You have a UK IRR17 Consent. Do you also need a registration for ionising radiation sources?

Operation of an accelerator (nominally 10MV and above)

In this example we are considering a linear accelerator which is being operated at an energy of at least 10 MV. 10 MV is considered the point where neutrons are produced, these generally being adventitious and therefore generally of no use. [For the physicists reading this, certain reaction cross sections can produce neutrons at lower acceleration energies, but still generally above 8 MV. From a radiation protection perspective, below 10MV neutrons are generally not considered an issue as the photon radiation shielding, or mitigation in walls and mazes, will also deal with the neutrons (and any neutron -> gamma photon reactions)].

This example could also be attributed to other accelerator types including cyclotrons, but in this case careful consideration of the specified practice needs to be considered to ensure the correct one is chosen. Also note that a linear accelerator in industrial irradiation (commonly known as an e-beam) will be under an industrial irradiation consent, but the issues described here could still be possible.

The production of neutrons in this example can lead to neutron activation products. These products vary, some short lived examples are shown below.

• Al-28 via reaction Al-27 (n,γ) Al-28, beta emitter (with a 1.78 MeV photon), with a half life of 2.3 minutes.
• Cu-62 via reaction Cu-63 (γ,n) Cu-62, positron emitter (with 0.511 MeV photons), with half life of 9.7 minutes.
• Mn-56 via reaction Mn-55 (n,γ) Mn-56, beta emitter (with a 0.85 MeV photon), with a half life of 2.6 hours.
• W-187 via reaction W-186 (n,γ) W-187, beta emitter (with a 0.48/0.69 MeV photon), with a half life of 23.9 hours.

The examples above are for illustration only, the actual neutron activation products will depend on the energy of the accelerator and the component elemental composition which make up the accelerator (and fittings / walls etc).

Some longer lived neutron activation products could include for example.

• Mn-54 electron capture (with a 0.83 MeV photon), with a half life of 312 days.
• Co-60 beta emitter (with 1.1/1.3 MeV photon), with a half life of 5.2 years.
• Ta-182 positron emitter (with a 0.511 MeV photon), with a half life of 115 days.
• W-181 electron capture (with a 0.057 MeV photon), with a half life of 121 days.

You get the picture, running the accelerator at 10MV or above will produce neutron activation products. The production of adventitious radioactive material from the operation of an accelerator will create an additional radiation protection hazard once the accelerator has been switched off. Merely removing the electrical supply does not mitigate all potential radiation hazards. Dose rates post irradiation could be anywhere between 10's -1000's of micro Sv / hour on contact. There will be a hybrid (average) half life of this dose rate (best determined by actual measurement with a dose rate monitor).

So, in many cases, it could be said that the dominant radiation hazard is NOT created by running the accelerator (since personnel are outside the shielding, unless they are the patient which is then not occupational exposure). The highest occupational exposure dose rates may actually be from the neutron activation products, when access is made into the accelerator shielded area (for setup, repair, service, dealing with a patient).

• It is absolutely the case that radiation protection from neutron activation products should be an integral part of the procedures for running the accelerator, in compliance with the consent for operation of an accelerator. That said, at this point - no registration is required for working with artificial radioactive materials. The reasoning is that neutron activation is an integral part of working with an accelerator at higher energies. [Note: you may well have a registration for work with artificial radionuclides anyway, due to other work you do. However, the point of this article is not to assume that this is the case, but instead determine what you need for the specific use of accelerators in this example].

What work might you do, related to the activated material, where no registration is required (i.e. all covered within the consent)?

• Maintenance work on the activated components.
• Removal of the activated components for replacement (and subsequent storage) - on the basis that the component is not 'waste' (there is a potential crossover here with environmental legislation). So the component still has to be useful.
• Training on the accelerator which incorporates neutron activated components.

All of the above can be classed as 'operation of an accelerator', and no registration is required.

However: if the activated component is removed from the accelerator and removed from site (either as radioactive material or radioactive waste) then a registration is required. This can no longer be claimed as acceleration operations, and a registration for work with artificial radionuclides will be required (which will also deal with the transport of radioactive materials).

We have HASS sources - do we need to consider a registration?

Consider a company which has a number of calibrator facilities for exposing radiation monitors to radiation fields. The company is likely to have a range of sources (probably at consent and registration level). For the purposes of this example we will assume they only have a consent for HASS (noting that Industrial Irradiation is not the same as calibration). The sources they have on site are as follows:

1. Cs-137 - 20 TBq (reference date is 1975)
2. Cs-137 - 200 GBq (reference date is 1988)
3. Co-60 - 300 GBq (reference date is 1995)
4. Co-60 - 1.5 TBq (reference date is 2001)
5. Am-241 - 95 GBq (reference data is 1981)

At the reference date activity, all the above sources are HASS, the thresholds are Cs-137 (100 GBq), Co-60 (30 GBq) and Am-241 (60 GBq).

This blog article was released on the 31 July 2023, so let's decay correct to this date and look at the activity now (we know that there is little point with Am-241, but just for fun!!). For this calculation we will assume all the sources reference dates are 1 January 19##. We therefore have the following:

1. Cs-137 - 9.78 TBq (still HASS)
2. Cs-137 - 88 GBq (not HASS)
3. Co-60 - 6.98 GBq (not HASS)
4. Co-60 - 76.9 GBq (still HASS)
5. Am-241 - 88.72 GBq (still HASS)

So source 2 (Cs-137, 88 GBq) and source 3 (Co-60, 6.98 GBq) are not HASS sources and are not covered under a consent. From a radiation safety perspective we feel that this makes little difference practically, since both sources still have significant activity and unshielded dose rates at 1m would still be high (6.7 mSv/h for the Cs-137 source, and 2.1 mSv/h for the Co-60 source). So their continued management under the HASS procedures for radiation safety are sensible and practical.

However, from a regulatory perspective, if you do not have a registration for these two non-HASS sources you are not complying with IRR17. As we have said earlier, it is likely (probable?) that a registration will already exist for non-HASS sources - but do not assume this is the case!

Where else could this potentially be an issue?

It is possible that shorter half life radionuclides might be an issue. Take for example the use of Ir-192 in Brachytherapy (a form of radiotherapy where the source is placed directly into the body via an automated after-loader). The HASS threshold for Ir-192 is 80 GBq. A fresh source delivered to a hospital might have an activity of around 400 GBq. The half life of Ir-192 is 74 days, and the hospital would aim be to replace the source within 1 half-life (broadly speaking, half the activity would lead to a doubling of the treatment time). The exchange takes place between the hospital and a licensed courier (generally a fresh source arrives, and the spent source is returned to the source supplier).

Suppose there is a delay (for some reason) and the spent source cannot leave site any time soon. We can calculate the time required to reach the Ir-192 HASS source threshold which is 171 days. Holding this source any longer on site means it is then no longer HASS, and would need to be held under a registration (the hospital most likely already has this for other sources).

Also note that the licensed courier removing the source would need to transport the source under a registration and not a consent, if they only had a consent they would not be complying with IRR17.

So as has been said before, you are probably OK. Perhaps most HASS source holders have registrations for work with artificial radioactive material anyway? Do they (?), read on!

You have a linear accelerator for cargo container screening and an x-ray unit for small package screening

This company has a single linear accelerator (linac) in a large shielded enclosure (6 MV accelerator). Cargo containers are driven into the enclosure, and the driver exits and is directed to a rest area. The linac is mounted on a gantry which moves up and down the container - security screening the content.

The enclosure has all the expected safety systems:

• e-stops (externally and internally).
• physical barriers on the entry and exit points.
• light curtains to stop the beam if somehow someone enters the enclosure.
• active lights showing linac status (include red flashing x-ray on indicators).
• CCTV to view the inside of the enclosure.
• audible indicators to indicate when the linac is about to start, and a diverse and distinctly different indication when x-rays are being generated.
• Interlocks on the rest room door (linac will terminate x-rays if this door is opened by the container driver during screening).
• detailed radiation risk assessment, local rules and contingency arrangements.

As expected, a consent is required for the above work (operation of an accelerator).

The company has a small office block beside the linac enclosure. In the front office is small cabinet x-ray system (160 kV, 1mA) which is used for screening small packages. It has an interlocked door to gain access to the screening areas (there are no open ports or leaded curtains on this particular model). When the unit is producing x-rays there is no access into the screening area, this is protected by two independent safety interlocks on the door. In addition, the door is also mechanically held closed by a magnetic lock which is energised before x-ray production can commence. As expected there are proportional local rules and a risk assessment for this unit.

Despite the significant compliance issues and engineering challenges to be addressed in order to obtain a consent to operate the linac, this company must have a registration to work with the small x-ray unit. Whilst the safety arrangements for the linac can also address working with the small x-ray unit, no credit can be gained from having the consent in place, only a registration will suffice.

Is your service contactor from overseas (outside the UK with no legal representation in the UK)?

This is simply a quick advert for a recent blog article released by Ionactive: Non-UK companies working with ionising radiation in the UK (opens in a new tab). It is relevant - even if the subject of consents and registrations in this blog article has been obvious to you, you need to consider the same requirements for any overseas contractor you invite into the UK to work on your systems. Do they have the required consents and registrations from HSE?