microwell the motor 62 is supplied to lower the detector 40 along the z axis the amplitude of movement is known and the spacings are compensated by rings 92 and 94 the window 87 of the detector is centered on the microwell and all contamination of photons emitted by the adjacent microwells is removed the determination of the height of each well by the encoder associated with the motor 62 permits if necessary an individualized and tailored treatment for each well and the possible use of various plates of wells as well as a control of the presence of the wells measurement is carried out and the results acquired are processed and transferred into the associated memory for a paper printout and or an ultimate assay the detector having a low duration of remanance it is almost immediately ready for a new measurement the interval of time between two measurements is of the order of one second by way of example once the assembly of the microwells has been visited the detector is brought into alignment with the abutments 78 and lowered to bear against the storage well 80 a derivative control can be carried out by initiating the detector it suffices to light the lamp and to carry out a measurement of the photons emitted whose quantity is completely known it can be noted that the use of the type of compact and specific detector as indicated above leads to numerous advantages particularly the compactness the simplicity and hence the reliability the high.