A computer-based well logging system is disclosed, for acquiring nuclear well log data, including gamma ray energy spectrum and neutron population decay rate data, and providing a real-time preentation of the data on an operator's display based on a traversal by a downhole instrument of a prescribed borehole depth interval.For acquiring energy spectrum data, the system has a multichannel analyzer including a pulse height analyzer and a memory. After a spectral gamma ray pulse signal coming from a downhole instrument over a logging cable is amplified and conditioned, the pulse height analyzer converts the pulse height into a digital code by peak detection, sample-and-hold action, and analog-to-digital conversion. The digital code defines the address of a memory location, or channel, corresponding to a particular gamma ray energy and having a count value to be incremented. After a period of time, the memory channels contain a spectrum of counts per incremental energy band. The spectrum data is then accessed by the system central processing unit (CPU) for analysis, and routed to the operator's display for presentation as a plot of relative gamma ray emissions activity versus energy level.For acquiring neutron decay rate data, the system has a multichannel scaling unit including a memory and a memory address generator. After a burst of neutrons downhole, thermal and epithermal neutron detector pulses build up and die away.Using the neutron source trigger as an initializing reference, the address generator produces a sequence of memory address codes, each code addressing the memory for a prescribed period of time, so as to define a series of time slots. A detector pulse signal produced during a time slot results in the incrementing of the count value in an address memory location. The process is repeated for every trigger, resulting in the production of time histogram data. The data is accessed by the CPU and routed to the operator's display.