The decay scheme of Kr⁸⁷

Abstract

Standard methods of scintillation spectroscopy were used to investigate the decay scheme of Kr⁸⁷. Natural krypton gas, containing 17 percent Kr⁸⁶, was irradiated in the 100 kilowatt V.P.I. research reactor to produce Kr⁸⁷ Which decays by beta emission to Rb⁸⁷. The halflife of Kr⁸⁷ was found to be 78 minutes in agreement with other investigators.

Gamma spectra and gamma-gamma coincidence measurements employed two integral line NaI(Tl) detectors with 3 in. diameter by 3 in. long crystals. Beta measurements were made using a 2 in. diameter by 1/2 in. long CaF₂(Eu) integral line detector.

Both the gamma spectrum and the beta spectrum were found to be complex. Energy values of 0.40, 0.85, 1.57, 1.75, 2.42, 2.97, and 3.30 MeV were assigned to excited states in Rb⁸⁷.

Possible parities and spins were assigned to most of the excited states from beta-ray log ft values. End-point energies of the beta groups populating the ground state and the first and second excited states were measured and used in conjunction with the gamma-ray energy measurements to calculate a value of 3.85 ±.04 MeV for the Kr⁸⁷ disintegration energy. Gamma-ray relative intensity measurements provided a percent abundance estimate of the beta groups populating the various Rb⁸⁷ energy levels.

Angular correlation measurements were performed for the 2.57 - 0.40 MeV gamma-gamma cascade proceeding from a level at 2.97 MeV. The results were consistent with log rt and shell model predictions and allowed a tentative assignment of 9/2⁺ to be made for this state. The ground state spin and parity or Kr⁸⁷ is inferred, on this basis, to be 7/2⁺.