If you're interested in the Chapel Bell experiments, the place to start looking would be NASA's
Apollo Mission Reports
for Apollo 14, 15, 16, and 17. That's about the only official
information I've ever been able to find on the subject. The Chapel Bell information falls under the "Approved Operational Tests" in Chapter 12 of
each entry. Although the entry varies slightly in each report, the one from the Apollo 14 Mission
12.3 APPROVED OPERATIONAL TESTS
The Manned Spacecraft Center participated in two of eight approved operational tests. Operational tests are not required to meet the objectives of
the mission, do not affect the nominal timeline, and add no payload weight.
The two operational tests were: lunar gravity measurement (using the
lunar module primary guidance system) and a hydrogen maser test (a Network and unified S-band investigation sponsored by the Goddard Spaceflight
Center). Both tests were completed, and the results of the hydrogen maser test are given in reference 9.
The other six tests were performed for the Department of Defense and the Kennedy Space Center. These tests are designated as follows.
a. Chapel Bell (classified Department of Defense test)
b. Radar Skin Tracking
c. Ionospheric Disturbance from Missiles
d. Acoustic Measurement of Missile Exhaust Noise
e. Army Acoustic Test
f. Long-Focal-Length Optical System.
(Bolded Emphasis Mine)
So, since Chapel Bell was an Operational Test (as defined above by NASA), we know the following pertinent things about the experiment:
1) It was not affected by the mission timeline.
2) It added no weight to the rocket itself.
Despite a certain thematic-sounding resemblance to the Saturn IVB impact on the moon (used to trigger seismic experiments left by Apollo 12), there is
no real reason to surmise that this and Chapel Bell were related; results of the SIVB impact experiment were not classified.
Personally, I'm inclined to think that Chapel Bell was related to the launch of the Saturn V that sent Apollos 14-17 into Earth Orbit. Given that
other Operation Test experiments ("Radar Skin Tracking", "Ionospheric Distrubance from Missiles", etc.) seem tied to the SV launch, I think that
Chapel Bell was probably a test of some other sort of tracking system, either space-based or land/sea/air-based, for tracking the launch and
trajectory of missiles, with the "Radar Skin Tracking" and other tests being used to evaluate the accuracy of this new tracking system.
This is only speculation, of course, but it does jive with the known qualities of Chapel Bell, especially the fact that the experiment did not depend
on when the mission was launched, added no net payload to the mission, and seems unrelated to the unclassified SIVB impact experiment.