The present invention relates to a method for preparing linear alpha olefin comonomers, such as 1-butene, 1-hexene or 1-octene, from ethylene monomer. In exemplary embodiments of the present invention, by using a hydrophobic porous membrane, an alkaline material such as sodium that is generated together with hydrogen gas in a hydrolysis reaction of a metal hydride compound can be eliminated effectively. The phosphor layer has a coating weight of 2. For example, the randomization list may include those signals that can be randomized upon exiting from a powered down state.