GEOLOGICAL SURVEY CIRCULAR 380

THE MODEL VI TRANSMISSION 

FLUOMMETER FOR THE 

DETERMINATION OF URANIUM

Thia report concerns wozk done on 

behalf of the U.S. Atomic Energy 

Commission and is published with 

the permission of the Commission.
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

GEOLOGICAL SURVEY CIRCULAR 330

THE MODEL VI TRANSMISSION FLUORIMETER FOR THE 

DETERMINATION OF URANIUM

By Charles A. Kinser

This report concerns work done on 

behalf of the U. 8. Atomic Energy 

Commission and is published with 

the permission of the Commission.

Washington, D. C., 1954

Free on application to the Geological Survey, Washington 25, D. C.
THE MODEL VI TRANSMISSION FLUORIMETER FOR THE 

DETERMINATION OF URANIUM

By Charles A. Kinser

CONTENTS

Page

Abstract.................................... 1

Introduction................................. 1

Description of the instrument................. 3

The ultraviolet lamp.................... 3

Power supply for the ultraviolet lamp..... 3

Fluorimeter head and

phototube housing..................... 3

Multiplier phototube

and high-voltage supply................ 3

Page

Description of the instrument Continued

Microammeter.......................... 3

Operation......;............................ 7

Selecting the standard deflection.......... 7

Preparation of standard curves........... 7

Measurement of uranium

in samples........................... 7

Performance................................ 9

Literature cited............................. 9

ILLUSTRATIONS

Page

Figure 1. Front view of fluorimeter................................................................... 2

2. Circuit for low-voltage power supply......................................................... 4

3. Top view of low-voltage power supply......................................................... 5

4. Circuit for multiplier phototube.............................................................. 6

5. Standard curves for fluorimetric determination of uranium. .................................... 8

ABSTRACT

An improved transmission fluorimeter (Model VI) 

for use in the determination of uranium consists of 

a line-operated, low-voltage d-c supply, powering 

a small 3-watt ultraviolet lamp as a source of long 

wavelength ultraviolet radiation; a Model V phototube housing and fluorimeter head containing the 

sample holder, shutter, and primary and secondary 

filters; an end-window multiplier phototube powered 

by a stable, commercially available high-voltage 

supply; and an electronic microammeter for measuring the output current from the photomultiplier 

tube. The instrument has excellent electrical 

stability and operates over a wide range of sensitivity. Its versatility makes it useful for both 

routine and research work.

INTRODUCTION

Transmission fluorimeters have been used for 

the measurement of uranium in alkali carbonate 

fluoride melts for several years. Detailed discussions of their advantages and operating principles 

by Fletcher and others (1954) and Grimaldi and 

others (1952) need not be repeated here. Other 

workers in the field have described experimental

portable and laboratory fluorimeters operating on 

the transmission principle (May and Fletcher, 1954).

In the construction of the Model VI fluorimeter 

(fig. 1) an effort was made to produce a laboratory 

instrument that has the following features: convenience of operation, electrical stability, compactness 

in arrangement of components, and wide latitude in 

the control of sensitivity.

The use of a commercially available high-voltage 

supply and ultrasensitive d-c microammeter adds 

materially to the ease of construction.

The entire instrument, with the exception of the 

microammeter, is operated from the regular 115-vol't 

a-c line, and has ample regulation to absorb line-voltage 

fluctuations. Current drain on the meter batteries is so 

low that they need to be replaced only about once a year.

The linearity of response of this instrument and its 

convenient step-wise sensitivity scales make possible the 

use of a set of standard curves covering three uranium concentration ranges, each a tenfold increase over the previous 

one.

All components are mounted on a baseboard 

12 inches wide by 24 inches long with all controls accessible from the front.
Figure 1. -Front view of fluorimeter.
The author is indebted to many of his colleagues 

in the Geological Survey for valuable suggestions and 

encouragement, especially to Mary H. Fletcher for 

assistance in various phases of the work, and to 

J. T. Bracken and W. R. Champion for advice on the 

electrical problems. This report is the result of work 

done on behalf of the Division of Research of the 

Atomic Energy Commission.

Fluorimeter head and phototube housing

The Model V fluorimeter head and phototube 

housing, as perfected in 1950 by Fletcher, May, and 

Anderson (1954), are used with the same primary and 

secondary filters, shutter, and sample holder. A 

complete description and detailed drawings are given" 

in the above reference and need not be repeated here.

DESCRIPTION OF THE INSTRUMENT 

The ultraviolet lamp

The ultraviolet light source is the 3-watt General Electric RP-12 lamp designed to operate on 

12 to 16 volts for fluorescent instrument-dial lighting 

on airplanes. This lamp was used successfully in a 

battery-powered fluorimeter designed in 1950 by 

May and Fletcher (1954). Its inner surface is coated 

with a phosphor which has a radiation peak in the long 

wavelength with high emission at 3650A which is considered the most desirable wavelength for the production of uranium fluorescence.

This lamp in its housing is very compact, extending only 3^ inches above the fluorimeter head. 

Its output has been ample when used with multiplier 

phototubes and sufficiently sensitive measuring instruments. It replaces the usual 100-watt ultraviolet lamp 

and obviates the necessity for bulky housings, supports, 

and adjustments. As the RP-12 lamp is of low wattage, 

it dissipates little heat and requires no blower to keep 

it cool. :

As with other ultraviolet lamps, a warm-up 

period of about 15 minutes is required to allow the 

output to stabilize before measurements are made.

The electric circuit for the lamp is shown in 

figure 2.

Power supply for the ultraviolet lamp

The low-voltage d-c power supply for the ultraviolet lamp was designed to operate from the regular 

115-volt, 60-cycle, a-c supply. As shown diagrammatically in figure 2, the voltage for this power supply 

is stabilized by a voltage regulator; the output is adjustable from 0 to 17 volts by a variable autotransformer and 

is rectified by a full-wave bridge-type selenium rectifier 

and filtered to give a nearly ripple-free voltage. Resistors 

R2 and R3 drop the voltage to the correct values for the 

electrodes of the lamp. A 0- to 25-volt d-c meter is 

placed across the output of the filter section.

All components, except the voltage regulator, are 

mounted on a low chassis and a panel (7 by 11 inches) and 

enclosed in a cabinet which is the same size as that of 

the high-voltage power supply (12i by 8% by 10| inches). 

Figure 3 shows the arrangement of the components in 

the low-voltage power supply.

A description of the wiring diagram and parts 

is given in figure 2.

The voltage regulator is located near the instrument 

and the high- and low-voltage supplies are operated from it.

1 Sockets for these lamps are manufactured by the Cole-Hersee Co., 

Old Colony Ave., Boston, Mass., and the H. A. Douglas Manufacturing Co., 

Bronson, Mich.

Multiplier phototube and high-voltage supply

An RCA 5819, 10-stage, end-window, multiplier 

phototube is used for detecting the uranium fluorescence. 

It is capable of multiplying the photo-electric'Current 

produced at the cathode by 600, 000 times when operated at 90 volts per stage.

The manufacturer recommends that for maximum 

stability the anode current should not exceed 100 microamperes and the anode supply voltage should not exceed 

1250. We usually operate our phototube at about 725 volts 

but occasionally use the range 500 to 1,000 volts for experimental purposes.

The 5819 phototube has an S-9 spectral response 

covering the range 3000 to 6400A with a maximum response at 4800A. The response at 5545A, which is the 

emission peak of uranium fluorescence in the fused pad, 

is 70 percent of the tube's maximum response.

A commercially available power supply2 has 

proved satisfactory in powering the phototube. This unit 

operates from the regular 115-volt 60-cycle, a-c line 

and has a continuous output of 500 to 3, 000 volts which 

can be varied by means of a coarse and a fine adjustment, with full regulation up to 1 milliampere 

at 2, 000 volts and 0. 3 milliampere at 3, 000 volts. The 

manufacturer's specifications state that an input voltage 

change from 105 to 125 volts will change the output voltage less than 0. 01 percent.

An output connector was mounted at the rear of 

the chassis and wired so that the high voltage leads to 

the multiplier phototube could be placed behind the 

cabinet. High-voltage connections between power 

supply, phototube, and meter were made with polyethylene-insulated, RG-29/U, coaxial cable.

Figure 4 shows the circuit diagram for the 

5819 multiplier phototube and the resistance values 

used in the voltage divider. It also indicates the connections for the high-voltage supply and for the meter 

for measuring the phototube output current.

Microammeter

For the measurement of the output current from 

the multiplier phototube a convenient ultrasensitive 

d-c microammeter is used (RCA WV-84A).

This meter provides a wide selection of ranges 

and gives a full-scale deflection for 0. 01, 0. 1, 1, 10, 

100, and 1, 000 microamperes. Such sensitivity and 

choice of ranges in the meter allows the operator to 

measure uranium fluorescence accurately over an 

intensity range of several thousandfold.

2 Model 306 PR (positive grounded), available from: Atomic Instrument Co., 84 Massachusetts Ave., Cambridge 39, Massachusetts.
115 va-c P.U

WWW

R! - 10 ohms, 20 w, wire-wound

R2 - 30 ohms, 10 w, wire-wound

RS - 15 ohms, 10 w, wire-wound

GI and C2 - 4000 [if, 25 v, (Mallory no. HC 2540)

T! - Constant-voltage transformer, 120 va (Sola no. 30806)

T2 - Variable autotransformer, 150 va, Powerstat type 10

TS - Step-down transformer, 115 v primary, 24 v secondary,

50 va (Chicago Transformer Co. no. NCF 2450) 

Rec - Selenium rectifier, full-wave bridge (Federal no.

106B1AX1)

M - 0-25 v, d-c meter, 31/2 in. (Triplett no. 321) 

S - Switch, DPST 

F - Fuses, 2 amp 

PL, - Pilot lamp, 115 v

Conn - Connector, 3 contact (Cannon XL-12 plug and 

XL-13 receptacle)

Figure 2. Circuit for low-voltage power supply.
Figure 3. Top view of low-voltage power supply. 

5
To high-voltage supply Anode

5819

M - RCA WV-84A ultrasensitive d-c microammeter

G - Ground, Shield of the RG-29/U cable serves as positive leads to

meter and power supply

R! -Resistor, 2 megohm, 1/2 w , >: 

R2 to R^i - Resistors, 1 megohm, 1/2 w

Figure 4. Circuit for multiplier phototube.
This microammeter is .battery-powered but inconvenience due to this feature is negligible. The 

miniature tubes draw so little current that battery 

replacement has been necessary only about once a 

year with the meter in use almost every day.

When measuring the fluorescence of a sample of 

unknown uranium content, it is desirable first to open 

the shutter with the meter on a low-sensitivity scale 

to protect the instrument against the possibility of 

damage by too much current. Then, with the shutter 

open, advance the sensitivity until the meter deflection 

indicates that the best range for that sample has been 

reached.

If the meter deflection is less than 0. 1 of the 

scale, the sensitivity can be advanced to the next higher 

range.

OPERATION

It is common practice in fluorimetric analysis to 

adjust the sensitivity of the fluorimeter against a standard prepared from a known amount of the substance to 

be measured. The preparation of a uranium standard 

for the adjustment of the sensitivity each time the instrument is used would be time consuming and unnecessary. Instead, a convenient secondary standard, the 

fluorescence and light-leakage of the filters in the instrument, is used in adjusting the instrument sensitivity.

The most convenient value for this secondary 

standard, which we call the "standard deflection, " is 

determined indirectly by first adjusting the instrument 

to the desired sensitivity against a uranium standard, 

then removing the standard and noting the meter deflection with the shutter open and no sample in place. 

The standard deflection can thereafter be used in adjusting and checking the sensitivity before and during 

analyses.

Selecting the standard deflection

1. Turn the ultraviolet lamp on and allow it to 

warm up for 15 minutes before use. The operating 

range recommended for this lamp is 12 to 16 volts. 

Our lamp is always operated at 14 volts for uniformity.

2. Turn on the high-voltage supply and adjust 

the output to about 725 volts.

3. Turn the meter on and move the sensitivity 

control to the 0. 1 range and, with the shutter closed, 

adjust the meter deflection to zero.

4. Place a standard pad containing 0. 01 microgram 

of uranium in the sample holder and slide it into place. 

The standard pad is prepared by fusion of 0. 01 microgram of uranium standard with 2. 0 g of fluoride carbonate flux under the controlled conditions adopted for 

use with samples.

5. Open the shutter and adjust the high voltage 

to give a meter deflection of about 0. 9. This adjustment need not be exact; it is made to insure an adequate 

deflection with 0. 01 microgram of uranium so that when 

standard curves are made later they will have a desirable slope (highdeflection/concentration ratio).

6. Close the shutter; remove the sample and 

open the shutter again.

7. Record the meter deflection. This is the 

standard deflection for the instrument. In practice, 

it is more convenient to adopt as the standard deflection the nearest tenth of full scale. A value of 0. 60 

has been adopted as the standard deflection for the 

instrument used in this laboratory.

Preparation of standard curves

Prepare a series of fused pads, in duplicate or 

triplicate, containing known amounts of uranium in the 

following three ranges (micrograms): 0 to 0. 01, 

0 to 0. 1, and 0 to 1. 0.

1. Turn on the ultraviolet lamp and allow it to 

warm up 15 minutes before use.

2. Turn on the high-voltage supply and adjust 

the output to about 725 volts. This is merely an 

approximation of the voltage required to produce the 

standard deflection.

3. Turn the meter on, move sensitivity control 

to the 0.1 range, and adjust the meter deflection to 

zero with the shutter closed.

4. Open the shutter with no sample in place, 

and adjust the fine control of the high-voltage supply 

until the standard deflection is obtained on the meter.

5. Close the shutter, place a flux blank (fused 

flux only, containing no uranium) in the sample holder 

and slide it into place.

6. Open the shutter and record the meter 

deflection.

7. In the same way record the fluorescence of 

all flux blanks and standard pads in the range of 0 to 

0. 01 microgram of uranium.

8. Turn the meter sensitivity control knob to 

the 1. 0 range and record the fluorescence for all 

flux blanks and standards in the range 0 to 0. 1 microgram of uranium.

9. Turn the meter sensitivity control knob to 

the 10 range and record the fluorescence for all flux 

blanks and standards in the range 0 to 1.0 microgram 

of uranium.

10. From the data obtained from the standard 

pads, construct the three curves relating meter deflections to micrograms of uranium as shown in 

figure 5.

Measurement of uranium in samples

In general the methods described in Geological 

Survey Circular 199 are used for the preparation and 

analysis of samples. We use "fused-flux" exclusively 

because it is more homogeneous and gives more consistent results in the lower range. Uranium separations are made by the extraction or carbonate methods 

when there is any likelihood of the presence of significant amounts of quenching elements. Final fusions are
MICROGRAMS OF URANIUM

.2

Curve A (O.I scale)

Curve B (1.0 scale)

Curve C (10 scale)

0.005

.050

.500

Figure 5. Standard curves for fluorimetric determination of uranium.
made over an open flame at a low temperature to 

minimize attack of the platinum dish and subsequent 

quenching of the fluorescence by'platinum (Price and 

others, 1945, 1953).

It is recommended that the meter zero and 

standard deflection be checked occasionally during 

use so that any deviation can be corrected.

The operations to be followed in the measurement of the fluorescence are listed below:

1. Prepare fused pads from each sample to be 

analyzed.

2. Turn the instrument on as before.

3. Adjust the meter to zero.

4. Adjust sensitivity to give the standard 

deflection with the meter on the 0.1 scale.

5. Measure the fluorescence of each sample 

and record for each the deflection and the meter scale 

used.

6. Read the micrograms of uranium corresponding with each deflection from the appropriate curve.

PERFORMANCE

This fluorimeter has been in constant use in 

the Geological Survey laboratory for a year and a half, 

serving as a research and a routine instrument, and 

has proved to be sensitive, stable, and versatile.

Its maximum sensitivity is greater than necessary for the fluorimetric determination of uranium 

because the lower limit of uranium measurements is 

set by the fluorescence reading on reagents alone the 

so-called "reagent blank. " As seen in the working 

curves in figure 5, which were established from uranium- standards, the most sensitive range (curve A) is 

from 0 to 0. 01 microgram, giving readings from 

0. 028 to 0. 089 microamperes. The lower reading' 

represents a reagent blank equivalent to about 

0. 0046 microgram of uranium. Much greater sensitivity than this is available in the instrument if needed 

by increasing voltages to the ultraviolet lamp and 

multiplier phototube, but further increase in sensitivity would correspondingly increase the reagent blank 

and the curve would become useless.

Curve B is used for measurements between 

0. 01 and 0.1 microgram of uranium (0. 03 to 0. 64 microamperes). The sensitivity is 1/10 of that used in 

curve A and the reagent blank is lowered correspondingly.

Curve C is used for measurements between 

0. 1 and 1. 0 microgram of uranium (0 to 6. 0 microamperes). At this low sensitivity the reagent blank 

has become insignificant.

The maximum amount of uranium that can be 

measured, without changing the voltage or aperture, 

seems to be limited by the amount of current that can 

be drawn from the multiplier phototube. When more 

than 50 microamperes is drawn from the tube the 

meter pointer drifts downward, presumably indicating tube fatigue.

When the uranium content of a sample being 

analyzed is too high or too low on the expected curve, 

it is only necessary to turn the sensitivity switch to 

the next range and read the uranium value from the 

corresponding curve.

When a new lot of reagents is put into use the 

reagent blank will usually change, necessitating the 

preparation of a new set of standard curves. It is 

desirable, therefore, to have a good supply of each 

lot of each reagent on hand so that it will not be 

necessary to make a new set of curves very often.

Working curves used in this laboratory over 

the period of a year and a half have shown excellent 

reproducibility; however, uranium standards and 

samples of known uranium content are run routinely 

to guard against inaccuracy that might occur in any 

step of the analysis.

LITERATURE CITED

Fletcher, M. H., 1954, A study of the critical 

factors jn the "direct" fluorimetric determination 

of uranium, in Grimaldi, F. S., and others, 

Collected papers on methods of analysis for uranium 

and thorium: U. S. Geol. Survey Bull. 1006, 

p. 5-1-68. [U. S. Geol. Survey Trace Elements 

Inv. Rept. 130. ]

Fletcher, M. H., May, Irving, and Anderson, J. W., 

1954, The design of the Model V transmission 

fluorimeter, in Grimaldi, F. S. , and others, 

Collected papers on methods of analysis for uranium 

and thorium: U. S. Geol. Survey Bull. 1006, p. 93-95. 

[U. S. Geol. Survey Trace Elements Inv. Rept. 133. ]

Fletcher, M. H., May, Irving, andSlavin, Morris, 1954, 

A transmission fluorimeter for use in the fluorimetric 

method of analysis for uranium, in Grimaldi, F. S., and 

others, Collected papers on methods of analysis for uranium and thorium: U. S. Geol. Survey Bull. 1006, p. 85-92. 

[U. S. Geol. Survey Trace Elements Inv. Rept. 104. ]

Grimaldi, F. S., May, Irving, and Fletcher, M. H. , 

1952, U. S. Geol. Survey fluorimetric methods of 

uranium analysis: U. S. Geol. Survey Circ. 199.

May, Irving, and Fletcher, M. H., 1954, A batterypowered fluorimeter for the determination of uranium, in Grimaldi and others, Collected papers 

on methods of analysis for uranium and thorium: 

U. S. Geol. Survey Bull. 1006, p. 97-104. [U. S. 

Geol.. Survey Trace Elements Inv. Rept. 135. ]

Price, G. R. , Ferretti, F. J. , and Schwartz, S. , 

1945, The microfluorometric determination of 

uranium: AECD 2282.

_______1953, Fluorophotometric determination 

of uranium: Anal. Chemistry, v. 25, p. 322-331.

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