Bubble Detectors Research Articles

Australasian perfusion incident survey.

An anonymous postal survey about perfusion accidents, incidents and safety procedures was conducted retrospectively in all identifiable cardiac surgery units in Australia and New Zealand over an 18-month period from January 1994 to July 1995. Responses were received from 69% of all eligible perfusionists representing 39 to 42 operating units. The most frequent incidents reported were heater/cooler failure (43% of respondents), urgent return to bypass following circuit disposal (38%), air embolus in a circuit not reaching the patient (24%), accidental cannula displacement (28%), protamine-induced circuit clotting postbypass (20%), hospital power failure (31%) and oxygenator membrane leaks (24%). There were 11 serious injuries and 10 deaths reported, giving an overall rate of serious injury or death of one in 1300 cases. However, the perfusion-related injury rate was lower, at one injury or death per 2500 perfusions. The use of safety equipment was widespread with low-level alarms in use by all respondents, bubble detectors by 74%, arterial line filters by 82% and written or computerized checklists by 80%. While the rate of injury was lower than that reported in surveys done elsewhere, the rate of reporting of incidents was greater and this may reflect a changing attitude of perfusionists to accountability in the delivery of their services. The data suggest that the level of safety in perfusion in Australasia is high but that improved incident reporting may help to further improve practices.

Advances in Superheated Drop (Bubble) Detector Techniques

State-of-the-art neutron dosemeters based on superheated drop (bubble) detectors are described. These are either active systems for area monitoring, which rely on the acoustical recording of drop vaporisations, or passive pen size ones for personal dosimetry, based on optical bubble counting. The technological solutions developed for the construction of robust devices for health physics applications are described with special emphasis on methods adopted to reduce mechanical shock and temperature sensitivity of the detectors. Finally, a review is given of some current research activities. In particular, a new approach to neutron spectrometry is presented which relies on the thermal effects for the definition of the response matrix of the system.

Bubble detectors—A maturing technology

Since the development of the first bubble detector over 10 yr ago, there has been continuing expectation that it would solve the well-known problems of personal neutron dosimetry. Research in the intervening years has led to a much better understanding of this interesting technology and to the development of a variety of radiation detectors that have found diverse applications in radiation physics. In recent years, a bubble detector has been developed for personal neutron dosimetry that is increasingly being adopted by many groups world-wide. Although this dosimeter has improved significantly the status of neutron dosimetry, there is continuing research to improve the properties of bubble detectors, not only in this application, but for general radiation detection.

Effect of gamma energy, temperature and shelf life on the response of gamma and BD-100R neutron bubble detectors

The use of commercially available bubble detectors for gamma and neutron detection has been reported by several groups. We have carried out systematic investigations to study the response of gamma bubble detector as a function of energy, the effect of waiting time on sensitivity of BD-100R neutron bubble detector and the effect of shelf life on both types of bubble detectors. Our results show that the response of the gamma bubble detector is energy dependent. Waiting time of up to 260 hours for BD-100R neutron detector has no significant effect. Both the detectors have a limited shelf life. These factors must be taken into account while using these detectors.

Studying the response of CR-39 and BD-100R detectors for neutron dosimetry in the light of ICRP-60 recommendations

The latest radiobiological findings show that the damage caused by the neutrons to human body is far greater than was previously thought. The International Commission on Radiological Protection, therefore, revised Q for neutrons and made recommendations in their Report No. ICRP-60 which have serious consequences for many operational neutron dosimetry services. The new recommendations include the reduction in dose limits from 50 mSv to 20 mSv per year, change in the quality factors and the dose estimation in some circumstances down to a few mSv per year. The overall effect of the ICRP-60 recommendations is to reduce the detection threshold in order to account for the reduction in the effective equivalent dose. We have studied the impact of ICRP-60 recommendations on the response of CR-39 based cubical neutron dosimeter and BD-100R bubble detector and the results obtained are presented in this article.

Improving the beam quality of the neutron radiography facility using the SLOWPOKE-2 at the Royal Military College of Canada

At the SLOWPOKE-2 Facility at the Royal Military College of Canada, a neutron radiography facility has been designed and installed, and the beam quality has been improved by performing a series of radiographs using American Standard for Testing and Materials (ASTM) E 545 indicators. Other means of determining the progress such as bubble detectors and activation foils were used. Modifications to the nosepiece of the beam tube including shielding and linings for fast neutron and gamma radiation were made.

Bubble Detectors and the Assessment of Biological Risk from Space Radiations

Experiments using bubble detectors in several space missions have provided important data on neutron fields inside satellites. These data, in conjunction with irradiations of bubble detectors using high energy ions, have prompted a re-examination of the applicability of terrestrial radiation dosimetry techniques in a space environment where the radiation is so vastly different. These investigations have raised questions on the approach being used for space dosimetry and the relevance of conventional dosimetric quantities for assessments of biological detriment. The basic mechanisms behind the bubble detector and several models of biological damage have been compared. It appears that the bubble detector can be formulated to mimic the biological behaviour predicted or explained by the models. This is perhaps not surprising since the bubble detector is based on energy deposition over distances of tens of nanometres and is, therefore, a true nanodosemeter. Perhaps the bubble detector can provide a direct and better indicator of true biological detriment from space radiation than dosimetric quantities currently derived from a variety of radiation detection devices.

Spent Fuel Assay with Thermally Stabilised Bubble Detectors

Neutron emission from spent fuel assemblies was investigated with BD-100R bubble detectors stabilised at 20°C in a container using Peltier elements, at 35-45°C external temperature in the vicinity of spent fuel assemblies. The intensity of fast neutrons was found to fall exponentially with a 0.13 cm -1 attenuation constant, with increasing vertical distance from the assemblies. The fast neutron emission rate was measured as a function of cooling time and it was seen that only fast neutrons emitted from the top end of the assemblies were detected. The near-neighbour effect (i.e. the effect of first neighbours) was also measured. If an assembly is stored in a hexagonal lattice of 160 or 225 mm storage distance, 70-80% or 10-20% of neutrons, respectively, were found to come from neighbours. The results obtained are discussed for determining burnup of spent fuel assemblies.

Neutron Ambient Dosimetry with Superheated Drop (Bubble) Detectors

A prototype neutron area monitor was developed which improves the performance of superheated drop detectors based on halocarbon-12. The detectors are thermally controlled: this removes external temperature effects while ensuring dose equivalent response optimised with respect to its energy dependence. The system was first characterised through calibrations with monoenergetic neutron beams. In the intermediate energy range, where experimental investigations were not possible, Monte Carlo response calculations were carried out. The prototype was then extensively tested by means of simulated and in-field irradiations with broad neutron spectra. All these tests indicated a remarkably constant dose equivalent response regardless of the neutron energy distributions. The current device is a fairly delicate system which can be operated reliably when environmental conditions are not extreme. Nevertheless, when it was possible to employ it, this monitor demonstrated an accuracy far superior to that of conventional meters used in routine surveillance.

Significant Safety Advantages Gained with an Improved PressureRegulated Blood Pump

A prototype of a non-occlusive pressure-regulated blood pump (M-pump) was evaluated in-vitro for safety in a comparative study with the roller and centrifugal pumps. The M-pump consists of collapsible tubing of unique design wrapped under tension around a rotor without a stator. The prototype M-pumps were tested in vitro to evaluate performance with respect to flow/pressure characteristics, hemolysis, bubble generation (cavitation) and durability. The M-pump and centrifugal pump did not overpressurize at any RPM when the pump outlet was occluded, but the roller pump reached pressures in excess of 1000 mmHg. The M-pump did not generate negative pressures upon occlusion of the inlet, whereas the roller and centrifugal pumps produced near-vacuum pressures. Furthermore, the M-pump was unable to empty a blood reservoir when the height of the pump inlet was placed slightly above the reservoir outlet. The levels of micro bubbles in the M-pump were significantly lower than the roller and centrifugal pumps upon sudden restriction of the pump inlet as determined with an ultrasonic bubble detector. The results of our in-vitro evaluation of the M-pump have shown it to have lower hemolysis than the centrifugal pump and lower or comparable hemolysis to roller pumps at flowrates of 0.1, 0.5, 4.0 and 6 L/min. We determined that the M-pump design possesses important safety advantages over roller and centrifugal pumps for cardiopulmonary bypass applications.

Testing the Temperature Compensated BD-PND Bubble Detector

The first results are presented of a study of the BD-PND bubble dectector. A large batch of these neutron detectors was tested for their main characteristics by irradiation with a 252 Cf source. This included an investigation on the reproducibility, the batch uniformity of the results and linearity with dose equivalent. The change in sensitivity after activation of the detector is another parameter investigated. Over a large temperature range (14 to 47°C) the extent to which the BD-PND bubble detectors are really temperature independent was investigated. Probably due to a limited lifetime of the temperature compensation, a progressive rise of sensitivity with temperature was found. Checks were also made for any change in sensitivity during the lifetime of the detectors and a few parameters that could influence this sensitivity were studied.

Neutron Spectrometry with Bubble Damage Neutron Detectors

A neutron spectrometer based on a set of bubble damage detectors is available designed for neutrons with energies from 10 keV to 20 MeV. Its capabilities in the fields behind the shielding of high energy particle accelerators have been studied in two reference fields created in the Joint Institute of Nuclear Research behind the shielding of a 660 MeV proton phasotron. It was found out that the spectra estimation following from the neutron bubble detector spectrometer correlates reasonably well with the spectra obtained through a Bonner spectrometer combined with the 12C (n,2n) activation reaction.

Geographical influence on the radiation exposure of an aircrew on board a subsonic aircraft

Radiation fields on board a subsonic aircraft have been studied on board an airbus A310-300 during the flights Prague - Abu Dhabi - Bangkok and Bangkok - Abu Dhabi - Prague, during February 1995. A complex set of mea­ suring instruments has been used for these studies: tissue equivalent proportio­ nal counter, moderator-type neutron rem-meter, environmental radiation dose rate meter, thermoluminescent and track etch detectors and bubble detectors. The results obtained are presented and analyzed; they are compared with the results obtained in the flights Prague - Montreal - Prague. Conclusions concer­ ning the influence of geographical parameters on the aircrew exposure levels are formulated.

Acoustic cavitation and bioeffects in the vascular system.

An in vivo bolus generation system has provided information concerning acoustic cavitation in blood and associated bioeffects. Microbubble boluses produced in the canine abdominal aorta by tone bursts of 1.8 MHz focused ultrasound were detected in distal arteries using medical ultrasound scanners and a resonant bubble detector. At the maximum acoustic intensity, 19,000 W/cm2(ISPTA), 125–250 ms bursts generated contrast enhancement persisting several cardiac cycles. Intensities down to 3,700 W/ cm2 yielded progressively weaker boluses while shorter and weaker boluses were produced with 64–0.5 ms bursts at the maximum acoustic intensity. There was a 50% occurrence of vascular wall effects (by histology) but no immediate mechanical failure. Oxygen ventilation has been shown to destabilize IV injected contrast agents and similarly, cavitation thresholds were elevated in the vena cava. Resonant bubble dectection indicated the presence of 7 μm diameter bubbles but the bubble size range is unknown. These results provide insight into bubble production by acoustic cavitation but any bioeffects must be examined in the context of arterial bolus production where the risk of significant damage may be less than that of alternative procedures. [Work supported in part by USPHS 5 RO1 DK42290.] a)Current address: Acuson, Inc., Sunnyvale, CA.

Neutron dosimetry in French nuclear power plants. Problems and their solutions in 1995

Personal neutron dosimetry in nuclear power plants is one of the hardest to achieve because there is no nuclear reaction that is both efficient and which ensures a suitable discrimination between 50 keV to 2 MeV fast neutrons and gamma photons. Neutron doses being low, the method used until now has been based on ambient dosimetry and the spent time in exposed areas. The advent of bubble detectors meets our immediate requirements until the direct reading electronic neutron dosimeter, which is still at the feasability research stage, can be utilized.

Estimation of Neutron Energy Spectra with Bubble Detectors: Potential and Limitations

Estimation of Neutron Energy Spectra with Bubble Detectors: Potential and Limitations

Estimation of Neutron Energy Spectra with Bubble Detectors: Potential and Limitations

Estimation of Neutron Energy Spectra with Bubble Detectors: Potential and Limitations

Active Neutron Spectrometry with Superheated Drop (Bubble) Detectors

Active Neutron Spectrometry with Superheated Drop (Bubble) Detectors

Active Neutron Spectrometry with Superheated Drop (Bubble) Detectors

Active Neutron Spectrometry with Superheated Drop (Bubble) Detectors

The Combined Use of Bubble Dosemeters and Electrochemically Etched Track Detectors

The use of polycarbonate bottles as track detectors makes it possible to overcome some of the shortcomings of the electrochemically etched dosemeters such as the complexity of the etching apparatus, the strong angular dependence, and the difficulty of measuring the neutron incident angle. Because of its shape, the bottle provides a dosemeter with isotropic response and separates electrically the two etching electrolytes, as required for the electrochemical etching processes. Since the polycarbonate bottles are used typically as containers of bubble detectors, a detector combination is thus achieved, which can be used to good advantage to solve the complex problem of personal neutron monitoring.