Dead time

For detection systems that record discrete events, such as particle and nuclear detectors, the dead time is the time after each event during which the system is not able to record another event. An everyday life example of this is what happens when someone takes a photo using a flash - another picture cannot be taken immediately afterward because the flash needs a few seconds to recharge. In addition to lowering the detection efficiency, dead times can have other effects, such as creating possible exploits in quantum cryptography.

Overview

The total dead time of a detection system is usually due to the contributions of the intrinsic dead time of the detector (for example the drift time in a gaseous ionization detector), of the analog front end (for example the shaping time of a spectroscopy amplifier) and of the data acquisition (the conversion time of the analog-to-digital converters and the readout and storage times).

The intrinsic dead time of a detector is often due to its physical characteristics; for example a spark chamber is "dead" until the potential between the plates recovers above a high enough value. In other cases the detector, after a first event, is still "live" and does produce a signal for the successive event, but the signal is such that the detector readout is unable to discriminate and separate them, resulting in an event loss or in a so-called "pile-up" event where, for example, a (possibly partial) sum of the deposited energies from the two events is recorded instead. In some cases this can be minimised by an appropriate design, but often only at the expense of other properties like energy resolution.

Dead time (imprisonment)

Dead time is time spent institutionalized that does not count as credit toward the defendant's sentence. An example would be time spent confined in a mental hospital while the defendant is being restored to competency to stand trial. Halfway house time pending sentencing can also sometimes be dead time.

In the U.S., federal law provides that a defendant shall be given credit toward the service of a term of imprisonment for any time he has spent in official detention prior to the date the sentence commences (1) as a result of the offense for which the sentence was imposed; or (2) as a result of any other charge for which the defendant was arrested after the commission of the offense for which the sentence was imposed; that has not been credited against another sentence.

References

Dead Time

Dead Time can refer to:

See also