Gamma-ray Emission Probabilities Research Articles

A PC-based program for displaying decay data from the Nuclear Energy Agency's JEF-2 database

A computer program has been written in C which provides a convenient way of displaying a portion of the radioactive decay data incorporated in the JEF-2 library. Through use of a mouse or keyboard, nuclides of interest can be selected from a visual display in a “Chart of the Nuclides” form. Principal information includes half lives, decay modes, gamma-ray and alpha-particle emission energies and emission probabilities plus their uncertainties. Spectral data can be printed or displayed on screen in numerical or graphical form; alternatively data can be printed or spooled to disk files.

Precise measurement of the gamma-ray emission probability for 175Yb

The emission probabilities for the γ-rays of 175Yb were accurately measured by a 4πβ (ppc)-γ (HPGe) coincidence apparatus using a live-timed bi-dimensional data acquisition system. The emission probability of the main 396 keV γ-rays was 0.1315 ± 0.0016, a value that was about twice the evaluated values.

Determination of X-ray and gamma-ray emission probabilities of 51Cr and 88Y

Absolute X-ray and gamma-ray emission probabilities in the decay of 51Cr and 88Y have been determined using sources made from standard solutions. The activities of the radionuclides were determined using the KX-gamma-coincidence technique with NaI(Tl) scintillation counters of different thicknesses. The uncertainty in the activity measurements was 0.2%. The X-ray emissions from the 51Cr and 88Y sources were determined by the defined solid-angle method using a NaI(Tl) crystal. A 2π proportional counter was also used to study 51Cr decay, while the emission probability of the 320 keV gamma-ray of 51Cr was measured by the defined solid-angle method using a scintillation detector and a calibrated HP Ge spectrometer.

Determination of photon emission probabilities of radionuclides using a Si(Li) detector calibrated by the primary standard source, BESSY

BESSY is an electron storage ring which is optimized for use as a primary radiometric standard source for the infrared to X-ray region. The relative uncertainty of the spectral photon flux Φ E is less than 0.45% (1σ) in the spectral range 5 < E < 15 keV. Measurements in undispersed synchrotron radiation produced a quantum detection efficiency for a Si(Li) detector with relative uncertainties of less than 0.5%. The calibrated detector was used to measure the photon flux of radioactive standards of known activity ( 57Co, 65Zn and 88Y) in the photon energy range from 5 to 15 keV. From these measurements, the K α X-ray and gamma-ray emission probabilities p( E) of the radionuclides were deduced. Our results for the K α X-ray lines of 57Co, p(6.4 keV)=0.501(5) and 65Zn, p(8.0 keV)= 0.346(3) and for the ratio p( 57 Co; 14.4 keV)/p( 88 Y; 14.1 keV)=0.179(4) have small uncertainties and are not affected by uncertainties in the fluorescence yields. They confirm recommended data.

Measurements of absolute and relative emission probabilities of gamma- and X-rays and data evaluation in the decay of 155Eu

More accurate values for the X- and gamma-ray emissions of 155Eu would be useful for improving the efficiency calibration of detectors in the low-energy region. Samples of 155Eu were produced by neutron irradiation of high-purity 154Sm (99.2%). The resulting solution consisted of 99.7% 155Eu, with impurities of 152Eu (< 0.1%) and 154Eu ( < 0.2%). 4πβγ coincidence equipment was used to determine the specific activity of 155Eu. Absolute and relative photon emission probabilities were measured with a Ge-planar spectrometer, which was calibrated on the basis of generalized energy response functions. Spectral distortions were taken into consideration to obtain precise values for the absolute and relative emission probabilities of X-rays and low-energy gamma-rays. Re-evaluation of 155Eu gamma- and X-ray emission probabilities and half-life has been performed using the results of our measurements and new data published in the literature.

The re-evaluation of decay data for the U-238 chain

Non-neutron nuclear data (half-lives, transition intensities, radiation energies and emission probabilities) have been re-evaluated for the radionuclides that constitute the decay chain of uranium-238 on the basis of new absolute measurements undertaken in recent years. A new value of 0.00839±0.00012 has been evaluated for the 1001 keV gamma ray emission probability of 234mPa which is used to normalise the relative data. Branching ratios for isomeric transitions and beta decay to the ground state are extremely important and need to be determined with good accuracy. The need for new absolute measurements of the decay parameters for 234Th is also emphasized.

Determination of gamma-ray emission probabilities for 75Se, 166mHo and 192Ir by a self-consistent method

The gamma-ray emission probabilities for 75Se, 166mHo and 192Ir have been measured precisely using a 4πβ(ppc)-γ(HPGe) coincidence system. When determining the gamma-ray detection efficiency function, these nuclides were used as secondary standards in conjunction with a few primary standard sources. This method is considered to give self-consistent results and to be effective when there are insufficient suitable standards.

Precise Measurement of Gamma-Ray Emission Probability for Germanium-75.

The emission probabilities for the γ-rays of 75Ge were accurately measured by a 4πβ counter, a high purity germanium γ-ray detector and a coincidence apparatus using a live-timed bi-dimensional data acquisition system. Two series of measurements were carried out; in the first a 4πβ counter with pressurized Ar 90% plus CH4 10% mixture was used, and in the second that with CF4 gas at atmospheric pressure was used. The emission probability of the main 265 keV γ-rays was 0.1020±0.0017, that was smaller than the evaluated value, 0.113 ± 0.011 (Nucl. Data Sheets, 1981), by about 10%, and the certainty was improved by about six times.

Decay scheme data for 101Mo and 101Tc

New measurements of relative gamma-ray emission probabilities in the decay of 101Mo and 101Tc are reported. Previously published conversion-electron data have been used along with the gamma-ray data to formulate self-consistent decay schemes.

Measurement of the gamma-ray probability per decay of Si-31

The gamma-ray emission probability per decay for the 1266-keV transition of 31Si has been measured. This radionuclide was obtained by means of the 31P(n,p) 31Si reaction in a fast neutron flux at the IPEN 2 MW research reactor. The sample activity has been measured by the 4πβ-γ coincidence method and the efficiency tracing technique was applied using 24Na as the tracer. The gamma-ray counting has been performed in a calibrated HPGe spectrometer. The resulting emission probability per decay obtained for 31Si was 5.537 × 10 −4 with an overall error of 1.21% (one standard deviation).

Beta-particle and gamma-ray emission probabilities in the decay of 160Tb

Relative γ-ray intensities in the decay of 160Tb were precisely measured using two semiconductor detectors. These intensities were used to calculate particle and γ-ray emission probabilities along with their corresponding uncertainties by employing equations derived with standard mathematical error propagating technique (Browne, 1986, 1988).

Decay data of 141Ce

A 4πβ-gamma coincidence system and several efficiency calibrated semiconductor spectrometers were used to determine the following 141Ce/ 141Pr decay data: 1. The β-transition probability to the 145 keV level of 141Pr, b 1. 2. The total conversion coefficient of the 145 keV transition to the ground state of 141Pr, α T. 3. The gamma-ray emission probability of the 145 keV photons, P γ. The results are b 1 = 0.697(6), α T = 0.452(8), P γ = 0.480(5). The value of b 1 is in agreement with most of the values reported in the literature for this quantity. The value found for α T is higher than all experimental values determined previously but agrees well with the theoretically calculated value for an M1 transition with 0.48% E2 admixture ( α T = 0.4565). The value for P γ agrees with the value determined by Hansen et al. (1979), P γ = 0.482(3). In addition, emission probabilities of K and L x-rays following the decay of 141Ce are determined experimentally.

Study of the [formula omitted] decay chain

A study has been made of the gamma-ray and conversion-electron spectra in the decay chain 149Gd(9.4 d) → 149Eu(93.1 d) → 149Sm, following the electron-capture decay of 149Tb, Gamma-ray and conversion-electron emission probabilities were measured with a double-focusing magnetic spectrometer, and internal conversion coefficients, multipolarities and mixing ratios were deduced for several transitions of 149Eu and 149Sm. These values have been compared with previously published data. Gamma-ray emission probabilities have also been measured for 145Sm, 145Pm and 145Nd, which originated via the alpha-decay branch of 149Tb.

Activity measurement of 75Se using integral gamma-ray counting with a 4π-NaI(Tl) detector

In the high efficiency integral counting method the activity A is obtained from A = N/ϵN, where N is the integral countrate and ϵN the average detection efficiency per disintegration. This efficiency is calculated for 75Se using the energy-dependent calibration of the 4π-NaI(Tl) detector and 75Se decay scheme data. The calculation includes the decay via the isomeric state. An assumption in this calculation is the nonexistence of a direct EC decay to the ground state. The overall uncertainty of the 75Se activity obtained is 0.35% (standard deviation). Gamma-ray emission probabilities are determined by gamma spectrometry with germanium and Si(Li) detectors using the activity value measured.

Determination of 239Pu and 241Am LX-ray intensities using a Simplex method for fitting peaks

Accurate values of the LX and gamma-ray emission probabilities for 239Pu and 241Am in the energy region 10–60 keV, are required in several applications including environmental surveys, safeguard measurements for nuclear plants, as well as for the calibration of Si(Li) or Ge detector efficiency.We have measured the emission probabilities of the uranium L-shell X-rays from the decay of 239Pu and neptunium L-shell X-rays from the decay of 241Am. In addition, the emission probabilities of the low-energy gamma rays characterizing these radionuclides have been evaluated.Gamma and LX-ray spectra were obtained using a calibrated planar-Ge detector. The computer code fits the spectra using a Lorentzian line and a step function both convolved with a Gaussian function. The background continuum is also fitted. The least-squared fit is obtained using a Simplex minimization procedure.

Standardisation of 125Sb and 154Eu, and measurement of absolute gamma-ray emission probabilities

A method has been devised to separate 125Sb from its short-lived daughter 125mTe. This technique was based on the repeated use of columns of anion exchange resin and supplemented by chemical procedures chosen to avoid any steps involving evaporation. which in initial trials gave severe problems due to the volatility of the antimony. Standardisation by 4πβ-γ coincidence counting was carried out within a few days of the separation, allowing for the daughter which grows in at about 0.25% per day. Beta counting efficiencies, as measured by the ratio of coincidence to gamma count rates, of up to 90% and 95% respectively were obtained for the two gamma-ray energy windows used. The ingrowth was monitored over a period of one month by gamma-ray spectrometry, using the weak 109 keV gamma-ray of 125mTe, to check the original separation.Samples of 154Eu were produced by neutron irradiation of high purity 153Eu, which was obtained by passing inactive europium through the NPL isotope separator. A solution of the 154Eu was standardised by coincidence counting, again using two gamma-ray energy windows, to give efficiencies of 96% and 98%.Absolute gamma-ray emission probabilities were measured for both nuclides using a germanium spectrometer calibrated with a range of nuclides of known activities and gamma-ray emissions. Sources were positioned 55 cm from the detector to ensure that real summing effects were negligible.

Decay scheme data for 154Eu, 198Au and 239Np

Measurements of relative and absolute gamma-ray emission probabilities in the decays of 154Eu, 198Au and 239Np are reported. For the first two radionuclides previously published conversion-electron and beta-branching data have been used with the gamma-ray data to formulate self-consistent decay schemes.

Gamma-ray emission probabilities in the decay of 65Ni and 125Sb

An evaluation has been carried out of previously published gamma-ray emission probabilities in the radioactive decay of 125Sb. Beta branching ratios and internal conversion coefficients have been taken into account in testing the consistency of the total decay scheme. Measurements have also been made of the absolute gamma-ray emission probabilities in 65Ni and 125Sb using a combination of high resolution gamma-ray spectroscopy and 4πβ-γ coincidence techniques

ICRM intercomparison of the relative gamma-ray emission probabilities of 75Se

There are a number of discrepancies in the reported gamma-ray emission probabilities of 75Se. An international work programme was proposed and agreed by members of the Beta- and Gamma-ray Spectrometry Working Group (SWG) of the International Committee for Radionuclide Metrology (ICRM) to study these data. The first step has been the measurement and intercomparison of the relative gamma-ray emission rates, the second step will be a series of activity measurements conducted under the auspices of the Bureau International des Poids et Mesures (BIPM), while the final stage will involve the combination of these two previous sets of data to deduce the gamma-ray emission probabilities per decay for 75Se. The organisation of the international measurement programme for the relative gamma-ray emission probabilities, the source supplied, and the evaluation methods are described. The results are also discussed in terms of the applicability of 75Se as a calibration standard. Finally, future plans to complete the programme are briefly outlined.

Gamma-ray emission probabilities of the daughters of 238U

A wealth of decay data has been obtained and reported in recent years, much of it in “Decay Data of the Transactinium Nuclides”. IAEA Technical Reports Series No. 261 (1986). The decay data for the daughters of 238U have been notable by their absence in such compilations and, since there is a need for such data, a set of experiments has been performed to measure their gamma-ray emission probabilities. Uranium samples of known mass and isotopic concentration were dissolved in aqueous solution, and analyzed with a high-purity germanium gamma-ray spectrometer. Some of these samples also contained multi-line calibration nuclides with well-known relative emission probabilities and the well-known emission probabilities of the 235U gamma rays were also used to provide an absolute emission probability reference. Since self-absorption of the sample was included in the effective detector efficiency, there was no need for a separate calculation of this absorption. Gamma-ray emission probabilities for the energy range 63 to 1937 keV are reported, and sources of error are discussed, including those in the efficiency curve.