To measure the influencing factors associated with the analysis of ²²⁶Ra gamma spectra in order to obtain more acurate and precise measuring result on a basis of further optimizing the gamma spectrometry method for ²²⁶Ra activity.

A laboratory-based HPGe gamma spectrometer was used to carry out the studies on tracking measurement of sample sealing time, measurement of background fluctuation with lead shielding, analytical method, and selection of characteristic gamma ray energy peak of its daughter nuclides in ²²⁶Ra measurement.

After the sample was sealed for 12 d, the decay products of ²²⁶Ra-²²²Rn basically reached equilibrium. The day and night fluctuations of ²²²Rn in the shielded lead room were obvious but had no obvious regularity. The way of filling nitrogen into the shielded lead room could reduce or avoid the influence of background fluctuations. For 31 soil samples measured after 23 days of sealing, the result of using the efficiency curve method showed that the ²²⁶Ra result calculated from the 351.9 keV energy peak were generally higher than the 609.3 keV energy peak, and the higher ratio ranged from 8.0% to 20.7%. The result of relative comparison method showed that the deviation ratio of the two peaks ranged from -4.1 % to 10.3 %.

It is recommended to consider the uncertainty attributed from decay equilibrium about 4 % of measured at 12 d after the sample is sealed. When filling nitrogen through the shielded lead chamber to avoid background fluctuations, attention must be paid to the matching relationship between the volume of the lead chamber and the nitrogen filling flow. When the efficiency curve method is used to analyze the activity of ²²⁶Ra, the ²¹⁴Bi ( 609.3 keV ) energy peak has the effect of cascade coincidence addition, so ²¹⁴Bi(609.3 keV) energy peak should be avoided. When the relative comparison method is used to analyze the activity of ²²⁶Ra, both two energy peaks of ²¹⁴Pb ( 351.9 keV ) and ²¹⁴Bi ( 609.3 keV ) can be used.

γ-spectrometer; ²²⁶Ra; ²²²Rn