Neutron production in the interaction of 2-GeV protons with nuclei

The double-differential cross sections for neutron production in the interactions of 2-GeV protons with Be, Al, Cu, Cd, and Pb nuclei were measured by the time-of-flight method in the region of angles larger than 30°. The respective experimental data are analyzed within the phenomenological model of four moving sources, including those associated with neutron emission in primary nucleon-nucleon collisions, the decay of a hot source (fireball), the multifragmentation process, and the deexcitation of nuclear fragments via neutron evaporation. Temperature-parameter values are universal for all sources and are virtually independent of the target nucleus and of the projectile energy in the region above 0.5 GeV. It is found that, for all of the above reactions, the relative contribution to the mean neutron multiplicity from the decay of a hot source and multifragmentation is about 41%.     

Fission cross sections of medium-weight and heavy nuclei induced by 1 GeV protons

Coincidence studies performed in 4π geometry with silicon detectors and parallel plate avalanche counters have been used to measure total fission cross sections of²³⁸U,²³²Th,²⁰⁹Bi,²⁰⁸Pb,¹⁹⁷Au,^natYb,^natHo,^natTb,^natSm,^natTe,^natAg and^natNi nuclei induced by 1 GeV protons. The experimental results agree qualitatively with cascade-evaporation calculations.     

Total cross sections for fission of heavy nuclei by intermediate-energy protons

The results of measuring total cross sections for proton-induced fission of ^natPb, ²⁰⁹Bi, ²³²Th, ²³³U, ²³⁵U, ²³⁸U, ²³⁷Np, and ²³⁹Pu nuclei at proton energies from 200 to 1000 MeV are reported. The measurements were carried out in steps of ≈100 MeV. Complementary fission fragments were detected in coincidence by two parallel-plate avalanche gas counters placed in the beam line on both sides of the thin target close to it. Energy and isotope dependences of the fission cross sections are analyzed.     

Elastic scattering of 1-GeV protons by nuclei

The calculated elastic scattering of 1.04-GeV protons by ²⁰⁸Pb, ⁵⁸Ni, and ⁴⁰Ca is compared with experiment. The effects of the spin-orbit potential, Pauli and short-range correlations, variations in the ratio of the real to the imaginary part of the nucleon-nucleon scattering amplitude at 0° are found to have similar effects. Further experiments are required before these effects can be disentangled. Changes of the neutron density compared to the proton density can be distinguished. The proton polarization by elastic scattering by ²⁰⁸Pb and ⁴⁰Ca is calculated omitting the effects of correlations.     

Systematization of cross sections for the production of residual nuclei on separated tin isotopes in reactions induced by various-energy protons

Cross sections for the production of residual nuclei on the isotopes ^{112,118,120,124}Sn irradiated with 0.66-, 1.0-, 3.65-, and 8.1-GeV proton beams were investigated. A ten-parameter semiempirical formula was used to systematize the cross sections in question. A comparative analysis of parameter values obtained at different proton energies was performed.     

Measurement and simulation of the cross sections for nuclide production in 93Nb and natNi targets irradiated with 0.04- to 2.6-GeV protons

The cross sections for nuclide production in thin ⁹³Nb and ^natNi targets irradiated by 0.04- to 2.6-GeV protons have been measured by direct γ spectrometry using two γ spectrometers with the resolutions of 1.8 and 1.7 keV in the ⁶⁰Co 1332-keV γ line. As a result, 1112 yields of radioactive residual nuclei have been obtained. The ²⁷Al(p, x)²²Na reaction has been used as a monitor reaction. The experimental data have been compared with the MCNPX (BERTINI, ISABEL), CEM03.02, INCL4.2, INCL4.5, PHITS, and CASCADE07 calculations.     

Measurement and simulation of the cross sections for nuclide production in natW and 181Ta targets irradiated with 0.04- to 2.6-GeV protons

The cross sections for nuclide production in thin ^natWand ¹⁸¹Ta targets irradiated by 0.04–2.6-GeV protons have been measured by direct γ spectrometry using two γ spectrometers with the resolutions of 1.8 and 1.7 keV in the ⁶⁰Co 1332-keV γ line. As a result, 1895 yields of radioactive residual product nuclei have been obtained. The ²⁷Al(p, x)²²Na reaction has been used as a monitor reaction. The experimental data have been compared with the MCNPX (BERTINI, ISABEL), CEM03.02, INCL4.2, INCL4.5, PHITS, and CASCADE07 calculations.     

Measurement and simulation of the cross sections for nuclide production in 56Fe and natCr targets irradiated with 0.04- to 2.6-GeV protons

The cross sections for nuclide production in thin ⁵⁶Fe and ^natCr targets irradiated by 0.04–2.6-GeV protons are measured by direct γ spectrometry using two γ spectrometers with the resolutions of 1.8 and 1.7 keV for the ⁶⁰Co 1332-keV γ line. As a result, 649 yields of radioactive residual product nuclei have been obtained. The ²⁷Al(p, x)²²Na reaction has been used as a monitor reaction. The experimental data are compared with the MCNPX (BERTINI, ISABEL), CEM03.02, INCL4.2, INCL4.5, PHITS, and CASCADE07 calculations.     

Collinear three-body disintegrations of tungsten nuclei by 1-GeV protons

The (2E, 2V) measurement method is applied to analyze the kinematics of the separation of two complementary collinear fragments of the disintegration of tungsten nuclei by 1-GeV protons. In addition to the main process of binary fission, three branches of collinear three-body disintegration, which are associated with various mechanisms of the excitation of a deformed fissioning nucleus, are observed.     

Investigation of semicoherent interactions of 1-GeV protons with silicon

An experiment on studying the ²⁸Si(p, p′ γ ₀ X)²⁴Mg semicoherent reaction is carried out at the MAG setup on the 1-GeV proton beam of the U-10 ITEP accelerator. Two particles, proton and γ-ray photon, which accompanies the transition of the ²⁴Mg* nucleus from the first excited state to the ground state, are detected. When the events with the proton emission angle from 3° to 6.5° are selected, the following four processes are observed: the direct knockout of a nuclear α cluster by a proton, the formation of a _ΔSi isobaric nucleus, the formation of a Δ₁₂₃₂ isobar, and the production of a π ⁰ meson at rest in the nuclear coordinate system. The cross sections for the indicated processes are obtained.     

Measurement and simulation of the cross sections for the production of 148Gd in thin natW and 181Ta targets irradiated with 0.4- to 2.6-GeV protons

The cross sections for the production of ¹⁴⁸Gd in ^natW and ¹⁸¹Ta targets irradiated by 0.4-, 0.6-, 0.8-, 1.2-, 1.6-, and 2.6-GeV protons at the ITEP accelerator complex have been measured by direct α spectrometry without chemical separation. The experimental data have been compared with the data obtained at other laboratories and with the theoretical simulations of the yields on the basis of the BERTINI, ISABEL, CEM03.02, INCL4.2, INCL4.5, CASCADE07, and PHITS codes.     

Volume reflection of 1-GeV protons by a bent silicon crystal

The volume reflection of 1-GeV protons by a bent crystal has been observed. The crystal is made of single crystal silicon. The (111) atomic planes are bent owing to the elastic quasimosaicity effect, which makes it possible to reduce the crystal length for a beam to 30 μm. It is found that the probability of the reflection effect is higher than the probability of the channeling effect (0.71 vs. 0.63), and the deflection angle of the protons reflected inside the crystal is equal to 1.39 ± 0.04 in terms of the critical angle for channeling under the conditions of the experiment (170 μrad). The width of the reflected peak is equal to 1.76 ± 0.04 in the same units. The protons that are not involved in channeling at the angular position of maximum channeling undergo volume reflection and are deflected in the direction opposite to the channeled beam by the angle 1.01 ± 0.05 in terms of the critical angle for channeling. The width of the reflected peak is equal to 1.94 ± 0.08 in the same units. Original Russian Text ? Yu.M. Ivanov, N.F. Bondar’, Yu.A. Gavrikov, A.S. Denisov, A.V. Zhelamkov, V.G. Ivochkin, S.V. Kos’yanenko, L.P. Lapina, A.A. Petrunin, V.V. Skorobogatov, V.M. Suvorov, A.I. Shchetkovsky, A.M. Taratin, W. Scandale, 2006, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2006, Vol. 84, No. 7, pp. 445–450.     

Production cross sections for the heaviest nuclei in complete fusion reactions induced by heavy ions

Production of the heaviest nuclei in complete fusion reactions induced by heavy ions has been considered in a systematic way in the framework of the conventional barrier passing model coupled with the statistical model. Available data on excitation functions for fission and production of evaporation residues (ER) in very asymmetric combinations induced by ions lighter than Ne on actinide target nuclei are described rather well in the framework of these models. The data allow one to adjust model parameters and to reveal the quasi-fission effect caused by the interaction with deformed target nuclei, which is manifested in the suppression of the ER production at sub-barrier energies. For reactions induced by Mg and heavier projectiles, quasi-fission is starting to suppress fusion (ER production) at energies above the Coulomb barrier. One has to introduce empirically the quantity of the fusion probability P_fus to reproduce the ER excitation functions in the framework of the conventional approach. The exponential dependence of P_fus on the combined fissility parameter (a similar parameter that was introduced for the extra-push energy scaling) was found in search for scaling for the P_fus values resulting from the data analysis.     

Differential cross sections for excitation of atomic hydrogen by protons

Calculations are presented for the differential cross section for the excitation of atomic hydrogen to the (2s + 2p) level by protons at 50, 100 and 150 keV, employing a close-coupling pseudo-state model. Good agreement is obtained with the recently published data.     

Isotopic production cross sections of residues in reactions induced by relativistic heavy ions with protons and deuterons

The isotopic production cross sections of heavy residues in relativistic heavy-ion collisions have been investigated in inverse kinematics. The primary reaction products were fully identified in mass and atomic number prior to beta decay using the fragment separator FRS. The huge collection of data obtained helps in the understanding of the two main reaction mechanisms involved: fragmentation and fission. These data provide basic information for future radioactive ion beam facilities and for technical applications like intense neutron sources by means of spallation targets.     

Absolute excitation cross sections for the 41 S-, 41 D- and 31 P-levels of helium excited by fast protons

We have measured absolute cross sections for proton excitation of the 3¹ P-,4¹ S- and 4¹ D-levels of He in the energy range from 200 keV to 1 MeV. Calibration with a tungsten lamp mounted in the collision chamber and normalization on the high energy first Born approximation 3¹ P values for protons and electrons were used to obtain absolute data. At 1 MeV the experimental results agree within 10% with the first Born approximation values.     

Cross sections of the interactions of He nuclei with protons

⁴He-p collisions at two values of⁴He momenta 8.6 GeV/c and 13.6 GeV/c as well as the³He-p collisions at 13.5 GeV/c have been studies using the one-meter JINR hydrogen bubble chamber. Total, elastic, topological and reaction cross sections have been measured. The cross sections have been determined on a sample of minimum biased events.     

Quasielastic channel of single-stage nuclear fission induced by 1-GeV protons

Experimental indications that there exists single-stage fission of ²³⁸U and ²³²Th nuclei that is induced by a nearly transverse flux of intranuclear nucleons are obtained from an experiment that employs a two-arm time-of-flight spectrometer exposed to a beam of 1-GeV protons. A nearly transverse flux of mean multiplicity about 10 to 15 nucleons is initiated by a recoil nucleon of mean momentum about 240 MeV/c in the quasielastic scattering of an incident proton.     

Formation of 24Mg* in the spallation of 28Si nuclei by 1-GeV protons

The ²⁸Si(p, p′γ₀ X)²⁴Mg reaction has been studied at the ITEP accelerator by the hadron-gamma coincidence method for a proton energy of 1 GeV. Two reaction products are detected: a 1368.6-keV γ-ray photon accompanying the transition of the ²⁴Mg* nucleus from the first excited state to the ground state and a proton p′ whose momentum is measured in a magnetic spectrometer. The measured distribution in the energy lost by the proton in interaction is attributed to five processes: the direct knockout of a nuclear α cluster, the knockout of four nucleons with a total charge number of 2, the formation of the _ΔSi isobaric nucleus, the formation of the Δ isobar in the interaction of the incident proton with a nuclear nucleon, and the production of a π meson, which is at rest in the nuclear reference frame. The last process likely corresponds to the reaction of the formation of a deeply bound pion state in the ²⁸P nucleus. Such states were previously observed only on heavy nuclei. The cross sections for the listed processes have been estimated.