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At its meeting in 1972, the CCRI (at that time the CCEMRI) decided on a series of radiation qualities to be used for comparisons in low- and medium-energy x-radiation. These qualities are specified in terms of the generating potential and the half-value layer, that is, the thickness of aluminium or copper required to reduce the air kerma rate at the reference point by half. Since that time, an additional comparison quality at 25 kV has been added. More recently, mammography comparison qualities have also been introduced at the BIPM.
| Generating potential/kV |
Half-value layer/mm |
|
| Aluminium |
Copper |
|
| 10 |
» 0.036 |
|
| 30 |
0.18 |
|
| 25 |
0.25 |
|
| 50 1 |
1.0 |
|
| 50 2 |
2.3 |
|
| 100 |
4.0 |
0.15 |
| 135 |
|
0.50 |
| 180 |
|
1.0 |
| 250 |
|
2.5 |
1. Commonly referred to as the 50 kVb quality.
2. Commonly referred to as the 50 kVa quality.
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Summary
