Nuclear density gauges

Rules and guidelines for the use of Nuclear density gauges.

What Nuclear density gauges are

Nuclear density gauges (NDM) measure the density and moisture of compacted matter eg, soil, aggregates, asphalt and concrete. They can be used in civil engineering, construction, mining and scientific research.


Because NDMs use a radiation source, a Source licence is needed to operate them.

If your facility has a Source licence, you can use a Nuclear density gauge.

If you are a service engineer who is servicing and/or maintaining the equipment, you need to apply for an additional Use licence.

Download the Use licence application forms.


Most NDM users complete a recognised external training course.

View a list of nuclear density gauge training providers.

It is also possible to train your staff in-house. The training procedure, material and assessment must cover all required aspects of radiation safety and protection and be clearly documented. 

Rental and change of location

You can rent your NDM to another company if they hold a current source licence.

You must notify the Office of Radiation Safety of any change of storage location e.g. if you:

  • rent out the NDM
  • move the NDM around different branches in your organisation.

The location of the NDM must always be accounted for and recorded in the movement log.

View more information on how to notify the change of a registered source.


Your NDM must be secured with a padlock. While an R-clip can prevent the shutter opening, a padlock is more secure. 

A padlock on the NDM, along with a lock on the transport case, helps deter and delay unauthorised access and use of the radiation source.


Where possible your NDM should be collected and returned each day to its normal storage location.

If this is not possible, make sure the temporary storage location meets the safety and security requirements. This can be on the job site or another suitable location. 

If you can’t organise a suitable temporary storage location the NDM must remain in your vehicle. Do not bring it into your living accommodation.

If storing the NDM in your vehicle, ensure that:

  • the NDM and transport case are locked
  • the NDM transport case is covered to not attract attention
  • other tools and valuables are hidden from sight or removed from the vehicle to reduce the potential of an opportunistic break-in  
  • the vehicle is parked on private property (off public roads) and preferably in a locked garage
  • the vehicle is locked and (if installed) the security alarm is on
  • the NDM is more than 3 meters from high occupancy areas, eg bedroom
  • you visually inspect the NDM once a day and keep a record.

Class 7 placarding on vehicles providing temporary storage for radiation sources 

If radioactive sources are temporarily stored in a vehicle over night because they can't be returned to their usual storage destination, it is our view that class 7 placarding still applies according to transport and security requirements.

IAEA Transport Regulations 107(b) exempt radioactive material from Regulations only if it is moved within an establishment that is subject to safety regulations (ie, in NZ, we interpret these Regulations as our Radiation Safety Regulations) and where the movement does not involve public roads or railways. This exemption is incorporated in the Radiation Safety Act 2016 as part of the definition of transport (C). 

While the Office of Radiation Safety understands the concern around attracting unnecessary interest from members of the public when seeing class 7 placards on temporary storage vehicles, this concern does not outweigh the responsibility to display class 7 placards at all times.

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