- Email: [email protected]
A three-channel low-background counting unit
Technical notes
120
Continued from previous page]
b
d e t e r m i n a t i o n of the accuracy of the p h o t o g r a m metric procedures is m a d e in Reference ¢4).
Acknowledgements--Thanks are due to O.
LAMM, Professor of Physical Chemistry, for his interest in this work a n d to B. HALLERT, Professor of Photog r a m m e t r y , for inciting us to e n d e a v o u r in this field a n d for a valuable discussion o n stereophotography. Financial support from the Swedish State Councils for T e c h n i c a l a n d for Nuclear R e s e a r c h is gratefully acknowledged. LARs-G. ERWALL Division of Physical Chemistry T. W~STERt,q_ARK
Royal Institute of Technology Stockholm, Sweden References Fio. 1. Stereo pin-hole camera with two pin holes. h is the distance betv, een the pin holes z, is the distance between the film plane and the pin-hole plane zl is the distance between the pin-hole plane and the plane of source S" z is the distance between the planes of the sources S" and S' x x and x, are the planar "co-ordinate" for the sources S' and S" from P. The following equations are readily deduced. zt -[- zs zt
vt + vs vs
Zx + z zs
ut us
c h
h b -- h
xx z a + z h d" = zs = b - - h and thus z,h zx - - c -- h
z.ah z = --Zl + b _ h dh xl -- b - - h eh XS - - C - - h "
"S' and S* are the radioactive sources. P is the vertical projection of the "right" pin hole n the lower source plane. The line connecting S' and P is parallel to the corresponding line in the film plane. Thus the vertical and horizontal distances between S" and P are obtained as well as the direction S' -- P, i.e. the position of S' is unambiguously determined. In analogy with this the position of S" and other sources can be obtained.
l. PREUSS L. E. and JENKINS' G. Nucleonics 16, 98 (1958). 2. HALLERT B. Private c o m m u n i c a t i o n . 3. HALLERT B. K. Tekn. Htgsk. Handl. No. 123 (1958). 4. HALLERTB. Photogramm. Engng. p. 84 ( M a r c h 1955).
A Three-channel Low-background Counting Unit
(Received 17 May 1960) LOW-BACKGROUND counters based o n anti-coincidence circuits are in general use for the assay of lowactivity 3-emitting samplesJ 1,~) T h e u n i t to be described was designed a n d built in the R e g i o n a l Physics D e p a r t m e n t for m e a s u r e m e n t s in the r a n g e 1-10 counts/rain on Sr 9° a n d yg0 samples. I t has the following features: (a) three c h a n n e l operation w i t h o u t interaction, (b) continuous o p e r a t i o n without a d j u s t m e n t of controls, a n d (c) ease of sample presentation. Construction
of castle
As shown in Fig. 1, three end w i n d o w G M 4 L B counters are m o u n t e d on a brass framework at the centre of a cylinder formed b y the screen Geiger tubes, type G.26Pb. Sixteen of these tubes, each 11 in. long, are a r r a n g e d in a d o u b l e layer to form the surface of the cylinder a n d each e n d is closed b y a vertical b a n k of five counters. T h e complete assembly is c o n t a i n e d in a 4 in. thick shield built from steel bricks. T h e external dimensions are 30 × 20 × 24 in. h i g h a n d the total weight is 1½ tons. T h e samples, w h i c h are p r e p a r e d o n s t a n d a r d m e t a l disks, are held in brass slides w h i c h are t h e n inserted t h r o u g h small slits in the castle. T h e outputs of the e n d
Technical notes
121
amplifier, a pulse lengthener and a driver stage for a mechanical register.
window counters are fed into three pre-amplifiers located in the castle. The combined outputs of the screen tubes are applied to another pre-amplifier. By a suitable switching arrangement monitoring of individual screen tubes is provided. Since the apparatus is limited to pure /%emitters there is no interaction between channels when samples are counted simultaneously.
R.F. osdllator E~I.T. supplies
Electronic counting equipment
Four are required. These give outputs continuously variable •in the range 0-2000 V. The voltages are monitored by meters mounted on the front panels. The use of stabilized H.T. supplies in conjunction with R.F. oscillators ensures high E.H.T. stability.
This consists of three identical channels. Each channel comprises the following: (a) Stabilized power supply. (b) Anti-coincidence unit. This incorporates twin pulse amplifiers, pulse shapers, variable delay circuits, and anti-coincidence circuit. (c) Discriminator and counting unit. The sample count rates are in the range which can be counted directly by a mechanical register. The complete counting unit consists of a voltage-discriminating
Table 1 shows the background count-rates at various stages of castle construction, with and without screening. The GM4LB input sockets to each anti-coincidence unit are duplicated to enable the unscreened background to be monitored simultaneously with the screened background. This simplifies the setting-up procedure.
I-4
Shielding and screen/ng eIRclency
CliANNEL I
I.o ,ittttttttttttttltttttttttttt
...it. tttit~ "
O.t
Z
i 1.4
IqJ
ttttt.t z tliittlitt t
C MJUINI~L
[tllitttilllllltlltttil|Ilttttititll|tit
1.0
t ttt:ttittttitt I I
i0.6 I.d
C J,,l&ll l i l l L 11
t t t i tl t i.c zz Ixl;lt it ttlltllttt itltittt l lllitz _ ._~ . . . . . lt---tttttltt, t i
NOV.
D~.
JA
N.
FIJ.
MAR.
FIG. 2. Record of background variations.
Technical notes
122 TABLE r Unscreened (counts/min)
Shielding Base
and to acknowledge a grant of money from the Medical Research Council for the purchase of components. D. ROWAN Regional Physics Department W. STEVENSON
Screened (counts/min)
12
6
Base + walls
8
2.5
Base + walls + roof
6.5
1
Western Regional Hospital Board Glasgow, Scotland
References 1. VOLCHOKH. L. and KULP J. L. Nucleonics 13, 49 (1955). 2. BRYANT F. J., MORGAN A. and SPICER G. S.
Counting procedure
Atomic Energy Research Establishment--R.3030
After initial setting-up no further adjustment of controls is necessary. The counting procedure merely consists of the insertion of samples and the operation of count switches. The changing of samples is quickly and simply carried out. Each sample is counted for 24 hr, the background being taken as the mean of the count-rates for the 24 hr before and after the sample count. Fig. 2 shows the variation of the background count-rate for each channel from October 1959 to March 1960. The proper functioning of the unit is checked each day by monitoring the background for 2 hr. This is incorporated in the above counting sequence.
H.M.S.O. (1959).
A Simple Plastic Scintillation C~lmter for Tritiated Hydrogen (First received28 April 1960 and in final form 12 May 1960)
Counting etlldency
THIS detector was designed to measure the tritium content of hydrogen coming from a palladium chromatography column. The requirements were for a sensitive detector with a small, vacuum-tight volume. The method of construction is illustrated in Fig. 1. A rectangular piece of plastic phosphor* 0"1 mm thick was heated in a stream of hot air, bent into a cylindrical shape, and inserted in the 5 m m bore Pyrex tubing with short lengths of coiled wire at either end to retain it in position. The glass was passed through a diametrical hole in a cyclindrical perspex light guide to which it was optically coupled with silicone oil. The sides and end of the light guide were coated with a diffuse reflector of antimony dioxide-based paint.
The counting efficiency for strontium-90 was estimated by using a standard sample of 0-01 m/~c. The percentage efficiency for each channel has remained within the limits of 33-0-34.1, 40.742.5, 33.4-34-6, respectively. The efficiency for yttrium-90 was about 20 per cent using a standard of 0.02 m/to.
Conclusions The unit described has been in continuous use for 6 months during which time approximately 100 samples of low-activiW Sr90 have been assayed. The operation of the unit has been so simplified that these assays are now part of the routine duties of the laboratory assistants.
Acknowledgements The authors would like to thank Dr. J. M. VALENTINE for his help and advice Vacuum
top
* Type NE 102 Nuclear Enterprises Ltd., Edinburgh.
Metal couplingF ~ ~ Palcsitr sscintillator p e x
Black-cooted copilloryspirol
Wire coil
, ~ " Metallight-shield , ~
Fio. 1.
~'~ Photomult|pller
120
Continued from previous page]
b
d e t e r m i n a t i o n of the accuracy of the p h o t o g r a m metric procedures is m a d e in Reference ¢4).
Acknowledgements--Thanks are due to O.
LAMM, Professor of Physical Chemistry, for his interest in this work a n d to B. HALLERT, Professor of Photog r a m m e t r y , for inciting us to e n d e a v o u r in this field a n d for a valuable discussion o n stereophotography. Financial support from the Swedish State Councils for T e c h n i c a l a n d for Nuclear R e s e a r c h is gratefully acknowledged. LARs-G. ERWALL Division of Physical Chemistry T. W~STERt,q_ARK
Royal Institute of Technology Stockholm, Sweden References Fio. 1. Stereo pin-hole camera with two pin holes. h is the distance betv, een the pin holes z, is the distance between the film plane and the pin-hole plane zl is the distance between the pin-hole plane and the plane of source S" z is the distance between the planes of the sources S" and S' x x and x, are the planar "co-ordinate" for the sources S' and S" from P. The following equations are readily deduced. zt -[- zs zt
vt + vs vs
Zx + z zs
ut us
c h
h b -- h
xx z a + z h d" = zs = b - - h and thus z,h zx - - c -- h
z.ah z = --Zl + b _ h dh xl -- b - - h eh XS - - C - - h "
"S' and S* are the radioactive sources. P is the vertical projection of the "right" pin hole n the lower source plane. The line connecting S' and P is parallel to the corresponding line in the film plane. Thus the vertical and horizontal distances between S" and P are obtained as well as the direction S' -- P, i.e. the position of S' is unambiguously determined. In analogy with this the position of S" and other sources can be obtained.
l. PREUSS L. E. and JENKINS' G. Nucleonics 16, 98 (1958). 2. HALLERT B. Private c o m m u n i c a t i o n . 3. HALLERT B. K. Tekn. Htgsk. Handl. No. 123 (1958). 4. HALLERTB. Photogramm. Engng. p. 84 ( M a r c h 1955).
A Three-channel Low-background Counting Unit
(Received 17 May 1960) LOW-BACKGROUND counters based o n anti-coincidence circuits are in general use for the assay of lowactivity 3-emitting samplesJ 1,~) T h e u n i t to be described was designed a n d built in the R e g i o n a l Physics D e p a r t m e n t for m e a s u r e m e n t s in the r a n g e 1-10 counts/rain on Sr 9° a n d yg0 samples. I t has the following features: (a) three c h a n n e l operation w i t h o u t interaction, (b) continuous o p e r a t i o n without a d j u s t m e n t of controls, a n d (c) ease of sample presentation. Construction
of castle
As shown in Fig. 1, three end w i n d o w G M 4 L B counters are m o u n t e d on a brass framework at the centre of a cylinder formed b y the screen Geiger tubes, type G.26Pb. Sixteen of these tubes, each 11 in. long, are a r r a n g e d in a d o u b l e layer to form the surface of the cylinder a n d each e n d is closed b y a vertical b a n k of five counters. T h e complete assembly is c o n t a i n e d in a 4 in. thick shield built from steel bricks. T h e external dimensions are 30 × 20 × 24 in. h i g h a n d the total weight is 1½ tons. T h e samples, w h i c h are p r e p a r e d o n s t a n d a r d m e t a l disks, are held in brass slides w h i c h are t h e n inserted t h r o u g h small slits in the castle. T h e outputs of the e n d
Technical notes
121
amplifier, a pulse lengthener and a driver stage for a mechanical register.
window counters are fed into three pre-amplifiers located in the castle. The combined outputs of the screen tubes are applied to another pre-amplifier. By a suitable switching arrangement monitoring of individual screen tubes is provided. Since the apparatus is limited to pure /%emitters there is no interaction between channels when samples are counted simultaneously.
R.F. osdllator E~I.T. supplies
Electronic counting equipment
Four are required. These give outputs continuously variable •in the range 0-2000 V. The voltages are monitored by meters mounted on the front panels. The use of stabilized H.T. supplies in conjunction with R.F. oscillators ensures high E.H.T. stability.
This consists of three identical channels. Each channel comprises the following: (a) Stabilized power supply. (b) Anti-coincidence unit. This incorporates twin pulse amplifiers, pulse shapers, variable delay circuits, and anti-coincidence circuit. (c) Discriminator and counting unit. The sample count rates are in the range which can be counted directly by a mechanical register. The complete counting unit consists of a voltage-discriminating
Table 1 shows the background count-rates at various stages of castle construction, with and without screening. The GM4LB input sockets to each anti-coincidence unit are duplicated to enable the unscreened background to be monitored simultaneously with the screened background. This simplifies the setting-up procedure.
I-4
Shielding and screen/ng eIRclency
CliANNEL I
I.o ,ittttttttttttttltttttttttttt
...it. tttit~ "
O.t
Z
i 1.4
IqJ
ttttt.t z tliittlitt t
C MJUINI~L
[tllitttilllllltlltttil|Ilttttititll|tit
1.0
t ttt:ttittttitt I I
i0.6 I.d
C J,,l&ll l i l l L 11
t t t i tl t i.c zz Ixl;lt it ttlltllttt itltittt l lllitz _ ._~ . . . . . lt---tttttltt, t i
NOV.
D~.
JA
N.
FIJ.
MAR.
FIG. 2. Record of background variations.
Technical notes
122 TABLE r Unscreened (counts/min)
Shielding Base
and to acknowledge a grant of money from the Medical Research Council for the purchase of components. D. ROWAN Regional Physics Department W. STEVENSON
Screened (counts/min)
12
6
Base + walls
8
2.5
Base + walls + roof
6.5
1
Western Regional Hospital Board Glasgow, Scotland
References 1. VOLCHOKH. L. and KULP J. L. Nucleonics 13, 49 (1955). 2. BRYANT F. J., MORGAN A. and SPICER G. S.
Counting procedure
Atomic Energy Research Establishment--R.3030
After initial setting-up no further adjustment of controls is necessary. The counting procedure merely consists of the insertion of samples and the operation of count switches. The changing of samples is quickly and simply carried out. Each sample is counted for 24 hr, the background being taken as the mean of the count-rates for the 24 hr before and after the sample count. Fig. 2 shows the variation of the background count-rate for each channel from October 1959 to March 1960. The proper functioning of the unit is checked each day by monitoring the background for 2 hr. This is incorporated in the above counting sequence.
H.M.S.O. (1959).
A Simple Plastic Scintillation C~lmter for Tritiated Hydrogen (First received28 April 1960 and in final form 12 May 1960)
Counting etlldency
THIS detector was designed to measure the tritium content of hydrogen coming from a palladium chromatography column. The requirements were for a sensitive detector with a small, vacuum-tight volume. The method of construction is illustrated in Fig. 1. A rectangular piece of plastic phosphor* 0"1 mm thick was heated in a stream of hot air, bent into a cylindrical shape, and inserted in the 5 m m bore Pyrex tubing with short lengths of coiled wire at either end to retain it in position. The glass was passed through a diametrical hole in a cyclindrical perspex light guide to which it was optically coupled with silicone oil. The sides and end of the light guide were coated with a diffuse reflector of antimony dioxide-based paint.
The counting efficiency for strontium-90 was estimated by using a standard sample of 0-01 m/~c. The percentage efficiency for each channel has remained within the limits of 33-0-34.1, 40.742.5, 33.4-34-6, respectively. The efficiency for yttrium-90 was about 20 per cent using a standard of 0.02 m/to.
Conclusions The unit described has been in continuous use for 6 months during which time approximately 100 samples of low-activiW Sr90 have been assayed. The operation of the unit has been so simplified that these assays are now part of the routine duties of the laboratory assistants.
Acknowledgements The authors would like to thank Dr. J. M. VALENTINE for his help and advice Vacuum
top
* Type NE 102 Nuclear Enterprises Ltd., Edinburgh.
Metal couplingF ~ ~ Palcsitr sscintillator p e x
Black-cooted copilloryspirol
Wire coil
, ~ " Metallight-shield , ~
Fio. 1.
~'~ Photomult|pller