rad/elec defender....

I dont consider myself a Defender PRO, but I have played this combination twice over the last 5 years. Once in the very begining (May-June 04) and more recently after returning to the game from a 2+ year absence. Also I can only offer advice during the first 20 or so levels, so take that for whats its worth.

As far as synergy, Electric blast's secondary effect is rather unspectacular at first, especially if your like me and slot ACC first, damage next, and then later fine-tune other things into the attacks. That alone is a big reason why many shy away from Electric blasts.

Radiation on the other hand offers ALL KINDS of goodies, and the best part is you get ALOT of basics for survival and grouping VERY early.
You could say that Radiation is a great pairing for Electric because of its added controls that become available like Lingering Radiation, Choking Cloud and eventually EMP. But these added controls would help ANY secondary, so once again not a particular boost to Electric blast.

Some keys to playing both sets can be found in the guide section, but I will point out a couple of things that I have found that are helpful playing this combo.

1) Get Radiation Infection as soon as possible. I took the AoE Heal at level one and CB just because I like healing as a defense. At level 2 I took Lightning Bolt to speed up fights, and then RI at 4th. I would not take it any later than 6th.

2) Skip Enervating Field until after Stamina. Its very tempting to take it sooner, but its much more expensive as a toggle, and once you hit SOs and have Stamina, its very nice to have. Before that, it can drain you dry quite fast. On the flip-side though, if you mostly team, you can take it earlier because its very helpful to have both these toggles on a team.
Additionally, you should (once you have both of these toggles) anchor them to different enemies. Teams will continually drop your anchors before the fight is over, so having them on different targets means you can be bringing up a new anchor, but still have the team under the umbrella of the other toggle.

3) Short Circuit and endurance drain strategy seems very nice, but from what I understand is a late-blooming tactic (since I have yet to suceed at building a sapper character). You are welcome to try building in a sapper tactic, but I would skip that strategy early and rely on radiation until you start having lots of extra slots and more freedom to choose powers.

4) Electricity has only 2 Single target blasts, and this creates a problem building an attack chain. I am a big fan of Air Superiority for filling in on Electric, but it can get rather annoying taking AS on EVERY character, so consider other options like Flurry, Veteran reward Sands of Mu, or even Boxing (if you plan on taking Tough/Weave).
But here is another option which I personally shoot for. Turn Ball Lightning into a usuable third attack. You will need to slot ACC and DMG just like a regular attack, but that still leaves room for 1-2 more slots. I have taken Hasten on all my RAD/ELEC characters so I usually slot Ball Lightning at 1ACC, 3DMG, 2END. Pre-stamina this is very hard to pull off, but once Stamina kicks in, you will be surprised what AIM+BL+LB+CB+AS can do. With the decent Endurance Recovery that you get from 3-slotted Stamina and AM, you should be able to throw Ball Lightning around like crazy (if slotted for End reduction + Hasten)

Check out some guides for both sets and have fun. Its a good Character combination.