Small is beautiful: low activity alpha and gamma sources for small-scale radiation protection research experiments

Figures & data

Table 2. Gamma radiation dose rates in µGy/h in cells grown in Petri dishes of varying diameter stacked on the euxenite-(Y) source.

	Stack position and dose rate in µGy^−h
Dish diameter	1	2	3	4	5	6
60 mm*	63 (60–67)	36 (34–38)	19 (18–20)	11 (10–11)	6.7 (6.3–7.0)	4.5 (4.2–4.7)
90 mm*	55 (52–59)	31 (29–33)	16 (15–17)	9.5 (8.9–10)	5.9 (5.5–6.2)	3.9 (3.7–4.2)
110 mm*	49 (45–53)	28 (26–30)	14 (13–15)	8.4 (7.8–9.1)	5.2 (4.8–5.6)	3.5 (3.2–3.7)
110 mm^#	51 (46–56)	29 (26–32)	15 (14–17)	8.8 (7.9–10)	5.4 (4.9–5.9)	3.6 (3.2–4.0)

Stack position 1 indicates a Petri dish standing directly on the source. Values in brackets represent dose rate ranges. Asterisk (*) marks values derived from thermoluminescence detector measurements. Hashtag (#) marks values derived from calculations based on source activity measurements.

Figure 1. Pictures of the euxenite-(Y) source embedded in the lead tray. a: View from top. b: source positioned inside an incubator with two stacked cell culture dishes.

Figure 2. Energy spectrum of the euxenite-(Y) source with characteristic isotope peaks measured with a High Purity Germanium detector. The spectrum was truncated at 1750 keV. Peaks from overlapping radionuclides are labeled by lists of radionuclides.

Table 1. Activities of the major radionuclides detected in the euxenite-(Y) mineral.

Radionuclide	Activity (kBq)	Uncertainty kBq)	Activity per kg (kBq)
^234mPa	397.5	26.4	1351.9
^226Ra	360.1	18.9	1224.7
^214Pb	332.1	30.1	1129.5
^214Bi	359.5	15.5	1222.7
^235U	14.1	0.95	48.0
^231Pa	14.1	3.03	48.0
^227Th	14.5	2.33	49.3
^219Rn	14.7	3.3	50.0
^232Th	9.15	0.39	31.1
^228Ac	9.31	0.58	31.7
^212Pb	7.82	1.26	26.6
^212Bi	10.1	1.19	34.4
^208Tl	8.89	0.63	30.2
^40K	0.64	0.13	2.2

Figure 3. Results of TLD dosimetry of the euxenite-(Y) source. Panel a: distribution and readings (in µGy/h) of TLD dosimeters on the source. Rings symbolize radii of 5, 20, 30, 40, 50 and 55 mm. Numbers in italics above the arrow represent the calculated average dose rate for an area between two radii. Panel b: black circles represent the average dose rate measured at each radius. Error bars represent standard deviations from the individual measurements.

Figure 4. MN frequencies (grey bars) and percent of binucleated cells (black dots) in U2OS cells exposed to gamma radiation from the euxenite-(Y) source for 192 h. Cells receiving 10.5 mGy were exposed in stack position 1 at 55 µGy/h and cells receiving 5.9 mGy were exposed in stack position 2 at 31 µGy/h. Asterisks mark large differences (d = 0.8–1.3, Cohen’s effect size). Error bars represent standard deviations from 3 independent experiments. BNC: binucleated cell.

Table 3. Fitted mean energy values with standard deviations and fluence for the three investigated ²⁴¹Am alpha sources (#1, #2 and #3).

Source ID	Mean energy (keV)	Fluence (counts/(s cm^2))
#1	4 850 ± 170	1.937 ± 0.051
#2	4 780 ± 210	2.524 ± 0.094
#3	4 920 ± 160	2.156 ± 0.051

The differences in fluence result from a 30% uncertainty of the ²⁴¹Am activity as declared by the producer.

Table 4. Fitted mean energy values with standard deviations for the three investigated alpha sources (#1, #2 and #3) measured in three different collimator locations on the source surface.

Source ID	Energy (keV)	Counts
#1	4 770 ± 150	124 ± 11
	4 800 ± 150	105 ± 10
	4 770 ± 140	137 ± 12
#2	4 640 ± 260	168 ± 13
	4 710 ± 180	184 ± 14
	4 680 ± 130	176 ± 13
#3	4 840 ± 140	173 ± 13
	4 820 ± 150	300 ± 17
	4 840 ± 140	231 ± 15

Number of counts are given to show the uniformity of these sources.

Figure 5. The alpha exposure setup. Panel A: polyethylene dish with Mylar foil strapped to the bottom. Panel B: A polyethylene lid with a drilled hole to allow air exchange is placed on top of the dish.

Figure 6. Characteristics of the ²⁴¹Am sources. Panel a: energy spectra for the three ²⁴¹Am sources. Data points represent measurements, lines represent Gaussian fits. Panel b: Graphical presentation of dose rate homogeneity of a source to cells growing on 2.5 µm Mylar calculated by Monte Carlo simulation using the Geant4 framework. Panel c: Dose rate across the source with 95% confidence intervals.

Figure 7. MN frequencies (grey bars) and percent of binucleated cells (black dots) in U2OS cells exposed to alpha radiation from a ²⁴¹Am source for 100 h. Asterisks mark very large differences (d > 1.3, Cohen’s effect size). Error bars represent standard deviations from 3 independent experiments. BNC: binucleated cell.