Total cross sections for photoabsorption on light nuclei in the energy range 600–1500 MeV

Experimental data of the GRAAL Collaboration on the total cross sections for photoabsorption on deuterium and carbon targets at gamma-ray energies in the range between 600 and 1500 MeV are presented. The experiment was performed in a beam of photons obtained by the method of the Compton backscattering of laser photons at the electron storage ring of the European Synchrotron Radiation Facility (ESRF, Grenoble, France) by using a wide-aperture detector covering a solid angle close to 4π. The total photoabsorption cross sections were determined by two independent methods: by subtracting the emptytarget background and by summing partial cross sections for meson photoproduction. The total cross sections for photoabsorption on quasifree protons and neutrons are shown to agree both in magnitude and in shape within a 5% precision of the measurements. In contrast to data previously available in the literature, both cross sections show distinctly the F ₁₅(1680) resonance at a photon energy of about 1 GeV. Data obtained in the present experiment for the cross sections for photoabsorption on a free and a bound nucleon are compared. This comparison reveals a substantial role of two-nucleon correlations in estimating the nuclear-medium effect on meson photoproduction.     

Calculation of proton total reaction cross sections for some target nuclei in incident energy range of 10–600 MeV

In this study, proton total reaction cross sections have been investigated for some isotopes such as ¹²C, ²⁷Al, ⁹Be, ¹⁶O, ¹⁸¹Ta, ¹⁹⁷Au, ⁶Li, and ¹⁴N by a proton beam up to 600 MeV. Calculation of the proton total cross sections has been carried out by the analytic expression formulated by M.A. Alvi by using Coulomb-modified Glauber theory with the Helm model nuclear form factor. The obtained results have been discussed and compared with the available experimental data and found to be in agreement with each other.     

Time features of delayed neutrons and partial emissive-fission cross sections for the neutron-induced fission of 232Th nuclei in the energy range 3.2–17.9 MeV

The energy dependence of the relative abundances of delayed neutrons and the energy dependence of the half-lives of their precursors in the neutron-induced fission of ²³²Th nuclei in the energy range 3.2–17.9 MeV were measured for the first time. A systematics of the time features of delayed neutrons is developed. This systematics makes it possible to estimate the half-life of delayed-neutron precursors as a function of the nucleonic composition of fissile nuclei by using a single parameter set for all nuclides. The energy dependence of the partial cross sections for emissive fission in the reaction ²³²Th(n, f) was analyzed on the basis of data obtained for the relative abundances of delayed neutrons and the aforementioned half-lives and on the basis of the created systematics of the time features of delayed neutrons. It was shown experimentally for the first time that the decrease in the cross section after the reaction threshold in the fission of ²³²Th nuclei (it has a pronounced first-chance plateau) is not an exclusion among the already studied uranium, plutonium, and curium isotopes and complies with theoretical predictions obtained for the respective nuclei with allowance for shell, superfluid, and collective effects in the nuclear-level density and with allowance for preequilibrium neutron emission     

Simple approximation of cross sections for nuclear reactions involving Z = 3–12, 14 nuclei

A compact cross section data base is obtained for almost 5000 nonresonance nuclear reactions involving stable and unstable Be, B, C, N, O, F, Ne, Na, Mg, and Si isotopes. The calculations are performed using the Sãn Paulo potential and the barrier penetration formalism. The calculated cross sections are approximated by simple analytical formulas. The results are necessary for simulating nuclear burning in neutron stars.     

Study of the 24Mg(α, 12C)16O reaction in the energy range Elab = 24.9–27.76 MeV

The ²⁴Mg(α,¹²C)¹⁶O and ²⁴Mg(α, α')²⁴Mg reactions have been used to search for resonances in the ²⁸Si compound nucleus. The excitation functions were measured in the energy range between 24.9 and 27.76 MeV. Angular distributions of ¹²C nuclei and elastic and inelastic scattering of α-particles have been measured at energies corresponding to extrema of excitation functions. Significant anomalies have been found at E_ex = 31.5 and 33,1 MeV. The spins and parities of these structures are assigned as 9⁻ and 11⁻, respectively.     

Fusion and transfer cross sections of 3He induced reaction on Pt and Au in energy range 10–24.5 MeV

In experiments performed by accelerated ion ³He-beam irradiated gold and platinum targets on the cyclotron U-120M of the Nuclear Physics Institute of the Czech Academy of Sciences, ?e?, reactions of complete and incomplete fusion and nucleon transfer reactions in the ³He energy range from 10 to 24.5 MeV have been investigated. To determine the yield of the nuclides resulting from the nuclear reaction, the activation technique has been used. The obtained data are analyzed using models based on statistical calculations and compared with similar results for other light stable particles. Transfer reactions with positive Q values have relatively high cross sections in the energy range below the Coulomb barrier. These cross sections continue to grow with increasing ³He energy, and, in the case of capturing neutron from target nucleus by a nucleus of ³He, the excitation functions of these reactions reach their maximum almost at the Coulomb barrier of the reactions.     

Measurement of the total photoabsorption cross section on a proton in the energy range 600–1500 MeV at the GRAAL

The total photoabsorption cross section on a free proton was measured at the GRAAL facility in the energy range E _γ = 600−1500 MeV. The large-aperture LAGRANγE detector and a liquid hydrogen target were used in the experiment performed with a back-scattered Compton gamma beam. To improve the accuracy, two alternative methods were employed. First, a subtraction method of using empty-target measurements allowed the cross section σ _tot to be evaluated directly because of a low level of the electromagnetic background. Second, an algorithm for evaluating σ _tot on the basis of summing the dominating partial cross sections was developed. Experimental results obtained for σ _tot by the two methods are compared with existing data. The article was translated by the authors. Published in Russian in Yadernaya Fizika, 2008, Vol. 71, No. 1, pp. 76–83.     

Analysis of data on proton-proton scattering in the energy range 100–1300 MeV

The results of a partial-wave analysis of data on proton-proton interaction in the energy range 100–1300 MeV are presented. The real parts of phase shifts were found for states of orbital angular momentum up to L = 9, while their imaginary parts were determined for states of orbital angular momentum up to L = 5. The sixth parameter of the S matrix was introduced in order to describe states of total angular momentum J = 2 and 4. The inelasticity thresholds were chosen individually for each state and were found to be substantially different from one another. The resulting solution was characterized by χ ² = 1.155 per point in the case where the number of experimental data was 12 841 and by a large imaginary part of the phase shift in the ³ P ₂-wave state at the edge of the energy range. Special features of the interaction in orbital states are discussed along with the energy dependence of integrated amplitudes and amplitudes of the scattering matrix at zero angle.     

K-shell ionization of Si,Ti, Cu and Ag for incident protons,4He and14N ions in the energy range of 0.17–2.0 MeV/amu

K-shell X-ray production cross sections of Si, Ti, Cu and Ag were measured for incident protons,⁴He and¹⁴N ions in the energy range of 0.17≦E ₁/A ₁≦2 MeV/amu. The experimental ionization cross sections are compared with calculations according to the simple Plane Wave Born Approximation (PWBA) theory as well as the corrected PWBA model (PWBABC). Strong deviations of the experimental cross sections from theZ ₂ ¹ scaling are observed and discussed quantitatively.     

Measurements of differential and angle-integrated cross sections for the ~(10)B(n, α)~7Li reaction in the neutron energy range from 1.0 eV to 2.5 MeV

Differential and angle-integrated cross sections for the ~(10)B(n,α)~7 Li,~(10)B(n,α_0) ~7 Li and ~(10)B(n,α_1) ~7 Li~*reactions have been measured at CSNS Back-n white neutron source.Two enriched(90%) ~(10)B samples 5.0 cm in diameter and～85.0 μg/cm~2 in thickness each with an aluminum backing were prepared,and back-to-back mounted at the sample holder.The charged particles were detected using the silicon-detector array of the Light-charged Particle Detector Array(LPDA) system.The neutron energy En was determined by TOF(time-of-flight) method,and the valid a events were extracted from the E_n-Amplitude two-dimensional spectrum.With 15 silicon detectors,the differential cross sections of a-particles were measured from 19.2°to 160.8°.Fitted with the Legendre polynomial series,the(n,a) cross sections were obtained through integration.The absolute cross sections were normalized using the standard cross sections of the ~(10)B(n,α) ~7 Li reaction in the 0.3-0.5 MeV neutron energy region.The measurement neutron energy range for the ~(10)B(n,α) ~7 Li reaction is 1.0 eV≤E_n 2.5 Me V(67 energy points),and that for the ~(10)B(n,α_0) ~7 Li and~(10)B(n,α_1) ~7 Li~*reactions is 1.0 eV≤E_n1.0 MeV(59 energy points).The present results have been analyzed by the resonance reaction mechanism and the level structure of the ~(11)B compound system,and compared with existing measurements and evaluations.     

Energy dependence of the optical potential for 16O + 28Si,elastic scattering in the energy range of E = 55–215 MeV

The energy dependence of an optical potential which reasonably fits all of the existing experimental data on ¹⁶O + ²⁸Si elastic scattering in the energy range of E = 54.7–215.2 MeV is studied. The real part of the potential found for this system shows a transition from a proximity to a double-folding type of the potential as a result of quenching of the Pauli principle effects with an increase of the incident energy. The imaginary part shows a transition from a surface-transparent to a strongly absorptive type of the potential.     

Investigation of the 19F(n, α)16N reaction excitation function in neutron energy range of 4–7.35 MeV

New method based on ionization chamber with Frisch grid and digital signal processing was developed for experimental investigation of ¹⁹F(n, α)¹⁶N reaction. The chamber filling gas with CF₄ additive was used as the fluorine-containing target. The experimental investigation of ¹⁹F(n, α)¹⁶N reaction cross-section in 4–7.35 MeV energy range is represented in this work. The total cross section of ¹⁹F(n, α)¹⁶N reaction was measured as well as partial cross-section for sum of α₀-α₃ and sum of α₄ and α₅ reaction channels.     

The β-delayed α-spectrum of 16N,and its role in defining the astrophysical cross section for 12C(α,γ)16O

It has proven to be very difficult to determine the astrophysically important cross section for ¹²C(α, γ)¹⁶O at the relevant energies (∼300 keV) from radiative capture measurements. The present paper summarizes a new measurement of the β-delayed α-spectrum of ¹⁶N that substantially improves our knowledge of the E1 α-capture cross section on ¹²C at 300 keV. The paper concludes with a brief discussion of the status of the total ¹²C(α, γ)¹⁶O cross section at 300 keV.     

Photofission of 238Pu, 240Pu, and 242Pu in the energy range 5–10 MeV

The cross sections for the photofission of plutonium isotopes ²³⁸Pu, ²⁴⁰Pu, and ²⁴²Pu in the energy range 5–10 MeV have been measured by using a beam of bremsstrahlung photons from the microtron installed at the Institute of Physics and Power Engineering (Obninsk). The energy regions below the fission barrier and above 6 MeV have been scanned with pitches of 0.05 and 0.1 MeV, respectively. In deriving the absolute cross section for ²³⁸Pu photofission, ²³⁸U photofission has been employed as a reference reaction. In measurements involving ²⁴⁰Pu and ²⁴²Pu nuclei, the neptunium isotope ²³⁷Np, which is characterized by a more regular dependence of the photofission cross section on excitation energy than ²³⁸U, has been chosen for the first time as a reference nucleus. The measured cross sections as functions of energy show resonance structures in the vicinity of the fission threshold that are consistent with those previously observed in the energy dependences of fissilities for corresponding direct reactions. The partial-wave cross sections for the J ^π K = 1^?0, 1^?1, and 2⁺0 photofission channels have been determined as functions of energy. At energies below some 5.5 MeV, the total cross section for photofission of each plutonium isotope being studied receives a significant contribution from quadrupole interaction. Within the one-dimensional model of a two-humped fission barrier, the parameters of the barriers for ²³⁸Pu, ²⁴⁰Pu, and ²⁴²Pu have been extracted from data and have then been compared with estimates based on previous measurements.     

Commercial cyclotrons. Part I: Commercial cyclotrons in the energy range 10–30 MeV for isotope production

A survey of commercial cyclotrons for production of medical and industrial isotopes is presented. Compact isochronous cyclotrons which accelerate negative hydrogen ions in the energy range 10–30 MeV have been widely used over the last 25 years for production of medical isotopes and other applications. Different cyclotron models for the energy range 10–12 MeV with moderate beam intensity are used for production of ¹¹C, ¹³N, ¹⁵O, and ¹⁸F isotopes widely applied in positron emission tomography. Commercial cyclotrons with high beam intensity are available on the market for production of most medical and industrial isotopes. In this work, the physical and technical parameters of different models are compared. Possibilities of improving performance and increasing intensity of H^? beams up to 2–3 mA are discussed.     

Experimental results on40Ca(μ−,v μγ)40K* and16O(μ−,v μγ)16N**)

Photon spectra from radiative muon capture in doubly closed shell nuclei¹⁶O and⁴⁰Ca have been measured with a pairspectrometer. The⁴⁰Ca data agree with the most recent of the three previous experiments, for¹⁶O no other measurements exist. The comparison with theoretical calculations indicates that a careful treatment of the nuclear response function is required, ifg _P is to be determined from the data.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.     

Measurement of the $$^{232}$$ Th(n,f) cross section with quasi-monoenergetic neutron beams in the energy range 2–18 MeV

The European Physical Journal A - The E1 contribution to the capture reaction $$^7\mathrm {Li}(n,\gamma )^8\mathrm {Li}$$  is calculated at low energies. We employ a coupled-channel...