National Physical Laboratory

IR Modelling Ionising Radiation Modelling

NPL offers consultancies, collaborations and training, based on our scientists' wealth of experience in Monte Carlo radiation modelling and other modelling techniques.

How can NPL help you?

At NPL we routinely use mathematical modelling techniques to underpin our world-leading expertise in ionising radiation measurements. This gives us a wealth of experience in Monte Carlo simulation codes and finite element calculations, and enables us to offer a combination of modelling and measurement to suit a particular application. Bringing both approaches to bear on a problem allows each to validate the other and provides unmatched confidence in the outcome.


NPL welcomes enquiries regarding consultation or collaboration in problems where modelling may be able to provide a solution. Typical areas include the design of detectors, shielding, or irradiators, and validation/optimisation work for existing designs or facilities.

As the UK’s National Measurement Institute, we are also able to offer high-quality measurements using our state-of-the-art facilities as part of the model validation process, or provide advice on measurement techniques. NPL offers many services based on dosimetry measurements traceable to the UK National Standards.

Monte Carlo modelling

The application of Monte Carlo methods is one of the most important techniques that NPL’s scientists use in calculating the effects of ionising radiation and optimising radiation measurements.

A Monte Carlo calculation provides a realistic simulation of radiation transport, i.e. the scattering and absorption processes undergone by ionising radiation (photons, electrons, neutrons, protons, light ions, etc.) as it passes through different materials and geometries.

We use a wide variety of radiation transport codes, including EGSnrc, GEANT4, FLUKA, MCNP, MCNPX and PTRAN, to model a range of applications across many technical areas. NPL is independent of the providers of these codes so we are able to select the most appropriate code or codes for a particular problem.

The NPL clinical linear accelerator modelled using EGSnrc: X-rays (yellow) and electrons (green)

Many of the simulations take advantage of the NPL distributed computing grid that makes use of the spare capacity of hundreds of desktop computers across the site. This enables us to carry out, in a matter of hours, simulations that would take days or weeks on a single machine, significantly reducing the turnaround time.


  • Radiation shielding design and evaluation to ensure adequate shielding
  • Radiotherapy standards and research work for both reference conditions and small-field work, and in geometries such as for brachytherapy, and in molecular radiotherapy.
  • Industrial radiation processing such as medical device irradiations with electron beams or gamma-rays from cobalt-60.
  • Neutron spectrometer responses to allow the incident neutron spectrum to be deduced from the measured pulse height distribution.
  • Neutron dosimeter responses to predict the performance of radiation protection instrumentation in typical workplace fields
  • Radioactive waste assays, calculating the response of Germanium detectors to gamma radiation from sources in low-level waste drums
MCNP model
MCNP model of a tissue-equivalent proportional counter, displayed using the visualisation code SABRINA (left) and a well-type ionisation chamber with an inserted 192I High Dose Rate Brachytherapy source, modelled using egspp (right)

Analytical and numerical modelling 

Other modelling techniques also play an essential role. Finite element analysis is used extensively in the design of radiation detectors, for example to model the transfer of heat in calorimeters, or to calculate the electric fields within ion chambers or gas counters.


Electric field strength calculation
Electric field strength calculation (left) in the new 5cc primary standard cavity chamber (right), calculated using the COMSOL Multiphysics finite-element code


Training and Conferences

At NPL we are committed to the dissemination of knowledge and technical information. We have hosted many UK Monte Carlo User Group (MCNEG) meetings and international workshops on Monte Carlo codes and training courses on the EGS system.

For more information please contact Mark Bailey or David Shipley