what is the true reason Venus has this atmosphere? is it because of vicinity to the sun, or because of radiation forces with a concentration of CO2? at what levels of CO2 concentration, and the highest known spike of radiation concentrations, and the overlapping bounce of radiation in the atmosphere with the carbons constitute a full covering?
Venus has a runaway greenhouse effect. The reasons are several. First, is its closeness to the sun. Objects near the sun are far hotter than those further from it.
Second, which is relative to the first reason, is that Venus doesn't have oceans of water that the Earth has. Venus never had oceans of water. There is a small amount of evidence that shows Venus had maybe 6 feet deep ponds and other small bodies of water, but nothing compared to the oceans we experience here on Earth. The water that was on Venus evaporated very quickly due to Venus' location near the sun.
Remember, these oceans act as carbon sinks which absorb the CO2 from the atmoshphere and store it in carbonaceous rocks, such as limestone, at the bottom of the ocean. Without oceans, the CO2 accumulated very quickly and in great amounts.
Third, is Venus' mass. Mercury, you will notice, is even closer to the sun than Venus is, but it doesn't have a runaway greenhouse effect. Venus has enough mass to hang on to its atmosphere, where as Mercury is not massive enough, and its escape velocity is much lower, allowing the atmosphere to escape into space.