In-situ characterization of samples by experts, using high resolution gamma spectrometers, is required if low resolution NaI detector-based hand-held radionuclide identification devices are unable to provide definite spectral identifications. In some remote locations, the use of liquid N-2 cooled HPGe detectors is not possible. Electrically cooled HPGe detectors are not always a feasible alternative, as they are expensive, bulky and heavy. Therefore we have developed a portable gamma spectrometer with a unique, nearly room temperature semiconductor (CdTe) detector to close this gap. The technology of CdTe crystal growing developed at ACRORAD (Japan) and the technology of p-i-n structures with high breakdown voltage developed at PNPI (Russia) allowed creation of high performance detectors with dimensions of 13.9mm x 13.8mm x 2.23 mm, i.e. with a sensitive volume of more than 400 mm 3 . The spectrometer system uses a charge loss correction circuit to improve energy resolution, and detector temperature stabilization by Peltier cooler to ensure consistent operation of the detector during field measurements over a wide range of ambient temperatures. The system can operate continuously for up to 12 hours on rechargeable batteries. Using the combination of the hardware with dedicated software, the device can determine the isotope vector of Pu and U samples without calibration and characterize unknown, shielded or masked radionuclides. Experimentally, we have recently been able to perform the first Uranium and Plutonium isotopic analysis with a device other than a cryogenically-cooled germanium spectrometer. The CdTe spectrometer is capable of measuring small plutonium reference samples and uranium samples with the mass of a few grams in about 20 minutes, with an energy resolution ≤ 2.0 keV for the gamma line of 186 keV (U-235) and ≤ 0.5 % FWHM for the gamma line 662 keV (Cs-137). Thus, the efficiency of γ-radiation registration for such a detector in the energy range from 200 keV to 1500 keV is equivalent to a HPGe detector with sensitive volume about 3 cm 3 . This extends significantly the express measurement capability for nuclear materials examination for highly portable instruments. The development of this device has been supported under Research Contracts of the International Atomic Energy Agency and the US DOE Research Grant.

Earlier developed CdTe p–i–n detectors technology (energy resolution is close to the Ge ones) gives a possibility to solve various tasks of γ-active materials control. For inspection of the materials irradiating γ-quanta with energies of 100–400keV (for example, U, Pu), it is sufficient to increase the sensitive area of detector up to 4–5cm2 (with the thickness about 2.5–3mm). It might allow measurement of the nuclear materials characteristics using standard software, designed for Ge detectors. The research results for large square CdTe p–i–n detectors and detection systems development will be demonstrated in this work. The factors limiting energy resolution and other characteristics (peak-to-background ratio, shape of amplitude distribution, charge losses) of the large CdTe detectors will be discussed.

Several portable instruments are designed using previously reported CdTe detector technology. These can be divided into three groups according to their energy ranges: (1)3–30keV XRF analyzers, (2)5–120keV wide range XRF analyzers and (3)γ-ray spectrometers for operation up to 1500keV. These instruments are used to inspect several hundreds of samples in situ during a working day in applications such as a metal alloy verification at customs control. Heavy metals are identified through a 3–100mm thick package with these instruments. Surface contamination by heavy metals (for example toxins such as Hg, Th and Pb in housing environmental control), the determination of Pb concentration in gasoline, geophysical control in mining, or nuclear material control are other applications. The weight of these XRF probes is about 1kg and two electronic designs are used: one with embedded computer and another based on a standard portable PC. The instruments have good precision and high productivity for measurements in situ. The detection limit of Ce is about 0.03% when measured in the presence of 10% barium for 15s. The detection limit when measuring K-shell X-ray of heavy metals contamination is about 0.1mg/cm2 for 15s. Two types of probes for γ-spectrometry with small and large (>30mm 3) detector volumes provide both high- and low-activity of nuclear fuel analysis. The maximum distance between the probes and electronics unit is 20m. The γ-spectrometers are equipped with electronics to correct signal distortion due to slow carrier effects. This allows the instrument to achieve an energy resolution of about 2.5keV at 662keV. Several modes to process spectra are possible including semiquantitative and total real-shape fitting.