By Andrew Aloia BBC Sport Last updated on 11 October 2021 11 October 2021 . From the section Football Watson was a trailblazer who helped transform how football was played There are two murals of black footballers facing one another across an alleyway in Glasgow. One helped shape football as we know it, the other is Pele. Andrew Watson captained Scotland to a 6-1 win over England on his debut in 1881. He was a pioneer, the world's first black international, but for more than a century the significance of his achievements went unrecognised. Research conducted over the past three decades has left us with some biographical details: a man descended of slaves and of those who enslaved them, born in Guyana, raised to become an English gentleman and famed as one of Scottish football's first icons. And yet today, 100 years on from his death aged 64, Watson remains something of an enigma, the picture built around him a fractured one. His grainy, faded, sepia image evokes many differen
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Iran nuclear deal: Why do the limits on uranium enrichment matter?
Image copyrightAFPImage captionPresident Hassan Rouhani (R) says Iran is retaliating against US sanctions
Iran has announced it is lifting all limits on nuclear research - the latest step in scaling down its commitments made under a 2015 nuclear deal with world powers.
President Hassan Rouhani said from 6 September the country would begin developing centrifuges to speed up the enrichment of uranium.
Under the accord, Iran agreed to limit its sensitive nuclear activities and allow in international inspectors in return for the lifting of crippling economic sanctions.
Last year, the US withdrew from the deal and reimposed sanctions. Iran responded by abandoning two other key nuclear commitments in July.
What is enriched uranium?
Enriched uranium is produced by feeding uranium hexafluoride gas into centrifuges to separate out the most suitable isotope for nuclear fission, called U-235.
Low-enriched uranium, which typically has a 3-5% concentration of U-235, can be used to produce fuel for commercial nuclear power plants.
Highly-enriched uranium has a concentration of 20% or more and is used in research reactors. Weapons-grade uranium is 90% enriched or more.
Image copyrightGETTY IMAGESImage captionIran's low-enriched uranium stockpile was limited to 300kg for 15 years under the nuclear deal
Under the nuclear deal, Iran is allowed to enrich uranium only up to a 3.67% concentration, to stockpile no more than 300kg (660lbs) of the material, and to operate no more than 5,060 centrifuges.
Another part of the deal instructs Iran not to accumulate more than 130 tonnes of heavy water, which contains more hydrogen than ordinary water, and to redesign its heavy-water nuclear reactor at Arak. Spent fuel from a heavy-water reactor contains plutonium, which can be used in a nuclear bomb.
They noted that Iran would need roughly 1,050kg of 3.67% enriched uranium to be able to produce enough weapons-grade material for one bomb.
Image copyrightGETTY IMAGESImage captionIran is allowed to operate 5,060 uranium enrichment centrifuges at Natanz
But the experts warned that if Iran resumed higher levels of enrichment, that would pose a more serious proliferation risk and shorten the "break-out time" - the time it would theoretically take to acquire enough fissile material for one bomb, if Tehran chose to do so.
Before the nuclear deal was implemented in 2016, Iran had a sufficient amount of 20% enriched uranium and number of centrifuges that its "break-out time" was estimated to be about two to three months.
The deal slowed the "break-out time" to at least a year. But any reversal of Iran's commitments on uranium enrichment would see that start to shorten.
The steps Iran has taken could lead to it being found to be in "material breach" of the nuclear deal, which would allow other parties to "snap back" the UN and EU sanctions that were lifted.
No member of the UN Security Council would be able to veto such a move.
Why did Iran stop abiding by its commitments?
The Iranian economy has slumped since President Donald Trump withdrew from the deal in May 2018 and began reinstating sanctions. He said the deal was flawed and that he wanted to force Iran's government to renegotiate the terms - something it refused to do.
Image copyrightAFPImage captionIran's oil exports - the government's principal source of revenue - have more than halved
The other parties to the deal - the UK, France, Germany, China and Russia - criticised Mr Trump's decision and said they remained committed to the deal.
In May 2019, the White House stepped up pressure on Iran by ending exemptions from secondary sanctions for countries still buying Iranian oil.
It also ended exemptions for countries participating in deals under which Iran exchanged its surplus low-enriched uranium for un-enriched ore concentrate known as "yellowcake" and sold its surplus heavy water. Such transfers allowed Iran to continue production of both materials without exceeding the stockpile limits.
Iran's President Hassan Rouhani subsequently said it would retaliate against the US sanctions by suspending its commitment to comply with the stockpile caps.
Image copyrightAFPImage captionDonald Trump's decision to end sanctions waivers for importers of Iranian oil sparked protests
Officials noted that article 36 of the nuclear deal allows one party to "cease performing its commitments… in whole or in part" in the event of "significant non-performance" by other parties. They said the US violated the deal a year ago and that European countries had failed to deliver its promised economic benefits.
The European Union has set up a mechanism for facilitating trade, known as Instex, which essentially allows goods to be bartered between Iranian and foreign companies without direct financial transactions. It became operational on 29 June, but Iran said it did not meet its needs.
Does Iran want a nuclear bomb?
Iran insists it has never sought to develop such a weapon.
The international community does not believe that, pointing to evidence collected by the IAEA suggesting that until 2003 Iran conducted "a range of activities relevant to the development of a nuclear explosive device". Some of those activities continued until 2009, according to the IAEA.
By Andrew Aloia BBC Sport Last updated on 11 October 2021 11 October 2021 . From the section Football Watson was a trailblazer who helped transform how football was played There are two murals of black footballers facing one another across an alleyway in Glasgow. One helped shape football as we know it, the other is Pele. Andrew Watson captained Scotland to a 6-1 win over England on his debut in 1881. He was a pioneer, the world's first black international, but for more than a century the significance of his achievements went unrecognised. Research conducted over the past three decades has left us with some biographical details: a man descended of slaves and of those who enslaved them, born in Guyana, raised to become an English gentleman and famed as one of Scottish football's first icons. And yet today, 100 years on from his death aged 64, Watson remains something of an enigma, the picture built around him a fractured one. His grainy, faded, sepia image evokes many differen
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