Calibration of a liquid xenon detector with ${}^{83}\mathrm{Kr}{}^m$

We report the preparation of a ${}^{83}\mathrm{Kr}{}^m$ source and its use in calibrating a liquid xenon detector. ${}^{83}\mathrm{Kr}{}^m$ atoms were produced through the decay of ${}^{83}\mathrm{Rb}$ and introduced into liquid xenon. Decaying ${}^{83}\mathrm{Kr}{}^m$ nuclei were detected through liquid xenon scintillation. Conversion electrons with energies of 9.4 and 32.1 keV from the decay of ${}^{83}\mathrm{Kr}{}^m$ were observed. This calibration source will allow the characterization of the response of noble liquid detectors at low energies. ${}^{83}\mathrm{Kr}{}^m$ may also be useful for measuring fluid flow dynamics, both to understand purification in noble liquid-based particle detectors, as well as for studies of classical and quantum turbulence in superfluid helium.

Figure 1

Energy level diagram (in keV) for the ${}^{83}\mathrm{Rb}$ decay. Each ${}^{83}\mathrm{Rb}$ decays $75\%$ of the time to the long-lived isomeric ${}^{83}\mathrm{Kr}{}^m$ level 41.5 keV above the ground state, which subsequently decays in two steps, emitting a 32.1- and then a 9.4-keV conversion electron.

Figure 2

Photograph of apparatus for ${}^{83}\mathrm{Kr}{}^m$ measurement in liquid xenon.

Figure 3

Schematic of apparatus for ${}^{83}\mathrm{Kr}{}^m$ measurement in liquid xenon.

Figure 4

Calibration peak from ${}^{57}\mathrm{Co}$ $\gamma$ rays, indicating a signal yield of 11.1 pe/keV.

Figure 5

After sealing the ${}^{83}\mathrm{Kr}{}^m$ generator, a NaI detector confirms the decay of ${}^{83}\mathrm{Rb}$ within the generator. The black curve is a 511-keV $\gamma$-ray peak from ${}^{22}\mathrm{Na}$, the red curve is a 662-keV $\gamma$-ray peak from ${}^{137}\mathrm{Cs}$, and the blue curve is a peak due to 521-, 530-, and 553-keV $\gamma$ rays from ${}^{83}\mathrm{Rb}$ decaying in the ${}^{83}\mathrm{Kr}{}^m$ generator.

Figure 6

The gas handling system for the xenon detector. The ${}^{83}\mathrm{Kr}{}^m$ generator is attached to valves V1 and V4 of the main system and may be separately evacuated while the detector is in operation. Closing valve V7 and opening valves V1–V4 permits the ${}^{83}\mathrm{Kr}{}^m$ to be entrained in xenon flow into the detector.

Figure 7

Experimental ${}^{83}\mathrm{Kr}{}^m$ peaks measured with liquid xenon scintillation, corresponding to the 9.4- and 32.1-keV conversion electrons. Noise events create a non-Gaussian tail in the 9.4-keV peak below 5 keV, whereas above 38 keV a non-Gaussian tail is seen for the 32.1-keV peak due to 32.1- and 9.4-keV conversion electrons, which cannot be resolved.

Figure 8

The activities of both energy peaks after doping ${}^{83}\mathrm{Kr}{}^m$ into the liquid xenon detector. An exponential was fit to the coincidence trigger rate after it began to decay subsequent to the introduction of the ${}^{83}\mathrm{Kr}{}^m$. The standard root fitting routine was used. The red curve is the 32.1-keV conversion electron with a measured half-life of 1.856 $\pm$ 0.036 h, and the blue curve is the 9.4-keV conversion electron with a measured half-life of 1.846 $\pm$ 0.049 h. The decays of both peaks were consistent with the previously measured 1.83-h half-life of ${}^{83}\mathrm{Kr}{}^m$.

Figure 9

The half-life of ${}^{83}\mathrm{Kr}{}^{{\frac{7}{2}}^{+}}$ was measured to be $156.94\pm 0.32$ ns, in agreement with previous measurements.