Proportional detector, counting rate

The spectrometer is set to the appropriate Bragg angle 0 of the requisite characteristic wavelength, and only these X-rays will reach the detector and be counted. The detector employed is the gas proportional counter, which can operate at much faster count rates than the EDS crystal detector. 

The central assumption of ion counting is that ions arrive at the detector at random, i.e., that the probability of arrival of an ion is the same for any time interval of a same length. The number , of ions i arriving at any collection device during the time interval dt is therefore subject to Poisson statistics , is proportional to 5t, the average count rate is n/8t, and its... 

The counting efficiency (e) of the proportional detector is calculated as the ratio of the net count rate, in s, to the activity (A), in Bq, of this standard radionuclide solution. The net count rate is the standard s gross count rate (RG) minus the detector s background count rate (RB). The reported disintegration rate (A) is the product of the radionuclide concentration, in Bq L 1, and the amount of counted sample, in L, adjusted for the radioactive decay of the radionuclide between standardization and measurement. Equation 2A.1 is the general form of this equation. 

In the correlation method the neutron flux density of the specified region is determined from the ratio of pulse measmement channel count rate to detector sensitivity s(E). If we assume that the neutron spectrum in the area of neutron detector location does not depend on the type of SRP being stored in the pit, then for all the measurements s(E) is a constant value. In the next calculations it can be assumed as 1 and thus, the coimt rate being measured can be assumed equal to the value of proportional neutron flux density. 

If the applied voltage is not too high, the size of the output pulse is proportional to the amount of energy deposited in the detector by the incoming radiation particle/ photon. (This is why the detector is called a proportional counter.) It is called a counter because the number of output pulses are counted by a counting system. The read-out can be either a total number of counts or a count rate (in cpm or cps). 

The count rate is a measure of the rate at which individual radiation particles/ photons cause pulses in the detector. For this reason, proportional counters can be used to determine the amount of radioactivity in a sample. The proportionality of the detector can be used to distinguish between different radiation energies of types of radiation, based on pulse size. 

The schematics of the instrument installation are shown in Fig. 9.13. The RADAIR instrument develops readouts on 4 continuous measuring channels of activity concentrations of artificial a, P, emitters and natural radon in Bq m and of the ambient y dose in pGy h. These activity concentration readouts are divided from countings in 1000 s cycles, of the activity deposited on the filter taken from samples of the surrounding air. The filter automatically advances after remaining 24 hours in front of the stack of two semiconductor detectors. The first detector located above the filter, delivers a net counting rate in proportion to the activity deposited on the filter. The... 

Proportional counter This radiation detector that produces a measurable amplified voltage pulse of height proportional to the energy of photons hitting it it gives a linear response at high counting rates. 

The efficiency increases with crystal size. The user should be aware, however, that when the detector volume increases, the background counting rate increases too. In fact, the background is roughly proportional to the crystal volume, while the efficiency increases with size at a slower than linear rate. Thus, there may be a practical upper limit to a useful detector size for a given experiment. 

Mulitwire proportional chambers (MWPC) have been developed for use as position-sensitive focal detectors for magnetic spectrometers. They can provide excellent position resolution, operate with counting rates as high as 10 counts/s, and provide a large solid angle at the focal plane of the spectrometer. 

In the most common type of fission counter, the interior surface of the detector is coated with a fissile isotope (Fig. 14.4). When fission takes place, one of the fission fragments (denoted as FFj in Fig. 14.4) is emitted toward the center of the counter and is detected. The other (FF2) stops in the fissile deposit or the wall of the counter. The counting rate of a fission counter is proportional... 

---