Schlattl Helmut, Zankl Maria, Eder Heinrich, Hoeschen Christoph
GSF-National Research Center for Environment and Health, Institute of Radiation Protection, Ingolstaedter Landstrasse 1, 85764 Neuherberg, Germany.
Med Phys. 2007 Nov;34(11):4270-80. doi: 10.1118/1.2786861.
The shielding properties of two different lead-free materials-tin and a compound of 80% tin and 20% bismuth-for protective clothing are compared with those of lead for three typical x-ray spectra generated at tube voltages of 60, 75, and 120 kV. Three different quantities were used to compare the shielding capability of the different materials: (1) Air-kerma attenuation factors in narrow-beam geometry, (2) air-kerma attenuation factors in broad-beam geometry, and (3) ratios of organ and effective doses in the human body for a whole-body irradiation with a parallel beam directed frontally at the body. The thicknesses of tin (0.45 mm) and the tin/bismuth compound (0.41 mm) to be compared against lead correspond to a lead equivalence value of 0.35 mm for the 75 kV spectrum. The narrow-beam attenuation factors for 0.45 mm tin are 54% and 32% lower than those for 0.35 mm lead for 60 and 120 kV; those for 0.41 mm tin/bismuth are 12% and 32% lower, respectively. The decrease of the broad-beam air-kerma attenuation factors compared to lead is 74%, 46%, and 41% for tin and 42%, 26%, and 33% for tin/bismuth and the spectra at 60, 75, and 120 kV, respectively. Therefore, it is recommended that the characterization of the shielding potential of a material should be done by measurements in broad-beam geometry. Since the secondary radiation that is mainly responsible for the shielding reduction in broad-beam geometry is of low penetrability, only more superficially located organs receive significantly enhanced doses. The increase for the dose to the glandular breast tissue (female) compared to being shielded by lead is 143%, 37%, and 45% when shielded by tin, and 35%, 15%, and 39% when shielded by tin/bismuth for 60, 75, and 120 kV, respectively. The effective dose rises by 60%, 6%, and 38% for tin, and 14%, 3% and, 35% for tin/bismuth shielding, respectively.
针对在60、75和120 kV管电压下产生的三种典型X射线光谱，将两种不同的无铅材料（锡以及80%锡和20%铋的化合物）用于防护服的屏蔽性能与铅的屏蔽性能进行了比较。使用了三个不同的量来比较不同材料的屏蔽能力：（1）窄束几何条件下的空气比释动能衰减因子；（2）宽束几何条件下的空气比释动能衰减因子；（3）对于正面平行光束全身照射人体的情况，人体器官和有效剂量的比值。与铅比较的锡（0.45 mm）和锡/铋化合物（0.41 mm）的厚度对应于75 kV光谱下0.35 mm铅当量值。对于60 kV和120 kV，0.45 mm锡的窄束衰减因子分别比0.35 mm铅的窄束衰减因子低54%和32%；0.41 mm锡/铋的窄束衰减因子分别低12%和32%。对于60、75和120 kV的光谱，与铅相比，锡的宽束空气比释动能衰减因子的降低分别为74%、46%和41%，锡/铋的宽束空气比释动能衰减因子的降低分别为42%、26%和33%。因此，建议通过宽束几何条件下的测量来表征材料的屏蔽潜力。由于在宽束几何条件下主要导致屏蔽降低的二次辐射穿透性低，只有更浅表的器官接受显著增加的剂量。对于60、75和120 kV，与铅屏蔽相比，女性乳腺组织接受的剂量在锡屏蔽时分别增加143%、37%和45%，在锡/铋屏蔽时分别增加35%、15%和39%。锡屏蔽时有效剂量分别增加60%、6%和38%，锡/铋屏蔽时有效剂量分别增加14%、3%和35%。
