Mmm...belated reply here, I fear.
I won't repeat most of the stuff Sweno and Sofa said - I agree with a lot of their recommendations. What I'll add is stuff they didn't mention, or things that I disagree with.
Mind, I don't have a Rad/Rad defender. However, I do have a 50 Rad/Rad corruptor, and that's where I'm coming from. A corruptor, granted, has higher base damage than a defender. But IIRC it ain't THAT much higher, only something like 10-15% or so. But anyway...
Radiation Emission
Radiant Aura: Do realise that even with SOs this is pretty much the worst AoE heal in the game. You will never be a great healer. Suck it up and move on. =D
Radiation Infection: As Sweno said, the ToHit Debuff is what you should enhance here, not the Def debuff. However, as it is a Def debuff, you can slot an Achilles Heel chance for -resistance debuff in this power. You can also slot Achilles Heel procs in your Radiation blasts. Think about this - if you're looking to do damage, more -res is a good way to go.
Accelerate Metabolism: This is a great buff. If you take it, you may want to - as Sweno and I do - set up a bind or macro to warn people when you're ready to fire it, which is generally a good idea for AoE buffs.
Enervating Field: Take it, love it, but you already know this.
Mutation: Some rad players actually don't take this, especially if they solo often. Depends on how team-friendly you want to be.
Lingering Radiation: I think there's some wiggle room in how you wanna slot it. Personally, I think you want accuracy and recharge at the very least. It needs to hit, and you want it up as often as possible. But don't underestimate the utility of the slow element here.
Choking Cloud: Think about this one carefully. As Sweno demonstrates, it is a stunningly effective power when six-slotted. The problem is that it's only good when six slotted. Anything less kind of sucks. The endurance cost is immense. It's also less useful if you intend to stay at range...which is Sofa's suggestion for blast choices, though I disagree with that. Still, realise it only comes into its own when you're in the middle of the fray. But if you're in the fray, well, Radiation Infection and Enervating Field may be protection enough.
Fallout: Fallout does a great deal of damage, but using it effectively is difficult. If your ally's corpse isn't well-placed, the boom won't be that useful. Moreover, people may rez (or someone else might rez them) before you get the boom off. You can use Recall Friend to reposition the corpse, but by now you're drifting into very fiddly and silly territory.
EM Pulse: Not much to add here. Strongly recommended, regardless of whether you use it regularly or only as a panic button. Think about the utility of chaining this with your nuke, Atomic Blast.
Radiation Blast
(This is where I disagree a lot with Sofaspud. He's working on the premise that it's best to stay at range and blast from far away. His power choices reflect that. However, he's an Emp/Rad. You're not. You're a Rad/Rad. I think that makes a big difference.)
Neutrino Bolt: As Sweno indicated, it is possible to use this as a utility power rather than an attack proper. Consider even slotting this full of procs - chance for hold, chance for resistance debuff, and so on. The fact it can be spammed non-stop makes it a good choice to proc out.
X-Ray Beam: This is a decent single-target attack, but depending on your other attack choices and recharge, you may not need this. I don't regret not having it.
Irradiate: As you see, Sweno and Sofaspud disagree on this. Me? I'm with Sweno. This is an excellent power to take. Why? Look, it's an AoE. AoE damage is generally better than single target damage on teams. Yes, you need to fire it at point-blank range, but between Radiation Infection and Enervating Field, that's fine. Also, I believe it does a higher defense debuff than the other blasts in the Radiation set.
Electron Haze: This is a cone. It hits multiple enemies. As I've noted, this is a Good Thing. However, do note that Electron Haze is a very skinny cone, and the range isn't great. I do suggest slotting this for range as well as the usual accuracy/damage. Better yet, use set IOs or Hami-Os to enhance range in addition to everything else. While I like Electron Haze, do realise it has a long animation for not that much damage - this is enough to cause some folks to avoid it. Your milage may vary.
Proton Volley: I don't like this. Surprised? Well, think about it for a second. It does a lot of damage, and there's some utility in having a snipe power. However, it also takes a long time to use - regardless of whether you're interrupted or not, it roots you for a while and takes ages to animate. This may not be a very efficient use of time. Secondly, you're probably going to open fights with your toggle debuffs, not a snipe. Moreover, if you're using Irradiate, Electron Haze, and Cosmic Burst...their short ranges mean you want to be up close anyway... probably within your own debuff zone.
Some people say a snipe is worth it as a pulling power, but there are very few things in the game that really need a snipe to pull. Neutrino Bolt works well enough for me.
Aim: Due to all your defense debuffs, the primary bonus of this power - increased tohit - is actually not as useful. However it is a damage buff, and that's good. You can delay this till later in your build though.
Cosmic Burst: No debate HERE though. THIS is your BEST single target attack. However, I do suggest enhancing this (at least in part) for range, given that - like most high damage single target blasts - it requires you to be very close. Which is another reason why I don't think Proton Volley is worth it.
Neutron Bomb: It's a targeted damage AoE. Let's say this again. It's a targeted AoE. AoE is your friend.
Atomic Blast: It's a nuke. Nuke does big boom. Big boom is good.
However, as you know - nuke also drains your endurance. But here's the thing. Defenders can get Power Sink from the Elec Ancillary Power Pool. Power Sink is an autohit point-blank AoE end drain...that restores your end.
So what you can do is nuke, pop one small blue inspiration, fire Power Sink off any survivors, and be back to full. Two or three enemies should be enough to fill your bar back up, and as a Defender your nuke probably won't COMPLETELY wipe out the bad guys, especially if there's Bosses. This is a favourite tactic of mine. =D
Mind you, even without Power Sink... the end crash isn't really THAT big a deal. Just make sure you carry a bunch of blues, and combo other inspirations to make new ones as you progress through a mission.
-- Acyl
I won't repeat most of the stuff Sweno and Sofa said - I agree with a lot of their recommendations. What I'll add is stuff they didn't mention, or things that I disagree with.
Mind, I don't have a Rad/Rad defender. However, I do have a 50 Rad/Rad corruptor, and that's where I'm coming from. A corruptor, granted, has higher base damage than a defender. But IIRC it ain't THAT much higher, only something like 10-15% or so. But anyway...
Radiation Emission
Radiant Aura: Do realise that even with SOs this is pretty much the worst AoE heal in the game. You will never be a great healer. Suck it up and move on. =D
Radiation Infection: As Sweno said, the ToHit Debuff is what you should enhance here, not the Def debuff. However, as it is a Def debuff, you can slot an Achilles Heel chance for -resistance debuff in this power. You can also slot Achilles Heel procs in your Radiation blasts. Think about this - if you're looking to do damage, more -res is a good way to go.
Accelerate Metabolism: This is a great buff. If you take it, you may want to - as Sweno and I do - set up a bind or macro to warn people when you're ready to fire it, which is generally a good idea for AoE buffs.
Enervating Field: Take it, love it, but you already know this.
Mutation: Some rad players actually don't take this, especially if they solo often. Depends on how team-friendly you want to be.
Lingering Radiation: I think there's some wiggle room in how you wanna slot it. Personally, I think you want accuracy and recharge at the very least. It needs to hit, and you want it up as often as possible. But don't underestimate the utility of the slow element here.
Choking Cloud: Think about this one carefully. As Sweno demonstrates, it is a stunningly effective power when six-slotted. The problem is that it's only good when six slotted. Anything less kind of sucks. The endurance cost is immense. It's also less useful if you intend to stay at range...which is Sofa's suggestion for blast choices, though I disagree with that. Still, realise it only comes into its own when you're in the middle of the fray. But if you're in the fray, well, Radiation Infection and Enervating Field may be protection enough.
Fallout: Fallout does a great deal of damage, but using it effectively is difficult. If your ally's corpse isn't well-placed, the boom won't be that useful. Moreover, people may rez (or someone else might rez them) before you get the boom off. You can use Recall Friend to reposition the corpse, but by now you're drifting into very fiddly and silly territory.
EM Pulse: Not much to add here. Strongly recommended, regardless of whether you use it regularly or only as a panic button. Think about the utility of chaining this with your nuke, Atomic Blast.
Radiation Blast
(This is where I disagree a lot with Sofaspud. He's working on the premise that it's best to stay at range and blast from far away. His power choices reflect that. However, he's an Emp/Rad. You're not. You're a Rad/Rad. I think that makes a big difference.)
Neutrino Bolt: As Sweno indicated, it is possible to use this as a utility power rather than an attack proper. Consider even slotting this full of procs - chance for hold, chance for resistance debuff, and so on. The fact it can be spammed non-stop makes it a good choice to proc out.
X-Ray Beam: This is a decent single-target attack, but depending on your other attack choices and recharge, you may not need this. I don't regret not having it.
Irradiate: As you see, Sweno and Sofaspud disagree on this. Me? I'm with Sweno. This is an excellent power to take. Why? Look, it's an AoE. AoE damage is generally better than single target damage on teams. Yes, you need to fire it at point-blank range, but between Radiation Infection and Enervating Field, that's fine. Also, I believe it does a higher defense debuff than the other blasts in the Radiation set.
Electron Haze: This is a cone. It hits multiple enemies. As I've noted, this is a Good Thing. However, do note that Electron Haze is a very skinny cone, and the range isn't great. I do suggest slotting this for range as well as the usual accuracy/damage. Better yet, use set IOs or Hami-Os to enhance range in addition to everything else. While I like Electron Haze, do realise it has a long animation for not that much damage - this is enough to cause some folks to avoid it. Your milage may vary.
Proton Volley: I don't like this. Surprised? Well, think about it for a second. It does a lot of damage, and there's some utility in having a snipe power. However, it also takes a long time to use - regardless of whether you're interrupted or not, it roots you for a while and takes ages to animate. This may not be a very efficient use of time. Secondly, you're probably going to open fights with your toggle debuffs, not a snipe. Moreover, if you're using Irradiate, Electron Haze, and Cosmic Burst...their short ranges mean you want to be up close anyway... probably within your own debuff zone.
Some people say a snipe is worth it as a pulling power, but there are very few things in the game that really need a snipe to pull. Neutrino Bolt works well enough for me.
Aim: Due to all your defense debuffs, the primary bonus of this power - increased tohit - is actually not as useful. However it is a damage buff, and that's good. You can delay this till later in your build though.
Cosmic Burst: No debate HERE though. THIS is your BEST single target attack. However, I do suggest enhancing this (at least in part) for range, given that - like most high damage single target blasts - it requires you to be very close. Which is another reason why I don't think Proton Volley is worth it.
Neutron Bomb: It's a targeted damage AoE. Let's say this again. It's a targeted AoE. AoE is your friend.
Atomic Blast: It's a nuke. Nuke does big boom. Big boom is good.
However, as you know - nuke also drains your endurance. But here's the thing. Defenders can get Power Sink from the Elec Ancillary Power Pool. Power Sink is an autohit point-blank AoE end drain...that restores your end.
So what you can do is nuke, pop one small blue inspiration, fire Power Sink off any survivors, and be back to full. Two or three enemies should be enough to fill your bar back up, and as a Defender your nuke probably won't COMPLETELY wipe out the bad guys, especially if there's Bosses. This is a favourite tactic of mine. =D
Mind you, even without Power Sink... the end crash isn't really THAT big a deal. Just make sure you carry a bunch of blues, and combo other inspirations to make new ones as you progress through a mission.
-- Acyl