Thermal background noise

The energies of the j8 particles from most /3 emitters are very low. This, of course, leads to low-energy photons emitted from the fluors and relatively low-energy electrical pulses in the PMT. In addition, photomultiplier tubes produce thermal background noise with 25 to 30°/o of the energy associated with the fluorescence-emitted photons. This difficulty cannot be completely eliminated, but its effects can be lessened by placing the samples and the PMT in a freezer at -5 to — 8°C in order to decrease thermal noise. 

There have also been recent improvements to reduce background noise, which is caused by random thermal motions of electrons in the detection coil and in the first amplifier range.15 Cryoprobes in which the coil and first amplifier are cooled to 30 K and the size of sample coil reduced lower electrical resistance and noise. A further benefit noted by Grivet et al.15 is that "the smaller the probe, the closer the conductors are to the sample and the higher the measure of the coil s [efficiency], as felt by the nuclei."... 

The thermal stability of a conductivity detector is of great importance. Effective thermostating is highly required, as the temperature greatly affects the mobility of ions and, therefore, conductivity. A 0.5-3% increase of conductivity is usually expected per degree Celsius. Close temperature control is necessary to minimize background noise and maximize sensitivity this is an especially important issue if nonsuppressed eluents are used. 

At a difference with thermal detectors, the background noise of photoconducting detectors is frequency-dependent. If it is assumed that the photoconductor is used to detect radiation at a frequency just above its cut-off frequency z/c, the detectors with a cut-off in the near IR display a much smaller background noise than those with a cut-off at lower energies. This is because in the near IR, the black body emissivity contribution at room temperature and below is very small. 

There are a number of sources of noise which must be considered in the design of an IR imager which uses a CCD readout. Apart from the pattern noise discussed in Section 6.1 which may result from responsivity variations, thermal dark current variations or clock noise feed through, there can be noise associated with the uniform background flux, noise associated with uniform thermal generation, noise associated with the input circuit used to put signal into the CCD, noise associated with signal transfer in the CCD and noise associated with readout from the CCD. 

The second background noise source is due to the spontaneous thermal movement of the electrical charged carriers across resistors, or... 

R Bennett. Applications of a modulated laser for FT-Raman spectroscopy. Part 2. Signal-to-noise enhancement and removal of thermal backgrounds. Spectrochim Acta 51A 2001—2009, 1995. 

It is to be noted that medical thermometer must measures to an accuracy of 0.1 °C. However non-invasive temperature measurement of inside a biological body is challenges and difficulties, especially for a microwave radiometer which measure thermal noise power, which is several orders of magnitude smaller than that of background noise since the system must operate at room temperature, not at liquid helium temperature like radio telescope. Moreover, it is expected to operate in a normal room (not in a shielded room). Therefore, the present target value of measurement accuracy of our system is 1 °C. 

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