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Calibration factors for the type 1383A β-γ ionization chamber for low energy γ-emitters
202
Technical notes
about 5 hr. Tow et al.“) leave recently similar figure for 1 Is1 hll\lZ.
reported
a
International Journal of Applied Radiation and Isotopes, 1967, Vol. 18, pp. 202-203. Pergamon Press Ltd. Printed in Northern Ireland
Calibration Factors for the Type 1383A p-y Ionization Chamber for Low Energy y-emitters
Summary Preliminary studies using macroaggregated human serum albumin tagged with technetium-99m for lung scanning in rabbits arc very encouraging. No problems were encountered in the preparation of the and, as might be Tcssm tagged macroaggregates, predicted, the administration of the prepared macroaggregate suspension results in very selective localization of activity in the lungs and high counting rates. Because of the extremely favorable 6 hr halflife and low photon energy of this isotope, large doses may be used to provide a counting rate which will facilitate rapid scanning, while reducing total patient radiation exposure. For these reasons it appears that MAA tagged with TcsSm may be the preferred agent for lung scanning. Acknowledgments-We are indebted to Mr. S. T. POXON and Nuclear Consultants Corporation of St. Louis for their generosity in supplying us with human serum albumin tagged with Tcssm for use in our experimental work. We would also like to give particular thanks to Mrs. CAROLYN SIMON and Mrs. MARY SUE ROSE for their technical assistance in the experimental work herein described. C. C. PETERSON F. J. BONTE Department of Radiology University of Texas Southwestern Medical School Parkland Memorial Hospital Dallas Texas
Bibliography 1. Tow D. E., WAGNER H. N., LOPER-MAJANO V., SMITH E. M. and MIGITA T. Am. J. Roentg. 96,
664 (1966). 2. WAGNER H. N., SABISTOND. C., JR., MCAFEE J. G. and Tow D. E. New Engl. J. Med. 271,377 (1964). 3. TAPLIN G. V., JOI~NSOND. E., DORE E. K. and KAPLAN H. S. J. Nucl. Med. 5, 259 (1964). 4. TAPLIN G. V., JOHNSON D. R., DORE E. K. and KAPLAN H. S. U.C.L.A. Med. School, A.F.C. Contract AT (04-l)-Gen-12, (1964). 5. WHITLEY J. F., QUINN J. L., HUDSPETH A. S. and PRICHARD R. W. Radiology 81, 884 (1963). 6. QUINN J. L., WHITLEY J. E., HUDSPETH A. S. and W~rrs F. C. J. Nucl. Med. 5, 1 (1964). T. P., HENDRICK C. K. and SCHREIBER 7. HAYNIE M. A. J. Nucl. Med. 6, 347 (1965). 8. BONTE F. J. and CURRY T. S. III Am. J. Roentg. 96, (1965). 9. BONTE F. J. and CURRY T. S. III Radiology 85, 1120 (1965).
(Received 9 September 1966 ; and in jinalform 19 October 1966) IN THE original design of the type 1383A chamber(l) a nickel plated brass liner was used to prevent high energy electrons from the source from entering the ionization volume. This liner not only reduces the response of the chamber to low energy y-rays but also the tolerances on both its composition and thickness introduce a large scatter in the sensitivities of different chambers. However the sensitivities of the chambers without liners are the same to within rt2% for y-ray energies down to 120 keV. TABLE 1. Mean values of ionization currents (corrected to a pressure of 760 mm ofHg and a temperature of 22°C) in chamber type 1383A, serial number 14
Radioactive nuclide
Ionization current (A x lo-r2/mc) (1 g of solution in a 2 ml ampoule) without liner 11.1 ( :k3.0%) 9.6 ( ?:!Tq.O::)
co57 Tcssm (in isotonic saline) 1131
-.
AU’s* Mn54 Nas2
12.3 12.5 21.0 54.8
(* 1.2%) (&0.7%) (&0.7%) (&-O-7%)
___~
The calibration figures for the type 1383A chamber without liner are given in Table 1. Since at these y-ray energies the self absorption of the sample and the wall absorption of the ampoule are significant, these calibration factors only apply for 1 g of solution in an NPL type 2 ml ampoule. The details of the ampoule arc given in Fig. 1. The errors quoted in
FIG. 1
on five Shows matching ‘I‘c!‘~“’ .Il:\.\ lung photoscans and chest roentgenograms Scans show the same verv selective accumulation of isotope in the pulmonar) \~asculatuw as has heen found with Iis hlrL\ scans in the past. Note the normal appc*aranc~’ of the rabbit lungs on post-scan radiographs.
Frc:. 1. rahhits.
,
Technical notes
203
(Received 26 September 1966 ; and in final form 20 October 1966)
pressure. The transmission of the optical system was such that no single photon could generate more than one photo-electron. The intensity of the light could be reduced by inserting in the beam a perforated metal foil the transmission of which was measured by a spectrophotometer to be 41 per cent. Figure 1 shows the observed counting rate with and without this filter in the beam as a function of the polarizing potential across the counter. Pulses due to the radiation from the discharge tube are detected above about 1.95 kV while those below this voltage are due The solely to the general background radiation. ratios of the counting rates attributable to the radiation from the discharge tube with and without the filter are also shown in Fig. 1 (right hand ordinate). The agreement between these ratios and the known transmission of the filter clearly indicates that these pulses are due to single photo-electrons. The photon output of the discharge tube was then increased to the practical limit and at the same time an amplifier with a considerably longer integration time constant was substituted for the normal amplifier. This necessitated an increase in the dead time from the normal 2 psec to 100 psec and this, coupled with the
IN STUDYING the behaviour of radiation detectors it is of interest to examine their response to single primary electrons. A convenient way to generate such electrons is by means of the photoelectric effect using suitable optical radiation. Since the intensity of such radiation and/or the efficiency of the photoelectric conversion process are rarely known the question arises as to whether an instrument is in fact detecting single photo-electrons or multiple electrons which are generated within the appropriate time constant of the detector-amplifier system. CAMPBELL and LEDINCHAM~~) have established that a proportional counter can detect single electrons by comparing the mean pulse height with those due to X-rays of known energy. A rather simpler technique which is applicable to all pulse radiation detectors is the following. If photo-electrons, of essentially zero energy, are generated in a purely random fashion then the probability that one electron will be born in any time r is approximately NT (for NT << l), where N is the rate at which single electrons are generated. However the probability that two electrons will be born in time 7 is, to the same approximation, ( NT)~. If now N is reduced by a known fraction f the observed counting rate will also be reduced by f in the case of single-electron pulses, but will be reduced by f 2 for pulses depending on two electrons. Light from a small glow discharge tube was focussed through a transparent window and onto the aluminium cathode of a proportional counter filled with a 90% argon-l00/0 methane mixture at atmospheric
FIG. 1. The counting rate (left hand ordinate) from a proportional counter as a function of counter potential. The open circles are the ratios (right hand ordinate) of the counting rates with and without a filter of 41 per cent transmission.
the table are estimates of the overall error and include both the error in the absolute measurement and the error in the measurement of the ionization current, but do not take into account the errors due to the difference in response between the standard chamber held at NPL( 14) and any other chamber. A. WILLIAMS ROSEMARY A. BIRDSEYE National Physical Laboratop Teddington Middlesex Reference 1. DALE J. W. G., PERRY W. E. and PULFER R. F. Int. J. a)$. Radiat. Isotopes 10, 65 (1961).
Intrmational Journal OfApplied Radiation and Isotapes, 1967, Vol. 18, pp. 20%204. Pcrgamon Press Ltd. Printed in Northern Ireland
The
Detection in
Pulse
of
Single
Radiation
Photo-electrons Detectors
Technical notes
about 5 hr. Tow et al.“) leave recently similar figure for 1 Is1 hll\lZ.
reported
a
International Journal of Applied Radiation and Isotopes, 1967, Vol. 18, pp. 202-203. Pergamon Press Ltd. Printed in Northern Ireland
Calibration Factors for the Type 1383A p-y Ionization Chamber for Low Energy y-emitters
Summary Preliminary studies using macroaggregated human serum albumin tagged with technetium-99m for lung scanning in rabbits arc very encouraging. No problems were encountered in the preparation of the and, as might be Tcssm tagged macroaggregates, predicted, the administration of the prepared macroaggregate suspension results in very selective localization of activity in the lungs and high counting rates. Because of the extremely favorable 6 hr halflife and low photon energy of this isotope, large doses may be used to provide a counting rate which will facilitate rapid scanning, while reducing total patient radiation exposure. For these reasons it appears that MAA tagged with TcsSm may be the preferred agent for lung scanning. Acknowledgments-We are indebted to Mr. S. T. POXON and Nuclear Consultants Corporation of St. Louis for their generosity in supplying us with human serum albumin tagged with Tcssm for use in our experimental work. We would also like to give particular thanks to Mrs. CAROLYN SIMON and Mrs. MARY SUE ROSE for their technical assistance in the experimental work herein described. C. C. PETERSON F. J. BONTE Department of Radiology University of Texas Southwestern Medical School Parkland Memorial Hospital Dallas Texas
Bibliography 1. Tow D. E., WAGNER H. N., LOPER-MAJANO V., SMITH E. M. and MIGITA T. Am. J. Roentg. 96,
664 (1966). 2. WAGNER H. N., SABISTOND. C., JR., MCAFEE J. G. and Tow D. E. New Engl. J. Med. 271,377 (1964). 3. TAPLIN G. V., JOI~NSOND. E., DORE E. K. and KAPLAN H. S. J. Nucl. Med. 5, 259 (1964). 4. TAPLIN G. V., JOHNSON D. R., DORE E. K. and KAPLAN H. S. U.C.L.A. Med. School, A.F.C. Contract AT (04-l)-Gen-12, (1964). 5. WHITLEY J. F., QUINN J. L., HUDSPETH A. S. and PRICHARD R. W. Radiology 81, 884 (1963). 6. QUINN J. L., WHITLEY J. E., HUDSPETH A. S. and W~rrs F. C. J. Nucl. Med. 5, 1 (1964). T. P., HENDRICK C. K. and SCHREIBER 7. HAYNIE M. A. J. Nucl. Med. 6, 347 (1965). 8. BONTE F. J. and CURRY T. S. III Am. J. Roentg. 96, (1965). 9. BONTE F. J. and CURRY T. S. III Radiology 85, 1120 (1965).
(Received 9 September 1966 ; and in jinalform 19 October 1966) IN THE original design of the type 1383A chamber(l) a nickel plated brass liner was used to prevent high energy electrons from the source from entering the ionization volume. This liner not only reduces the response of the chamber to low energy y-rays but also the tolerances on both its composition and thickness introduce a large scatter in the sensitivities of different chambers. However the sensitivities of the chambers without liners are the same to within rt2% for y-ray energies down to 120 keV. TABLE 1. Mean values of ionization currents (corrected to a pressure of 760 mm ofHg and a temperature of 22°C) in chamber type 1383A, serial number 14
Radioactive nuclide
Ionization current (A x lo-r2/mc) (1 g of solution in a 2 ml ampoule) without liner 11.1 ( :k3.0%) 9.6 ( ?:!Tq.O::)
co57 Tcssm (in isotonic saline) 1131
-.
AU’s* Mn54 Nas2
12.3 12.5 21.0 54.8
(* 1.2%) (&0.7%) (&0.7%) (&-O-7%)
___~
The calibration figures for the type 1383A chamber without liner are given in Table 1. Since at these y-ray energies the self absorption of the sample and the wall absorption of the ampoule are significant, these calibration factors only apply for 1 g of solution in an NPL type 2 ml ampoule. The details of the ampoule arc given in Fig. 1. The errors quoted in
FIG. 1
on five Shows matching ‘I‘c!‘~“’ .Il:\.\ lung photoscans and chest roentgenograms Scans show the same verv selective accumulation of isotope in the pulmonar) \~asculatuw as has heen found with Iis hlrL\ scans in the past. Note the normal appc*aranc~’ of the rabbit lungs on post-scan radiographs.
Frc:. 1. rahhits.
,
Technical notes
203
(Received 26 September 1966 ; and in final form 20 October 1966)
pressure. The transmission of the optical system was such that no single photon could generate more than one photo-electron. The intensity of the light could be reduced by inserting in the beam a perforated metal foil the transmission of which was measured by a spectrophotometer to be 41 per cent. Figure 1 shows the observed counting rate with and without this filter in the beam as a function of the polarizing potential across the counter. Pulses due to the radiation from the discharge tube are detected above about 1.95 kV while those below this voltage are due The solely to the general background radiation. ratios of the counting rates attributable to the radiation from the discharge tube with and without the filter are also shown in Fig. 1 (right hand ordinate). The agreement between these ratios and the known transmission of the filter clearly indicates that these pulses are due to single photo-electrons. The photon output of the discharge tube was then increased to the practical limit and at the same time an amplifier with a considerably longer integration time constant was substituted for the normal amplifier. This necessitated an increase in the dead time from the normal 2 psec to 100 psec and this, coupled with the
IN STUDYING the behaviour of radiation detectors it is of interest to examine their response to single primary electrons. A convenient way to generate such electrons is by means of the photoelectric effect using suitable optical radiation. Since the intensity of such radiation and/or the efficiency of the photoelectric conversion process are rarely known the question arises as to whether an instrument is in fact detecting single photo-electrons or multiple electrons which are generated within the appropriate time constant of the detector-amplifier system. CAMPBELL and LEDINCHAM~~) have established that a proportional counter can detect single electrons by comparing the mean pulse height with those due to X-rays of known energy. A rather simpler technique which is applicable to all pulse radiation detectors is the following. If photo-electrons, of essentially zero energy, are generated in a purely random fashion then the probability that one electron will be born in any time r is approximately NT (for NT << l), where N is the rate at which single electrons are generated. However the probability that two electrons will be born in time 7 is, to the same approximation, ( NT)~. If now N is reduced by a known fraction f the observed counting rate will also be reduced by f in the case of single-electron pulses, but will be reduced by f 2 for pulses depending on two electrons. Light from a small glow discharge tube was focussed through a transparent window and onto the aluminium cathode of a proportional counter filled with a 90% argon-l00/0 methane mixture at atmospheric
FIG. 1. The counting rate (left hand ordinate) from a proportional counter as a function of counter potential. The open circles are the ratios (right hand ordinate) of the counting rates with and without a filter of 41 per cent transmission.
the table are estimates of the overall error and include both the error in the absolute measurement and the error in the measurement of the ionization current, but do not take into account the errors due to the difference in response between the standard chamber held at NPL( 14) and any other chamber. A. WILLIAMS ROSEMARY A. BIRDSEYE National Physical Laboratop Teddington Middlesex Reference 1. DALE J. W. G., PERRY W. E. and PULFER R. F. Int. J. a)$. Radiat. Isotopes 10, 65 (1961).
Intrmational Journal OfApplied Radiation and Isotapes, 1967, Vol. 18, pp. 20%204. Pcrgamon Press Ltd. Printed in Northern Ireland
The
Detection in
Pulse
of
Single
Radiation
Photo-electrons Detectors