The Maypack Insert was designed to carry filters that maximise the absorption or filtration of airborne iodine either in the form of particles or vapour and to fit into the Maypack Adapter BTS495.
The design consists of a cylindrical tube mounted with gauze retainers and locking rings to accommodate the appropriate filter papers and a spring to compress the charcoal bed on assembly to prevent shakedown.
The ‘Maypack’ adapter (BTS 495) is also manufactured by Bird & Tole, to accommodate the insert into a line either using the Stack Sampling unit BTS 327 (The range of sampling flow rates are typically from 10 – 30 litres per minute) or attached directly onto a Bird & Tole Air Sampling Unit’s (BTS 601 Series) Filter Holder.
Assembly of filters in the Maypack (upstream to downstream) is as follows:
- A high efficiency particulate filter eg. A Millipore type AA filter or a Whatman glass fibre filter type GF/A.
- One or two activated charcoal impregnated filters – typical, Bird & Tole BTS 684.
- A bed of 20 – 25g of activated Coconut charcoal (BTS 703) giving a layer about 25mm thick.
As a rough guide:
The airborne iodine collected in the pack may be quantitatively assessed by either direct gamma counting or by separate measurements of the activity on individual components of the pack. The latter can give information on the chemical or physical form of the iodine*.
Millipore glass fibre filter: Iodine absorbed into particals.
Charcoal loaded filters: Iodine vapour and some Methyliodide (Organic iodine).
Charcoal granules: Inorganic iodine compounds as vapour (also iodine vapour & Methyliodide if Charcoal filter papers are omitted.)
Notes on the specification of sampling media
Glass fibre filter - Whatman type GF/A Collection efficiency > 99.9% for particles of 0.6um at a face velocity of 25cm/s.
Carbon paper – Whatman glass fibre, impregnated with Charcoal type ACG/B. Collection efficiency of elemental iodine vapour > 99.9% at a face velocity of 9cm/s.
Charcoal bed of activated charcoal, Sutcliff Speakman 208C 10/18 mesh, derived from coconut shell.
Coconut shell carbons have a very small pore radii and are therefore ideal for adsorption of small molecules, usually in a gaseous phase. Coal based carbons contain larger pores and liquid phase applications to absorb the larger type of molecule.
BTS495 - Maypack Adapter
BTS492 - Maypack Insert
NB: Please specify SS at the end of the order code if Stainless Steel is preferred