Threshold Photoneutron Cross Section for<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">Be</mml:mi></mml:mrow><mml:mrow><mml:mn>9</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>

Berman, B. L.; Hemert, Rudy L. Van; Bowman, C.D.

doi:10.1103/physrev.163.958

Cited by 37 publications

(25 citation statements)

References 20 publications

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“…4.4 -4.8. Regarding the discrepancy in the t h e d neutron flux 19 and its effect on the fast neutron flux, the MCNP calculations compare well with the DORT calculations.…”

Section: Neutron Flux Resultssupporting

confidence: 58%

General purpose photoneutron production in MCNP4A

Gallmeier¹

1995

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This report has beer1 reproduced directly from the best available copy. LIST OF TABLES G1 G2 Nd= element identifier = number of protons in nucleus = number of protons and neutrons in nucleus = integer = electron = positron = neutron = neutron mass = energy of the photoneutron = photon = energy of photon = threshold energy of photoneutron production reaction = velocity of light = angle between photon and photoneutron fiight direction = photoneutron cross section = maximal value of the photoneutron cross section regarding the angle 8 = photoneutron crew section caused by a magnetic dipole transition = photoneutron cross section caused by a electric dipole transition = magnetic dipole moment of the proton = magnetic dipole moment of the neutron = nuclear magneton = classical deuteron radius = singlet scattering length of deuterium = triplet effective range of the potential for deuterium = reduced mass of the proton-neutron system = Planck's constant = magnitude of isotropic photoneutron direction = magnitude of anisotropic photoneutron direction = distance = activity = Wattenberg constant = effective Wattenberg constant = ratio of activity above threshold energy and total activity = density = number density = photoneutron source strength = reduction factor caused by self-shielding of photons in photoneutron sources = reduction factor caused by self-shielding of photoneutrons in photoneutron sources = mass ABSTRACT A photoneutron production option was implemented in the MCNP4A code, mainly to supply a tool for reactor shielding calculations in beryllium and heavy water environments of complicated three-dimensional geometries.Photoneutron production cross sections for deuterium and beryllium were created. Subroutines were developed to calculate the probability of photoneutron production at photon collision sites and the energy and flight direction of the created photoneutrons. These subroutines were implemented into MCNPQA. Some small program changes were necessary for processing the input to read the photoneutron production cross sections and to install a photoneutron switch. Some arrays were installed or extended to sample photoneutron creation and loss information, and output routines were changed to give the appropriate summary tables.To verify and validate the photoneutron production data and the MCNP4A implementations, the yields of photoneutron sources were calculated and compared with experiments. In the case of deuterium-based photoneutron sources, the calculations agreed well with the experiments; the beryllium-based photoneutron source calculations were up to 30% higher compand with the measurements. More accurate beryllium photoneutron cross sections would be desirable. To apply the developed method to a real shielding problem, the fast neutron fluxes in the heavy-water-filled reflector vessel of the Advanced Neutron Source reactor were investigated and compared with published DORT calculations. Considering the complete independence between the calculations, the merely 10 to 20% lower fluxes obt...

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“…4.4 -4.8. Regarding the discrepancy in the t h e d neutron flux 19 and its effect on the fast neutron flux, the MCNP calculations compare well with the DORT calculations.…”

Section: Neutron Flux Resultssupporting

confidence: 58%

General purpose photoneutron production in MCNP4A

Gallmeier¹

1995

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“…In order to describe the observed shape of the 1/2 + level, a connection has been made between the 9Be(7, n) and the 9Be(e, e') reactions in the following way. The (7, n) cross section for the excitation of an isolated level near threshold is written in the notation of [7] as a Breit-Wigner form ~,. where ,~= 1/k and k is the photon wave number, g =(2J + 1)/[2(21+ 1)] with J= 1/2 and I-3/2 for the excited state and ground state spins, respectively, and E R is the resonance energy.…”

Section: Inelastic Electron Scattering Spectramentioning

confidence: 99%

“…In particular, the measured spectra from inelastic proton scattering have been interpreted [4,5] as a three-body break-up of 9Be in terms of the Watson-Migdal final-state interaction formalism [6]. Other approaches simply use a Breit-Wigncr expression [7], an R-matrix formalism [3] or as published very recently [8] a single-particle potential model description for the shape and width of the 1/2 + level in 9Be. Incidentally, the nuclear structure aspect of the positive parity states in the p-shell [9][10][11][12][13] reflects itself in this level and its E 1-decay to the ground state for which e.g.…”

Section: Introductionmentioning

confidence: 99%

Line shape and excitation strength of the first excited state in9Be

Kuechler

Richter

Witsch

1987

Z. Physik A - Atomic Nuclei

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Dedicated to Professor Theo Mayer-Kuckuk on the occasion of his 60th birthdayThe line shape and the excitation strength of the very weak first excited J~= 1/2 + state at Ex= 1.684 MeV in 9Be has been investigated with high-resolution inelastic electron scattering at Eo=45 and 49 MeV and scattering angles 0=105% 117 ~ 129 ~ and 165% and with high-resolution inelastic proton scattering at E0=13 MeV and 0=15 ~ and 18 ~ Due to lying just above the neutron threshold the level has a strongly asymmetric line shape which in both experiments can be described consistently with a Breit-Wigner expression modified on the low energy side by the threshold behaviour of the cross section. The resonance energy is ER = 1.684_+ 0.007 MeV and the width F = 217 __ 10 keV in the c.m. system. A single particle potential model calculation reproduces the line shape and the resonance parameters fairly well. In addition, the inelastic electron scattering form factor has been measured. In the range of momentum transfers q = 0.24-0.46 fm-1 it is dominated by a 0P3/2 --" 1 $1/2 particle-hole transition. The transition is mainly longitudinal and of isoscalar nature with a strength of B(E1)T =0.027 _+0.002 e 2 fm 2, but a small M2 contribution of B(M2)T = 8.8_+ 1.5 #~ fm z has also been detected.

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“…The data of Berman et al exhibit the maximum cross section 1.6 mb at 6 keV above the n + 8 Be threshold (E t = 1.665 MeV) and decrease to 1.2 mb at 40 keV [28]. Parametrizing the photoneutron cross sections by σ γn = 1.6 exp(-4E) mb (E in MeV) with E = E γ -E t [13] resulted in the CF88 reaction rate N 2 A < ααn > as…”

Section: Resonances Of 9 Bementioning

confidence: 99%

“…Early measurements of photoneutron cross sections for 9 Be were carried out with monochromatic γ rays from radioactive isotopes [22,23,24,25,26] and with bremsstrahlung [27,28].…”

Section: Resonances Of 9 Bementioning

confidence: 99%

Astrophysical reaction rate for α(αn,γ)9Be by photodisintegration

et al. 2002

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We study the astrophysical reaction rate for the formation of 9 Be through the three body reaction α(αn, γ). This reaction is one of the key reactions which could bridge the mass gap at A = 8 nuclear systems to produce intermediate-to-heavy mass elements in alpha-and neutron-rich environments such as r-process nucleosynthesis in supernova explosions, s-process nucleosynthesis in asymptotic giant branch (AGB) stars, and primordial nucleosynthesis in baryon inhomogeneous cosmological models. To calculate the thermonuclear reaction rate in a wide range of temperatures, we numerically integrate the thermal average of cross sections assuming a two-steps formation through a metastable 8 Be, α + α ⇀ ↽ 8 Be(n,γ) 9 Be. Off-resonant and on-resonant contributions from the ground state in 8 Be are taken into account. As input cross section, we adopt the latest experimental data by photodisintegration of 9 Be with laser-electron photon beams, which covers all relevant resonances in 9 Be. Experimental data near the neutron threshold are added with γ-ray flux corrections and a new least-squares analysis is made to deduce resonance parameters in the Breit-Wigner formulation. Based on the photodisintegration cross section, we provide the reaction rate for α(αn, γ) 9 Be in the temperature range from T 9 =10 −3 to T 9 =10 1 (T 9 is the temperature in units of 10 9 K) both in the tabular form and in the analytical form for potential usage in nuclear reaction network calculations.The calculated reaction rate is compared with the reaction rates of the CF88 and the NACRE compilations. The CF88 rate, which is based on the photoneutron cross section for the 1/2 + state in 9 Be by Berman et al., is valid at T 9 > 0.028 due to lack of the off-resonant contribution. The CF88 rate differs from the present rate by a factor of two in a temperature range T 9 ≥ 0.1. The NACRE rate, which adopted different sources of experimental information on resonance states in 9 Be, is 4-12 times larger than the present rate at T 9 ≤ 0.028, but is consistent with the present rate to within ±20% at T 9 ≥ 0.1. 2

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Threshold Photoneutron Cross Section forBe9

Cited by 37 publications

References 20 publications

General purpose photoneutron production in MCNP4A

General purpose photoneutron production in MCNP4A

Line shape and excitation strength of the first excited state in9Be

Astrophysical reaction rate for α(αn,γ)9Be by photodisintegration

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