用低能弱γ源测量电子对的近阈产生截面

MEASUREMENTS OF THE CROSS SECTION OF ELECTRON PAIR PRODUCTION NEAR THRESHOLD USING A LOW INTENSITY ^(60)Co γ RAY SOURCE

用2.7μCi的^(60)Co弱γ源和NaI(Tl)与Ge(Li)双探测器符合测量方法,测量了Al,Zn,Sn,Pb四种样品的电子对产生绝对截面。测量结果与前人用很强γ源得到的结果相符合,并验证了在近阈条件下,对产生截面满足Jaeger关系式:σ_(pair)=(Z^2+aZ^4)σ_0,求得对^(60)Co源γ光子,α=(1.51±0.23)×10^(-4),σ_0=(1.95±0.11)×10^(-2)mb。

The absolute cross sections of electron pair production in Al, Zn, Sn and Pb have been measured using a 2.7 μci ^(60)Co γ-ray source and two detectors (Ge(Li) and Nal(Tl)) in coincidence. The results are in good agreement with published works using high intensity ?-ray source. The measurements prove that the Z-dependence of the cross section near threshold satisfies the equation σ_(pair)= (Z^2 + aZ^4)σ_0 of Jaeger. We also obtained a = (1.51±0.23)×10^(-4), σ_0= (1.95±0.11)×10^(-2) mb for ^(60)Co γ-rays.