Lazarus effect (physics)
The Lazarus effect (Lazarus Syndrome), the resuscitation ( "revival") of silicon - detectors at low temperatures .
In 1997, Vittorio Palmieri , Kurt Borer , Stefan Janos , Cincia Da Viá and Luca Casagrande from the University of Bern discovered that cooling down non-functional silicon particle detectors to temperatures below 130 K can restore them to a functional state. In other words, the “dead” detectors can be “reanimated” by such a process. In analogy to the biblical story, this phenomenon was called the " Lazarus effect" (resuscitation).
description
In semiconductor radiation detectors , the charge carriers ( electrons and defect electrons ) created by ionization are accelerated by an external electric field and the associated electric current is registered as a signal of the radiation passing through the detector. When using silicon detectors in environments with increased radiation exposure , the crystal lattice of the semiconductor results in both free charge carriers and lattice defects . The latter are caused by high-energy particles that interact with the lattice atoms as they pass through semiconductor material and thereby shift them out of their state of equilibrium in the crystal lattice. These disturbances are called vacancies and Interstitial refers to form in the detector material temporary traps ( English trap ) for free charge. The traps lead to a weakening of the signal; if the number is too large, the detector can no longer be used.
The explanation for the Lazarus effect lies in understanding the dynamics of radiation damage in the crystal lattice. At room temperature , such grid disturbances can briefly trap the charge carriers that have arisen. Interactions (e.g. lattice vibrations) can re-ionize the traps and the trapped charge carriers return to the conduction or valence band after a certain time . This time is usually longer than the characteristic readout time of the reading electronics , which measure the electrical charge after the high-energy particle has passed through. This leads to a weakening of the measured signal and thus to a lower signal-to-noise ratio (until the detector becomes too insensitive and therefore unusable). At temperatures lower than 130 K, the thermal vibrations of the grille are significantly weaker compared to room temperature. This increases the time (days to years, depending on the temperature and the disturbance) in which the trapped charge carriers are emitted back into the conduction band or into the valence band. Since occupied trapping points cannot catch any more load carriers, such a trapping point no longer leads to a weakening of the signal. This effect makes detectors with a high number of grid disturbances usable again.
literature
- Raising the dead detectors. In: CERN Courier. March 29, 1999 ( online ).
- Radiation hard silicon detectors lead the way. In: CERN Courier. January 1, 2003 ( online ).
Web links
Individual evidence
- ↑ Vittorio Giulio Palmieri, Kurt Borer, Stefan Janos, Cinzia Da Viá, Luca Casagrande: Evidence for charge collection efficiency recovery in heavily irradiated silicon detectors operated at cryogenic temperatures . In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment . tape 413 , no. 2–3 , 1998, pp. 475-478 , doi : 10.1016 / S0168-9002 (98) 00673-1 .