In response to Cliff's question on neutron meters

[P.Moutonnet]

P.Moutonnet writes: 

In response to Trevor Finch:
- I agree completely with the idea that a full drum of water (equipped
with an access tube the same size and the same product of those used
outfield) should give the REFERENCE for count rates;
- the measurement taken in the shield should be considered as standard
values and not used for calculating the ratio R of the calibration
curve;
- when different SMNP have the same geometry (i.e. the neutron source
centered in the middle of a tube counter 10-12 cm active length)
REFERENCE count rates can be used for cross-calibrations;
- when the probes have not the same geometry (i.e. first model of
Campbell probe which had the source at the extremity of a long detector)
there is no more linearity, and the REFERENCE value is not sufficient.
In that case the response curve in-between the probes should be
established over the full range of soil water content.

For a SMNP equipped with a centered neutron source and a tube counter
10-12 cm long, we obtained the following calibration curves (according
to Trevor formulation):

- sandy soil,	VSW = 0.726 R + 0.006
- silty soil,	VSW = 0.941 R - 0.016
- clayey soil	VSW = 1.054 R - 0.040

Hoping to be helpful.


>----------
>From: 	owner-sowacs@aqua.ccwr.ac.za[SMTP:owner-sowacs@aqua.ccwr.ac.za]
>Sent: 	Thursday, 19 March 1998 10:39
>Subject: 	In response to Cliff's question on neutron meters
>
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>Trevor Finch writes:
>