|Year : 2012 | Volume
| Issue : 3 | Page : 103-104
Prospective survey of accelerator safety
Distinguished Fellow, Manipal Centre for Natural Sciences, Manipal University, Manipal- 576 104, Karnataka, India
|Date of Web Publication||5-Sep-2013|
P K Sarkar
Distinguished Fellow, Manipal Centre for Natural Sciences, Manipal University, Manipal- 576 104, Karnataka
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Sarkar P K. Prospective survey of accelerator safety. Radiat Prot Environ 2012;35:103-4
Accelerators are devices that accelerate atomic and sub-atomic charged particles to high energies and generate ionizing radiation from the interaction of energetic particles with matter. Recent estimates have indicated that the number of accelerators is increasing at the rate of about 200 per year worldwide, mostly to be used for industrial and medical purposes. Concurrently, there is also a trend towards application of accelerators of high energy and high intensity to address the problems of nuclear waste transmutation, fissile material breeding and possible power production.
Increasing the use of particle accelerators have opened up a vast area in radiation physics research as well as in different applications. The radiation environment in those accelerators is quite different from the conventional nuclear installations. Unlike the case of nuclear reactors and other nuclear facilities, the radiation source term in accelerators is neither steady nor homogeneous. This radiation can originate anywhere in the accelerating channels. New ideas and modalities need to be developed in order to assess the radiation environment in these installations.
Several recent radiation accidents resulting in overexposures of radiotherapy patients have focused attention on the serious consequences of equipment failures in Linear Accelerator Treatment Units. Acceptance of the risks of operating an accelerator facility requires that the nature and magnitude of all sources of risk are understood and that the operating parameters are controlled to be consistent with the assumptions of the safety analysis. As it is, the challenge presented to the health physicist is nowhere greater than in accelerator installations, where the radiation environment may be extremely complex and the technique of measurement or theoretical evaluation unfamiliar.
To address these issues and many more, several review articles are published in this issue of Radiation Protection and Environment (RPE) covering different aspects of accelerator safety. These articles are written by experts in this field who have many years of experience of dealing with radiological and other safety issues related to particle accelerator used in research, industry and medicine. The following are highlights of the articles published.
Dr. Iyer emphasizes that a careful analysis of the various safety issues particularly in case of possible accidental conditions is required for a realistic evaluation of their impact related to accelerators used for medical applications where apart from the external dose involved, internal dose issues under normal operation and in case of abnormal operational conditions such as target rupture, accidents, spills, etc., also need evaluation. He has presented an analysis for a typical release of activity into the vault environment and the dose implications during radio pharmaceutical processing when substantial fractions of the volatile positron emitting radiopharmaceuticals are released into the atmosphere. Analysis of possible dose to a member of the public using typical release rates is also presented and shown to be not negligible.
Prof. Nakamura in his overview gives a brief summary on the experimental results on thick target neutron yields produced by light and heavy ions having wide energy range from MeV to GeV and data on the production of radionuclides due to the spallation process, together with induced activities by the proton to the U ion, as aslo benchmark experiments on neutron shielding using various accelerators of MeV to GeV energies. These three items are essential and important for radiation safety of accelerator facility.
Dr. Assano reviews the radiation safety related to electron accelerators, mainly synchrotron radiation facilities, for accelerator radiation safety systems consisting of safety interlock, radiation shielding and radiation monitoring systems. These systems depend strongly on the characteristics of machines such as the maximum electron energy. He overviews conceptual safety systems and radiation sources for synchrotron radiation facilities including the evaluation methods of shielding.
Dr. Mukherjee highlights the important radiation safety aspects related to safe operation of proton therapy and radioisotope production medical cyclotrons where parasitic gamma and neutron radiation are produced during the operation. Furthermore, high level of gamma radiation produced by the activated cyclotron components could impose radiation exposure to maintenance crew. Hence, radiation safety is imperative to safe and reliable operation of medical cyclotron facilities. He suggests that a sound operational health physics procedure can assure the minimisation of radiation exposure to patients and members of the public abiding the regulatory guidelines.
Dr. Sunil discusses the radiological safety aspects of accelerator driven systems (ADS) that have lead bismuth eutectic (LBE) as the spallation target as well as a coolant. The system has several advantages, such as inherent safety from a runaway chain reaction, independence of the reactivity due to delayed neutrons, resistance to nuclear proliferation, ability to transmute long-lived minor actinides and fission products and to convert thorium to fissile uranium. In the irradiated target, residual activity in LBE is a major concern particularly because of the formation of radiotoxic polonium isotopes. He has presented the time evolution of the major isotopes present in LBE along with the residual gamma dose rates.
Dr. Nandy discusses the crucial role played by nuclear reaction models in theoretical estimation of radiation environment in accelerator facilities where experimental data are scantily available. She describes the exciton and hybrid models for pre-equilibrium reaction, the Weiskopf-Ewing formalism for compound nuclear emissions and quantum molecular dynamics (QMD) model for spallation reactions. She shows that the code EMPIRE and the hybrid model code ALICE give a reasonable estimate of dose and induced activity in proton accelerator facilities up to about 200 MeV until the pion production becomes significant. The code HION can be a preferred choice for neutron dose simulation in low energy heavy ion (HI) accelerators. The QMD model can be used satisfactorily to estimate the induced activity and absorbed dose for proton and HI reactions at several hundreds of MeV to GeV per nucleon.
Dr. Sarkar discusses the radiological risk associated with particle accelerators mainly for high-energy and high-current accelerators used for accelerator driven systems and radioactive ion beam facilities. He has emphasized the need for carrying out probabilistic safety analysis including human reliability analysis for particle accelerators to avoid accidents that might occur due to human error or equipment failure.
I wish to thank the Editorial Board for assigning me this wonderful job. It has been a great pleasure for me to edit this special issue of the journal on a subject so dear to my heart, as I have spent my entire professional life working in this particular field. Hope this issue will prove useful to the practitioners of radiation protection and the researchers in the field of accelerator safety.
Indian Association for Radiation Protection (IARP) and the Members of the Editorial Board of Radiation Protection and Environment (RPE) gratefully thank Dr. P.K. Sarkar, Ex. BARC and Distinguished Fellow, Manipal Centre for Natural Sciences, Manipal University, Manipal (Karnataka) for accepting our invitation to serve as Guest Editor for this special issue of RPE on accelerator safety.