Drowning in a radioactive sea of nuclear jargon, mixing up Bushehr and breakout, plutonium and Parchin, centrifuges and code 3.1?

As Iran and six world powers negotiate in Switzerland on ending the crisis over Tehran's nuclear programme, here is an A-to-Z glossary of the key technical terms:

A is for Arak

Until 2014, Iran was building a heavy water reactor at Arak. In theory, once operational, it could give Iran plutonium, the alternative to uranium for a nuclear weapon.

B is for Breakout

The time Iran would need, in theory, to make a worth of nuclear material. The powers want this "breakout time" extended to at least a year to give them time to react.

C is for Centrifuge

Machines that "enrich" uranium gas by spinning it at supersonic speeds, increasing the proportion of a fissile isotope, known as U-235, used for different purposes (see enrichment below).

D is for Downblending

Under a November 2013 interim deal (see JPOA below), Iran "downblended" its stock of converted uranium enriched to medium purities to low.

E is for Enrichment

Natural uranium contains 0.7 percent U-235. Enriched to 3.5-5.0 percent, it can be used for nuclear power reactors, 20 percent for nuclear medicines and 90 percent for a bomb. The process gets progressively easier.

F is for Fuel

Iran says its programme is to make fuel for 20 future reactors. Russia is contracted to fuel Iran's only existing plant, Bushehr, until 2021.

G is for Gachin

A uranium mine. The powers want to keep a closer eye on mines to ensure uranium is not being taken to secret enrichment sites.

H is for HEU

Iran would need around 1,000 kilogrammes of low-enriched uranium (LEU) to make enough highly-enriched uranium (HEU) for one bomb. It currently has some 8,000 kg of LEU.

I is for IAEA

The UN atomic watchdog, the International Atomic Energy Agency, keeps close tabs on Iran's nuclear activities and would have a beefed-up role under any deal.

J is for JPOA

The Joint Plan of Action, the November 2013 "interim deal" under which Iran froze certain nuclear activities in exchange for minor sanctions relief.

K is for Khan

Pakistani nuclear scientist Abdul Qadeer Khan, believed to have shared expertise with Iran.

L is for Light-Water

If Arak is changed to a light-water reactor, it will significantly rediuce the amount of plutonium than can be extracted from the spent fuel.

M is for Missiles

Western powers want Iran's ballistic missiles programme to be covered under any deal, but Tehran does not.

N is for Natanz

Iran's main enrichment facility, with some 17,000 IR-1 centrifuges installed, including 1,000 faster IR-2M machines, but with a capacity of some 50,000.

O is for Oman

Oman was where Iran and the US held secret talks which dated back to 2012 and led to the current diplomatic effort.

P is for P5+1

The group of six powers negotiating with Iran: the US, Russia, China, Britain, France and Germany. All except Germany have nuclear weapons.

Q is for Qom

Iran's second main enrichment facility Fordo, near the holy city of Qom, is built into a mountain, making it virtually impregnable to military strikes.

R is for R&D

The powers want strict limits, or a complete stop, of Iran's research and development of newer, faster centrifuges.

S is for SWU

Separative Work Units -- a measure of the efficiency of centrifuges.

T is for TRR

The Tehran Research Reactor, originally supplied by the US, used to make nuclear medicines.

U is for UF6

Uranium hexafloride, the gaseous form of uranium for enrichment.

V is for Virtual Nuclear Weapon State

A country whose expertise and facilities put them on the threshold of being able to make nuclear weapons.

W is for Weaponisation

The work needed to be done to put uranium or plutonium in a bomb.

A stalled IAEA probe covers allegations Iran did research in this area -- the infamous "possible military dimensions" (PMD) file -- including at Parchin.

X is for Xenon

Can be used for testing centrifuges

Y is for Yellowcake

Processed uranium ore, then converted into uranium tetrafluoride and uranium hexafloride (see above). Not for eating, and not really yellow.

Z is for Zirconium

Metal used for cladding fuel rods in a reactor.

And ... 3.1

Modified Code 3.1, part of Tehran's contract with the IAEA revoked by Iran. This, like the so-called Additional Protocol which Iran stopped implementing, allows for closer oversight.