Technical Guidance

Here you will find data and articles on radiation shielding, frequently asked questions (FAQ), monitor performance, specific gamma ray constants, mathematical derivations, radiation protection widgets  - everything we have personally found useful from our own tool kit. New resources will be uploaded here from time to time.

For formal radiation safety advice, visit our Radiation Protection Adviser (RPA) services page. 

  • Geometry / radioactivity distribution with detector response (dose rate / CPS) widget

    Published: Apr 13, 2025

    Source: Design & implementation by Dr Chris Robbins (Grallator) / Facilitated by Ionactive radiation protection resource

      Tags:
    • Geometry effects
    • Radioactivity distribution
    • Dose Rate
    • CPS
    • counts per second
    • Neutron activation
    • Contamination
    • Collimator
    • Detector response
    • Inverse square law
    • radiation detection
    • contamination measurement
    • Surface contamination
    • Surface activation

    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.

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  • Dose Rates from HASS (High Activity Sealed Sources)

    Published: Dec 07, 2024

    Source: Ionactive Radiation Protection Resource

      Tags:
    • High Activity Sealed Source
    • HASS source
    • Dose Rate
    • Dose rate at 1m
    • Radioactivity
    • Industrial Radiography
    • Industrial Irradiation
    • Co-60
    • Cs-137
    • Ir-192
    • Se-75
    • Am-241
    • AmBe

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

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  • High Activity Sealed Sources (HASS) Radioactivity Thresholds

    Published: Dec 07, 2024

    Source: Ionactive Radiation Protection Resource

      Tags:
    • HASS
    • HASS source
    • HASS thresholds
    • Radioactive source
    • sealed radioactive source
    • Sealed Source
    • IAEA
    • D value

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

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  • Criticality widget - Simulation of critical mass, geometry, reflector, multiple masses & delayed neutrons

    Published: Aug 10, 2024

    Source: Design & implementation by Dr Chris Robbins (Grallator) / Facilitated by Ionactive radiation protection resource

      Tags:
    • Criticality
    • Critical mass
    • Criticality simulation
    • Neutrons
    • Prompt neutrons
    • Delayed neutrons
    • Fissile material
    • Nuclear material
    • Neutron multiplication factor (k)
    • Fission
    • mean neutron lifetime
    • Neutron lifetime
    • Reactivity
    • Sub-critical
    • Critical
    • SuperCritical
    • Spherical geometry
    • Rectangular geometry
    • Fission products
    • Neutron reflector
    • Neutron moderator

    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

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  • Criticality and delayed neutrons

    Published: Aug 08, 2024

    Source: Dr Chris Robbins, Grallator / Ionactive radiation protection resource

      Tags:
    • Criticality
    • Critical mass
    • Delayed neutrons
    • Neutrons
    • Nuclear material
    • Fissile material
    • Neutron multiplication factor (k)
    • Fission
    • mean neutron lifetime
    • Prompt neutrons
    • Fission products
    • Eigenvalues
    • Neutron lifetime
    • Reactivity
    • Sub-critical
    • Critical
    • SuperCritical

    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.  

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  • Radiological and Nuclear Hazards - the R and N in CBRN

    Published: Jun 09, 2024

    Source: Ionactive Radiation Protection Resource

      Tags:
    • CBRN
    • Radiological
    • Nuclear
    • Critical mass
    • Criticality
    • Neutrons
    • Nuclear reactor
    • Nuclear weapon
    • Radiation safety
    • Chain reaction
    • Fission
    • Protons
    • Nuclear gauge
    • Strong nuclear force
    • Fissile material
    • Sub-critical
    • Critical configuration
    • Super critical
    • Prompt neutrons
    • Delayed neutrons
    • Little boy

    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.

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In the beginning, there was nothing, which exploded

– Terry Pratchett -