Re: neutron probe aluminium tube

[Nick Austin <nick.austin@agric.nsw.gov.au>]

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     Magdeline,
     
     I recommend a book by Dr E.L. Greacen (1981) called 'Soil water 
     assessment by the neutron method, and published by CSIRO Australia. 
     Unfortunately it's now out of print, but you may be able to borrow a 
     copy from somewhere. Chapter 7, 'Field installation and maintenance', 
     describes a method for installing access tubes encased in a slurry:
     
     'The slurry, consisting of 40% kaolinite, 10% Portland cement and 50% 
     water by weight, is placed in the bottom of an oversize hole (6-10 mm 
     larger in diameter than the access tube) by pouring through a plastic 
     pipe and using a push rod to empty the pipe before removing it from 
     the hole. This will avoid coating the sides of the hole with the 
     slurry. The tube, sealed at the bottom, is inserted into the slurry to 
     displace it up the full length of the tube, filling the annular space 
     between soil and tube.'
     
     The chapter goes on to say 'Williams (pers comm) compared neutron 
     counts in tubes with and without slurry. Three types of slurry were 
     used; kaolin/cement, local clay material/cement and soil/cement. 
     Higher count rates were obtained in the tubes with a slurry due, 
     probably, to the bound water present in the slurry'.
     
     We've used the technique routinely in duplex red-brown earth soils and 
     have had very satisfactory results. Calibration was, however, 
     performed on tubes installed in a similar fashion.
     
     Hope this helps
     
     Regards
     
     Nick
     
     PS Unless you like being slurried, try and get someone else to push 
     the access tubes in!
     
     ___________________________________
     
     Nick Austin
     Water Use Efficiency Advisory Unit
     PO Box 865 DUBBO NSW 2830 AUSTRALIA
     nick.austin@agric.nsw.gov.au
     +61 2 6881 1280 (Direct)
     +61 2 6881 1270 (Switch)
     +61 2 6881 1295 (Fax)
     ___________________________________

     


______________________________ Reply Separator _________________________________
Subject: neutron probe aluminium tube 
Author:  <owner-sowacs@aqua.ccwr.ac.za> at smtpgwy
Date:    26/08/1999 19:05


Dear subscribers,
     
I have a slight dilemma. I have recently installed a neutron probe aluminium 
access tube and the hole drilled for installation is slightly larger than 
the tube (only about < 5mm diameter). Should I leave the small air gap as it 
is or fill it with bentonite? Which will affect my readings more?
     
Thanks
     
     
****************************************************************
     
Magdeline Pokar,                Tel: 0113-2335231 (O)
School of Earth Sciences,             0113-2343795 (H) 
University of Leeds,                Fax: 0113-2335259
Woodhouse Lane,                        email: M.Pokar@earth.leeds.ac.uk 
Leeds, West Yorkshire,
LS2 9JT. UK