Lead shielding thickness - what are the lead codes?

Source: Ionactive Radiation Protection Resource

Lead shielding for radiation protection

Lead shielding is a popular material of choice in radiation protection - its use for shielding gamma and x-rays goes back to the first discovery / use of such ionising radiations. It's density is particularly important in this regard (about 11.3 g/cm3) and lead is malleable so it can be easily bent / pushed into a shape / wrapped around pipes and so on. This malleability means it is not so good as a construction material so unlike concrete radiation shielding which may perform two functions (shielding and structural), lead shielding has to be supported in some way (i.e. within laminated boards for relatively thin lead, and using a steel supporting structure where significant lead is required).

Where significantly thick lead is required (e.g. 10's - 100's mm), lead bricks are often the better option and these will usually come in 50mm and 100mm options and will be shaped so they can lock into each other so providing continuous shielding - these options will not be considered further in this particular resource.

Since lead codes relate to specific thickness dimensions there is often a compromise required, so you may need to use a lead code above what you actually require in order to meet your shielding specification (this can result in over shielding). However it is often desirable to mix more than one lead code to more closely meet the shielding design without excessive over shielding. This has the added advantage of minimising the weight - due to it's density lead can create serious manual handling issues - a single 1m2 sheet of Code 3 lead (1.32 mm) will weigh around 15kg, and much more if the lead is laminated into plywood or plasterboard (which is often the case for wall and ceiling shielding).

Let's take a look at the lead codes.

Lead codes (Code 3 - Code 8)


Lead Code
Lead
(mm)
Weight
(kg/m2)
Code 3

1.32

15.0
Code 4
1.8
20.4
Code 5
2.24
25.4
Code 6
2.65
30.1
Code 7
3.15
35.7
Code 8
3.55
40.3

The above data is compatible with BS EN 12588 and the lead thickness will have a ± 5% tolerance. The weight data is provided for general information and is rounded to one significant figure.

General comments

You will find that lead codes (i.e. sheet lead shielding) tend to be used for relatively low energy applications (i.e. up to about 150 kVp if we are considering x-ray tubes). For 150 kV it is often reported that the TVT (10th Value Thickness) is 0.95 mm lead (so practically 1 mm lead). Whilst this is a good working assumption, at lower kV the first two TVT will be much lower than this - this is very prominent for about 50-70 kV (but is seen to a lessor extent right up to 150 kV). For 25-50 kV the TVTs are not surprisingly much less.

Nothing in life is to be feared, it is only to be understood. Now is the time to understand more, so that we may fear less

– Marie Curie -