RN detection Flashcards
Define nuclear forensics
the use of scientific techniques to investigate potentially criminal uses of radiological and/or nuclear material. most commonly used for counter proliferation purposes, but does have growing use in health and safety outside of civil nuclear too.
3 goals of nuclear security policies
–
Development and control of military applications of nuclear energy
Finding ways to curb the proliferation of states, or even non state actors, with nuclear capabilities;
failing that
Receiving best possible information on the nuclear programme or weapon arsenal of other states.
a growing fourth area - reduce the use of RN material as a non monetary criminal currency
4 linkages that nuclear forensics can provide
people
places
materials
events (including time components)
IAEA definition of nuclear forensics
Nuclear forensics is the examination of nuclear or other radioactive materials, or of evidence contaminated with radionuclides, in the context of legal proceedings under international or national law related to nuclear security
Types of radiation for detection
Alpha
Beta
Gamma
Neutron
Muon - not radioactive but part of high energy physics which most RN physicists are best placed to study this as well
Detection for alpha/beta
scintillator
Signal analyser
types of detector for gamma
Gamma spectrometers consist of a (usually HPGe )
detector used for measuring photon energies, a
pre amplifier, an amplifier, an analogue to digital
converter (ADC ) and a multichannel analyser
(MCA).
types of detector for neutron
He-3 gas with photomultiplier giving a count per unit time response
what is a neutron particle?
3 quarks, 1 up and 2 down which are generated in some nuclear decay chains and neutral in charge so very difficult to detect.
present in the decay chains of plutonium and uranium which could indicate the presence of special nuclear material. this is useful for standoff detection.
what is and alpha particle?
a helium atom without the electrons, low travel distance and low penetration properties (sheet of paper will stop them)
what is an neutron particle?
3 quarks, 1 up and 2 down which are generated in some nuclear decay chains, most usefully the decay chains of plutonium and uranium which could indicate the presence of special nuclear material. this is useful for standoff detection.
what does a scintillator do?
converts energy lost by ionising radiation into pulses of light in solids or liquids which then interacts with a photocathode to give an electron multiplied in a Photo Multiplier Tube (PMT) to give electrical signal
What does the signal do?
analysed by a multi channel analyser and the intensity of each alpha particle energy is taken. it is the intensity at each energy level that allows an analyst to work out what types of radioactive material is present. noting there will probably be multiple elements in differing quantities so the decay chain is useful to cross reference with.
materials for scintillators
organic (plastic) or inorganic (ZnS or NaI)
how do you limit thermal noise?
electron hole production creates noise which can be mitigated by cooling in liquid nitrogen.
What are the axis of a gamma spectrum graph?
y axis - counts
x axis - particle energy
What happens to the signal in a gamma spectrometer?
The preamplifier converts a charge pulse to a
voltage pulse, while the amplifier provides a
voltage gain . The ADC transforms the signal to a
digital pulse that is used as input to the MCA. The
MCA sorts the pulses according to their pulse
height , which is proportional to the photon
interaction energy.
AWE objective for nuclear forensics
Develop and provide end to end operational response capabilities for detection, recovery, analysis, characterisation and technical attribution from all scenarios, exploiting nuclear and conventional forensics capabilities.
what does nuclear forensics + conventional forensics =
total forensic exploitation
Define nuclear characterisation
is the determination of a sample’s characteristics. It
typically involves an elemental analysis of the sample, most often including isotopic analysis of nuclear materials (i.e. U and Pu) and selected minor
constituents (e.g. Pb ). It also includes physical characterization e.g. measuring the key dimensions of solid samples, or for powders particle size and shape distribution.
Define nuclear reconstruction
is the process of combining the information from
interpretation with all other available information (e.g. from forensic analysis of non nuclear evidence associated with the sample or from intelligence sources) to determine as full a history as possible of the RN material. This phase is called attribution in the contexts of investigations of nuclear trafficking and terrorism events.
what are the skills AWE have that make them import to the UK in nuclear security?
Hazardous materials of concern are used as part of AWE’s other core MOD programmes in
support of the UK’s nuclear deterrent over the last 60 years.
Unique knowledge base in AWE’s personnel and AWE’s facilities for characterisation of
explosives, bulk SNM, radioactive materials.
AWE provides key RN technical support to the UK CBRNE Operational Response
RN types of signature that can be assessed
Shape
Measurement
marking
grain analysis
microscopy
chemical characteristics - composition of the uranium
rare earth elemental pattern of the ore
major, minor and trace constituents
