Gamma spectrometry


Photon spectrometry is a widely used nuclear measurement technique that identifies and quantifies radionuclides emitting X- and gamma-rays in a sample.
It is non-destructive and does not require specific sample preparation. Conventional spectrometers are designed around semiconductor detectors, usually high-purity germanium (“hyperpure germanium” HPGe).

The radionuclides measured by this method emit X or gamma photons of specific energies and their interactions with the detector depend on several variables (geometry or conditioning: physical shape of the object, density, quantity, measured quantity, type of container, type of emission energy, size, shape and nature of the detector,…).

 

 

Energies from a few keV to a few MeV are covered. The LNHB has about ten HPGe detectors used for gamma and X-ray spectrometry, each adapted to a specific range of energy and/or activity (a few becquerels to a few hundred megabecquerels).
This measurement method requires energy and efficiency calibration. Its metrological use requires the use of high quality metrological standard sources, the activity of which has been characterized by means of primary measurement methods available in the laboratory which allow relative standard uncertainties of less than or equal to 1%.

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Measurement geometries

 

 

X-ray spectrometry is particularly focused on the range of energies below 10 keV and requires the implementation of specific techniques, while gamma-ray spectrometry is focused on energies up to 2.5 MeV.

The measurement of environmental samples requires special conditions, such as extremely low background noise.
They are measured in an underground facility, thus allowing the measurement of weak activities (of the order of a few millibecquerels).
In particular, it includes a HPGe detector equipped with an anti cosmic radiation device.

 

At the LNHB, this method is used for different studies:

COFRAC CERTIFICATE ISSUANCE:

The LNHB can link to the SI laboratories using gamma-ray spectrometry techniques by issuing calibration certificates under COFRAC accreditation for the measurement of different types of radioactive sources.

CONTROL OF THE PURITY OF RADIOACTIVE SOLUTIONS:

Radioactive solutions may contain impurities due to manufacturing defects or simply from the decay scheme. Gamma-ray spectrometry identifies all gamma and X-ray emitting radionuclides in a single sample. This information can be used for specific studies (e.g. optimisation of production processes, determination of the influence of impurities on a global measurement).

FUNDAMENTAL NUCLEAR DATA:

Measurements are carried out to determine photon emission probabilities of different radionuclides, thus contributing to the improvement of decay schemes evaluated by DDEP .

Processing software

Various software packages have been developed to ensure the detailed processing of spectra and the calculation of corrective factors necessary for quantitative analyses.

Our job: metrology

dosimetry

Implemented methods for the establishment of national references must be adapted to the radiation type and its intensity. They are based on measurement technics such as calorimetry, ionometry and chemical dosimetry.

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Radioactivity

The variety of the emitted radiation and physical forms of the sources oblige to adapt the measurement process in order to establish national references: methods with defined geometries, or 4 π countings geometries, coincidence countings, etc.

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