Cross Section Measurements for (n,d*)(n,t) and (n,n'α) Reactions

Cross sections for some (n,d*),(n,t) and (n,n'α)reactions have been measured by using the activation method relative to cross sections of ²⁷Al(n,α)²⁴Na or ⁹³Nb(n,2n)^92mNb reactions in neutron energies around 14MeV.In this paper some of the published cross section data have also been listed and compared with our results.The neutron energies were determined by the method of cross section ratios for the reactions of ⁹⁰Zr(n,2n) ^89m+gZr and ⁹³Nb(n,2n)^92mNb.     

Cross Section Measurements for (n,2n),(n,p)and (n,α) Reactions on Strontium Isotopes at the Neutron Energy About 14MeV

Cross-sections for ⁸⁴Sr(n, 2n)⁸³Sr, ⁸⁶Sr(n, 2n)^{85mSr,86Sr(n, 2n)85Sr,88Sr(n, 2n)87mSr,84Sr(n, p)84Rb,86Sr(n, p)86Rb, 88Sr(n, p)88Rb and 88Sr(n,α)85mKr reactions were measured at neutron energies from 13.5 to 14.6MeV using activation technique and γ-ray spectrometry. The neutron flux was determined using the monitor reaction 93Nb(n, 2n)92mNb and the neutron energies were measured by the method of cross section ratios for $^{90}$Zr(n, 2n)$^{89m+g}$Zr to $^{93}$Nb(n, 2n)$^{92m}$Nb reactions. The results of present work were compared with data published previously.}     

Excitation of isomeric states in the (γ,n), (n, 2n), and (γ, 2n) reactions on the 113In nucleus

The induced-activity method was used to measure the isomeric ratio of the yields of the (γ, n), (n, 2n), and (γ, 2n) reactions on the ¹¹³In nucleus. The energy dependence of the isomeric ratios of the yields of the photonuclear reactions ¹¹³In(γ, n)^112m,g In and ¹¹³In(γ, 2n)^111m,g In is studied in the energy range of 12–35 MeV.     

New data on (γ, n), (γ, 2n), and (γ, 3n) partial photoneutron reactions

Systematic discrepancies between the results of various experiments devoted to determining cross sections for total and partial photoneutron reactions are analyzed by using objective criteria of reliability of data in terms of the transitional photoneutron-multiplicity function F _i = σ(γ, in)/σ(γ, xn), whose values for i = 1, 2, 3, ... cannot exceed by definition 1.00, 0.50, 0.33, ..., respectively. It was found that the majority of experimental data on the cross sections obtained for (γ, n), (γ, 2n), and (γ, 3n) reactions with the aid of methods of photoneutron multiplicity sorting do not meet objective criteria (in particular, F ₂ > 0.50 for a vast body of data). New data on the cross sections for partial reactions on ¹⁸¹Ta and ²⁰⁸Pb nuclei were obtained within a new experimental-theoretical method that was proposed for the evaluation of cross sections for partial reactions and in which the experimental neutron yield cross section σ ^expt(γ, xn) = σ(γ, n) + 2σ(γ, 2n) + 3σ(γ, 3n) + ..., which is free from problems associated with determining neutron multiplicities, is used simultaneously with the functions F _i ^theor calculated within a combined model of photonuclear reactions.     

Investigation of 238U in the (n,n′γ) reaction

An irradiation of ²³⁸U with a beam of reactor fast neutrons permits revealing about 550 gamma transitions associated with the respective (n, n′γ) reaction and with fission fragments. The use of all known data on gamma radiation from fission fragments makes it possible to identify gamma transitions belonging to ²³⁸U with a high probability. The scheme of levels and gamma transitions is composed for ²³⁸U. New levels (including those of spin-parity J ^π = 0⁺) at excitation energies below 2 MeV are proposed. The low-lying levels in the rotational band for two-phonon octupole excitations are determined. It is found that a hybrid state is formed upon the crossing of this band and the band based on two-quasiparticle excitations. This hybrid state must involve excitations of both types. A small value of the rotational-band parameter in the isomer of energy 2559.0(4) keV is explained by the contribution to this state from two-quasiparticle configurations belonging to the 1k _17/2 subshell. The same circumstance may also be responsible for an enhanced yield of ternary fission for this isomer.     

Measurements of a partial cross section for the reaction 58Ni(n, γ0)59Ni

The partial cross section for radiative neutron capture accompanied by gamma transitions to the ground state of the ⁵⁹Ni nucleus was measured as a function of energy by a new neutron-spectrometry method that employed the shift of a primary gamma transition in response to a change in the energy of the captured neutron. The reaction ⁷Li(p, n)⁷Be was used as source of neutrons for the present measurements. The protons that induced this reaction were accelerated by a Van de Graaff electrostatic generator to energies exceeding the reaction threshold by 60 keV, in which case an appropriate geometry of the experiment permitted irradiation of the sample under study with neutrons whose energy ranged between 10 and 120 keV. The partial widths of some resonances and radiative strength function for hard primary M1 gamma transitions were determined in addition to the above cross sections.     

Cross sections for the 16O(γ, 2n), 19F(γ, 2pn), 27Al(γ, 2pn), 51V(γ, α) and 51V(γ, α3n) reactions to 300 MeV

Yield and cross section results have been obtained for some photonuclear reactions in ¹⁶O, ¹⁹F, ²⁷Al and ⁵¹V targets by measuring the radioactivities of the product nuclei in samples that had been irradiated with bremsstrahlung in the 20–300 MeV energy range. The reactions studied were ¹⁶O(γ, 2n), ¹⁹F(γ, 2pn), ²⁷Al(γ, 2pn), ⁵¹V(γ, α) and ⁵¹V(γ, α3n). The cross sections at energies above 150 MeV have been interpreted in terms of the contributions from various reaction mechanisms. The reactions in O, F and Al generally have important contributions from both quasi-deuteron and pion emission processes. In the ⁵¹V reactions, the additional pion reabsorption mechanism also makes important contributions. The reaction cross sections at energies below 150 MeV are used to determine the total cross sections for photon absorption at energies above the giant-resonance region and below 150 MeV. The resulting total cross sections are generally consistent with those determined from neutron-counting experiments.     

Investigation of 166Er in the respective (n,n′γ) reaction

Physics of Atomic Nuclei - The spectrum, angular distribution, and linear polarization of gamma rays from the (n, n′γ) reaction on 166Er were measured in a beam of reactor fast neutrons....     

Investigation of 88Sr in the reaction Sr(n, n′γ)

With the aid of a beam of fast reactor neutrons, the gamma-ray spectrum and angular distributions of gamma rays with respect to the neutron-beam axis are measured in the reaction Sr(n, n′γ) along with the lifetimes of ⁸⁸Sr levels. Values of the multipole-mixture parameter δ are found for gamma transitions between levels.     

The influence of the spin-orbital bond on direct photonuclear reactions (γ, n) and (γ, p)

The Courant model for direct photonuclear reactions is modified by using the wave functions of a shell model with spin-orbital bond. It is shown that the introduction of spin-orbital interaction does not influence the cross-section. The changes caused by the spin-orbital bond are apparent only on the angular distribution, which has the Courant forma+bsin² , but with a different value ofb/a, i.e. the anisotropy coefficient. New selection lawsj j, j j±1 are found. The introduction of spin-orbital interaction permits the negative value of the anisotropy coefficient, found in some experimental papers, to be explained in a natural way.

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- - (, n) (, )

: - . , . , - , , a+bsin² , , b/a, . . . j j, j j±1. - , .

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Excerpt from diploma work done at Faculty of Technical and Nuclear Physics in Prague.

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In conclusion the author thanks lecturer J. Kvasnica for the choice of subject and valuable remarks.     

Systematics of (γ, 2n) reactions

The (γ, n) and (γ, 2n) cross sections in I¹³⁷ and Au¹⁹⁷ were mesured from threshold up to 22 MeV. A comparison is made between the experimental result and the evaporation theory. Other data available in the literature are included.     

18F production in the 19F(γ, n) reaction

A race-track microtron is used to measure the yield of ¹⁸F in the reaction ¹⁹F(γ, n) at an energy of the electron beam of 55 MeV. ¹⁸F is widely used in positron emission tomography for high-sensitivity diagnostics. The currently available data are not sufficient to make accurate estimates of the yield of ¹⁸F in isotope production experiments using the reaction (γ, n). The value of σ^?1 estimated in this work is (1.7 ± 0.1) mb.     

Study of the 4He (γ, p)3H and 4He(γ, n)3He reactions

The cross sections and angular distributions for ⁴He(γ, p)³H and ⁴He(γ, n)³He have been measured.     

Isomeric cross-section ratios and total cross sections for the 59Co(n, 2n)58g,mCo, 58Ni(n,p)58g,mCo and 59Co(γ, n)58g,mCo reactions

The isomeric ratios and excitation functions were measured for the ⁵⁹Co(n, 2n)⁵⁸Co reaction in the neutron energy range 12–18 MeV and for the ⁵⁸Ni(n, p)⁵⁸Co reaction in the neutron range 2–18 MeV. The isomeric ratio is also presented for the ⁵⁹Co(γ, n)⁵⁸Co reaction induced by photons from 30 MeV electron bremsstrahlung.The results are compared with the statistical-model predictions. Use was made of modified nuclear level density formulae based on the superconductivity theory, which account for the pairing and shell effects. In all cases investigated, the calculated isomeric ratios show good agreement with experimental data, whereas the calculated total cross sections do not agree with the measured values. The disagreement may be due to the fact that no account was taken of the gamma emission in competition with the neutron emission from the residual nucleus.     

Cross sections for some (n,p) and (n, α) reactions

The cross sections for the Mg²⁴(n, p) Na²⁴, Al²⁷(n, α)Na²⁴, Si²⁸(n, p)Al²⁸, Cr⁵²(n, p)V⁵² and Fe⁵⁶(n, p)Mn⁵⁶ reactions have been measured for neutrons produced by the H³(d, n) He⁴ reaction. The activation method was used, with the gamma rays which are emitted following beta decay being counted with a Na(Tl) scintillation crystal. The Mg²⁴(n, p)Na²⁴ cross section is found to be 219±26 mb at 13.0 MeV. The Al²⁷(n, σ)Na²⁴ cross section varies smoothly from 139 mb at 13.0 MeV to 106 mb at 15.7 MeV. The Si²⁸(n, p)Al²⁸ cross section changes smoothly from 370 mb at 12.3 MeV to 160 mb at 18.3 MeV, with a broad peak at 13.5 MeV with the maximum value of 380 mb. The Cr⁵²(n, p)V⁵² cross section decreases slowly from 125 mb at 12.3 MeV to 72 mb at 18.3 MeV. The Fe⁵⁶(n, p)Mn⁵⁶ cross section is found to be 131±15 mb at 15.3 MeV. The results are generally in agreement in those cases where previous results of others exist.     

Measurements of the Cross Sections and A y for D(p, n) Inclusive Breakup Reaction at 170 MeV

The effects of three-nucleon force (3NF) has been actively studied by using the nucleon–deuteron (Nd) scattering states. The differential cross sections of the elastic Nd scattering at the energy below 150 MeV can be well reproduced by incorporating 3NF in the Faddeev calculation based on modern nucleon–nucleon (NN) interactions. On the other hand, the differential cross sections of Nd elastic and inelastic scatterings at 250 MeV show large discrepancies between the data and the Faddeev calculations with 3NF. It indicates the presence of the missing features of the three nucleon system at this energy region. For the systematic study about the energy dependence of this large discrepancies, we measured the differential cross sections and the vector analyzing power A _y for the ²H(p, n) inclusive breakup reaction at 170 MeV. The experiment was carried out at RCNP by detecting scattered neutrons by using the neutron detector NPOL3. The data was compared with the results of the Faddeev calculations with and without the 3NF.     

Bilinear Identities and Hirota’s Bilinear Forms for the (γn, σk)-KP Hierarchy

In this paper, we discuss how to construct the bilinear identities for the wave functions of the (γ_n, σ_k)-KP hierarchy and its Hirota’s bilinear forms. First, based on the corresponding squared eigenfunction symmetry of the KP hierarchy, we prove that the wave functions of the (γ_n, σ_k)-KP hierarchy are equal to the bilinear identities given in Sec.3 by introducing N auxiliary parameters z_i, i = 1, 2,?…?, N. Next, we derived the bilinear equations for the tau-function of the (γ_n, σ_k)-KP hierarchy. Then, we obtain the bilinear equations for the taufunction of the mixed type of KP equation with self-consistent sources (KPESCS), which includes both the first and the second type of KPESCS as special cases by setting n = 2 and k = 3. Finally, using the relation between the Hirota bilinear derivatives and the usual partial derivatives, we show the procedure of translating the Hirota’s bilinear equations into the mixed type of KPESCS.