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Radioisotopes
Units and Measurements of Radioactivity
The SI unit of measurement of radioactivity
is the Becquerel: 1 Becquerel (Bq) = 1 Disintegration per second
The more commonly encountered units
are disintegration per minute (dpm) and curie (Ci)
| Conversion factors: |
|
|
| 1 Bq |
= 60 dpm |
|
| 1 Ci |
= 3.7 x 1010 Bq |
= 2.22 x 1012 dpm |
| 1 millicurie (mCi) |
= 3.7 x 107 Bq |
= 2.22 x 109 dpm |
| 1 microcurie (µCi) |
= 3.7 x 104 Bq |
= 2.22 x 106 dpm |
| 1 day |
= 1.44 x 103 min. |
= 8.64 x 104 sec. |
| 1 year |
= 5.26 x 105 min. |
= 3.16 x 107 sec. |
counts per minute (cpm) x (counting
efficiency)
Physical Properties of Commonly Used Radioisotopes
| Nuclide |
Half-lifetime |
Emission |
Energy, max. (MeV) |
Range of emission, max. |
Rec. shielding (half value layer) |
| 3H |
12.43 years |
ß |
0.0186 |
0.42 cm (air) |
— |
| 14C |
5,370 years |
ß |
0.156 |
21.8 cm (air) |
— |
| 32Pb |
14.3 days |
ß |
1.71 |
610 cm (air) |
Acrylic (1 cm) |
| |
|
|
|
0.8 cm (water) |
— |
| |
|
|
|
0.76 cm (Plexiglas®) |
— |
| 33Pb |
25.4 days |
ß |
0.249 |
49 cm |
Acrylic (1 cm) |
| 35S |
87.4 days |
ß |
0.167 |
24.4 cm (air) |
— |
| 125Ic |
60 days |
γ |
0.27–0.035 |
0.2 mm (lead) |
Lead (0.02 mm) |
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