Photon multiplier

An incident ion beam causes secondary electrons to be emitted which are accelerated onto a scintillator (compare this with the operation of a TV screen). The photons that are emitted (like the light from a TV screen) are detected not by eye but with a highly sensitive photon detector (photon multiplier), which converts the photon energy into an electric current. 

A further widely used multiplier is the photon multiplier. In this case the ions (positive or negative) elicit secondary ions formed by a conversion dynode, which are further accelerated towards a phosphorescent screen where they undergo conversion into photons detected by a photomultiplier (Fig. 1.34). 

Fig. 1.34 In the photon multiplier detector ions are transformed into photons which are detected by a photomultiplier.

To calculate equation (14) correctly, the structure factor magnitudes must be expressed on the absolute scale, that is, relative to the scattering factor of a single electron under the same conditions. In practice, the observed //, and hence Fhki obs values are on an arbitrary scale, depending on the crystal size, primary beam flux, photon-multiplying effect of the counter, and so on, which are in practice impossible to estimate. The scale factor K, required to bring Fhki obs to the absolute scale, can be found by means of a so-called Wilson plot, 2i gives also the overall temperature factor B (see below) of the stmcture... 

The detector converts ions of a given m/z value into a measurable electrical signal whose intensity is proportional to the corresponding ion current. With beam instruments (sectors, quadrupoles, or TOF analyzers) and the quadru-pole ion trap, the ions are first separated according to their m/z value before detection, usually by an electron multiplier or a photon multiplier. The operation of these most common detectors is briefly outlined below. 

Photon multiplier detector. (Reproduced from Ref. 3 with permission of John WQey Sons)... 

Equation (2.65) implies that if the signal-to-noise power ratio is unity, then the minimum detectable power is just the energy of a photon multiplied by twice the measurement bandwidth and divided by the quantum efficiency. For any real... 

S. Kinishita, T. Kushida High performance time-correlated single photon counting apparatus, using a side-on type photon multiplier. Rev. Sci. Instrum. 53, 469 (1983)... 

The isc efficiency is the percentage of the number of absorbed photons that actually yields a triplet state, whereas the et efficiency is the percentage of the number of triplet-state ligands that transfer their energy onto the lanthanide ion. The product is thus the number of triplets formed per absorbed photon multiplied by the number of transfers from a triplet onto the lanthanide per triplet formed, which results in the number of transfers from a triplet onto the lanthanide per photon absorbed by the ligand. 

A Hewlett-Packard HP5973 mass spectrometer equipped with a photon multiplier was used for determination of accurate mass and recording of mass spectra. Unless stated otherwise, the molecular ion was generated via Electron Impact (El). The following abbreviation was used ... 

We now consider a beam of radiation, intensity I(o)), uniformly filling the solid angle do. The power absorbed from this beam by one atom is given by the energy of one photon multiplied by the transition probability ... 

The energy absorbed from the beam as it passes through the volume-element is given by the energy of one photon multiplied by the number of upward transitions occurring in the time interval dt. If there are atoms per unit volume in the level i we have... 

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