keV 60Co Research Articles

Optimization of the gamma-ray spectrometry counting time based on uncertainties of radionuclides concentration in samples

This paper aims to propose an easy and fast method of optimization of the gamma-ray spectrometry counting time in determining natural radionuclides (Pb-210, Pb-212, Pb-214, Bi-212, Bi-214 and Ac-228) in order to minimize uncertainties in the concentration. The samples were measured by gamma-ray spectrometry with a hyper-pure germanium detector Canberra, 25% relative efficiency, effective resolution of 1.9 keV on the 1332.5 keV 60Co with associated electronics and coupled to a microcomputer. Multichannel Maestro A65-I model was used for spectrum acquisition and peak net area determination, and WinnerGamma/Interwinner 6.01 software was used for gamma-ray spectra analysis and to calculate the concentrations and associated uncertainties. The counting times used were 86,000 s and 150,000 s.

Isomeric ratios of the products of (γ, xnp) reactions on 90,91Zr nuclei for a maximum bremsstrahlung energy of 84 MeV

We present the results from measuring and calculatoffing the isomeric ratios for the 87m,gY nucleus produced in the 90Zr(γ, 2np)87g,mY and 91Zr(γ, 3np)87g,mY reactions, and for the 86m,gY nucleus produced in the 90Zr(γ, 3np)86g,mY and 91Zr(γ, 4np)86g,mY reactions. The method of measuring the induced activity of irradiated samples with a semiconductor spectrometer based on an HPGe detector with a relative efficiency of 20% and an energy resolution of 1.9 keV for the 1332 keV 60Co line was used to determine the isomeric ratios. The obtained results are compared to calculations using the TALYS code, employing statistical and preequilibrium model approaches.

Photoactivation of isomeric level in 115In

In this paper we have studied the photoactivation of an isomeric level of 115 In(336 keV, T 1 2 ∼ 4.5 h) using a strong 60 Co source and a set of intervening iron absorbers. We have considered the possiblity of the isomeric level activation by nonresonants processes involving the 1173 and 1332 keV 60Co photons. The existence of the nonresonant contribution to the activation of 115In has been confirmed. The nonresonant cross section σ NR T = (5.5 ± 0.8)×10 −32cm −2 is the same order of magnitude as those that have been found in our previous investigations.

Thermoluminescence Efficiency of LiF:Mg,Cu,P (MCP-N) Detectors to Photons, Beta-Electrons, Alpha Particles and Thermal Neutrons

The thermoluminescence efficiency, ?, of LiF:Mg,Cu,P (MCP-N detectors, commercially produced at the INP, Krakow, Poland), relative to 662 keV 137Cs gamma rays, has been measured for (i) 1250 keV 60Co gamma rays, (ii) filtered X ray beams of average energies in the range 15-300 kVp, (iii) 147Pm beta electrons, (iv) thermal neutrons and (v) stopping alpha particles of initial energies in the range 0.5-5 MeV. A rapid decrease of TL efficiency with decreasing mean photon energy from ? = 1.04 ± 0.02 for 60Co, ? = 0.93 ± 0.02 for 300 kVp X rays to ? 0.59 ± 0.016 for 15 kVp X rays was observed. The measured value of relative efficiency for 147Pm beta electrons was ? = 0.90 ± 0.02. The relative efficiency for alpha particles decreased from ? = 0.06 ± 0.004 to ? = 0.03 ± 0.007 for particles of initial energies of 5 MeV and 1 MeV, respectively. The measured response of MCP-N detectors after doses of thermal neutrons was equal to 0.72 x 1010 Gy.n-1.cm2, which corresponds to ? = 0.10 ± 0.01. The efficiency for 2.73 MeV 3H tritons was found to be ? = 0.155 ± 0.02. The rapid decrease of sensitivity of LiF:Mg,Cu,P with increasing ionisation density is a microdosimetric effect, resulting from the saturation of the TL signal from high energy deposits. An empirical relationship between the mean lineal energy, yF, and ? has been found which can be used to predict the TL efficiency of MCP detectors for photons and electrons. However, TL efficiency ? is not a unique function of yF so this relationship cannot be used to predict the value of ? over the whole range of ionisation densities (LET) of heavy charged particles stopping in the detector.

Photoactivation investigations WTH 113In and 87Sr

A 60Co source has been used to study the photoactivation of the 392 keV (T 1 2 = 99.5 min) isomeric level of 113In and the 388 keV (T 1 2 = 2.8 h) isomeric level of 87Sr. We have considered the possibility of the isomeric level activation by nonresonant processes involving the 1172 and 1332 keV 60Co photons. As observed in investigations of 115In and 111Cd, nonresonant processes were found to make significant contributions to the excitation of isomeric levels.

Anticoincidence-Shielded Ge(Li) Gamma-Ray Spectrometer for Marine Environmental Radionuclide Analysis

An anti-Compton γ-ray spectrometer has been developed, which possesses a number of characteristics particularly adapted to direct measurement of low-level complex mixtures of radionuclides in marine environmental samples. The detector assembly consists of a 42.7 cm3 coaxial Ge(Li) detector and a well-type 6″diam. × 4″ Nal(Tl) detector for the anticoincidence shield. The sample to be measured is placed on the Ge(Li) detector inside the well of the Nal(Tl) crystal. Suppression of the Compton background is particularly marked at the Compton edge when the assembly is operated in anticoincidence mode. The anticoincidence shield reduces the 137Cs Compton edge by a factor of 6.6 to provide a peak-to-Compton edge ratio of 210: 1 without reducing the full-energy peak efficiency by more than 2%. Similarly, for the 1,332.5 keV 60Co γ-rays the Compton edge is reduced by a factor of 7 to give a peak-to-Compton ratio of 85:1, though in this case the peak efficiency is reduced by a factor of 1.8 due to the cascade decay. This spectrometer has permitted the detection of a few pCi of fallout nuclides such as 137Cs and 95Zr, contained in 30 g environmental wet samples counted at intervals of 1,000 min.

Fast-neutron flux measurement with a lithium-drifted germanium detector

The use of lithium-drifted germanium detectors for fast-neutron flux measurement has been investigated. The proposed detection mechanism is observation of the internal conversion electrons emitted during the de-excitation of the 691 KeV 0 + state in 72Ge following excitation via fast-neutron scattering. A 4.0 cm 3 (approx.) planar Ge(Li) detector has been calibrated for neutron flux measurements over the energy range E n = 700−5000 keV. The absolute efficiency for this detector (ratio of neutrons detected to neutrons incident on the detector) has been determined to be (8.2±0.5) × 10 −4 at E n = 1500 keV which is about 10% of the full-energy peak efficiency for 1332 keV 60Co gamma rays. Cross-sections for excitation of the 691 keV 0 + state in 72Ge via neutron scattering have been extracted from the measured efficiency function. These cross-sections can be used to calculate efficiency functions for other detectors. Insensitivity to thermal neutrons, gamma-ray discrimination capability and stability are among the desirable features of this type of fast-neutron detector. Submicrosecond timing is not possible because of the isomeric nature of the 691 keV 0 + state in 72Ge. While Ge(Li) detectors suffer radiation damage from fast-neutron bombardment, the detector used for these measurements withstood an integrated dose exceeding 10 10 neutrons/cm 2 without serious deterioration of its performance.

Anticoincidence-Shielded Ge(Li) Gamma-Ray Spectrometer for Marine Environmental Radionuclide Analysis

An anti-Compton γ-ray spectrometer has been developed, which possesses a number of characteristics particularly adapted to direct measurement of low-level complex mixtures of radionuclides in marine environmental samples.The detector assembly consists of a 42.7cm3 coaxial Ge(Li) detector and a well-type 6 diam. ×4 NaI(Tl) detector for the anticoincidence shield. The sample to be measured is placed on the Ge(Li) detector inside the well of the NaI(Tl) crystal.Suppression of the Compton background is particularly marked at the Compton edge when the assembly is operated in anticoincidence mode. The anticoincidence shield reduces the 137Cs Compton edge by a factor of 6.6 to provide a peak-to-Compton edge ratio of 210:1 without reducing the full-energy peak efficiency by more than 2%. Similarly, for the 1, 332.5keV 60Co γ-rays the Compton edge is reduced by a factor of 7 to give a peak-to-Compton ratio of 85:1, though in this case the peak efficiency is reduced by a factor of 1.8 due to the cascade decay.This spectrometer has permitted the detection of a few pCi of fallout nuclides such as 137Cs and 95Zr, contained in 30g environmenal wet samples counted at inervals of 1, 000min.

A Total Absorption Ge(Li) Gamma Ray Spectrometer

A configuration of a large Ge(Li) detector has been developed which suppresses single, local interactions, particularly Compton scatterings. The peripheral n+ contact of a coaxial detector is split into two or more segments, and events are recorded from the central p contact if signals are coincidentally present on two segments of the n+ contact. A sum signal is derived from the central p contact through a high resolution preamplifier, and individual localization signals are taken from each segment of the n+ contact through simple voltage-sensitive preamplifiers. The maximum sensitivity of the system lies between 300 and 1300 keV where the Compton crosssection is dominant and many Compton scattered ?-rays are not sufficiently energetic to escape. The total absorption mode achieves about 20% of the photopeak efficiency of the detector operated in the normal singles mode. An increase in the ratio of the full energy peaks to the Compton continuum of 10:1 is found for 60Co ?-rays, and it is significantly greater for ?-rays of less than 1 MeV. The use of internal detector summing of the linear signal eliminates the need for complicated external preamplifier gain adjustment and stability. Capacitively coupled, voltage-sensitive preamps on each n+ segment add negligible noise and reduce the sum signal-to-noise ratio only to the extent that the input shunt capacitance used reduces the sum signal level by about 10%. Thus, a 30 cc split n+ detector yields 3.9 keV 60Co resolution in the coincidence mode compared with 3.5 keV when both n+ segments are grounded.