Technical Guidance

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.  

A 2009 video looking at radioactive and nuclear materials. In particular the nuclear hazard is considered in terms of critical mass and chain reaction, and also  by looking at power output in a nuclear reactor, as compared to a prompt critical excursion. Historical context is added by considering the Louis Slotin criticality incident.

Which is larger? 100 nSv or 0.1 micro Sv? Which sounds (or looks) larger? This resource considers magnitudes, units and prefixes. Whilst applicable to any situation which uses numbers, this resource considers how this applies to radiation protection. The animation was first posted to YouTube in 2012, it has now been upscaled and features on the Ionactive Vimeo channel direct from our website.