The ¹²C(π⁻,2γ)X reaction for stopped pions has been investigated at TRIUMF using two large Nal crystals (TINA and MINA) and two lead glass Cerenkov counters. A 20 MeV pion beam from the stopped π /μ channel (M9) was used. The incoming pion beam was defined by a 3-counter telescope (S₁,S₂,S₃) and was stopped in a 1.25 cm thick carbon target. The last telescope counter (S₃) determined the time of arrival of the pions. The four γ-detectors were located at +55°, +105°, -55°, and -135°, with respect to the incident pion beam. Scintillation counters were placed in front of each γ-detector in order to identify charged particles.
For the Nal crystals, time-of-flight information was used to separate neutrons and gammas originating from the (π⁻,nn) and (π⁻,nγ) reactions. Accidental coincidences from simultaneous (π⁻,γ) reactions generated by multiple pion stops in the target were rejected by measuring the energy deposited by the incoming pions in S₃.
A total of 2.5x10¹¹ pions were stopped, and after background subtraction, about 500 good events were observed at 6 different
opening angles (θ[sub γγ] = 50°, 80°, 110°, 120°, 160°, 170°). The total branching ratio for the ¹²C(π⁻,2γ) reaction was measured to be (1.2 ± 0.2)x0⁻⁵;
this value was found to be very sensitive to the low-energy threshold of
the Y~detectors. The good energy resolution (=10%) of the Nal crystals
permitted the investigation of the energy-sharing between the two photons
at θ[sub γγ] = 120°. The sum energy spectrum of the two photons peaks at 120 MeV
i
and has a width of about 40 MeV. Its shape indicates that most of the
available energy is carried off by the two photons and that the residual
nucleus, most likely ¹²B, is not highly excited.
Detailed theoretical calculations made by other authors predict
a total 2γ rate approximately 30% larger than our measured value. No
evidence for pion condensates or precondensate effects in ¹²C was found. / Science, Faculty of / Physics and Astronomy, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/21403 |
| Date | January 1979 |
| Creators | Mazzucato, Eddy |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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