Is it legal to build a cyclotron?

Verified August 2026

In the United States, yes — no federal law prohibits building or owning a particle accelerator, and no federal permit is required to construct one. What the law regulates is the machine as a radiation-generating device: once a device is capable of producing ionizing radiation when its controls are operated, state radiation-control programs — and, for anyone who sells or leases machines, a thin federal layer — take an interest. For a small cyclotron the burden that results is typically registration paperwork, not licensing, and in every state the practical questions are the same: does the state's accelerator definition reach your machine, what registration applies, and what documentation the radiation-control program expects.

What is actually regulated

Three distinct things attract regulation, and it helps to keep them separate:

• The machine, when energized. State codes define a "radiation machine" as (typically) any device capable of producing ionizing radiation, except devices whose only source is radioactive material. A pile of magnet steel and copper is not regulated; a device that accelerates protons when switched on is. Capability language matters — definitions regulate what a machine can produce, not what an operator intends.
• The radiation produced. Dose limits, posting, surveys, and interlock requirements attach to measured radiation levels at accessible surfaces. A machine whose beam terminates inside its own vacuum chamber and shows no measurable external radiation is in a very different position from one with an extracted beam — several state definitions turn on exactly this distinction (see the state survey).
• Radioactive material, if any is made. Accelerator-produced radioactive material is federally regulated (below). A low-energy proton machine with no deuterium, no targets, and no activation above exempt quantities produces none — but that is a fact to be established and documented, not assumed, and it changes if gases, targets, or energies change.

The federal layer — thinner than most people expect

NRC: does not license the machine

The Nuclear Regulatory Commission does not license particle accelerators as machines. Its jurisdiction covers accelerator-produced radioactive material (byproduct material under the Energy Policy Act of 2005 expansion; see NUREG-1556, Vol. 21). A machine that produces no radioactive material — no isotope production, no activation above exempt quantities — needs no NRC or Agreement-State materials license. Pure radiation-machine regulation is left entirely to the states.

FDA: a records-and-reports regime for manufacturers

FDA's Electronic Product Radiation Control program (FD&C Act; 21 CFR § 1000.3 and Parts 1000–1005) covers any electronic product that emits — or would emit without shielding — electronic product radiation, expressly including particulate radiation such as protons. There is no energy exemption at any level, and "particle accelerator" is a listed product category (21 CFR 1002.1, Table 1). But the obligations are the manufacturer's, and they attach on introduction into commerce — sale or lease: radiation-safety product reports, annual reports, testing and distribution records, accidental-radiation-occurrence reporting (§ 1002.20), and defect-notification duties (Parts 1003–1004). Notably, "manufacturer" includes assemblers. There is no accelerator performance standard, no federal type approval, and — for a nonmedical machine with no human-use claims — no medical-device pathway of any kind. A discretionary reporting exemption exists at 21 CFR § 1002.50 for products that cannot emit hazardous radiation, are produced in small quantities, or are used by trained individuals for research or training — but it is granted in writing by FDA, not self-declared.

FCC: the RF system is ISM equipment

Charged-particle acceleration is expressly an industrial, scientific, and medical (ISM) application under 47 CFR Part 18. A cyclotron's RF system therefore falls under Part 18 rather than amateur or unlicensed-device rules. Operation on a designated ISM frequency (6.78 MHz and 13.56 MHz both sit in the range typical of small cyclotrons) faces materially lighter emission limits than operation on a non-designated frequency; either way, RF containment is a design requirement, and equipment marketed commercially requires a Supplier's Declaration of Conformity backed by EMC measurements.

OSHA: workplaces only

OSHA's ionizing-radiation rule (29 CFR § 1910.1096) includes high-speed protons and requires whatever surveys are necessary to evaluate the hazard in a workplace. Workplace electrical equipment must also be "approved" — in practice, listed or field-evaluated by a nationally recognized testing laboratory. Neither applies to a purely private, non-employment setting, but institutional environmental-health-and-safety offices apply equivalent expectations regardless.

One more federal note: a powered-down accelerator containing no radioactive material is ordinary freight under DOT rules — transporting the machine itself is not a regulated radioactive shipment.

The state layer — where the real rules are

Almost all practical regulation of particle accelerators happens through state radiation-control programs. Most states adapt the Conference of Radiation Control Program Directors' Suggested State Regulations for Control of Radiation (CRCPD SSRCR) — Part H covers nonmedical radiation-generating devices from 5 keV through 1 MeV, and Part I covers "accelerators" — but the SSRCR is a model, not law, and states have adapted it unevenly. The pivotal text is the model definition (SSRCR Part A § A.2, July 2021), adopted verbatim or nearly so by the great majority of states:

"'Accelerator' means any machine capable of accelerating electrons, protons, deuterons, or other charged particles in a vacuum and of discharging the resultant particulate or other radiation into a medium at energies usually in excess of 1 MeV."

That definition has two limiting elements, and both matter for small machines. A cyclotron whose beam terminates on an internal probe inside the vacuum chamber arguably never "discharges into a medium"; and a machine operating tens of keV below 1 MeV sits far under the energy language. But "usually" is a soft qualifier, not a hard floor — a regulator retains discretion to read a sub-MeV machine in — so the definitional argument is a reading of the text, never a guarantee. Across the 51 jurisdictions surveyed (full survey with citations), as verified August 2026:

• 35 states use the CRCPD-model definition (extraction clause plus the soft "usually >1 MeV" language);
• 2 keep the extraction clause but drop any energy floor (New Jersey, South Carolina — with opposite practical effects);
• 2 define accelerators broadly with no floor and no extraction clause (Illinois's accelerator part, Tennessee);
• 1 (Michigan) sets a firm 1 MeV floor;
• 9 never define the term at all, capturing accelerators through generic "radiation machine" language instead;
• 2 (Idaho, Wyoming) currently have no applicable machine program.

Where a machine does fall under a state's rules, the mechanism is usually registration — a form, a modest fee, and conditions such as a responsible individual, written operating and emergency procedures, radiation surveys, interlocks and warning devices, operator training, and records. A minority of states license instead (application review, radiation safety officer, sometimes committee and shielding review) — Arkansas, Hawaii, Maine, North Carolina, and South Dakota are in that group, and Pennsylvania licenses machines that meet its accelerator definition. Educational or hobby use creates no general exemption anywhere.

The "incidental radiation" exemption — read the lead-in

Most state codes carry a CRCPD-derived clause exempting electronic equipment from registration when the dose-equivalent rate does not exceed 0.5 mrem (5 µSv) per hour averaged over 10 cm² at 5 cm from any accessible surface. That figure recurs nationwide because it descends from the model rule. But the lead-in wording is dispositive, and it varies: the common form exempts equipment producing radiation "incidental to its operation for other purposes" — language written for CRTs, rectifiers, and RF cavities whose radiation is a byproduct. A cyclotron's operation is radiation production, so the conservative reading — and the one this site presents as the planning assumption — is that the exemption does not fit a purpose-built accelerator, however low its external emissions, and that routine registration is the expected outcome. A few states use more favorable wording (New Hampshire, Virginia, Washington), a few use stricter or older variants, and a few have no such clause at all; the survey table records each state's wording status with its citation.

Thresholds that change the picture

• ≥1 MeV: essentially every state's accelerator regime engages.
• Extracting a beam from the vacuum chamber: extraction-clause states reclassify the device as a true particle accelerator.
• More than 0.5 mrem/h at 5 cm from any accessible surface: measurement-based exemptions evaporate; generic radiation-machine registration applies almost everywhere.
• Producing radioactive material (deuterium operation, targets, activation): NRC/Agreement-State materials licensing attaches on top of everything above.
• State quirks: e.g., New Jersey's machine exemption additionally requires an operating potential of 5 kVp or less — internal dee voltages typically exceed that regardless of external emission.

What builders actually do

The pattern that emerges from the state codes is consistent, and it is not burdensome for a fixed installation:

1. Identify the state radiation-control program before the machine can first be energized. Every state and DC has one (or, for Idaho and Wyoming, a defined absence); the CRCPD maintains a directory of state programs and contacts.
2. Ask the program in writing how it classifies the machine — particle accelerator, generic radiation machine, or exempt — rather than relying on a private reading of the definition. Written determinations are routine business for these agencies, and "usually in excess of 1 MeV" is their discretion to exercise, not the builder's.
3. Expect to register, and document the machine as if registration applies: design records, a radiation survey with calibrated instruments under maximum operating conditions, interlock descriptions, and operating procedures. The survey is the document that everything else turns on — it is what substantiates any exemption argument and what a registration reviewer asks for first.
4. Institutions route this through their existing radiation-safety program. A university that already registers X-ray diffractometers has an RSO and a registration amendment process; a cyclotron enters as one more radiation machine, at whatever level the state's classification puts it.

Outside the United States the structure is entirely different (many countries license all accelerators nationally); this section covers US law only.