Coincidence gate

Figure 23.11. Exclusive OR and coincidence gates. From S. P. Perone and D. O. Jones, Digital Computers in Scientific Instrumentation,...

A block diagram of the electronic circuitry components of the LSM-1 is reprinted in Figure 10 by the permission of Nuclear Enterprises, Inc. The photomultiplier tubes are matched EMI 9805a, 2 inches in diameter, contain low potassium glass, are of Venetian blind design, with a 40 nanosecond coincidence gate. 

Fig. 12. MicroChannel plate detector count rate vs. delay of coincidence gate (see delayed gate of Fig. 11).

Initial evidence linking Hebb s coincidence detection rule to learning and memory. As the unique receptor in the brain with the coincidence-detection property, the NMDA receptor is an ideal candidate to gate the formation of memory at the synaptic level. Early observations demonstrated that infusion of NMDA receptor blockers into brain ventricles resulted in animals poor performance in the hidden-platform water maze. At first, this seemed to provide evidence for the role of hippocampal LTP in memory formation. Unfortunately, careful analyses revealed that poor performances in the water maze tests... 

With the LS-5B instrument, the printing of the sample photomultiplier can be delayed so that it no longer coincides with the flash. When used in this mode, the instrument measures phosphorescence signals. Both the delay of the start of the gate (tA) and the duration of the gate (t ) can be selected in multiples of lOps from the keyboard. Delay times may be accurately measured, by varying the delay time and noting the intensity at each value. 

The luminescence spectrum of the Canada apatite contains the yellow band, which is similar to Mn + emission in the Ca(II) site (Fig. 5.71). Nevertheless, this band has short decay time, which is not suitable for strictly forbidden d-d transitions in Mn +. It dominates in the time-resolved spectrum with a delay of 10 ps and gate of 100 ps when the shorter-lived centers are quenched, while the longer-Hved ones are not detected. A change in the lifetime may be indicative of the energy transfer from Mn + by a radiationless mechanism. A condition necessary for this mechanism is coincidence or a close distance between energy level pairs of the ion sensitizer and the ion activator. Here, the process of luminescence is of an additive nature and a longer duration and greater quantum yield of the activator luminescence accompany a reduced... 

We use the standard model [18, 19, 20] for Fermi-liquid leads adiabatically connected to the wire. We assume that the action (3) is applicable for x < L only. At large x the interaction strength K(x—y), Eq. (1), is zero. This model can be interpreted as a quantum wire with electron interaction completely screened by the gates near its ends. Electric fields of external charges are assumed to be screened in all parts of the wire. A simple modification of this model describes electrically neutral leads [20]. All results coincide for our set-up and the model [20]. 

The residence time was determined for our neutron counter by measuring the time intervals between beta start signals and neutron stop signals. With a residence half-time of 11 ms and a coincidence resolving time of 40 ms. 92 of the true coincidence events were included. The fraction of true events not detected does not influence the present results because we normalize the Pn measurements to a known Pn value measured under identical conditions. The coincidence rate was measured by a simple overlap coincidence module where the beta pulse Input was stretched to 40 ms by a gate and delay generator. To measure the accidental coincidence rate, the same beta pulse was sent to a second coincidence module and overlapped with neutron pulses which had been delayed 45 ms. After correcting each coincidence rate for deadtime effects, the difference was the true coincidence rate. 

An a-y coincidence experiment was performed using a cooled Si(Li) detector for the detection of photons and a Si detector for the detection of a-particles. Three parameter events were collected on tape and one dimensional spectra were later generated in coincidence with various gates. The spectra showed that the and a3Q are in prompt coincidence with L X-rays and the delay occurs at the 27.4 keV level. The analysis of the time spectrum between the group and the 27.4 keV photopeak gave a half-life of 38.3 - 0.3 ns, in agreement with previous measurements. 

---