The Indian Nuclear tests - Summary
D. Ramana, Matt Thundyil and V.
Three years ago in May 1998, India conducted five nuclear tests and
declared itself a state with nuclear weapons . The process had its beginnings with the
launch of a study group for high-pressure physics in January 1962 by Homi Bhabha after
authorization by Prime Minister Nehru [2-3]. The tests marked the culmination of a process
accelerated in 1989 by Rajiv Gandhi and made operational in 1994. Despite having
demonstrated the nuclear capability in 1974, Indias announcement that its tests in
1998 included weapon designs and sub-kiloton experiments [3, 4] indicated that it was the
last of the "threshold" states to weaponize .
They further stated that the test results
were in conformance with the design yields. In addition, a range of technologies was
tested. The tests and their yields were met with considerable skepticism in the Western
media, academic and strategic circles. The Indian scientists responded to this by
releasing a number of detailed analyses of the data they had collected. The data released
included imagery, analyses of seismic measurements and radiochemical data. Despite this,
skepticism has continued to be voiced regarding the various yield claims. The skepticism
regarding the tests has implications for deterrent credibility. This article seeks to
address the claims and counterclaims from a scientific standpoint in order to evaluate the
validity of the various assertions. To accomplish this, we will analyze the various claims
and address the physics that ought to objectively define the conclusions reached.
Table 1 - The Shakti Devices
43 +/- 3 kt
Boosted primary with Li-D secondary. Inert mantle.
12+/- 3 kt
Advanced fission Pu based
Low yield weapon
Reactor grade Pu?
India stated that the three nuclear tests, codenamed Shakti (Strength),
were conducted on May 11, 1998 and the last two on May 13, 1998. The tests were conducted
in different shafts, which had been dug in the previous two decades. Mrs. Indira Gandhi
authorized the S-1 shaft [over 200m deep] and the S-2 shaft [over 150m deep], in 1982. The
shafts were sized respectively for a boosted fission weapon, four times the size of POK-I
and an advanced fission weapon of same size as POK-I . Prime Minister Narasimha Rao
authorized the third shaft in 1995 for a sub-kt test. PM Deve Gowda authorized the other
two shafts in 1996 and PM Inder Gujral authorized another unused shaft. Clearly, the
program had varying degrees of support from all the Prime Ministers in office despite
differing political views. India came close to testing on three different occasions: 1982
under Mrs. Gandhi, 1995 under Mr. Rao and 1996 under Mr. Vajpayee. A brief description of
the various tests and official Indian claims is in Table 1.
The sequence and location of these tests are critical in understanding
how the measured data is analyzed. There are three types of analyses in the open
literature. The primary analysis is based on the seismic measurements of the body wave
magnitude of the seismic event itself. These values are correlated to the yields by means
of correlations that are dependent on the site geology and subject to calibration
accuracy. A second means of analyses is based on the radio chemical isotopes that are
measured. These can indicate the extent and efficiency of the fission and fusion devices.
A third means is by comparison of the surface topography after the test to other tests.
This is also subject to the geologic characteristics of the site.
Initial Western reaction concurred with the Indian claims. The USGS
reported a seismic reading of 5.2 for mB on the Richter scale, which was similar to the
Indian reports for S-1 and S-2. Roger Clark and Peter Zimmermann suggested agreement with
the announced yields. A direct comparison of this measurement to the Pokhran-I test
indicates that the measured yield exceeds the POK-I test by 2.4 to 2.5 times (7). The
distinction between POK-I and POK-II is that the former test involved only one device,
whereas the latter test involved two simultaneous tests and involves the concomitant wave
Soon after, there were a number of counter claims (9) questioning the
results of the tests. Wallace (10), and Barker (11) led these challenges. In summary,
these concluded that the Indian tests did not provide results to match the announced
values. The Federation of American Scientists (FAS) provides a comprehensive rebuttal of
these early reports taking into account the recent work on the subject (7). The FAS study
is closer to the Indian position. It, however, estimates the S-1 yield was only about
30kT, compared to the Indian claims of 43kT. This estimate is based on the relative
magnitude of the seismic measurements of POK-1 and S-1/S-2, as indicated above.
The Bhabha Atomic Research Center (BARC) responded to the preliminary
objections by publishing a series of papers arguing that the yields were in accordance
with the design objectives. The first paper (13, 13 a) argues in favor of the necessity of
accounting for the interference in seismic waves caused by the simultaneous S-1 and S-2
detonations. As the devices were aligned in an E-W direction, they determined, from
physical considerations, that interference of the seismic waves of the twin explosions
could only be neglected in a narrow azimuthal window. This window was determined to be +/-
20 degrees off the North South axis. They also updated the seismic constants used for mB
wave magnitude for Pokhran site.
Their next paper (14) specifically addressed the Wallace and Barker
papers and argued for the necessity of accounting for wave interference and site bias. In
addition, they compared close-in ground accelerations from measurements to those values
published in the scientific literature for similar events. A third approach taken was to
compare the values to those of the earlier test in 1974. Based on all these three
approaches BARC argued that the results were acceptable.
BARC followed up with another paper based on the regional waves, which
are not detected by far away seismic stations (15). These waves are not detectable over
tele-seismic distances and hence are unavailable to other stations. Here BARC compared the
Lg & Rayleigh long period waves and again substantiated their case.
Further, they presented an overview paper (16) summarizing all the
analyses and concluding that the test results were in conformity with design values. A key
scientist involved with the tests, R.
Chidambaram, also separately confirmed the data and
analyses presented (21). The seismic measurements and the auxiliary issues pertaining to
the nature of the waves measured and the interference effects is critical, as the
magnitude of the tests are determined from these mB values. As the mB values are reported
on an exponential scale, relatively small differences in the values used result in orders
of magnitude differences in the claimed yields.
Discrepancy in Analyses
The determination of yield by seismic methods is not an easy process.
Seismic records of previous tests do not sufficiently characterize the test site at
Pokhran, nor is the site earthquake prone to calibrate the site. There are also site bias
errors due to propagation of the short period seismic waves i.e. P-waves, which are
detected from afar. A brief non-technical description of the seismic phenomena involved in
the detection of nuclear explosions is provided here.
The basic process involved is the propagation of elastic waves in
layered media, following the detonation of the explosive device. The explosive event
results in the generation of waves-long period Rayleigh waves with an attendant Airy phase
and the short period P - waves. The latter travel faster and are the first to arrive at
distant locations, which are also called tele-seismic distances. The Rayleigh waves
attenuate as an inverse function of distance and are limited to regional observations.
Consequently, Rayleigh waves are not easily measured at great distances from the seismic
event. The Rayleigh waves, are the first surface waves to arrive at regional locations and
these are followed by the Lg phase of very fast oscillations of increasing amplitude.
Following this, there is a big jump in amplitude due to the Airy phase which start
diminishing in amplitude (Lg phase). However, the Airy phase diminishes inversely as a
function of the distance raised to the five-sixths power. This is a simple consequence of
the stationary phase principle for oscillatory integrals with degenerate phase (31). In
other words, the Airy phase attenuates more slowly than the regular Rayleigh waves and
accounts for the jump in amplitude in the seismograms.
Wallaces methodology only addresses the P-waves that travel
faster and have shorter wavelength. They are thus affected by local anomalies more than
the Rayleigh waves, which have longer wavelength. If one looks at seismograms of the POK-2
from stations outside India these, record only the P-waves whereas those from India record
all the local wave phenomena. However, to the casual observer it appears that the Nilore
station should have picked up the regional seismic wave patterns, as it is located in the
Rayleigh wave area. The fact those seismograms in India do show these patterns indicate
that there is a seismic barrier between the Indian plate and the location of Nilore. It is
likely that the Himalayan fault is responsible for the non-propagation of the surface
waves to Nilore and the Kyrgyz network. This could account for the discrepancies in the
seismograms in India and outside. Clearly, the complete seismic signature of the POK-II
event was not detected outside India.
In addition to this is the issue of interference caused by twin wave sources separated
by a short distance. A brief study of wave dynamics indicates that when there are multiple
wave sources separated by a short distance, the space surrounding these sources
experiences interference of the waves. This interference is both constructive and
destructive depending on spatial location. When constructive interference occurs, the
amplitude of the resultant wave is greater than either of the interfering waves. When
destructive interference occurs the amplitude of the resultant wave is similarly,
adversely, affected. In addition, the interference at a given location will be a function
of the frequency of the wave. If we consider S-I and S-II to be point sources of waves,
the interference that results from the simultaneous detonations, at a specific measurement
location will be a function of the location of the station with respect to the test site.
Since measurements are available from a
multiplicity of locations, it is possible to test the existence of seismic interference
patterns. If no interference existed, the various stations at varying azimuthal locations
would have measured substantially similar values. In order to understand the various
issues involved here, a plot of mB versus azimuth was performed based on that data from
the FAS . The graph
shows there is a definite interference with the stations located in the East West
axis showing lower values than those that are on the North-South axis. To further
appreciate the implication of the observed range of values, it is necessary to understand
that the mB values are on the Richter scale, and are thus exponential functions of the
explosive energy measured.
To understand the phenomena, a qualitative and quantitative analysis
was performed. The reference to Sikka et al in the appendix is  Consider two sources
S-1 and S-2 located per Figure1 as
two emitting dipoles.As can be seen, there is interference due to the phase shift caused
by the delay in the seismic waves from the physical separation of the two tests. This
interference is a function of the frequency of the complex waves created after the
explosion. There are optimum locations that have minimal distortion based on the frequency
of the waves. From Eqn. 8 in the Appendix the optimum viewing locations for different
frequencies may be obtained.
Table 2- Frequency versus viewing angle
Table 2 indicates that the
optimum viewing angle for seismic waves greater than 2.5 Hz is +/- 20 degrees of
the N-S axis passing through the test site for minimal distortion. One has to ascertain
the frequency content of the Indian explosions. This is graphed in Figure 6 of reference
26. The POK-II explosion had a large component in the high frequencies. In fact, Gupta et
al in (26) and (20) specifically state that the seismic signals from the POK-II event
peaked in the frequency range 3.5 to 6 Hz. Hence as is evident from Table 2, the method
(adopted by BARC) of selecting mB values in certain limited stations along the N-S axis
reduces the error due to interference. Since the Gauribidanur Seismic Array Station (GBA)
is roughly 26 degrees off the North- South axis through Pokhran, reference to Table 2
shows that seismic waves from the POK-II event underwent destructive interference at the
GBA location. Thus an upward correction to the mB value is warranted. As a result, of this
interference related correction, the combined yield of the devices is estimated to have a
body wave magnitude of 5.4. This corresponds to a yield around 5 times that of POK-I (7).
Sublette indicates some reluctance to admit the corrections to the GBA data, but does not
address the scientific aspects of wave interference. Based on Indian and recent Western
claims regarding POK-I, it is reasonable to conclude that S-1/S-2 had a combined yield of
A study of Figure 2 in reference 15 shows the various components in the
seismic wave resulting from a test explosion. It typically comprises of the P, Pn, Lg,
Rayleigh wave with Airy phase. The figure documents the seismogram for the POK-II event as
recorded at Bhopal (Figure 2a) and Nilore (Figure 2b). Remarkably, measurements at Nilore
do not show the surface waves or Rayleigh waves. It only shows the faster moving short
period waves that are affected by local anomalies. These components are not present in the
seismograms outside India as they attenuate and do not cross over seismic faults. A study
of the seismograms indicates similar anomalies in seismograms of Chagai at Bhuj, and Ajmer
The anomaly in seismic signature was noted as early as the May 17, 1998
by Negi (34) who noted that the POK-I had a higher Richter reading than POK-II. The lower
reading from a larger explosion can be explained by the interference from the simultaneous
initiation of S-1 and S-2.
BARC published their radio-chemical analysis estimate of the S-1 yield
(17). The raw data has not been presented as it could reveal the specifics of the weapon
design. However, it provides a qualitative method of determining the efficacy of the
tests. The paper also reveals the various decay elements found in the post-shot debris.
Among the elements detected are isotopes of Ruthenium, Cesium, Manganese and Scandium.
However, the analysis was done based only on those isotopes, which do not decay further
e.g. 54 Mn and 46 Sc. It is instructive to compare the decay products detected in
S-1 debris and those depicted in a paper by Drell (22). It could provide insight into the
design used and indicates conclusively that fusion had occurred.
A preliminary estimate from radio-chemical data for S-2 is given as 13
+/- 3 kt (16). The radio-chemical confirmation of the yields of S-3, S-4 & S- 5 is
also provided (18). This analysis also does not have raw data but gives a graph of the
fission bye-products detected in the test holes and shows reaction did occur.
The radio-chemical analysis also provides the radius of cavity for the
S-1 device and states it as 40 +/- 4m. Based on Trehune (23) and the knowledge that the
test occurred in granite it is possible to independently confirm the yield. This method of
estimation results in a nominal yield of 37kT. This compares favorably with the Indian
report of 43 +/- 3 kT.
The basis of the radius of cavity estimate is not clarified. In the
same paragraph, there are statements about the crush zone radius and the distance of the
test hole to verify debris composition. In the error analysis section it is stated that
the uncertainty in the estimate of the radius of the cavity is within 15 percent. Lamb
(33) states that the yield estimate based on the radius of cavity determined by CORRTEX
technique is within 15 percent of that determined by radio-chemical analysis.
While it is not clear in all probability BARC determined the radius of
the cavity by means of this above technique which is arguably the most accurate method.
Carey Sublette (12) confirms that this method was used during the tests.
Sublette has given an excellent overview of the crater evidence and has
ably refuted Wallaces claims on that subject. Based on the surface features,
Sublette concluded that the S-2 estimate based on crater evidence was reasonably close to
what was claimed. This further suggests that the yield of S-2 was close to 10-12 kT. If
this was the case, it is reasonable to expect that S-1 had a yield of 38-45 kT, which is
well within the range claimed by BARC.
In an attempt to independently confirm this yield from the crater
morphology, Sublette suggests that the S-1 crater evidence indicates that it was either
over-buried or an imperfect explosion. Given that POK-I was buried at 107m and had a yield
of about 10 kt, it is possible to scale the required depth for a device four times as
powerful in the same terrain. As the depth is proportional to the cube root of the yield,
the scaled depth is about 170m in similar terrain. S-1 was reported in various sources to
be buried in a shaft over 200m and in granite. Hence, it is reasonable to accept that the
device was over-buried. Chengappa reports that Chidambaram and Sikka were aware of this
aspect and had stated this before informing the Prime Minister of the successful tests
Sublette also questions the sub-kiloton tests based on the lack of
imagery and any independently reported seismic evidence. The seismograms for POK-II at
Nilore show that it did not detect many of the components of the larger explosions. It is
possible that it would be challenging to detect much smaller signatures at Nilore.
Sublette is not convinced of the radio-chemical evidence presented by BARC (18), although
he does not question their veracity. However, BARC insists that the tests occurred as
From the crater imagery released by BARC, one can conclude that the
three sub-kiloton tests were performed and the radio-chemical data shows that the
chain reaction did occur.
BARC has presented seismic estimates of the yield based on short period
P waves, long period surface waves, and close in accelerations. These estimates give the
total yield for the May 11, 1998 tests as about 55kT. In addition, they have presented
results of the radio-chemical analysis. These radio-chemical estimates, give the
S-1 yield as 50 +/- 10 kT. The secondary data, including the radius of the cavity provides
an estimate of 37 kT. This is close to the design value of 43 +/- 3 kT. From the data
presented by BARC, the S-1 device performed to their expectations. Dr. P.K. Iyengar (32)
does not dispute the yield, but rather raises concerns over the efficiency of the fusion
device, which is a design sub-issue'
As discussed above the BARC conclusions are based on seismic
measurements that capture a clearer picture of the seismic spectrum than measurements from
afar. Clearly, the criticism of BARC results are based only the low short period seismic
waves, which have path and source aberrations. Furthermore, we are unaware of any
interference analysis of the POK-II event being performed in the seismic literature
besides that of BARC, and what has been presented to the best of our knowledge for the
first time in this note. BARC, while withholding the raw data for the radio chemical
estimates, could have presented the secondary data like radius of cavity and the crush
zone radius with more precision as these could be used to substantiate their results. The
radio-chemical estimate has not been challenged.
In a limited series of tests BARC scientists have, by their own
account, tried out a dozen ideas using three basic designs - fission, boosted fission and
fusion. As the program was not overt, they had to operate under severe constraints.
Ideally, they should have proofed S-1 to its full yield. However, that would mean
acquiring and evacuating the villages around the test site and would have disclosed their
plans. Hence, they tested the basic design and reduced yield. This is similar to the US
and USSR programs in later sixties and early seventies respectively (30). The tests
confirm that the fission process in its variations is fully understood. This is critical,
as the fission process is required to be most reliable aspect of a deterrent posture (30).
Chengappa (28) reports that reactor grade plutonium was used for one of
the devices tested. It is unclear which of the S-3 S-5 tests used the Reactor Grade
Plutonium. Kakodkar (4) says that the test site could handle 60 kilotons and other reports
suggest the total design yield was 55 kilotons. In all probability, the S-3 shaft was
capable of the difference. Besides Chengappa (29) states that the decision to conduct
simultaneous tests was taken just before the test date. The concern was that the S-1
explosion could damage the other shafts. Considering this, the S-3 was conducted and
probably the gas boosting was turned off as it could lead to crossing the site threshold.
Further information on the radio-chemical debris is required to determine conclusively if
reactor grade material was used. The data presented shows only that Cs 137 was detected at
various depths of the shaft.
The reactor grade material significantly increases the options for
India. Considering the material available from the CANDU reactors, India has the potential
to increase the number of weapons to handle any changes in the international security
environment. Previously, most Indian experts had suggested a minimum inventory in the low
hundreds based on weapons grade Plutonium. The decision to make use of reactor grade
material is a far-reaching one and needs further clarification.
A point to note is that, from the early 1962 decision to set up the
high-pressure physics study group to the 1998 tests three decades later, all were
under firm political control. The S-1 device was designed under authorization by the Prime
Minister in 1995 and was ready in 1997. The argument that the scientists drove the
decision to test is specious at best. Moreover, the fact that it was twenty years after
the 1974 test that India was able to deploy its deterrent shows the extent of political
No discussion of the Indian tests is complete without reference to the
Pakistani tests at Chagai in the same month. Much work has to be done to understand those
tests. In light of the geology of the terrain, it is possible that the yield was greater
than estimated based on short period waves or mB data. In fact, Sikka comments on this
possibility (16). Further Chanillo (20) compares the relative yields of the two events and
concludes that Chagai was at most half of the POK-II.
We can draw the following conlcusions based on the preceeding analysis:
- BARC has presented seismic estimates of the total yield based on short period P waves,
long period surface waves, and close in accelerations. These estimates give the total
yield for the May 11, 1998 tests as about 55kT. In addition, they have presented results
of the radio-chemical analysis. These radio chemical estimates, give the S-1 yield as 50
+/- 10 kT. The secondary data, including the radius of the cavity provides an estimate of
37 kT. This is close to the minimum design value of 40 kT. The S-1 device performed to the
design within expected margins. The radio-chemical data shows decay products from a fusion
- The combined yield of S-1/S-2 less the possible yield of S-1 (from the radius of cavity
calculation) indicates that S-2 was around 10-12kT. This is independently validated by the
imagery of the S-2 crater.
-chemical data shows that the chain reaction did occur in the three
- From the crater imagery released by BARC, one can conclude that the three sub-kiloton
tests were performed and the radio
-chemical data from the S-3 shot is required to determine if
reactor grade Plutonium was used. Based on shaft capacity this test is the most probable
candidate for using that material.
- Further understanding of the radio
The authors wish to thank Sagun Chanillo and Sanjay Badri Maharaj
for their deep support and clarifications. Without their encouragement and support this
paper would not have been put together.
 Chengappa, R., "Weapons Of Peace" Harpers Collins, India , ISBN
81-7223-330-2 page 432-433. It is stated that S-2 was a weapon from the inventory and was
one of the old stock. See also fas.org web site - http://www.fas.org/nuke/hew/India/IndiaShakti.html.
For an objective summary of the tests from a Western expert read http://www.thebulletin.org/issues/1998/ja98/ja98albright.html
[2a] Badri- Maharaj, Sanjay, " Armageddon Factor", Lancers ,
2000. Page 79 ISBN 81-7062-109-7
[2b] R. Ramachandran, " Pokhran-II The Technical Aspects" in
Mattoo, Amitabh, ed " Indias Nuclear Deterrent - Pokhran II and Beyond",
Har Anand, New Delhi 1998.
 Chengappa, WOP, page 332, page 382 for operational, and page 86 for
setting up the study group for high-pressure physics
 Interview with Dr. Anil Kakodkar, "We got everything we
wanted", Frontline, June 6, 1998 Vol 15, No. 12, http://www.the-hindu.com/fline/fl1512/15120290.htm
 Subramanian, T. S, " Technological success", Front
line May 23- June 05, 1998. http://www.the-hindu.com/fline/fl1511/15110130.htmSee
 Hersh, Seymour, "The Samson Option" Random House, New
York, page 179. Israel had crossed the threshold in early 1968. See also Aslam Begs
article" What entails signing the CTBT?" The News, April 03, 2001.
Pakistan had crossed the threshold in 1987 based on Gen. Aslam Begs insight.
 Chengappa, WOP page 34. Chidambaram asked authorization for six
tests to validate a dozen ideas. Also see reference 21.
 Chengappa, WOP, page 246 for quote on shaft capability of four
times POK-I. Shaft depth close to 200m page 247.
 Broad, William, "Big claims small evidence" Frontline,
Vol 15, No. 12. http://www.the-hindu.com/fline/fl1512/15120270.htm
 Wallace, Terry C. 1998. "The May 1998
India and Pakistan Nuclear Tests", Seismological Research Letters, September
1998. Preprint at http://www.geo.arizona.edu/geophysics/faculty/wallace/ind.pak/.
 Barker, Brian et al. 1998. "Monitoring Nuclear
Tests", Science, Vol. 281, 25 September 1998, pp. 1967-68.
 FAS web site update on India "What are the real yields
of Indias Test?" http://www.fas.org/nuke/hew/India/IndiaRealYields.html
 S.K. Sikka, Falguni Roy, G.J. Nair. 1998. "Indian Explosions
of 11 May 1998: An Analysis of Global Seismic Body Wave Magnitude Estimates", Current
Science 75, no. 5, 10 September 1998, pg. 491. BARC collection of links on POK-II and
rebuttal of Barker paper.http://www.barc.ernet.in/webpages/milestones/explosion.html
 S.K. Sikka, Falguni Roy, G.J. Nair, V.G. Kolvankar and Anil
Kakodkar. 1998. "Update on the yield of May 11-13, 1998 Nuclear Detonations at
Pokhran", BARC News Letter No. 178, Nov. 1998. Located at http://www.barc.ernet.in/webpages/letter/newsletter_year_1998/novletter.html
 Falguni Roy, G.J. Nair, et al. 1999. "Indian Explosions of 11
May 1998: An Analysis Regional Lg and Rayleigh waves", Current Science 76, no.
12, 25 December 1999. http://tejas.serc.iisc.ernet.in/currsci/dec251999/articles23.htm
 S.K. Sikka, Falguni Roy, G.J. Nair., et al., 2000.
"The recent Indian nuclear tests- A Seismic overview", Current Science
79, no. 9, 10 November 2000, pg. 1359. See ref 33 of this paper for the radio chemical
estimate of S-2. http://tejas.serc.iisc.ernet.in/currsci/nov102000/1359.pdf
 S.B.Manohar, B.S.Tomar, S.S.Rattan, V.K.Shukla, V.V.Kulkarni and
Anil Kakodkar. 1999. "Post Shot Radioactivity Measurements On Samples Extracted From
Thermonuclear Test Site", BARC News Letter No. 186, July 1999. Located at http://www.barc.ernet.in/webpages/letter/newsletter_year_1999/july99.html#POST
SHOT radioactivity measurements on SAMPLES.
 R.B. Attarde, V.K. Shukla, D.A.R. Babu, V.V. Kulkarni and Anil
Kakodkar. 1999. "Fission Signatures Of Tests On Sub-Kiloton Devices", BARC
News Letter No. 187, Nov. 1999. http://www.barc.ernet.in/webpages/letter/newsletter_year_1999/sep99.html
 IDC data summarized at fas web site:http://www.fas.org/nuke/hew/India/TN5-11REB.txt
 Chanillo, Sagun, "Relative yields of Pokhran and Chaghai
nuclear explosions" Current Science, vol. 79[Dec 25th, 2000], No.12,
 Chidambaram, R.C., Interview in Frontline, Jan. 15, 1999. http://www.the-hindu.com/fline/fl1601/16010840.htm
 Drell, Sidney, Hippel, Frank von, " Limited Nuclear
War", Scientific American, November 1976. The accompanying chart shows the
chain reaction of high energy neutrons from D-T fusion on a U-238 material. It identifies
similar decay products. Further investigation by those familiar with radio chemistry would
be necessary to see if there was a thin liner or yield enhancing material used in S-1.
 Terhune, Glenn. Et al, " Numerical Simulation of the
Baneberry event", Nuclear Technology, Vol. 46, Nov., 1976. Page 159- 169 Gives
the relationship for radius of cavity is Rc = k*[Y]^1/3 - k varies from 12 to 16. The
lower value being for hard rock like granite. The paper has numerical calculations to show
that this holds true. Using this relationship and knowing that the POK-1 cavity radius was
around 30m [Ref. 14] and the information that it was not in granite gives a method to the
yield for that explosion. Using k equals 14 leads to a yield of ~ 9.8kt for POK-I.
 Chowdri, Satybrata " What did Pokhran reveal?", Daily
Excelsior; May 09, 1999 . This article discusses the various technologies used and
also speculates on the purpose of the sub-kt tests.
 IPCS seminar; June 12, 1998. Please see last para for probable
weight of S-1 device. http://www.ipcs.org/issues/articles/115-ndi-jolie&mallika.html
Ramachandran [2b] says it took 500 nanoseconds for the X-rays to travel to the
secondary. By a trivial calculation this works out to 1.5 meters. The S-1 was at least
 Harsh Gupta, S.N.Bhattacharya, M.
Ravi Kumar, D. Sarkar, "Spectral characteristics of Pokhran and Chagai nuclear
explosions". Current Science, vol 76, 1117-1121 http://tejas.serc.iisc.ernet.in/currsci/april25/articles20.htm
 Chengappa, WOP, pages page 431- 432 on S-1 shaft depth and
 Chengappa, WOP, Pages 417- 418 on reactor grade material used in
one of the tests.
 Chengappa, WOP, pages 425 on last minute decision to explode
simultaneously to ensure no fratricide from S-1.
 Evernden, Marsh, "Yields of US and Soviet Nuclear
tests", Physics Today, August 1987. This paper documents the difficulties in
using seismic estimates without correction for site bias. It further quotes US officials
like Richard Wagner , former Asst to Secy of Defense, who state that testing the primary,
is critical to the design of the weapon. He further suggests that the primary and an
altered secondary could be tested which do not exceed the threshold values. It also states
that from 1965-74 the US and the USSR tested their advanced primaries and very few
 Ewing, W.M. , Jardetzky, W.S, and Press F. , Elastic Waves in
Layered Media, McGraw-Hill 
 Iyengar, P.K. "In testing times", Times of India, Feb.,
17, 2000. Also refer to discussion in Bharat Rakshak Monitor on the nuances of his
 Lamb, F. K., "Monitoring yields
of underground tests using hydrodynamic methods", In Nuclear Arms Technologies in the
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