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1.0. INTRODUCTION
The Model RS400-HTO portable tritium monitor is a small, high sensitivity, hand held, battery
operated fully gamma compensated survey meter with an RS232 serial data output. The
instrument case is constructed of light weight aluminum. A handle is attached for hand held survey
use. The instrument will measure tritium in its elemental and oxide form or can be configured to
measure oxide form only.
Note: This special version of the Model RS400-HTO has the Alkaline Battery Option.
1.1. PHYSICAL
DESCRIPTION
The Model RS400-HTO uses four identical ionization chambers arranged in a cruciform pattern.
Two ionization chambers, with a total volume of 400 cc, are used for measurement; the other two
chambers serve for gamma compensation.
The sample stream is drawn through the ionization chambers by means of a small rotary vane
pump, which is always plumbed at the outlet of the furthest down stream ionization chamber.
Attaching a good quality particulate filter ahead of the instrument sampling inlet prevents entry of
dust particulates.
A large easy to read liquid crystal digital panel meter with a range from 1 to 19,999
μ
Sv/hr is used
for measurement display.
Other units of measurement, such as MPCa, MBq/m
3
and
μ
Ci/m
3
or others may be specified by
the user at time of requesting a unit. The instrument exhibits a basic sensitivity of the order of 2
μ
Sv/hr, which it is able to attain due to the fact that it is immune to response to both radon and
cosmic ray noise.
A pair of “D” size batteries supplies power. While it is recommended that Alkaline cells be used,
the instrument will also operate with any type of D-cell batteries, although operating duration
maybe vary. Onset of battery depletion is signaled by illumination of an LED located next to the
meter face. An external power supply can be used by attaching to a small receptacle the side of
the instrument case. The same LED also signals red when the high voltage power supply (HVPS)
used for ionization chamber bias has a malfunction.
DO NOT SUBSTITUTE, use only the recommended external power supply
A ten-position alarm level stepped attenuator, adjustable over partial scale (2 to 1,000
μ
Sv/hr) is
located on the front panel. An OFF position is included. An acoustic signaler emits a steady tone
if the measurement exceeds the set point. An intermittent tone is heard if the sample air flow has
been interrupted. The acoustic alarm is silenced by a “MUTE” push button. The alarms are non-
latching.
External connections for RS232 serial data output has been provided.
For measurements of tritium in the presence of other radioactive gases by means of ionization
chambers appears, at first glance, to be impossible. However, recognizing that tritium oxide is
water, a tritium specific measurement is attained through the use of differential ionization chambers
with an HTO removal dryer interposed between the two ionization chambers. Since all radioactive
components, with the exception of the tritium component is present in both the upstream and
downstream ionization chamber, the net (subtracted) ionization current is now proportional only to
the tritium oxide.
For example: A cartridge filled with disposable desiccant can be interposed between the
measurement and compensation ionization chambers will yield a net measurement response only
to tritium oxide; HTO + other nuclide - (other nuclide) = HTO
Gas flow connections are made externally to the instrument by appropriate attachment of flexible
plastic hose. See Figure 2.
