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Search for the reaction /sup 40/Ca(. pi. /sup +/,. gamma gamma. ) at T/sub. pi. / = 50 MeV and critical opalescence

Conference ·
OSTI ID:5265364
; ;
We have searched for the inclusive process /sup 40/Ca(..pi../sup +/,..gamma gamma..) at T/sub ..pi../ = 50 MeV in order to look for nuclear critical opalescence in the double radiation capture. The reaction appeared to offer several advantages over others, including the high nuclear transparency of 50 MeV pions in a relatively heavy nucleus and the longitudinal coupling of the captured pion to the nucleus. The coincident ..gamma..-rays were detected in the arms of the LAMPF ..pi../sup 0/ spectrometer, which consists of active converters and multi-wire proportional chambers to locate the direction of the photons as well as total absorption lead glass counters to measured their energy. Backgrounds from the beam were reduced by demanding a positive signature of interaction in the target from four arrays of 10 scintillators each before and after the target. Data were acquired for momentum transfers of 140 MeV/c and 280 MeV/c and over the lowest 125 MeV of excitation of the final state. Theoretical estimates of the free cross section p(..pi../sup -/,..gamma gamma..)n are 23 nb/sr/sup 2/ in the experimental acceptance, a result which has been successfully linked to the measured /sup 12/C(..pi../sup -/,..gamma gamma..) stopping rate. Being an inclusive experiment at large momentum transfer, it was expected that the /sup 40/Ca(..pi../sup +/,..gamma gamma..) cross section would be some multiple of the free cross section. DWBA estimates of the cross section have been made in a relativistivic momentum space treatment. These calculations indicate the cross section should be 100 nb/sr/sup 2/. The preliminary result for 140 MeV/c shows no signal for the reaction at a 90% confidence limit of 32 nb/sr/sup 2/. The discrepancy between the calculations and the measurement possibly suggests a more complex reaction mechanism for in-flight radiative capture than for stopped capture.
Research Organization:
Los Alamos National Lab., NM (USA); Louvain Univ. (Belgium); North Carolina Univ., Chapel Hill (USA)
DOE Contract Number:
W-7405-ENG-36
OSTI ID:
5265364
Report Number(s):
LA-UR-82-1601; CONF-820828-2; ON: DE82018354
Country of Publication:
United States
Language:
English

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Related Subjects

651515 -- Nuclear Properties & Reactions
A=39-58
Theoretical-- Nuclear Reactions & Scattering-- (-1987)
651525* -- Nuclear Properties & Reactions
A=39-58
Experimental-- Nuclear Reactions & Scattering-- (-1987)
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ANGULAR DISTRIBUTION
CALCIUM 40 TARGET
CAPTURE
CHARGED-PARTICLE REACTIONS
CROSS SECTIONS
DISTRIBUTION
ELECTROMAGNETIC RADIATION
ENERGY RANGE
GAMMA RADIATION
GAMMA SPECTRA
HADRON REACTIONS
INCLUSIVE INTERACTIONS
INTERACTIONS
IONIZING RADIATIONS
MESON REACTIONS
MEV RANGE
MEV RANGE 10-100
NUCLEAR REACTIONS
PARTICLE INTERACTIONS
PION PLUS REACTIONS
PION REACTIONS
RADIATIONS
SPECTRA
TARGETS