The Chinese nuclear tests, 1964–1996

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From back in Chengdu the group flew to Urumqi, the capital of Xinjiang Province and the city nearest the Chinese nuclear weapons test site, known in the West as Lop Nur. Landing was followed by a grueling six-hour drive through mountains and desert to the new town of Malan, a settlement that does not appear on any maps of China but that serves as home for around 2000 members of the People's Liberation Army—a highly autonomous organization encompassing all the Chinese armed services—and perhaps 8000 civilians. The Stillman party was welcomed in the middle of the night with a lamb barbecue and an unending supply of fresh fruit. The serving staff at the banquet, all female PLA privates, spoke some English; the interpreters all spoke fluent English, including colloquialisms. Their regular jobs were to translate a flood of US publications into Mandarin for use by scientists at the test base.
The VIPs attending the Stillman visit had flown in from Beijing. Most spoke excellent English, and it seemed like they all talked about their children's achievements in the US. Even the engineer responsible for drilling vertical test shafts at Lop Nur had worked in the US during World War II; by 1990 his children were all enrolled in America's top engineering schools. The midnight barbecue in the Chinese desert seemed much like a cookout in the hills above Los Alamos.

In the morning the convoy again formed up for the two-hour ride into the test site itself, a facility seven times larger than the US Nevada Test Site. Stillman passed electric power substations, impressive VIP quarters, a high-bay building for assembling nuclear test devices, and a radioactive decontamination facility to deal with industrial waste and mishaps. Communications security was tight. At the time of Stillman's visit, drilling rigs were at work on 2- to 2.5-m diameter holes for nuclear device emplacement. Drilling technology was archaic by US standards; the drillers were advancing through the underlying granite at a rate of only two meters per day.
With the water table 20–40 m underground, most nuclear tests conducted in vertical shafts at Lop Nur were fired in water-saturated granite. The depth of burial equation used by the Chinese for such tests is DOB = 120 Y1/3, where Y is the nuclear yield in kilotons and DOB is the required depth of burial in meters. The factor of 120 changes as a function of the test-site geology but is appropriate for the Chinese granite formations. The firing depth calculated by this equation is actually the "safety depth," scaled to accommodate 110% of the expected yield.
The Chinese nuclear diagnostics were every bit as good as those used in American nuclear tests—if not better. For example, the NINT scientists showed Stillman several Chinese-built 5-megahertz oscilloscopes; their fastest scopes could record 1.5-gigahertz signals, well above the contemporary western capability.

NINT scientists had also developed and fielded a dual-axis PINEX (pinhole neutron experiment) "camera" to provide dual images in the deuterium–tritium burn region of a boosted primary—the fission portion of a thermonuclear device—during implosion, at exactly the desired moment. The unique dual-axis capability allowed the Chinese researchers to image either two time-sequenced events in a specific region of burn inside the nuclear device or to record events at two separate locations in the device at any given moment.
During the evenings at Lop Nur, Stillman was shown videotapes of some earlier nuclear-effects experiments. One such test, the CHIC-12 event, surrounded the nuclear explosive with a variety of targets placed at a distance: submarine-pen doors, underground military command bunkers, military aircraft, tanks, and even animals caged in place with instruments attached. Stillman noted with interest that Chinese procedures were identical to those followed in the US.

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