Random pulsing of neutron source for inelastic neutron scattering gamma ray spectroscopy

A method for logging the formations surrounding an earth borehole, comprising the steps of:

• initiating a succession of bursts of fast neutrons and irradiating said formations with said neutrons during a variable time interval for each of said bursts;
• detecting radiation occasioned in said formations as the result of said fast neutrons;
• terminating an individual burst of fast neutrons by shortening said variable time interval as a function of radiation detected during said individual burst;
• and
• varying the frequency of occurrence of said succession of discrete bursts to provide for a constant duty cycle of said succession of bursts.

A method for logging a formation surrounding a borehole, comprising the steps of:

• irradiating said formation with a succession of discrete bursts, at a given burst period, of fast neutrons, each burst having a variable time interval;
• detecting radiation occasioned in said formation by said fast neutrons;
• selecting a burst time interval, relative to said burst period, which reduces the contribution to the detected radiation of radiation occasioned by other than the inelastic scattering of fast neutrons;
• and
• limiting the number of fast neutrons generated in each of said bursts by shortening said variable time interval as a function of said detected radiation such that the mean burst time interval resulting corresponds to said selected burst time interval.

Apparatus for providing a radioactivity log of a formation surrounding a borehole, comprising:

• means for irradiating said formation with a succession of discrete bursts of fast neutrons, each burst having a variable time interval;
• means for detecting radiation occasioned in said formation by said fast neutrons;
• means for limiting the number of fast neutrons generated in an individual burst by shortening said variable time interval as a function of radiation detected during said individual burst;
• and
• means for varying the frequency of occurrence of said succession of discrete bursts to provide for a predetermined relationship between said variable time interval and the time interval between succeeding discrete bursts which follows each of said bursts.

Apparatus for logging the formations surrounding an earth borehole, comprising:

• means for initiating a succession of bursts of fast neutrons and irradiating said formations with said neutrons during a variable time interval of each of said bursts;
• means for detecting radiation occasioned in said formations as the result of said fast neutrons;
• means for terminating an individual burst of fast neutrons by shortening said variable time interval as a function of radiation detected during said individual burst;
• and
• means for varying the frequency of occurrence of said succession of discrete bursts to provide for a constant duty cycle of said succession of bursts.

Apparatus for providing a radioactivity log of a formation surrounding a borehole, comprising:

• means for irradiating said formation with a succession of discrete bursts, at a given burst period, of fast neutrons, each burst having a variable time interval;
• means for detecting radiation occasioned in said formation by said fast neutrons;
• and
• means for limiting the number of fast neutrons generated in each of said bursts by shortening said time interval as a function of said detected radiation such that the mean burst time interval resulting corresponds to a selected burst time interval, wherein said selected burst time interval is such that, relative to said burst period, the contribution to the detected radiation of radiation occasioned by other than the inelastic scattering of fast neutrons is reduced.

A well logging apparatus for the investigation of earth formations surrounding a borehole, comprising:

• means for generating a succession of bursts of radiation at a variable frequency, the time duration of each burst being variable;
• means for detecting, during a plurality of time intervals comtemporaneous with respective ones of said bursts, radiation occasioned in said formations by said radiation bursts;
• first means for controlling the time duration of each burst in accordance with the output of said detecting means;
• and
• second means for controlling the frequency of said succession of bursts in accordance with the output of said detecting means.

A method for providing a radioactivity log of a formation surrounding a borehole, comprising the steps of:

• irradiating said formation with a succession of discrete bursts of fast neutrons, each burst having a variable time interval;
• detecting radiation occasioned in said formation by said fast neutrons;
• limiting the number of fast neutrons generated in an individual burst by shortening said variable time interval as a function of radiation detected during said individual burst;
• and
• varying the frequency of said succession of discrete bursts as a function of said detected radiation.

Apparatus for providing a radioactivity log of a formation surrounding a borehole, comprising:

• means for irradiating said formation with a succession of discrete bursts of fast neutrons, each burst having a variable time interval;
• means for detecting radiation occasioned in said formation by said fast neutrons;
• means for limiting the number of fast neutrons generated in an individual burst by shortening said variable time interval as a function of radiation detected during said individual burst;
• and
• means for varying the frequency of said succession of discrete bursts as a function of said detected radiation.