Photoneutron Cross Sections in 14N

1972 ◽  
Vol 50 (15) ◽  
pp. 1689-1696 ◽  
Author(s):  
R. W. Gellie ◽  
K. H. Lokan ◽  
N. K. Sherman ◽  
R. G. Johnson ◽  
J. I. Lodge
Keyword(s):  
Excited States ◽  
Cross Section ◽  
Cross Sections ◽  
Neutron Emission ◽  
Giant Resonance ◽  
Sequential Decay ◽  
Dipole Resonance ◽  
Intermediate States ◽  
Integrated Cross Section ◽  
High Degree

Photoneutron distributions from 14N have been obtained by time-of-flight methods, for bremsstrahlung end-point energies increasing in 2 MeV steps from 15.5 to 29.5 MeV. A large part of the neutron yield is associated with the sequential decay of 14N to 12C, through well-defined intermediate states of 13C, at 7.55, 8.86, and 11.80 MeV, which are unstable against neutron emission. The (γ,n0) cross section for neutron emission to the ground state of 13N is found to agree very closely with the corresponding (γ,p0) cross section, implying a high degree of isospin purity for the giant dipole resonance of 14N. It is observed that the decay of the giant resonance proceeds freely through those odd-parity excited states of the A = 13 nuclei which are single hole states formed by the removal of a p-shell nucleon from the parent 14N.The integrated cross section for all neutron-producing interactions is found to be 88 ± 5 MeV mb.

Photoneutrons from 20Ne

1975 ◽  
Vol 53 (8) ◽  
pp. 795-801 ◽  
Author(s):  
J. G. Woodworth ◽  
J. W. Jury ◽  
K. H. Lokan ◽  
N. K. Sherman
Keyword(s):  
Excited States ◽  
Cross Section ◽  
Ground State ◽  
Giant Dipole Resonance ◽  
Time Of Flight ◽  
Photon Absorption ◽  
Absolute Cross Section ◽  
Energy Distributions ◽  
Dipole Resonance ◽  
Integrated Cross Section

Photoneutron energy distributions from a target of liquid neon have been measured at 90° by time of flight for bremsstrahlung endpoint energies increasing in 1 MeV steps from 19 to 32 MeV. The differential ground state cross section for the major (91%) isotope 20Ne has been obtained, together with an estimate of the strength of transitions to excited states of 19Ne. Six photoneutron groups are observed, reflecting photon absorption which correlates excellently with existing photoproton data, although the absolute cross section is about 10% smaller.It is noted that the giant dipole resonance, estimated by combining the photoneutron and photoproton data, is centered at approximately 20 MeV, which is anomalously low, and that the integrated cross section up to 28 MeV exhausts only half of the dipole sum.

PHOTONEUTRON THRESHOLD AND CROSS SECTION FOR 71Lu175

1958 ◽  
Vol 36 (4) ◽  
pp. 415-418 ◽  
Author(s):  
H. J. King ◽  
L. Katz
Keyword(s):  
Cross Section ◽  
Neutron Yield ◽  
Giant Resonance ◽  
Threshold Energy ◽  
Half Width ◽  
Bremsstrahlung Energy ◽  
Resonance Cross Section ◽  
Integrated Cross Section ◽  
Peak Value

The neutron yield resulting from photoneutron reactions in Lu175 has been measured as a function of peak bremsstrahlung energy up to 23 Mev. The threshold energy for this reaction was found to be 7.77 ± 0.05 Mev. The giant resonance cross section has a peak value of 225 millibarns at 16 Mev., a half-width of 8.4 Mev., and an integrated cross section to 23 Mev. of 1.9 Mev-barns.

The 16O(p, γ)17F Direct Capture Cross Section with an Extrapolation to Astrophysical Energies

1975 ◽  
Vol 53 (17) ◽  
pp. 1672-1686 ◽  
Author(s):  
H. C. Chow ◽  
G. M. Griffiths ◽  
T. H. Hall
Keyword(s):  
Elastic Scattering ◽  
Excited States ◽  
Cross Section ◽  
Cross Sections ◽  
Capture Cross Section ◽  
Scattering Cross Section ◽  
Scattering Data ◽  
Capture Cross ◽  
Scattering Cross ◽  
Elastic Scattering Cross Section

The cross section for the direct radiative capture of protons by 16O has been measured relative to the proton elastic scattering cross section for energies from 800 to 2400 keV (CM). The elastic scattering cross section was normalized to the Rutherford scattering cross section at 385.5 keV. The capture cross section for the reaction 16O(p,γ)17F, which plays a role in hydrogen burning stars, has been extrapolated to stellar energies using a theoretical model which gives a good fit to the measured cross sections. The model involves calculation of electromagnetic matrix elements between initial and final state wave functions evaluated for Saxon–Woods potentials with parameters adjusted to fit both elastic scattering data and binding energies for the ground and first excited states of 17F. Cross sections for capture to the 5/2+ ground and 1/2+ first excited states of 17F in terms of astrophysical S factors valid for energies ≤ 100 keV have been found to be: S5/2+ = (0.317 + 0.0002E) keV b (± 8%); S1/2+ = (8.552 − 0.353E + 0.00013E2) keV b (± 5%).

Giant dipole resonance in 4He

1980 ◽  
Vol 58 (11) ◽  
pp. 1555-1559 ◽  
Author(s):  
J. J. Bevelacqua
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Giant Dipole Resonance ◽  
Reasonable Agreement ◽  
Center Of Mass ◽  
Nucleon Nucleon ◽  
Nucleon Interaction ◽  
R Matrix ◽  
Dipole Resonance ◽  
Nucleon Nucleon Interaction

The 4He giant dipole resonance is calculated with the generalized R-matrix method of Lane and Robson. The model treats the center of mass correctly and includes noncentral components in the nucleon–nucleon interaction via the Sussex interaction. The 4He(γ,p)3H and 4He(γ,n)3He cross sections are sensitive to the 4He level spectrum, but are in reasonable agreement with the photonuclear data for level schemes which agree with the spectrum suggested by Fiarman and Meyerhof (FM). Other spectra which bracket the FM levels lead to poorer photonuclear cross sections. R-matrix model results also lead to a (γ,p)/(γ,n) cross section ratio which is about unity.

The 1 s -2 s excitation of hydrogen atoms by electron impact

1960 ◽  
Vol 258 (1293) ◽  
pp. 245-250 ◽  
Keyword(s):  
Electron Impact ◽  
Cross Section ◽  
Cross Sections ◽  
Born Approximation ◽  
Impact Excitation ◽  
Electron Impact Excitation ◽  
Hydrogen Atoms ◽  
Third Order ◽  
The Third ◽  
Intermediate States

The expression for the cross-section obtained from the second Born approximation by including only terms to the third order in the interaction energy is employed to calculate cross-sections for the electron impact excitation of the 2 s level of atomic hydrogen, allow­ance being made for distortion and polarization due to the 1 s , 2 s and 2 p 0.± 1 intermediate states. These cross-sections are compared with the available experimental data.

Hadron reactions study with the CMD-3 detector in e+e− collisions

2016 ◽  
Vol 31 (33) ◽  
pp. 1630038
Author(s):  
E. P. Solodov ◽  
A. N. Amirkhanov ◽  
A. V. Anisenkov ◽  
V. M. Aulchenko ◽  
V. S. Banzarov ◽  
...  
Keyword(s):  
Energy Range ◽  
Invariant Mass ◽  
Energy Dependence ◽  
Cross Section ◽  
Cross Sections ◽  
Final States ◽  
Preliminary Results ◽  
Mass Distributions ◽  
Electron Positron ◽  
Intermediate States

The CMD-3 detector has been taking data since December 2010 at the VEPP-2000 electron–positron collider. The collected data sample corresponds to about 60 inverse picobarn of integrated luminosity in the c.m. energy range from 0.32 GeV to 2.0 GeV. Preliminary results of the analysis of various hadronic cross-sections, in particular, [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], 3[Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] are presented. The processes with multi-hadron final states have several intermediate states which have to be taken into account to correctly describe the angular and invariant mass distributions, as well as cross-section energy dependence.

PHOTONEUTRON CROSS SECTIONS IN SILICON AND CALCIUM

1953 ◽  
Vol 31 (1) ◽  
pp. 70-77 ◽  
Author(s):  
R. G. Summers-Gill ◽  
R. N. H. Haslam ◽  
L. Katz
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Neutron Yield ◽  
Threshold Energy ◽  
Threshold Effect ◽  
Monitoring Method ◽  
Dose Monitoring ◽  
Γ Rays ◽  
Integrated Cross Section ◽  
Peak Value

Using the dropping apparatus and dose monitoring method previously reported, the cross sections for the reactions Si28(γ, n)Si27 and Ca40(γ, n)Ca39 have been measured by detecting positron activities in the residual nuclei. The Si28(γ, n)Si27 cross section has a peak value of 21 mbarns at 20.9 Mev. and an integrated cross section to 24 Mev. of 0.070 Mev-barns. The threshold energy is 16.9 ± 0.1 Mev. The Ca40(γ, n)Ca39 cross section has a peak value of 15 mbarns at 19.3 Mev. and an integrated cross section to 24 Mev. of 0.065 Mev-barns. The threshold is 15.8 ± 0.1 Mev.A comparison of our results with the neutron yield measurement of Price and Kerst at 18 and 22 Mev. gives good agreement. A further comparison with the neutron yield work of Baldwin and Elder is made.The sharp discontinuity in (γ, n) yields using lithium γ rays observed by Wäffler and Hirzel is explained as a threshold effect. Integrated cross sections increase more or less smoothly with Z.In addition, improved values for the half-lives of the residual nuclei Si27 and Ca39 have been measured. These are 4.45 ± 0.05 and 1.00 ± 0.03 sec. respectively.

A MODEL OF COLUMNAR JOINTING

2012 ◽  
Vol 22 (02) ◽  
pp. 1150006 ◽  
Author(s):  
MATHIAS JUNGEN
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Fracture Process ◽  
Variational Model ◽  
Minimal Energy ◽  
Rigorous Derivation ◽  
Basalt Flow ◽  
Columnar Jointing ◽  
Schwarz Symmetrization ◽  
High Degree

We propose to use nonlinear elasticity to model the propagation of cracks in cooling lava. In particular, our work aims to understand the enigmatic fracture process that leads to the formation of column joints. Column joints are plane fracture surfaces fragmenting a basalt flow into prismatic columns. These columns are characterized by their polygonal cross-section and usually exhibit a strikingly high degree of regularity. We present a variational model with the assumption that the fracture process seeks to minimize the total energy of the system. The expression for the elastic energy is simplified and the configuration of minimal energy is analytically determined by a rigorous derivation. Further, we study the behavior of the energy under Steiner and Schwarz symmetrization of the column cross-section. In particular, we prove that the minimum of the energy among all possible convex and bounded column cross-sections B ⊂ ℝ2 is attained when B is the two-disk. Our results thus give strong evidence supporting the conjecture that the minimal energy is attained for a regular hexagon when the column cross-section is further required to tile the plane.

scholarly journals High Resolution Laser Techniques Applied to Reaction Dynamics

1991 ◽  
Vol 11 (3-4) ◽  
pp. 177-186 ◽  
Author(s):  
Raymond J. Vetter
Keyword(s):  
High Resolution ◽  
Excited States ◽  
Cross Section ◽  
Cross Sections ◽  
Differential Cross ◽  
Single Mode ◽  
Light Polarization ◽  
Saturation Regime ◽  
Laser Techniques ◽  
Hyperfine Structures

The applications of high resolution laser techniques to crossed-beam experiments which are examined in this paper concern: (a) the reactivity of atomic/molecular excited states and the influence of light polarization and (b) the measurement of absolute and differential cross sections by use of the laserinduced fluorescence technique performed in a coherent saturation regime.Examples are provided by the crossed-beam study of the Cs(7P) + H2→CsH + H photochemical reaction, where two C.W. single-mode tunable lasers are used to excite Cs atoms and to probe CsH product molecules. It is shown how the fine and hyperfine structures of the Cs atom are involved in the reaction mechanism (harpooning). The measurement of the total cross section (≈4.10−16cm2) gives an indication of the overall efficiency of the reactive process (Cs atoms in the 7P state) with respect to the quenching ones (Cs atoms in 6S, 6P, 5D and 7S states). Finally, the differential cross section shows a marked forward “peaking” of CsH products which narrows with collision energy but which is rather independent of the product rotation.

THE MEASUREMENT OF PHOTONUCLEAR CROSS SECTIONS IN ISOTOPES LEADING TO SHORT-LIVED DECAY PRODUCTS

1952 ◽  
Vol 30 (3) ◽  
pp. 257-269 ◽  
Author(s):  
R. N. H. Haslam ◽  
R. G. Summers-Gill ◽  
E. H. Crosby
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Half Life ◽  
Half Width ◽  
Reaction Threshold ◽  
Parent Materials ◽  
Dosage Rate ◽  
Decay Products ◽  
Integrated Cross Section ◽  
Peak Value

A dropping apparatus, including a new means of dosage rate monitoring, has been designed to allow the observation of short-lived activities produced by betatron irradiation of various parent materials. The photonuclear cross section for the reaction S32(γ, n)S31 has been measured by this means. The cross section has a peak value of 24.6 millibarns at 20.1 ± 0.5 Mev., a half width of 4.5 Mev., and an integrated cross section of 0.12 Mev-barns. The reaction threshold was found to be 15.0 ± 0.1 Mev. The experiment has also yielded a new half life for S31 − 2.66 ± 0.03 sec.

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