The dose equivalent rate of 225Ac and its daughter equilibrium system were measured and calculated.In addition,the dose equivalent rates of 131I and 99mTc with the same activity were also calculated.The tenth-and half-value thicknesses of lead for 225Ac were derived based on measurement data.The results show that dose equivalent rate at 0.5 m,for unshielded 85.5 MBq 225Ac,is 4.56 times higher than dose equivalent rate maximum limit 2.5 μSv/h of personnel operation positions form standard.The measured and theoretical values of dose equivalent rate at 0.5 m are more consistent than those at 0.15 m for 225Ac source,especially under lead shielding conditions of 0 mm,5 mm,10 mm,15 mm,and 20 mm.For the same activity,measured dose equivalent rate of 225Ac is about half of 131I and about 1.5 times of 99mTc theoretical value.We should pay attention to external radiation protection during the use of 225Ac.It is suggested that,20 mm can be used as the lead tenth value thickness,and 5 mm as the lead half value thickness conservatively for 225Ac and its descendants.
225AcLeadRadiation protectionLead tenth value thicknessNuclear medicine
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