Meson exchange currents in neutron-proton bremsstrahlung

Journal Article · Tue Apr 15 04:00:00 EDT 2008 · Physical Review. C, Nuclear Physics

DOI:https://doi.org/10.1103/PHYSREVC.77.044001· OSTI ID:21189891

Yi, Li; Liou, M K; Schreiber, W M; Gibson, B F; Timmermans, R G. E. ^[1]

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1. College of Physics and Technology, Guangxi University, Nanning, Guangxi 530004 (China)

Background: The meson exchange current (MEC) contribution is important in the neutron-proton bremsstrahlung process (np{gamma}) when the two nucleon-scattering angles are small. However, our understanding of such effects is limited, and the reason why meson exchange current effects dominate the np{gamma} cross section has not been thoroughly investigated. Purpose: The primary focus of this investigation is to understand the origin of the MEC contribution, to identify the leading MEC amplitudes, and to comprehend why these MEC amplitudes dominate the np{gamma} cross sections. Method: We used a new method that combines the one-boson-exchange (OBE) approach with the soft-photon approach to define 10 different np{gamma} amplitudes. These amplitudes are used to calculate np{gamma} cross sections at 225 MeV for nucleon laboratory scattering angles lying between 12 deg. and 43 deg. The results of these calculations are then compared to investigate the meson exchange current effect in np{gamma}. Results: (i) The OBE amplitude M{sub np{gamma}}{sub ,{mu}}{sup PS} and the two-u-two-t special (TuTts) soft-photon amplitude M{sub np{gamma}}{sub ,{mu}}{sup TuTts} predict quantitatively similar np{gamma} cross sections. (ii) The MEC effect is found to be significant when the two nucleon-scattering angles are far from the elastic limit (45 deg.), but the effect is insignificant when the nucleon angles approach the elastic limit. (iii) The origin of the MEC effect and the leading MEC amplitudes have been identified in this investigation. Furthermore, the reason is now clear why the leading MEC amplitudes dominate the np{gamma} cross section when the nucleon-scattering angles are small. (iv) The contribution from the anomalous magnetic moments of the proton and the neutron is confirmed to be negligibly small. (v) In general, the theoretical cross sections using the amplitude M{sub np{gamma}}{sub ,{mu}}{sup PS}, or the amplitude M{sub np{gamma}}{sub ,{mu}}{sup TuTts}, are consistent with the triple differential cross sections recently measured at the Los Alamos National Laboratory. However, there exists an unexplained discrepancy between theory and experiment in some cases. Conclusions: The findings of this investigation have enhanced our understanding of the meson exchange current effect in np{gamma}. The comparative amplitude method introduced can be used for other bremsstrahlung investigations.

• OSTI ID: 21189891
• Journal Information: Physical Review. C, Nuclear Physics, Journal Name: Physical Review. C, Nuclear Physics Journal Issue: 4 Vol. 77; ISSN 0556-2813; ISSN PRVCAN
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
AMPLITUDES
BOSON-EXCHANGE MODELS
BREMSSTRAHLUNG
CURRENTS
DIFFERENTIAL CROSS SECTIONS
LANL
MAGNETIC MOMENTS
MEV RANGE
NEUTRONS
PHOTONS
PROTONS
SCATTERING