Technical Guidance

Gamma / x-ray dose rate measurements for radiation protection purposes are not always as simple as first expected. Is the emitting source true 4π geometry, 2π or collimated in some way? The same questions can be asked of the detector (most radiation monitors are 2π).  Furthermore, how do the photons scatter within the region between source and detector - do they leave the region before being detected, or are some of them scattered back towards the detector? Are the scatters truly random or could they be influenced in some way? This is the first of several radiation protection widgets, created for Ionactive by Dr Chris Robbins (Grallator), which will explore photon scattering and it's impact on radiation protection and detection. 

Imagine a geometry situation other than a simple point source of radiation from radioactive material. Further imagine the interior surface of a tungsten cone containing radioactive material from neutron activation - the distribution of activity being variable depending on the circumstances of the irradiation. What might the dose rate be,  measured by a radiation detector placed at the open end of the cone? How would this dose rate change with distance from the cone, with distribution of radioactivity within the cone, and with the shape of the cone? This is explored in our latest widget, developed for Ionactive by Dr Chris Robbins from Grallator.

Examples of use and radioactivity of typical HASS sources with their unshielded dose rate at 1m.  

A list of the most popular High Activity Sealed Source (HASS) - with their radioactivity thresholds.

This criticality widget presents a hands on interactive educational aid for understanding criticality in nuclear materials. The widget provides three sections; the first demonstrates neutron population in sub-critical, critical and supercritical systems for two different geometries. The same section also demonstrates the use of a reflector and how this can reduce the effective critical mass of the system for critical and supercritical conditions. The second section considers the approach of two subcritical fissile objects  - reaching critical and supercritical conditions. The final section considers delayed neutrons and how they can significantly alter the power build up (or drop) timescales over orders of magnitude from 10's of micro seconds to 100's of seconds (i.e uncontrollable vs controllable). This resource has been created for Ionactive by Dr Chris Robbins of Grallator

An article by Dr Chris Robbins of Grallator looking at the physics and mathematics of delayed neutrons in criticality scenarios.  The article demonstrates that delayed neutrons and neutron lifetime have a significant impact on the increase (or decrease) in power over orders of magnitude. The article is illustrated with screen shots from the new Ionactive criticality widget.