How to measure half life of long lived radioactive isotopes such as 10^22 years?
Half life determination: Part 6
Determination of t1/2 ~10^22 years or more
Longest half life measured till date
There are several radioisotopes which decays very very slowly with half life of i.e. quintillion to septillion (10^18 - 10^24) years. It is very difficult to detect the rare decay events and generated signals out of their decay.
One of such radioisotope is alpha emitter 209Bi. The decay heat and light was trapped by using high sensitivity BGO (Bi4Ge3O12) scintillating and optical bolometer. The obtained t1/2 was 1.9 (± 0.2) × 10^19 years [De Marcillac, P. et al (2003)].
Half life of two-neutrino double beta decay (2β2ν) decay emitter 150Nd was estimated using Time Projection Chamber [Artemiev, V. et al (1991) ]. The estimated half life was 1.88(±0.19)× 10^19 years [Artemiev, V. et al (1995)].
So far longest half life measured till today directly was of 124Xe. It is weakly interacting massive particles (WIMPs) emitter. It decays by two neutrino double electron capture (2νECEC) process. This rare event was detected by XENON1T detector which uses 3.2 t of ultra-pure liquid xenon (LXe). Walls of the Time Projection Chamber (TPC) chamber was made of highly reflective polytetrafluoroethylene and was equipped with 248 photomultiplier tubes (PMTs).
TPC is used for the measurement of the scintillation and ionization signals generated by particle interactions. Ionization electrons are thereafter converted into light by means of proportional scintillation.Basically TPC is a gas/liquid field ionization chamber with applied electrical and magnetic field to measure the nature of the particle and particle’ momentum. The measured half-life of 124Xe was 1.8 × 10^22 years, which is highest ever half life measured in the lab till 2019 [XENON Collaboration (2019)].
Advantage
Experimentally determined half life value
Disadvantage
Sophisticated and costly instrumentation
ReferenceArtemiev, V. A., Brakchman, E. V., Ivanovsky, M. A., Karelin, A. K.,
Kirichenko, V. V., Knyazev, V. M., & Zeldovich, O. Y. (1991).
The 136Xe double-beta-decay track experiment. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 303(2), 309-322. Artemiev, V., Brakchman, E., Karelin, A., Kirichenko, V., Klimenko, A.,
Kozodaeva, O., ... & Zeldovich, O. (1995). Half-life measurement of
150Nd 2β2ν decay in the time projection chamber experiment. Physics Letters B, 345(4), 564-568. De Marcillac, P., Coron, N., Dambier, G., Leblanc, J., & Moalic, J.
P. (2003). Experimental detection of α-particles from the radioactive
decay of natural bismuth. Nature, 422(6934), 876-878. XENON Collaboration (2019). Observation of two-neutrino double electron capture in 124Xe with XENON1T." Nature 568, no. 7753: 532-535. |
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