My following replies may seem harsh, but they are not meant to be. I'm here to help you learn and to help you from making regrettable mistakes. Please remember these forums are an educational resource that many other people base actions that directly impact the livelihood of their hives. When you tell the group you assume this or that is OK, you're giving them a green light to go and try it. Please try to refrain from making blind assumptions unless you have some supportive evidence (a book or your own testing) before posting an assumptive OK.
[... the salt is my idea...] [...it should be ok.]
Yeah but not natures, where do bees normally get salt during the winter, or even the spring?
If its not in nectar, and its not in pollen, I would not add it because you are likely to cause a dietry inbalance that is likely to cause illness or disease. Remember bees don't fly in colder temps, and if they don't fly they don't cleanse, if they don't cleanse, it sits in their gut and breeds, ferments, or whatever the unnecessary product does. At the very least, excessive waste fills the gut and makes it less useful for normal waste by-products, thus causing an unhealthy circumstance. This is why you never add anything more to the receipes than you are absolutely sure the bees need and the gut will absorb.
[radiation..hummm UV lights emmit alfa don't they? should have the same effect.]
UV doesn't penatrate deep, gamma does.
Gamma has a realitively short half life so it doesn't damage as much of the nutrition in the product.
A microwave does not work on the same principles so it is not a good alternative.
[...about blossoming.. ...when i should insert it.]
If plants are in bloom they have pollen. If there is a natural pollen source bees are substanually less likely to take up an artifical replacement, or possibly a suppliment, in place of fresh pollen.
[beeks...like to feed...in spring, ...but most of them feed them with syrup, and i've seen many of you opose to this.]
BKs are opposed to feedling light syrups in the fall as it causes excessive moisture in the hive, moisture that doesn't have the summer heat to evaporate and so it condensates in the hive wetting the bees and eventually freezing them. Most agree that feeding light 1:1 syrups are good for simulating the start of a spring flow, especially if it provided as a very slow flow (less holes in the feed jars).
[...don't feed them syrup but stuff that is called flat cake...]
In the US we make candy boards, sugar with as little water (moisture) as possible. This serves two purposes, first its food, second it gives the bees something to combine hive condensation with and have food as a by-product.
One point you must understand is nectar flows and that condition of that nectar. By condition I mean its thickness (ie 1:1 or 1:2 water to sugar ratios). If you feed the wrong ratios at the wrong time of the year, it is very possible to kill your bees. Remember you are simulating a flow and survival of the hive depends on the bees accurately reacting to the flow (real or poorly simulated).
I hope this has really expanded your understanding and I hope it serves as a strong building block for your future research and application.