|Test site||Ras Koh Hills, Chagai, Balochistan, Pakistan|
|Period||28 May 1998|
|Number of tests||5|
|Test type||Underground tests|
|Device type||Boosted fission/Fusion|
|Max. yield||40 kilotons of TNT (170 TJ)|
: 281–282 See note
Chagai-I is the code name of five simultaneous underground nuclear tests conducted by Pakistan at 15:15 hrs PKT on 28 May 1998.: 281  The tests were performed at Ras Koh Hills in the Chagai District of Balochistan Province.
Chagai-I was Pakistan's first public test of nuclear weapons. China's supply of nuclear reactor in 1993 and nuclear technology prior to that for the Chashma Nuclear Power Plant helped to achieve it. Its timing was a direct response to India's second nuclear test Pokhran-II, on 11 and 13 May 1998. These tests by Pakistan and India resulted in United Nations Security Council Resolution 1172 and economic sanctions on both states by a number of major powers, particularly the United States and Japan. By testing nuclear devices, Pakistan became the seventh country to publicly test nuclear weapons.: 14–15  Pakistan's second nuclear test, Chagai-II, followed on 30 May 1998.
Several historical and political events and personalities in the 1960s and early 1970s led Pakistan to gradually transition to a program of nuclear weapons development, that began in 1972. Plans for nuclear weapons testing started in 1974.: 182–183 : 470–476 Chagai-I was the result of over two decades of planning and preparation, Pakistan becoming the seventh of eight states that have publicly admitted to testing nuclear weapons.: 14–15 
The timing of Chagai-I was a direct response to India's second nuclear tests, Pokhran-II, also called Operation Shakti, on 11 and 13 May 1998.: 1–15 : 191–198 Chagai-I was Pakistan's first of two public tests of nuclear weapons. Pakistan's second nuclear test, Chagai-II, followed on 30 May 1998.
In 2005, Benazir Bhutto testified that "Pakistan may have had an atomic device long before, and her father had told her from his prison cell that preparations for a nuclear test had been made in 1977, and he expected to have an atomic test of a nuclear device in August 1977." However, the plan was moved on to December 1977 and later it was delayed indefinitely to avoid international reaction; thus obtaining deliberate ambiguity. In an interview with Hamid Mir in Capital Talk which aired on Geo News in 2005, Dr. Samar Mubarakmand confirmed Bhutto's testimony and maintained that PAEC developed the design of an atomic bomb in 1978 and had successfully conducted a cold test after building the first atomic bomb in 1983.
Safety and security required a remote, isolated and unpopulated mountainous area.: 470–476 The Geological Survey of Pakistan (GSP) conducted tests: 182 to select a "bone dry" mountain capable of withstanding a 20–40 kilotonne (kt) detonation from the inside. The scientists wanted dry weather, and very little wind to spread radioactive fallout.
Koh Kambaran located in the Ras Koh Hills was selected in 1978. Due to widespread imprecise reporting which mentioned the Chagai Hills region prior to the actual explosion, there is sometimes geographic confusion. Both the Chagai Hills and the Ras Koh Hills are situated in the Chagai District, but the Ras Koh Hills lie to the south of Chagai Hills, and are separated from the Chagai Hills by a large valley.
After India's Pokhran-II tests on 11–13 May 1998, statements by Indian politicians further escalated the situation. Prime Minister Nawaz Sharif curtailed his state visit to Kazakhstan to meet with President Nursultan Nazarbayev and returned to Pakistan.
The decision to conduct tests took place at a meeting that Sharif convened with the Chairman joint chiefs, General Jehangir Karamat, Dr. Abdul Qadeer Khan, Ishfaq Ahmad, and Munir Ahmad Khan and members of the Cabinet of Pakistan.: 101–102 In talks with Sharif, the President of the United States, Bill Clinton, offered a lucrative aid package in an attempt to get Pakistan to refrain from nuclear testing, and sent high level civic-military delegations led by Strobe Talbott and General Anthony Zinni to Pakistan to lobby against the tests.: 103–110  Popular public opinion in Pakistan was in favor of nuclear blasts. Information minister Mushahid Hussain was the first who argued for the tests in reply to the Indian nuclear tests. The Opposition leader, Benazir Bhutto, spoke emphatically in favour of Pakistani atomic tests.
At the NSC's cabinet meeting, the Pakistani government, military, scientific, and civilian officials were participating in a debate, broadening, and complicating the decision-making process.: 103 Chairman joint chiefs, General Karamat and Air chief ACM (General) Parvaiz Mehdi Qureshi supported the matter and left the decision on the government.: 269–270 Naval chief Admiral Fasih Bokhari and Finance Minister Sartaj Aziz argued against the tests on financial grounds; though Aziz later staunchly backed the decision to test calling it as "right decision.": 300–325 Dr. Abdul Qadeer Khan argued in favor of tests and was supported by Samar Mubarakmand and Munir Ahmad Khan while Dr. Ishfaq Ahmad argued that "the decision to test or not to test was that of the Government of Pakistan despite the say of the scientific community.": 271–275 Concluding the final arguments, Ishfaq Ahmad said: "Mr. Prime Minister, take a decision and, Insha'Allah, I give you the guarantee of success".: 276–277
With the G8 group's sanctions having very little effect on India and skepticism towards United States commitment, the Pakistani government economists built up the final consensus hardening around the idea that "there is no economic price for security".: 104–105 Despite being under pressure by U.S. President Bill Clinton, Prime Minister Sharif authorized the nuclear tests by ordering the PAEC in Urdu: "Dhamaka kar dein" (lit. "Conduct the explosion!"): 277
In 1999, in an interview given to Pakistani and Indian journalists in Islamabad, Sharif said: If India had not exploded the bomb, Pakistan would not have done so. Once New Delhi did so, We [Sharif Government] had no choice because of public pressure.
The observation post was established about 10 km (≈6.21 miles) from the test vicinity, with members of Mathematics Group and Theoretical Physics Group (TPG) led by Dr. Masud Ahmad and Asghar Qadir charged with calculating the nuclear weapon yield. Determination of accurate and precise blast yields and shock waves is challenging because there are different ways in which the yields can be determined. The TPG predicted the total maximum test yields with an energy equivalent to be ~40 kilotons of TNT equivalent, with the largest (boosted) device yielding 30–36 kilotons. Other scientists estimated a yield of 6–13 kilotons or, based on the seismic wave data, a yield of 12–20 kt. Theoretical Physics Group (TPG) and Dr. Abdul Qadeer Khan held to their estimates.: 200–202  The PAEC's mathematics division placed the scientific data in the public domain and published seismic activities, mathematical graphs, and mathematical formulas used to calculate the yield; though certain scientific information remains classified.
From scientific data received by PAEC, it appears that Pakistan did not test a thermonuclear device, as opposed to India. According to Ishfaq Ahmad, PAEC had no plans to develop a hydrogen device for economic reasons, even though back in 1974, Riazuddin proposed such a plan to Abdus Salam, Director of Theoretical Physics Group that time. From the outset, PAEC concentrated on developing smaller tactical nuclear weapons easily installed on Pakistan Air Force (PAF) aircraft, Pakistan Navy combatant vessels, and missiles.
Shortly after the tests, former chairman and technical director Munir Ahmad Khan famously quoted: "These boosted devices are like a half way stage towards a thermonuclear bomb. They use elements of the thermonuclear process, and are effectively stronger atom bombs..... Pakistan has had a nuclear capability since 1984 and all the Pakistani devices were made with enriched uranium."
On the other hand, Abdul Qadeer Khan further provided technical details on fission devices while addressing the local media as he puts it: "All boosted fission devices using Uranium 235 on 28 May. None of these explosions were thermonuclear, we are doing research and can do a fusion test if asked. But it depends on the circumstances, political situation and the decision of the government. As opposed to India's thermonuclear approach, Dr. N. M. Butt, senior scientist, stated that "PAEC built a sufficient number of neutron bombs— a battlefield weapon that is essentially a low yield device".
In Pakistan, the news of the nuclear detonations was met by street celebrations. Prime Minister Nawaz Sharif addressed the nation via the Pakistani government's state owned channel Pakistan Television (PTV), congratulated the public and days of celebration followed throughout Pakistan. The Directorate of Technical Development of PAEC which carried out the Chagai tests issued the following statement soon after the tests:
The mission has, on the one hand, boosted the morale of the Pakistani nation by giving it an honorable position in the nuclear world, while on the other hand it validated scientific theory, design and previous results from cold tests. This has more than justified the creation and establishment of DTD more than 20 years back.
These gifted scientists and engineers along with a highly dedicated team worked logically and economically to design, produce and test an extremely rugged device for the nation which enable the Islamic Republic of Pakistan from strength to strength.
After the test, the national media in Pakistan posted biographies of the involved scientists. Senior scientists and engineers were invited by academic institutes and universities to deliver lectures on mathematical, theoretical, nuclear and particle physics. The institutes bestowed hundreds of silver medals, gold medallions and honorary doctorates to the scientists and engineers in 1998.
The Chagai-I tests were condemned by the European Union, the United States, Japan, Iraq, and by many non-Organisation of Islamic Cooperation (OIC) countries. The United Nations Security Council adopted Resolution 1172, condemning the tests by both India and Pakistan. From 1998 to 1999, the U.S. held a series of talks with Pakistan to persuade them to become party to the Comprehensive Nuclear-Test-Ban Treaty (CTBT) and the Non-Proliferation Treaty (NPT), with Pakistan refusing amid a fear of lack of security commitment by the U.S. and the growing ties between India and the United States.
The U.S., Japan, Australia, Sweden, Canada, and International Monetary Fund (IMF) imposed economic sanctions on Pakistan. On the other hand, Saudi Arabia, Turkey, Azerbaijan, and Iran congratulated Pakistan where major celebrations took place.: 290 All new U.S. economic assistance to Pakistan was suspended in May 1998 though humanitarian aid continued. The composition of assistance to Pakistan shifted from monetary grants towards loans repayable in foreign exchange. In the long term, the sanctions were eventually permanently lifted by the U.S. after Pakistan became a front-line ally in the war against terror in 2001. Having improved its finances, the Pakistani government ended its IMF program in 2004.
The three main development teams were the Pakistan Atomic Energy Commission (PAEC) (including Ishfaq Ahmad, who was Chairman of the PAEC; Samar Mubarakmand; Irfan Burney, Anwar Ali; Hafeez Qureshi and Masud Ahmad), the Kahuta Research Laboratories (KRL) (including Abdul Qadeer Khan, who was Director General of KRL; and Tasneem M. Shah), and the Pakistan Army Corps of Engineers (PACE) (including Lieutenant-General Zulfikar Ali Khan).
Signed into law by Prime Minister Nawaz Sharif, 28 May is officially declared as Youm-e-Takbir (lit. Day of Greatness), as well as National Science Day, to commemorate the date of the first five tests and honour the scientific efforts to develop the program. Awards, such as Chagai-Medal, are given to various individuals and industries in the field of science. The Pakistani government established the Chagai-I Medal, first awarded in 1998 to the scientists who witnessed the tests. The granite mountains are visibly shown in the gold medallion and equal ribbon stripes of yellow, red and white.
Abdus Salam (1926–1996) was awarded the Nobel Prize in Physics in 1979 for the discovery of electroweak interaction. In 1998, the Government of Pakistan issued a commemorative stamp in his honour. In 1999, the government established a museum at the National Center for Physics, where Salam's contribution to scientific programs and efforts were recorded and televised.
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- Approximating and calculating the exact, accurate and precise yields are difficult to calculate. Even under very controlled conditions, precise yields can be very hard to determine, and for less controlled conditions the margins of error can be quite large. There are a number of different ways that the yields can be determined, including calculations based on blast size, blast brightness, seismographic data, and the strength of the shock wave. The Pakistan Government authorities puts up the yield range from 36-~40 kt depending on the mathematical calculations they had performed. On other hand, independent and non-government sanctioned organizations puts the figure at the possible 15–20 kt range. The explosion measured 5.54 degrees on the Richter Scale, the PAEC provided the data as public domain in the KNET sources.
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