187
ZERO-LEVEL LOCATION, CHANNELS
TOTAL-ABSORPTION GAMMA-RAY SPECTROSCOPY
180
181
182
183
184
185
186
187
188
189
190
2.615=MEV PHOTOPEAK LOCATION, CHANNELS/ 200
Fig. 4—Bismuth-214 matrix output error as a function of zero level
and “TI! photopeak location.
tion of the °T1 peak at channel 184.5 and the zero-energy position at
channel O for perfect calibration and the errors created by improper
calibration of the average field spectrum for the matrix amounts of
7453, Figure 5 shows the errors introduced in the 407a amounts present in May 1963. The radionuclides initially detected to be present on
Dec. 22, 1962, were “871, “4ce—™4pr, “Ba !9L ag MK MZ r_*Nb,
ics “mn, '°Sb, ‘1 and an unknown cluster providing lines of about
0.5 Mev. A recent study has attempted to determine the sources that
create the energy line at 0.5 Mev.
Calibrations were obtained for each noncoincident gamma source
in close geometry with the use ofa large tank of sand contaminated with
the desired radioactive source. For those sources providing the coincident gamma radiation, a solution containing the source was spread
and watered into the ground over a large detector solid angle on the
ground surface. With all input calibrations then known, the amounts of
each input relative to the calibration amounts were determined by
matrix-reduction techniques. These amounts were determined for each
gamma-ray-producing radionuclide for each 40-min spectrum and
plotted as a function of time in units of months. A typical period is
shown in Fig. 6, which shows ®Zr—*°Nb amounts.
Rainfall modulates the measured amounts of all inputs to a high
degree. Figure 7 shows the measured amounts of *!*Bi found to be pres-