Es capture cross sections/Thermal cross sections and resonance integrals!Formation of ls,m Esand" 4 *Es AbstractIntegral neutron cross sections have been measured for 2S3 Es. The partial thermal capture cross sections and resonance integrals forming the 39.3-hour 2 S4m Es and the 276-day 2 54g Es relative to cobalt standards are reported. Analysis of alpha spectra in experiments measuring 254m Es formation gives σ^, = 178 ± 15 and / = 3750 ± 200 barns. Mass spectrographs analyses in experiments measuring 254g Es formation give a t h = 5.8 ± 0.7 and / = 114 ±7 barns.In this paper we describe the measurement of the neutron capture cross section of 253 Es. 253 Es captures neutrons to form the 39.3-hour isomer, 2S4m Es, as well as the 275.7-day ground state 254g Es. (See Fig. 2.) Because of the marked difference in the spin states of these two nuclides, no isomeric transition has been detected in the decay of 254m Es to form 254g Es. Thus, neutron capture in 2S3 Es to form 254g Es provides the only pathway to that isotope. Capture in 253 Es to form 254m Es has the consequence of lowering the 2S4g Es yield by burning out the 253 Es target.

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