I am reading the book Darth Plagueis, and when an assassination attempt is made on him by use of a nuclear bomb, the book states that nuclear weapons are scarcely available.
I searched briefly but found nothing on this and wondered if an explanation is available. Why would nuclear weapons be rare in a universe with such advanced technology across the board?
They aren't as rare as they seem.
Proton torpedos and concussion missiles both were nuclear.
Thermal detonators (like the one Leia threatened Jabba with are nuclear fusion devices.
Please note that the first 2 bullet points listed are from Wookieepedia but aren't properly sourced, so I'm slightly skeptical of both.
The materials needed to build them were better used elsewhere (Ion engines used radioactive materials).
They had comparable power weapons that were cheaper and safer.
Capital ship turbolasers:
There are 12 heavy turbolasers and roughly 120 light turbolasers on an ISD1 (ref. SWICS).
The heavy turbolasers are roughly 125 times bigger than the light turbolasers (which were seen vaporizing asteroids in TESB).
If firepower is proportional to size (an unsubstantiated but not unreasonable postulate) then the sustainable power outputs of the heavy and light guns work out to 47 million TW and 375,000 TW respectively.
Refire rates seem to be roughly 1 shot per 2 seconds, so the energy level of each individual blast would have to be 94 million TJ (22 gigatons of TNT) for heavy turbolasers and 750,000 TJ ( 179 megatons) for light turbolasers.
(src: https://www.stardestroyer.net/Empire/Tech/Beam/Beam2.html)
HAVw A6 Juggernauts could produce heat on the level of a nuclear bomb.
The formation and dispersal of the heavy elements beyond iron-56 depends primarily on supernovas, particularly type II supernovas. Lenticular galaxies like the one shown below tend to contain primarily older and lower mass stars. This means fewer supernovas and lower concentrations of elements like plutonium and uranium throughout the galaxy. The paucity of fissile materials explains the rarity of nuclear bombs.
Prior to the Old republic giving Chancellor Palpatine the extraordinary powers that would lead to it becoming the empire, there were not great fleets of combat ships and weapons. At the time of Plagious the Republic had lived in peace for so long that there was not a great trade in weapons or need for Military grade weaponry. So yes at that time there were very few of these types of weapons available in the Republic.
With in few years of this incident the Empire would emerge and that demand and supply would grow exponentially.
It is also important to note that the word used was rare not that it was unheard of or even unpredictable that his enemies would use it. Just that the rarity and cost of such items helped Plagious to focus his investigation into the perpetrators on those people with the power and money to acquire them.
My best guess would be that nukes are long outdated by energy weapons as they are going to be soon in our reality. Nukes can be targeted and shot down by lasers in our world now. In the Star Wars movies they didn't show all of their tech or go into all of the history of how war evolved. I imagine that if a nuke were launched, that hidden laser turrets would emerge from bunkers automatically and easily destroy an oncoming missile or bomb. I have often wondered why the empire didn't send in drones with nukes on them in the battle of Hoth to destroy the rebels that way. My best guess is that the empire's main goal was to surprise the rebels and take captives to obtain information about the whereabouts of the rest of the alliance. The alliance would have had bases dispersed throughout the galaxy and if a nuke type device killed everyone then there would have been no one left to interrogate about the others. I played a computer game that you could use the Death Star to destroy whole planets (can't remember the game's name). If you destroyed too many planets then the whole empire would turn against you and join the Rebel Alliance. Using nukes that send out radiation poisoning killing millions of civilians would be a good way to get star systems against the Empire in a hurry.
