ISO 8939:2025
(Main)Decommissioning of medical cyclotron
Decommissioning of medical cyclotron
This document provides information and guidelines on the decommissioning of a medical cyclotron facility, with a focus on activated or contaminated parts. Useful information and guidelines are given on decommissioning strategy and plan, safety assessment, and various decommissioning activities. This document also provides the guideline on the estimation of activation level using Monte Carlo simulation and the methodology for the measurement of activated radionuclides in the main structure, system components, and shielding walls, ceilings and floors during operation and decommissioning. Financial provisions and radioactive waste management aspects are also included. This document can be used by organizations responsible for operation and decommissioning of a medical cyclotron facility. In addition, it is expected that organizations that design a medical cyclotron or manage radioactive waste generated by cyclotron can utilize or refer to this document in whole or in part.
Démantèlement des cyclotrons médicaux
General Information
Standards Content (Sample)
International
Standard
ISO 8939
First edition
Decommissioning of medical
2025-10
cyclotron
Démantèlement des cyclotrons médicaux
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Decommissioning planning for a medical cyclotron facility . 3
4.1 General .3
4.2 Responsibilities .3
4.3 Decommissioning strategy .4
4.4 Decommissioning plan .4
4.5 Project management . .5
4.6 Decommissioning activities .5
4.7 Safety assessment .5
4.7.1 Identification of relevant safety criteria .6
4.7.2 Risk assessment .6
4.8 Quality assurance programme.6
4.9 Radiation protection programme .7
4.10 Financial resources .8
4.11 Final radiological survey .8
4.12 Final decommissioning report .8
5 Activation evaluation . 8
5.1 General .8
5.2 Activation level estimation method .9
5.2.1 Monte Carlo computer simulation .10
5.2.2 Measurement of activation . .11
5.3 Nuclides of concern .11
6 Management of radioactive waste .12
6.1 General . 12
6.2 Minimization of waste . 13
6.3 Categorization and characterization of waste . 13
6.4 Discharge control of liquid or airborne radioactive effluents. 13
6.5 Onsite handling and processing of waste . 13
6.6 Onsite storage of waste.14
6.7 Shipment of waste .14
Annex A (informative) Measurement method for determining thermal neutron fluence rate on
concrete surface .15
Annex B (informative) Measurement method for determining specific activity using a
scintillation survey meter. 16
Bibliography . 17
iii
Foreword
This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies, and
radiological protection, Subcommittee SC 5, Nuclear installations, processes and technologies.
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radiological protection, Subcommittee SC 5, Nuclear installations, processes and technologies.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
Introduction
Many types of accelerators have been installed and operated in the last several decades primarily for nuclear
research and radioisotope production worldwide.
A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1934 in which charged
particles are accelerated outwards from the centre along a spiral path. Cyclotrons have been the best
sources of high–energy beams for nuclear physics experiments for the last several decades. Additionally,
cyclotrons can be used in particle therapy to treat various types of cancers. Ion beams from cyclotrons can
be used to penetrate the body and eliminate tumours by radiation treatment, such as in proton therapy.
Cyclotron beams can be used to bombard other atoms to produce various radioisotopes for diagnostic
imaging in positron emission tomography (PET), single photon emission computed tomography (SPECT)
and therapeutic applications in brachytherapy and alpha particle therapy. According to IAEA NW-T-2.9, it is
estimated to be over 1500 cyclotron facilities worldwide as of 2025.
Some cyclotron facilities have been dismantled and decommissioned because they have reached the end of
design life or because of ageing, accidents or other reasons like the changes in the purpose of use, location,
etc. Even though any standardized technical or administrative procedures for decommissioning of medical
cyclotron facilities have not been established yet, however, a safe decommissioning process is needed.
Therefore, it is necessary to analyse the major considerations such as activation and radioactive waste
management during the decommissioning of various kinds of cyclotron facilities.
Decommissioning actions typically involve different radiation protection strategies, such as radiological
surveys and monitoring; decontamination; dismantling and removal of structures, systems and components
and management of the radioactive waste generated during decommissioning. These actions are carried
out to achieve a progressive and systematic reduction in radiological hazards during decommissioning and
are conducted on a basis of planning and assessment to ensure the safety and protection of the workers, the
public and the environment and to ensure that the facility meets the planned decommissioning end state.
It is necessary to clarify the dismantling procedures at each stage from installation to decommissioning
of a medical cyclotron and to take measures to minimize decommissioning costs. This document aims to
develop proper decommissioning procedures and methods for medical cyclotron facilities, that accelerate
11 13 15 18
protons or deuterons for PET radiotracers ( C, N, O, F) by
— development of procedural guidelines for the decommissioning of a medical cyclotron facility,
— establishment of activation evaluation techniques for the end of operation of each cyclotron type, and
— consideration of the management of radioactive waste during the decommissioning of a medical cyclotron
facility.
v
International Standard ISO 8939:2025(en)
Decommissioning of medical cyclotron
1 Scope
This document provides information and guidelines on the decommissioning of a medical cyclotron
facility, with a focus on activated or contaminated parts. Useful information and guidelines are given on
decommissioning strategy and plan, safety assessment, and various decommissioning activities. This
document also provides the guideline on the estimation of activation level using Monte Carlo simulation and
the methodology for the measurement of activated radionuclides in the main structure, system components,
and shielding walls, ceilings and floors during operation and decommissioning. Financial provisions and
radioactive waste management aspects are also included.
This document can be used by organizations responsible for operation and decommissioning of a medical
cyclotron facility. In addition, it is expected that organizations that design a medical cyclotron or manage
radioactive waste generated by cyclotron can utilize or refer to this document in whole or in part.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 4037 (all parts), Radiological protection – X and gamma reference radiation for calibrating dosimeters and
doserate meters and for determining their response as a function of photon energy
ISO 29661, Reference radiation fields for radiation protection — Definitions and fundamental concepts
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated terms (VIM)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in the ISO 4037 (all parts),
ISO/IEC Guide 99, ISO 29661 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
clearance
Removal of regulatory control by the regulatory body from radioactive material or radioactive objects
within notified or authorized facilities and activities
[SOURCE: IAEA nuclear safety and glossary, 2022(interim)]
3.2
clearance level
value established by the competent authority, expressed in terms of activity, activity concentration or
surface contamination (fixed and non-fixed) at or below which radioactive material or radioactive objects
within authorized practice may be removed from any further regulatory control by the regulatory body
Note 1 to entry: Clearance levels are defined as generic and specific clearance levels.
[SOURCE: ISO 19461-1:2018, 3.5, modified — Note 1 to entry was added.]
3.3
cyclotron
type of particle accelerator in which the particles spiral inside one (1) or several D-shaped hollow metal
electrodes placed facing each other under the effect of a strong magnetic field, gaining energy through a
high-frequency alternating voltage applied between these electrodes
3.4
cyclotron facility
facility that consists of a hollow metal cylinder, dee-shaped electrode, a vacuum chamber, and a strong
electromagnet
3.5
decommissioning
administrative and technical actions taken to allow the removal of some or all of the regulatory controls
from a facility
[SOURCE: IAEA nuclear safety and glossary, 2022(interim)]
3.6
decommissioning plan
document containing detailed information on the proposed decommissioning (3.5) of a facility
[SOURCE: IAEA nuclear safety and glossary, 2022(interim)]
3.7
decontamination
complete or partial removal of contamination by a deliberate physical, chemical or biological process.
[SOURCE: IAEA NW-T-2.13]
3.8
medical cyclotron
type of particle accelerator used to produce radioisotopes which are essential for diagnostic imaging and
cancer treatment for medical purposes
3.9
Monte Carlo computer simulation
broad class of computational algorithms that rely on repeated random sampling to obtain numerical results
Note 1 to entry: Monte Carlo simulations are used to model the probability of different outcomes in a process that
cannot easily be predicted due to the intervention of random variables.
Note 2 to entry: They can also be performed by any other calculation codes and attention is to be given to the
assumptions made.
3.10
non-radioactive waste
waste that contains no radionuclides or radionuclides at activity concentrations equal to or less than
clearance levels (3.2)
3.11
radioactive waste
material for which no further use is foreseen that contains, or is contaminated with, radionuclides at activity
concentrations greater than clearance levels (3.2)
[SOURCE: IAEA nuclear safety and glossary, 2022(interim)]
3.12
radioactive waste management
all administrative and operational activities involved in the handling, pre-treatment, treatment,
conditioning, transport, radioactive material storage, and disposal of radioactive waste (3.11)
[SOURCE: ISO 12749-1:2020, 3.5.7]
3.13
responsible organization
any organizations that has the legal obligation to decommission (3.5) of a medical cyclotron facility (3.4), such
as a licensee, responsible authority or decommissioning company
4 Decommissioning planning for a medical cyclotron facility
4.1 General
Decommissioning planning for cyclotron facilities is similar to that of other nuclear or radiation facilities
which includes decommissioning responsibilities, plans, strategies, project management, safety assessments,
quality assurance programmes, radiation protection programmes, financing, decommissioning actions, the
disposition of radioactive waste and the completion of decommissioning actions.
A decommissioning plan should be developed during construction of the medical cyclotrons, be kept up-
to-date during operation and finalized prior to permanent shutdown and approved by the responsible
organization such as the regulatory body. All decommissioning activities should be conducted in accordance
with the decommissioning plan. Specifically, the radioactive waste of various categories to be produced
from the decommissioning project should be characterized through computer simulation and/or actual
measurement of activated or contaminated materials. The disposal path of decommissioned material should
be determined on the basis of radiological assessment.
Decontamination, dismantling, and other decommissioning actions for cyclotron facilities can be carried out
after permanent shutdown depending on the degree of activation. There are generally two decommissioning
options. First, dismantling starts immediately after the shutdown. Second, dismantling starts deferred,
which is called safe enclosure, so that short-lived radionuclides have some time to decay. It is possible that
a safe enclosure period will not be required if the cyclotron facility is relatively small and the radioactivity
is not too high to be managed with currently available dismantling technology. As a consequence, the time
period for decommissioning actions is shorter than those for large nuclear facilities, especially when a safe
enclosure period is not involved, and an activation study and administrative work for appropriate licenses
from safety authorities or regulatory bodies have already been completed.
Decommissioning of a cyclotron facility typically needs a phased decommissioning plan for the release
of parts of the facility from regulatory control during decommissioning actions. When all planned
decommissioning actions are complete and the planned end state is reached, the license for decommissioning
can be terminated, and the sites and remaining structures, if any, become available for unrestricted or
restricted reuse for other purposes.
Decommissioning of a cyclotron facility is usually conducted as a project. A decommissioning project is
a collaborative initiative involving supporting analyses and studies. Such a project is carefully planned
to ensure the safety of the planned actions. The goal is to achieve partial or complete removal of
regulatory controls from a facility. A decommissioning project usually starts when the preparation of the
decommissioning plan is initiated.
4.2 Responsibilities
The licensee (e.g. owner or operation organization of the medical cyclotron facilities) should plan for
decommissioning and should conduct decommissioning actions in compliance with the authorization
for decommissioning and with applicable requirements. The regulatory body should cooperate with the
licensee in order to maintain a strong safety culture throughout the decommissioning project. The licensee
should be responsible for all aspects of safety, radiation protection and protection of the environment during
decommissioning according to IAEA SSG-49.
The project management organizational structure, including an organization chart that indicates how the
decommissioning organization relates to the rest of the owner–operator organization, should be provided
by the licensee. This chart indicates all project units such as management, health and safety, operations,
quality assurance and administration according to IAEA SRS-45.
The safety training programme (both radiological and industrial) that the licensee will provide to each
employee should be described, including employment, annual, periodic and specialized training according
to IAEA SRS-45.
4.3 Decommissioning strategy
In principle, two possible decommissioning strategies are applicable: immediate dismantling and deferred
dismantling. A combination of these two strategies may be practically considered for safety or financial
considerations, and intended future use of the facilities or buildings. Entombment, in which all or part of the
facility is encased in a structurally long-lived material, is not an acceptable decommissioning strategy.
The licensee should select a decommissioning strategy, which will form the basis for decommissioning
planning. The strategy should be consistent with the national policy concerned with the management of
radioactive waste. In addition, a graded approach should be applied in all aspects of decommissioning in
determining the scope and level of detail for medical cyclotron facilities, consistent with the magnitude of
the possible radiation risks arising from decommissioning. The end state of the decommissioning should
be clearly described in terms of what the radiological and physical status of the facility or site will look
like when the activities are complete according to IAEA SRS-45. The decommissioning strategy should be
updated regularly to keep a good record of activities and to have a cost estimate. Safety should be assessed
for all facilities for which decommissioning is planned and for all facilities undergoing decommissioning.
4.4 Decommissioning plan
The decommissioning plan is the key document in the entire decommissioning process. Planning for
decommissioning should be completed prior to final shutdown. The following items are particularly likely to
[18]
be included in the decommissioning plan of medical cyclotron facilities :
— summary;
— introduction;
— facility description;
— radiological status;
— decommissioning strategy;
— project management;
— decommissioning activities;
— surveillance and maintenance;
— waste management;
— cost estimation and funding mechanisms;
— safety assessment;
— environmental assessment;
— non-radiological health and safety;
— quality assurance programme;
— emergency planning;
— physical security and safeguards;
— radiation protection programme;
— final radiological survey;
— proposed end state (or final state).
The end state of the decommissioning process should describe the objective of the overall decommissioning
project. The two possible end states of decommissioning projects are the so-called ‘green field’ and ‘brown
field’. The former refers to a site where the site and/or building of a decommissioned facility can be used
without any restrictions and can be released from regulatory control, and a farm site is one such example.
The latter refers to a site that requires restrictions on the access of the site and/or building only for a certain
period of time with some regulatory supervision, and the industrial site is one such example.
The end state for either green field or brown field is defined as the final status of decommissioning of a
medical cyclotron facility which fulfils its predetermined criterion defining the point at which a specific
task or process (i.e., decommissioning) is to be considered completed. The actual final status is tailored to
address the safety and environmental needs in each situation according to IAEA WS-R-5.
There is a range of documentation supporting the decommissioning plan that should be referenced and/or
summarized in the decommissioning plan.
4.5 Project management
The integrated management system of the licensee should cover all aspects of decommissioning, and the
following items should be considered:
— safety management policy including safety culture;
— organizational structure including responsibilities and authorities;
— staffing and qualifications including training;
— stakeholder engagement including regulatory interfaces;
— decommissioning and radioactive waste management procedures and record keeping;
— project management approach, including contractor and subcontractor involvement, if necessary;
— process-oriented knowledge management (POKM) for effective creation, dissemination, and utilization
of knowledge, and systemic and rigorous decision making in an organization.
4.6 Decommissioning activities
In the decommissioning plan, all decommissioning activities are described. Decommissioning techniques
should be selected such that protection and safety is optimized, protection of the environment is ensured,
and the generation of waste is minimized. As decommissioning progresses, such as decontamination,
dismantling and handling of large components, new hazards may arise. The impact of these activities
on safety should be assessed and managed so that the potential consequences of such new hazards are
prevented or are detected and mitigated. The licensee should implement the decommissioning plan,
including management of radioactive waste, in accordance with national policies.
A Gantt or Pert chart that provides details of the proposed decommissioning tasks in the order in which they
will occur should be provided. This includes the amount of time needed to perform each task and completion
dates for the activities according to IAEA SRS-45.
4.7 Safety assessment
Safety should be assessed for the planned decommissioning actions and incidents, including accidents
or situations that may occur during decommissioning, and such safety assessment should support the
decommissioning plan, according to IAEA GSR Part 6. The safety assessments should consist of site and
[9]
facility descriptions, the site operating history, nuclide concerned, the radiological status of the facility .
Safety should be assessed for all cyclotron facilities for which decommissioning is planned and all facilities
undergoing decommissioning. The safety assessment is an evaluation of the potential hazards associated
with the implementation of the decommissioning activities and their potential consequences according to
IAEA SRS-45. A safety assessment is a part of a decommissioning plan.
4.7.1 Identification of relevant safety criteria
The safety criteria to be applied to all decommissioning activities, which provide the basis against which the
safety assessment is to be evaluated, should be identified. The criteria are based on:
a) dose to workers,
b) dose to the public,
c) discharges to the environment,
d) exposure to chemical and other non-radiological hazards, and
e) spread of contamination within the facility.
Reference to non-radiological criteria that will be applicable during decommissioning activities should be
included, if applicable. Refer to IAEA SRS-45.
4.7.2 Risk assessment
A preliminary safety assessment of hazards is useful to predict the bounds of potential consequences
– both radiological and non-radiological - and to identify whether detailed analysis is required. Through
this, the potential hazards and initiating events can be identified. A bounding preliminary assessment
of consequences and frequency of occurrence should be carried out taking into account a frequency of
occurrence of hazardous events. Risk analysis should be conducted for both normal activities and accident
scenarios, and the conformity with the identified safety criteria should be demonstrated in advance. Refer
to IAEA SRS 77.
4.8 Quality assurance programme
All nuclear activities need a quality assurance programme. An identifiable procedure should be used to
register the radioactive material held by the licensee. For the decommissioning of cyclotron facilities that
handles large amounts of radioactive material, it is important to enhance the documentation procedures,
the radioactivity inventory determined during the radiological characterisation of the facility, which is
based on calculations and measurements, and work practices to minimize any loss of material, accidents
or abnormal occurrences. Quality assurance also encompasses lines of responsibility and the training of
operators and workers involved in the decommissioning and dismantling work. Specific work instructions
will be developed in preparation for the decommissioning work, together with all involved parties. The
detailed QA program is addressed in the decommissioning plan.
The QA program should ensure that the technical and quality assurance procedures are consistent with
applicable QA requirements. They need to be adequately documented and controlled. To ensure quality
maintenance during decommissioning activities, the management reviews are required. It needs to be
ensured that the QA program is applied to contractors and subcontractors. The procedure for notifying
the regulatory body of changes to the approved QA program, decommissioning plan or key members of the
organization, such as operators, radiation protection officers, CEOs, should be discussed.
The procedure for regular assessment of the scope, status, adequacy and conformity with the QA program by
management should be explained. A description of the training given to personnel responsible for performing
activities affecting quality should be provided, along with their qualifications. The self-assessment program
that is used to confirm that activities affecting quality comply with the QA program should be described.
The organizational responsibilities for ensuring that documented instructions, procedures and drawings
prescribe activities affecting quality and that they are accomplished through implementing these documents
should be described.
The procedures ensuring that the instructions, procedures and drawings include quantitative and
qualitative acceptance criteria to confirm that important activities have been satisfactorily performed
should be discussed.
A fully comprehensive quality assurance programme should include the following basic elements:
— design control;
— document control;
— procurement control;
— component identification;
— inspection;
— record management;
— control of testing and test equipment;
— calibration procedures;
— non-conformance procedures;
— control procedures for changes, records and audits;
— control of procedures and instructions.
Refer to IAEA TRS-414.
4.9 Radiation protection programme
The relevant dose limits for the exposure of workers and for the exposure of members of the public
should be applied during decommissioning. Radiation protection of persons who are exposed as a result
of decommissioning activities should be optimized with due regard to the relevant dose constraints
and controlled in accordance with a pre-established radiation protection program (RPP). Refer to
IAEA GSR Part 6.
The licensee’s RPP should be implemented commensurate with the scope and extent of licensed activities at the
site. This programme and associated operating procedures are the primary means used to administratively
establish safe radiation work practices and ensure compliance with applicable requirements. The licensee’s
RPP is to be fundamentally revised before starting decommissioning and dismantling work.
The radiation exposure of workers and the public should be kept as low as reasonably achievable. As
decommissioning proceeds, the RPP should be periodically reviewed and revised, if necessary. The RPP in
relation to decommissioning may include the following:
— equipment for radiation shielding, prevention of personnel contamination and minimization of intake of
radioactive materials (e.g. by providing local ventilation and filtration systems);
— personal dosimeters to record radiation doses received by workers;
— monitoring equipment for the external dose rate and surface contamination surveys for use in workplaces,
and for checking components and materials during decontamination, dismantling and handling;
— appropriate monitoring equipment for airborne radioactive substances in the workplace;
— creation of an (additional) radiation protection area for (temporary) storage of dismantled material.
Refer to IAEA SSG-49.
4.10 Financial resources
Responsibilities in respect of financial provisions for decommissioning should be set out in the national
legislation and/or regulation, if necessary. These provisions should include establishing a mechanism to
provide adequate financial resources and to ensure that they are available when needed for ensuring safe
decommissioning.
Refer to IAEA SSG-49.
4.11 Final radiological survey
The final decommissioning report should include a complete and detailed radiological survey report.
This survey should include:
— facility status;
— background radiation;
— detection limit and decision threshold, see ISO 11929-1;
— equipment used and calibration, see IAEA SRS-45;
— acceptable residual radioactivity levels, see IAEA SRS-45;
— operating history;
— decommissioning activities;
— final survey procedures; and
— survey findings.
4.12 Final decommissioning report
When decommissioning actions are complete, the licensee who is in charge of decommissioning
should prepare the final decommissioning report as a basis for the regulatory decision to terminate the
authorization for decommissioning. The licensee should demonstrate that the end state criteria specified in
the decommissioning plan and any additional requirements are met. This report should
— summarize the decommissioning plan, its updates and any related authorizations,
— include the final radiological survey report(s),
— describe the residual restrictions and their consequences,
— provide information on radiation exposures of workers,
— provide information on radioactive discharges to the environment,
— provide information on the management of radioactive waste and radioactive material, and
— provide detail on abnormal occurrences and incidents during decommissioning.
Refer to IAEA SSG-49.
5 Activation evaluation
5.1 General
One of the immediate concerns is the estimation of the activation level of the wall, ceiling and floor materials
in the activated regions of concrete near the target area of the cyclotron. In addition, the activation of the
cyclotron yoke, electromagnet coil, target assembly, semi-circular electrodes (dees), beam line components
(quadrupoles and, dipoles) and inner shielding materials of the cyclotron should also be considered. There
are two (2) methods for estimating the activation level of cyclotron components, Monte Carlo simulation
[9]
and sampling measurements .
The general dismantling procedures related to activation evaluation are listed in Table 1
Table 1 — Examples for specific applicable methods during dismantling which are defined based on
activation evaluation
Main part Specific procedure
Until the radiation level is acceptable for radiation protection strategy
1-1) Remove the highly active parts such as the target box and deflector which would
be activated by secondary neutrons and primary beam.
1-2) Disassemble the peripherals and conduct measurement to discriminate between
radioactive and non-radioactive parts in a place with low background
1) Accelerator structure 1-3) Conduct activation survey for large parts such as yokes and coils of the accelera-
and peripherals tor to determine the dismantling plan.
1-4) Conduct surface contamination (fixed and non-fixed) survey by direct or indirect
method.
1-5) Conduct dismantling work
1-6) Conduct confirmation measurement of the nonradioactive parts in a place with
background level.
Until the radiation level is acceptable for radiation protection strategy
2-1) Conduct surface contamination (fixed and non-fixed) survey by direct or indirect
method.
2-2) Conduct one or more activation surveys of concrete floors, walls, and ceilings.
2-2-1) Measure the thermal neutron flux distribution during operation with gold
foil, etc. before decommissioning.
2-2-2) Measure the depth distribution of activation by core boring at several
2) Concrete floors, walls,
locations with relatively high thermal neutron flux.
and ceilings
2-2-3) If beam load during system utilisation is available, simulate activation dis-
tribution by Monte Carlo calculation, and correlate results with activation
profile measurements.
2-3) Determine the dismantling or decontamination depth for each location from the
data of 2-2-2) and 2-2-3).
2-4) Dismantle the activated parts and/or decontaminate contaminated parts.
2-5) Conduct confirmation measurement of the nonradioactive parts and portions
5.2 Activation level estimation method
In cyclotrons, neutrons are generated by accelerated particles such as protons, deuterons and other ions
through nuclear reactions with the materials inside the chamber, target and surrounding materials. These
neutrons and accelerated particles interact with the cyclotron components (chamber, electrodes (dees),
beam line components (quadrupoles, dipoles), target assembly, magnet, etc.), and wall, ceiling and floor of
vault, causing activation.
Most of activated cyclotron parts and concrete walls, ceilings and floors around the cyclotron constitute
a large amount of the low- and very low-level radioactive waste (LLW and, VLLW respectively) in the
decommissioning procedure. Only a few parts of the accelerator and target area are highly activated.
Additionally, in the decommissioning stage, it is necessary to identify and evaluate the radionuclides
and activity of the target assembly and shielding material from cyclotron operation. The fact that
activated consumables and replacements generated during operation are generally disposed of during
decommissioning should also be considered.
Therefore, it is necessary to predict, minimize and measure the level of activation around the cyclotron
to minimize the amount of radioactive waste and exposure dose. The prediction and measurement of the
activation level determines the thickness of the shielding walls, ceilings and floors to be removed. This
also quantifies the amount of radioactive waste generated with determination of the method of radioactive
waste disposal for
— estimation and management of worker exposure dose during decommissioning, and
— establishment of recycling and re-use standards for cyclotron components
The methods for determining the activation level include:
a) computational analysis through Monte Carlo computer simulation,
b) radio-nuclide spectral analysis of cyclotron components and cyclotron room concrete using γ
spectrometry technique,
c) neutron fluence estimates using radio-nuclide spectral analysis of activated samples and dosimeters
attached to selected spots in the cyclotron room, and
d) activation depth profile analysis of the shielding materials by means of spectral analysis on the concrete
walls, ceilings and floors through concrete boring.
Among the above methods, activation should be evaluated by more than one method depending on the
situation and requirements based on the regulation of the medical cyclotron.
And other method available to estimate activation level can be referred to Annex A
5.2.1 Monte Carlo computer simulation
There are various computer simulation methodologies available for estimation of the activation in the
structural and shielding materials used in the cyclotron components based on the Monte Carlo algorithm.
The Monte Carlo method is suited to the estimation of stochastic processes, particularly called radiation
transport (i.e., mapping of electro-magnetic wave or particle trajectories), such as photons and neutrons,
through matter. To calculate the induced activity, dedicated activation codes can be further created to use
a more suitable activation calculation
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