е = 1012 V/сm (For comparison: in the hidrogen field Е = 109 V/см., at mica breakdown - 106V/см Uranium field E = 1011 V/cm, with relativistic compression – up to 1012 v/cm ) . At E ~1011 V/сm, respectively W ~1018 Вт/cм2 (1 m) electron is accelerated to relativistic velosity being closed to the light one. Therefore such field is defined as the relativistic one . Nevertheless, direct photonuclear reactions (nuclear excitations) are forbidden ?

  24. Parameters of electron beams produced on LUE-8,5 and a femtosecond laser of terawatt power • First INR experimental results and simulations show that study of photonuclear reactions at low energies can be carried out both with traditional electron accelerators and femtosecond lasers of terawatt power. Considerable progress achieved in recent years in this direction, now petawatt lasers are available in the world. So we can expect significant results in the near future.

  25. Conclusion • Exotic M1, M2, E2 toroidal, compression and scission nuclear excitation modes etc are not evidenced yet but they could be studied at present time using the modern experimental facilities. • Precise simulations are necessary.

  26. Thank you for attention Announcement The XV International Seminar on Electromagnetic Interactions of Nuclei (EMIN-2018) 8 – 11 of October 2018, INR, Moscow, Russia. www.inr.ac.ru/~pnlab/emin2018 SEMINAR TOPICS: • - Hadron spectroscopy and structure in resonance energy region • - Structure functions of hadrons and nuclei • - Multiple meson production on free and bound nucleons • - Fragmentation of nuclei by photons • - Polarization phenomena, spin physics • - Giant resonances in nuclei • - Ultraperipheral collisions of nuclei • - New developments and perspectives

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