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一、正电子源和样品实验中所用正电子源为~(22)Na,~(22)Na的β~+衰变放出一个正电子,过3PS后放出1.28Me_v的γ射线,因为3PS相对于正电子寿命来说可以忽略,所以用1.28Mev的γ射线产生的时刻作为所研究事件的起始时间是合理的.正电子进入样品后的热化时间也只有几个PS,所以用1.28Mev和0.511Mev的两种γ射线间的时间间隔代表正电子湮没寿命也是合理的.由于~(22)Na有起始γ射线作为时间零点,加上~(22)Na的半衰期长,约为2.6年,使用方便,β~+衰变效率高,所以是理想的正电子源.本实验用的~(22)Na源,系用~(22)NaCl密封于几个μm厚的镍箔或密勒(Mylar)膜内,再将源夹于两个相同的样品之间,形成所谓的“夹层”排到.这样会有一部分正电子在镍箔或密勒膜中湮没,精确测量时,可在计算机程序中扣除~(22)Na源的载体效应.本实验源强为8μci.
First, the positron source and the sample used in the experiment for the positron source ~ (22) Na, ~ (22) Na β ~ + decay emit a positron, after 3PS release 1.28Mev gamma rays, because 3PS relative to the positive Electron lifetime is negligible, so it is reasonable to use the 1.28Mev γ-ray generation time as the starting time of the studied event.The positron possesses only a few PS after the sample has been heated in the sample, so with 1.28Mev and 0.511 It is also reasonable that the interval between the two γ-rays of Mev represents the lifetime of positron annihilation.As ~ (22) Na has initial γ-ray as time zero and ~ (22) Na has a long half-life of about 2.6 years, Easy to use, β ~ + decay efficiency is high, so it is an ideal positron source.The ~ (22) Na source used in this experiment was sealed with ~ (22) NaCl in several μm thick nickel foil or Mylar ) Film, and then the source is sandwiched between two identical samples to form a so-called “sandwich.” Thus, a portion of the positrons are annihilated in the nickel foil or the Miller film. Accurate measurements can be performed in a computer program The carrier effect of ~ (22) Na-source was deducted from the experiment. The source intensity of this experiment was 8μci.