Development of a C-14 detector and measurement of delta C-14 in dated tree rings grown in 1043 to 1055

A proportional counter was constructed from plastic scintillator for measuring the C-14 contents in dendrochronologically dated tree ringas. The tree rings were individually converted to methane which, at one atmosphere pressure, was used as the counter gas. The wall, being a scintillator, serves as the 4π anti-coincidence shell for rejection of natural radioactivity in the material housing the proportional counter and penetrating cosmic ray muons. The output of the proportional counter, which is in anti-coincidence with the scintillation is recorded with a pulse height analyzer. After background subtraction, it yields the beta-decay spectrum of C-14 in the methane-filled proportional counter. The count rate obtained from the 5.5 liter effective volume counter for each year's sample is then referenced to a standard traceable to the National Bureau of Standards, and after corrections due to isotopic fracionation are applied, the ΔC-14 for each sample is determined. The fluctuations in the ΔC-14 are inspected, and used as an estimate for the energy content in the γ-ray burst of the Crab Nebula in 1054 A.D. Fluctuations due possibly to solar flares, neutron flux, cosmic ray muons, and sample preparation restrict the energy estimate to an upper limit of less than or equal to 1050 ergs