Radiation Protection System Research Articles

First-year experience with the BaBar silicon vertex tracker

Within its first year of operation, the BaBar Silicon Vertex Tracker (SVT) has accomplished its primary design goal, measuring the z vertex coordinate with sufficient accuracy as to allow the measurement of the time-dependent CP asymmetry in the neutral B-meson system. The SVT consists of five layers of double-sided, AC-coupled silicon-strip detectors of 300 μm thickness with a readout strip pitch of 50–210 μm and a stereo angle of 90° between the strips on the two sides. Detector alignment and performance with respect to spatial resolution and efficiency in the reconstruction of single hits are discussed. In the day-to-day operation of the SVT, radiation damage and protection issues were of primary concern. The SVT is equipped with a dedicated system (SVTRAD) for radiation monitoring and protection, using reverse-biased photodiodes. The evolution of the SVTRAD thresholds on the tolerated radiation level is described. Results on the first-year radiation exposure as measured with the SVTRAD system and on the so far accumulated damage are presented. The implications of test-irradiation results and possible future PEP-II luminosity upgrades on the radiation limited lifetime of the SVT are discussed.

IRPA-10: 10th International Congress of the International Radiation Protection Association.

The 10th International Congress of the International Radiation Protection Association (IRPA) was held on 14–19 May 2000 in Hiroshima. This conference is held every 4 years, a reasonable time interval that could usefully be copied by other international congresses, as it allows the development of new ideas and science for debate. Hiroshima is a bustling city, but also the selfstyled ‘‘city of peace’’. The conference centre is on the periphery of Peace Memorial Park, built on a site beneath the epicentre of the bomb. There are a number of statues and monuments within the park, the best known being the ‘‘A-bomb (Genbaku) dome’’, one of very few structures within a 1500 m radius to survive the blast and now a world heritage site. Each day the park receives hundreds of visitors of all ages and nationalities. The big issue at the conference was the debate on ‘‘controllable dose’’, a concept promoted by Roger Clarke in 1998, which has received much attention in the radiation protection community [1]. In 1999, the IRPA invited its member societies worldwide to comment on the proposals for major revision to the International Commission on Radiological Protection (ICRP) system for radiological protection. The outcome was a series of position papers from many member societies, including the UK Society for Radiological Protection, leading to a major debate in Hiroshima. The overall purpose was to review the current effectiveness of radiation protection and to provide input at an early stage to the ongoing work for a new or revised recommendation for the future. A full report of the debate was published in the Journal for Radiological Protection, to which the interested reader is referred [2]. It is sufficient to say here that the consultation process was widely acclaimed, that the basic principles of justification, optimization and dose limitation have proved sound and that in any review, defects and weaknesses should be corrected before introducing more radical change. Guidance on interpretation of the present system of radiation protection and means of communication with others needs amplifying, as well as involving other professional groups and the public. In summary, the radiation protection community received the Clarke proposal with interest but were conscious of the need to establish the existing framework more widely before introducing further changes. The proposals also threw up an interesting problem, not often considered in the past but becoming an increasing difficulty, namely that of language and terminology. Many different meanings and nuances can be put on a word in any one language, but the same word cannot always be directly translated into another language as the word may not exist or the concept is not understood. Traditionally, the conference opens with the Sievert Lecture and Award. Itsuzo Shigematsu (Japan) discussed lessons from the Atomic Bomb Survivors in Hiroshima and Nagasaki. He raised the possibility that the current survivors may reflect a resistant subpopulation that is not representative of overall human risk, and emphasized that radiation dosimetry remains essential for identifying an exposed population so that dose– response relationships can define the health risks of radiation. He pointed out that absolute risk is the fundamental index for assessing the frequency with which a radiation-induced disease occurs and concluded by describing the work of the Adult Health Study, which has been following a subsection of 20 000 survivors since 1958. Not only has this given data on emerging and nonfatal effects of radiation, but also on the ageing process in the Japanese population. The scientific programme was divided into 24 main topics, covering all aspects of radiation protection, from cosmic to underground, from medical to nuclear, from containment to communication with the public. The proceedings of this conference have been published on CD-ROM. This is a great improvement from before and Received 1 December 2000 and in revised form 29 May 2001, accepted 14 June 2001. The British Journal of Radiology, 74 (2001), 883–885 E 2001 The British Institute of Radiology

PIN PHOTODIODES FOR RADIATION MONITORING AND PROTECTION IN THE BABAR SILICON VERTEX TRACKER

We discuss the design, implementation and performance of the radiation monitoring and protection system used by the Silicon Vertex Tracker (SVT) in the BaBar detector. Using 12 reverse-biased PIN photodiodes mounted around the beampipe near the IP, we are able to provide instantaneous radiation dose rates, absorbed dose integrals, and active protection that aborts the circulating beams in the PEP-II storage ring when radiation levels exceed user-defined thresholds. The systems has reliably protected the SVT from excessive radiation damage and has also served as a key diagnostic tool in understanding radiation backgrounds at PEP-II.

The LNT-controversy and the concept of "controllable dose".

There is no firm scientific information on the potential health effects, such as increased cancer rates, due to low doses of ionizing radiation. In view of this uncertainty ICRP has adopted as a prudent default option the linear no-threshold (LNT) assumption and has used it to derive nominal risk coefficients. Subsequent steps, such as the comparison of putative fatality rates in radiation workers with observed accident rates in other professions, have given the risk estimates a false appearance of scientific fact. This has encouraged meaningless computations of radiation-induced fatalities in large populations and has caused a trend to measure dose limits for the public not against the magnitude of the natural radiation exposure and its geographic variations, but against the numerical risk estimates. In reaction to this development, opposing claims are being made of a threshold in dose for deleterious health effects in humans. In view of the growing polarization, ICRP is now exploring a new concept "controllable dose" that aims to abandon the quantity collective dose, emphasizing, instead, individual dose and, in particular, the control of the maximum individual dose from single sources. Essential features of the new proposal are here examined, and it is concluded that the control of individual dose will still have to be accompanied by the avoidance of unnecessary exposures of large populations, even if their magnitude lies below that acceptable to the individual. If a reasonable cut-off at trivial doses is made, the collective dose can remain useful. Misapplications of collective dose are not the deeper cause of the current controversy; the actual root is the misrepresentation of the LNT-assumption as a scientific fact and the amplification of this confusion by loose terminology. If over-interpretation and distortion are avoided, the current system of radiation protection is workable and essentially sound, and there is no need for a fruitless LNT-controversy. The new concept of controllable dose promises simplifications and improvements, but any major change of principles needs to be carefully considered in a broad discussion that ICRP is presently seeking.

Are public dose limits necessary?

The distinction between practices and interventions in the System of Radiation Protection has created a lot of confusion in the population and amongst decision-makers, especially with regards to the concepts of dose limits and intervention levels. The experience gained after the Chernobyl accident indicated that many actions taken led to an unnecessarily large expenditure of national resources and many instances occurred of contradictory national responses. A major reason was the mixture of dose limits for the population, which apply only to exposures from practices, and intervention levels, which apply only to protective measures in de-facto exposure situations. The existing System of Radiation Protection is revisited and it is suggested that the System can be revised with no dose limits for the public without causing a lower degree of protection of the population. With the widespread use of source-related dose constraints and practical restrictions on the sources of public exposure from practices, generally applicable dose limits are rarely limiting in any practical situation, even if dose constraints might, at least in principle, fail to take adequate account of the exposures from other practices. Constraints can be expressed as operational protection quantities, e.g., nuclide-specific release rates, dose rate at the fence of a facility, or nuclide-specific surface contamination density in the environment. A revised System of Radiation Protection without public dose limits would not cause any reduced protection of the public compared to the existing System, and it has a potential for removing much of the confusion with regards to application of intervention/action levels. It would also have the potential for improving public perception of radiation protection and radiation risks as well as for saving vast resources in intervention situations for better application in general health care of the public.

Analysis of Radiation Scatter during Angiographic Procedures: Evaluation of a Phantom Model and a Modified Radiation Protection System

To study the radiation scattering associated with the digital subtraction angiography (DSA) unit in angiographic procedures and to design an effective radiation protection shield based on these data. The number of scattered photons was measured at three points relative to the operator's position. Anteroposterior abdominal and lateral cranial fluoroscopy were evaluated. As protective devices, a lead curtain, sliding shields, and a brim-shaped image intensifier (II) hood were designed. In abdominal fluoroscopy, radiation was found to scatter to the operator's lower limbs from the underside of the catheter table, to the abdomen from the side of the patient's body, and to the head and neck from the table surface adjacent to the patient. The use of protective devices reduced exposure from 2.89 to 0.058 mR/min for the operator's lower limbs, from 0.987 to 0.069 mR/min for the operator's abdomen, and from 0.696 to 0.139 mR/ min for the operator's head and neck area. With lateral cranial fluoroscopy, radiation was detected to scatter to the operator's lower limbs from the underside of the catheter table, to the abdomen from the patient's temporal area, and to the head and neck from the patient's face. The use of protective devices reduced exposure from 0.248 to 0.010 mR/min for the operator's lower limbs, from 0.129 to 0.010 mR/min for the operator's abdomen, and from 0.162 to 0.018 mR/min for the operator's head and neck area. The characteristic directions of scattering to the operator were identified. An effective modified radiation protection system was designed based on this information.

Dose field in hiroshima and the risk of radiation-induced cancer

The dose distribution of γ-neutron radiation over the earth's surface as a result of the atomic explosion in Hiroshima is of decisive value for establishing the risk coefficients for death from radiation-induced cancer. At the same time, this radiation field is unique, since the ratio of its components varies both with distance from the hypocenter and with dose. For the DS 86 dosimetric system, the relation between mortality from solid cancer and dose has a linear, zero-threshold character. For this reason, the linear zero-threshold dependence is used as a basis for the entire system of radiation protection. However, the DS 86 results depend strongly on the choice of the coefficients of relative biological effectiveness of neutrons, which have not been established adequately. New data, which could change the dosimetric system and lead to a reexamination of the risk coefficients at low dose, are analyzed. 3 figures, 1 table, 7 references.

Reduktion der Strahlenexposition in der interventionellen Angiographie für Patient und Untersucher

In a retrospective analysis of vascular interventional procedures, relations between parameters of the examination and radiation exposure of patient and medical personnel are examined. 1208 vascular interventional procedures are evaluated. Interventional procedures are divided into three groups: percutaneous transluminal angioplasty, implantation of a stent, thrombolysis. Mean values of the radiation dose of patient and radiology personnel are reported for these examinations. The mean value of the radiation dose of the physician was 7 microSv (maximum 24 microSv), that of the patient 1548 cGy.cm2 (maximum 8485 cGy.cm2). The quantity of X-rays to the patient may be lowered by using pulsed fluoroscopy and by reducing the number of radiographs. Reduction of the number of radiographs may be achieved by using the last-image hold and the road mapping mode. The operator's dose can be decreased by using additional radiation protection systems like a MAVIG-radiation protection wall. The radiation dose reduction was 61% for the physician and 17% for the patient.

From chimney sweeps to astronauts: cancer risks in the work place: the 1998 Lauriston Taylor lecture.

Percival Pott, in 1775, was the first to note an association between overt cancer and a carcinogen in the work place when he astutely observed an elevated incidence of scrotal cancer in small boys who assisted chimney sweeps. In their "workplace" astronauts and crew of high altitude jet-liners are exposed, not only to low linear energy transfer (LET) radiation but also to HZE (high energy + high atomic number) particles and to neutrons-for which no human epidemiological data exist. The current system of radiation protection is based on risk estimates from low LET radiations, delivered in large doses and at high dose-rate, coupled with the assumption of a linear no-threshold model. In extrapolating to low doses and dose-rates, and to high LET radiations, it would be helpful if the mechanisms of radiation carcinogenesis were known. Unfortunately that is not the case, though progress has been made toward that end. Many human leukemias and lymphomas appear to be due to specific chromosomal translocations, while solid tumors usually involve multiple mutations in oncogenes, deletions in suppressor genes, and/or chromosomal rearrangements. Genomic instability and immortality are hallmarks of cancer and it is attractive to hypothesize that this is due to a mutation in a gene or genes responsible for the stability of the genome. Examples abound of a small DNA change inactivating a gene and leading to major biological consequences. This could result from a single particle, especially a HZE particle, or a recoil proton from the absorption of a neutron. In this context the assumption of a threshold is hazardous, and the linear no-threshold hypothesis still appears to be prudent and conservative.

182 血管撮影装置に対する放射線防護具の規格化に関する研究

182 血管撮影装置に対する放射線防護具の規格化に関する研究

Contents, vol. 386 (1997)

Late-onset effects of exposure to ionising radiation on the human body have been identified by long-term, large-scale epidemiological studies. The cohort study of Japanese survivors of the atomic bombings of Hiroshima and Nagasaki (the Life Span Study) is thought to be the most reliable source of information about these health effects because of the size of the cohort, the exposure of a general population of both sexes and all ages, and the wide range of individually assessed doses. For this reason, the Life Span Study has become fundamental to risk assessment in the radiation protection system of the International Commission on Radiological Protection and other authorities. Radiation exposure increases the risk of cancer throughout life, so continued follow-up of survivors is essential. Overall, survivors have a clear radiation-related excess risk of cancer, and people exposed as children have a higher risk of radiation-induced cancer than those exposed at older ages. At high doses, and possibly at low doses, radiation might increase the risk of cardiovascular disease and some other non-cancer diseases. Hereditary effects in the children of atomic bomb survivors have not been detected. The dose–response relation for cancer at low doses is assumed, for purposes of radiological protection, to be linear without a threshold, but has not been shown definitively. This outstanding issue is not only a problem when dealing appropriately with potential health effects of nuclear accidents, such as at Fukushima and Chernobyl, but is of growing concern in occupational and medical exposure. Therefore, the appropriate dose–response relation for effects of low doses of radiation needs to be established.

医療における放射線防護の意識調査 : 第2報 職業被曝と放射線防護体系について

医療における放射線防護の意識調査 : 第2報 職業被曝と放射線防護体系について

新しい血管撮影用放射線防護具の開発

A new system of radiation protection for angiographers was developed and its effect evaluated. The system consists of two components for radiation protection : one to protect the abdominal area and the other to protect the head and neck area. The first is composed of a lead curtain attached beneath the tissue table and a movable lead barrier next to the patient's trunk. The second is brim-shaped leaded rubber attached to the image intensifier. In abdominal angiography, the radiation protection system reduced X-ray scatter to 1% of the non-protective condition for the angiographer's abdominal area and to 50% for the head and neck area. This new system reduced X-ray scatter from the patient and enhanced the safety of the angiographer.

Exposure doses due to indoor 222Rn in the Ukraine and basic directions for their decrease

More than 9500 measurements of an average indoor 222Rn concentration are made by a method of the passive track dosimetry all over the Ukraine in houses of different architectural design and with different types of building materials. A calculation was made of a weighted average population exposure dose due to 222Rn in air of residential buildings. The dose is estimated at the level of 3.8 mSv per year. A radiation protection system for the protection of the Ukrainian population against exposure to radon is scientifically founded. The system includes technical requirements of measuring facilities, establishment of a system of a quality assurance for measurements of 222Rn in air and a system of control on the basis of relevant radiological services, justification of countermeasures acceptable for Ukraine against exposure to 222Rn.

182 血管撮影装置に対する放射線防護具の規格化に関する研究(第25回秋季学術大会一般研究発表予稿集)

182 血管撮影装置に対する放射線防護具の規格化に関する研究(第25回秋季学術大会一般研究発表予稿集)

149 効果のあった被曝低減法術者被曝低減用プロテクターの試作

149 効果のあった被曝低減法術者被曝低減用プロテクターの試作

Radiation protection systems for the final focus test beam at SLAC.

The Final Focus Test Beam (FFTB) is a new beam line at the Stanford Linear Accelerator Center designed to test new beam optics concepts, hardware, and techniques necessary to achieve and measure the small spot sizes required for future generations of high-energy e+e- linear colliders. The FFTB takes a 47 GeVc-1, 1 kW electron beam at the end of the Stanford Linear Accelerator Center linear accelerator and transports it to the FFTB beam dump. A radiation protection system was designed and installed for the FFTB with the primary goal that the integrated dose equivalent outside the shielding resulting from beam loss would not exceed 10 mSv y-1. This system is comprised of shielding, a beam containment system and a personnel protection system. This paper presents various aspects of radiation safety at Stanford Linear Accelerator Center that were considered in the design of the FFTB radiation protection system. Beam tests were conducted in which the performance of various beam containment devices and the shielding effectiveness were evaluated. Preliminary results from these tests are presented.

Application of an alanine dosimetry system for industrial irradiation and radiation protection

This paper reports the application of alanine dosimetry in radiation processing. Continuous checks of the EPR measuring conditions as well as using high-quality alanine dosimeters and consistent technique for dose determination guarantee an accuracy of about ±3% intermediate dose levels. The alanine dosimetry system was applied for dose mapping measurements during irradiator qualification and performance qualification of different products, routine dosimetry, and special radiation protection application within the gamma irradiator.

Discrete analog electronics for high-resistivity silicon detectors used for X-ray and γ-ray spectroscopy in whole-body monitoring

The work is aimed at developing an in vivo spectroscopy system for radiation protection monitoring to improve the lung detection of 239Pu and 241Am. Silicon components have been investigated for high-resolution spectroscopy (2 keV) at room temperature to measure 59.5 keV 241Am gamma rays. The requirements and constraints of such device are reviewed. The work is focused on analog electronics and detector development. As a first step, multi-channel electronic circuits based on a low-noise charge-sensitive preamplifier have been built by carrying the FETs and feedback capacitances close to the strips. The performance is presented for a large-area strip silicon detector (3 × 3 cm 2). Measurements are compared with simulations and discussed with respect to application requirements.

Technologically enhanced radioactivity: An overview

Man first increased his radiation exposure above the natural baseline when he began cave-dwelling and mining and working metals and minerals. Since then the understanding of technologically enhanced radioactivity and of the associated exposure pathways has increased to the present state which is described by UNSCEAR (1993, Sources and effects of ionizing radiation, UN Scientific Committee on the Effects of Atomic Radiation, Report to the General Assembly, UN, New York) as ‘sketchy’ and ‘not sufficient to enable reliable estimates’. This review of present-day knowledge suggests that many non-nuclear industries are indeed capable of generating significant critical group or collective exposures or both. Doses can be delivered to workers and to populations living in the vicinity of industrial sites. Notable amongst these types of industry are the phosphate-processing industries (fertilizers, detergents, chemicals), fossil-fuel burning, oil and gas extraction, mining of almost all kinds, ore and heavy mineral processing and the forest industries, such as pulp making and biofuel use. There is a growing awareness of the problem but a two-tier system of radiation protection and discharge control is liable to continue, particularly in developing countries, with an imbalance in the understanding and limitation of radioactivity emissions from non-nuclear versus nuclear industries and also in radiological protection of workers. This review, covering historical and current aspects, suggests that there is a need for further study of technological enhancement of radioactivity and that the first international conference dedicated to the subject is extremely worthwhile and should become the first landmark meeting in a long and important series.