Quasifree Nucleon-Nucleon Bremsstrahlung at 197 MeV

Abstract

Quasifree nucleon-nucleon bremsstrahlung processes have been studied at 197 MeV by bombarding a target of liquid deuterium with a 90% polarized proton beam. A $\gamma$ detector gave the directions of photons of energy $E_{\gamma }>~40$ MeV; spark chambers triggered by large-area counters were used to determine the direction (s) and range (s) of the energetic charged particle(s) which emerged in coincidence with a $\gamma$ ray. Samples of events from three final states were extracted: (1) $p+d\to n_s+p+p+\gamma$; (2) $p+d\to p_s+d+\gamma$; (3) $p+d\to p+d+\gamma$. Events of type (1) exhibited angular distributions and a $\gamma$ spectrum in agreement with free $\mathrm{pp}\gamma$ results, while the cross sections were reduced by a factor of 0.50±0.10. Differential cross sections for reaction (2) were found to be reduced by a factor of 0.75±0.15 from the values predicted for the free capture reaction; the $\gamma$-ray asymmetries were in good agreement with predictions from deuteron photodisintegration; the branching ratio for the production of the $n-p$ system in the slightly unbound final state to that in the bound ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ final state was found to be 0.22±0.04. The cross section for reaction (3) was small, and its study was strongly limited by the detection thresholds of the spark chambers. Events from the reaction $p+d\to p_s+n+p+\gamma$ could not be identified with our apparatus, but they were the only other contributors to the coincidence rates between a $\gamma$ ray and a single charged particle. By subtracting the measured contributions from reactions (1)-(3) from them, we obtained differential cross sections for quasifree $n-p$ bremsstrahlung at three angles. We deduced cross sections for free $\mathrm{np}\gamma$ from them and found ${\sigma }_{\mathrm{np}\gamma }=35\mathrm{}\pm 12$ μb. This result implies a ratio $\frac{{\sigma }_{\mathrm{np}\gamma }}{{\sigma }_{\mathrm{pp}\gamma }}=50\mathrm{}\pm 20$.