Gamma-ray Sum Research Articles

Performance of a compact multi-crystal high-purity germanium detector array for measuring coincident gamma-ray emissions

The Multi-sensor Airborne Radiation Survey (MARS) detector is a 14-crystal array of high-purity germanium (HPGe) detectors housed in a single cryostat. The array was used to measure the astrophysical S-factor for the 14N(p,γ)15O⁎ reaction for several transition energies at an effective center-of-mass energy of 163keV. Owing to the granular nature of the MARS detector, the effect of gamma-ray summing was greatly reduced in comparison to past experiments which utilized large, single-crystal detectors. The new S-factor values agree within their uncertainties with the past measurements. Details of the analysis and detector performance are presented.

Comprehensive radioassays of samples using the PANDA device

The PANDA (Particles And Non-Destructive Analysis) device is a measuring system developed for non-destructive analysis of samples for safety, security and safeguards. It consists of two complementary measurement positions. The position sensitive alpha–gamma coincidence setup of PANDA has been updated with a pile-up rejection circuit. This article demonstrates, using a 241Am source, that this circuit can be used to identify gamma-ray sum peaks in the spectra. The second measurement position reported here hosts a 10-mm2 windowless silicon drift detector that detects electrons and X-rays with a very good energy resolution. An experimental value of 0.30keV for full width at half maximum was obtained at 17.7keV energy (Np X-rays). Conversion electron spectrometry, for example, provides an independent, complementary means to study actinides whose low energy transitions are often highly converted.

Efficiency loss in HPGe detectors due to beta and gamma sum coincidence

Among the secondary detection effects in gamma-ray spectroscopy with HPGe detectors that reduce the peak area and must be properly taken into account in accurate measurements, the less well known is counting loss by beta and gamma-ray sum coincidence. The fraction of lost counts was estimated assuming that a photon detection event can sum either with the coincident beta-ray or its bremsstrahlung in the detector capsule or surrounding materials. The beta-ray was tracked through all the materials between source and detector. The result was calculated as a sequence of integral expressions evaluated numerically, without resorting to simulation. It is shown that the counting losses due to this effect are negligible for most calibration sources in typical detector arrangements.

Neutron Activation Cross-Section Measurements from 16 to 20 MeV for Isotopes of F, Na, Mg, Al, Si, P, Cl, Ti, V, Mn, Fe, Nb, Sn, and Ba

Cross sections have been measured with the activation technique at various neutron energies in the range of 16.0 to 20.5 MeV for the following 22 reactions: 19F(n,p)19O, 23Na(n,p)23Ne, 23Na(n,α)20F, 25Mg(n,p)25Na, 27Al(n,p)27Mg, 28Si(n,p)28Al, 29Si(n,p)29Al, 29Si(n, np + pn + d)28Al, 31P(n,α)28Al, 35Cl(n,2n)34mCl, 37Cl(n,p)37S, 46Ti(n,p)46mSc, 50Ti(n,p)50g+mSc, 51V(n,p)51Ti, 55Mn(n,α)52V, 56Fe(n,p)56Mn, 57Fe(n, np + pn + d)56Mn, 57Fe(n,p)57Mn, 93Nb(n,α)90mY, 93Nb(n,2n)92mNb, 119Sn(n,p)119gIn, and 138Ba(n,2n)137mBa. The half-lives for the reaction products range from 11 s to 10.15 days. Quasi-monoenergetic neutrons were produced via the 3H(d, n)4He reaction. In some cases isotopically enriched materials were used to enhance the reaction yield or to facilitate correction for interfering reactions leading to the same product. The gamma rays emitted from the irradiated samples were measured with a high-purity germanium detector. A pneumatic sample transport system was used to limit the decay of the radioactive products between neutron irradiation and gamma-ray counting. All cross sections were obtained as ratios to the standard reaction 27Al(n,α)24Na, using as secondary neutron fluence references the 27Al(n,p)27Mg reaction as well as a calibrated Bonner sphere. Corrections have been applied for sample-irradiation and counting environment geometric effects, neutron absorption and multiple scattering, time variation of neutron-source strength, neutron-source angular distributions, secondary neutrons from the target, gamma-ray absorption, and gamma-ray sum coincidences. A detailed analysis of the uncertainty sources was performed. The present results are compared with other measurements and evaluated data. For seven reactions, measured cross sections have been obtained for the first time beyond 15 MeV. These new data help appreciably to resolve discrepancies in evaluated data files.

Measurement ofK-electron capture probability (P k ) in the decay of197Hg (64.1 h)

TheK-electron capture probability (P K ) for the 268.7 and 77.3 keV states of197Au in the decay of197Hg (64.1h) have been determined from theKX-ray gamma ray summing in a HPGe X-ray detector. The measured values,P k (268.7)=0.746±0.033 andP k (77.3)=0.774±0.036 are found to be in good agreement with the theoretical results.

Revision of the ANSI N42.14 performance standard for Ge gamma-ray spectrometry

A major revision of the American National Standards Institute (ANSI) Standard N42.14, “Calibration and Use of Germanium Detectors for the Measurement of Gamma-Ray Emission Rates of Radionuclides”, is in process. The revised standard is more detailed and addresses aspects of Ge gamma-ray spectrometry not covered in the previous standard. Instructions are provided for initial setup, energy calibration, efficiency measurement, and measurement or calculation of corrections for pulse pileup, radioactive decay and absorption. Performance tests are provided (1) to evaluate the peak-finding algorithm, (2) to verify the independence of the net-peak area with respect to the base-line height, (3) to evaluate the doublet-fitting algorithm, and (4) to verify the accuracy of pulse pileup corrections. A simple procedure to assess the magnitude of cascade-coincidence summing is presented. The assignment of uncertainties, averaging of multiple measurements and propagation of uncertainties are discussed. Appendices to the standard contain procedures for optional use in the (1) setup and characterization of a Ge gamma-ray spectrometer, (2) preparation of working standards or QC samples, (3) measurement of the peak position and area, (4) correction for cascade gamma-ray summing, and (5) construction of a detector shield.

(L+M+. . .)/K capture ratio in the decay of207Bi

The K-capture probabilities and (L+M+. . .)/K capture ratio to the 1633.3 keV level, a first forbidden unique transition, and to the 569.7 keV level, a second forbidden nonunique transition, in the decay of 207Bi have been measured using X-ray and gamma-ray summing in one and two intrinsic Ge detectors. The results are compared with the theoretical estimates using the theory of Behrens and Buhring (1971). The ratio of nonrelativistic to relativistic nuclear matrix elements is estimated for the second forbidden nonunique transition to the 569.7 keV level.

AnomalousM4conversion coefficient inTem52125

The absolute $M4$ $K$-conversion coefficient of the 109.3 keV transition in $_{52}^{125}\mathrm{Te}^{m}$ decay is measured using $K$-x-ray gamma ray summing in a Ge(Li) x-ray detector. The measured $K$ conversion coefficient is 10% lower than the theoretical value.RADIOACTIVITY $^{125}\mathrm{Te}^{m}$, chemical separation, Ge(Li) x-ray detector, measured ${\ensuremath{\alpha}}_{K}$ and ${\ensuremath{\alpha}}_{T}$ of 35.5 and 109.3 keV transitions.

Collective Rotation of 238U at High Spins

An experimental study of the actinide nucleus 238U was performed by Coulomb excitation with 208Pb projectiles. The E2-transition matrix elements in the ground state band were measured up to spin 28 by comparing experimental Coulomb excitation yields to semiclassical calculations and by analysing Doppler broadened line shapes measured in coincidence with a gamma-ray sum spectrometer. The E2-metrix elements agree within their errors with the rigid rotor predictions. Neither an increase of the collective transition strength at high spin due to centrifugal stretching as predicted by the Rotation Vibration Model nor a cutoff in collectively as postulated by the Interacting Boson Model is observed. The excitation energies in the ground state band show the presence of an aligned angular momentum of 5ℏ at spin 30 which can be explained by a crossing of an aligned band at ℏω ≈ 250 keV. The octupole band shows a constant angular momentum alignment of 3ℏ (above spin 7) and no indication of a bandcrossing.

K-electron capture probability in the decay ofAgm108(127 yr)

The K-electron capture probability (P/sub k/) in the decay of /sup 108/Ag/sup m/ (127 yr) has been determined from a measurement of the Pd K x-ray intensities as well as from the analysis of the K x-ray gamma-ray sum peak. From the measured value of P/sub k/ (0.85 +- 0.04) the ground-state mass difference between /sup 108/Ag and /sup 108/Pd is estimated as Q/sup +/ = 1926/sup +infinity//sub -/169 keV.

Absolute K-conversion coefficients from the X-ray gamma ray summing in Ge(Li) detectors

A new method for the determination of absolute K-conversion coefficient is described. The K-conversion coefficients of the 569.7 keV and 1063.6 keV gamma rays in the decay of 207Bi(38 yr) and 316.5 keV gamma ray in the decay of 192Ir(74.2 d) are measured and they are found to agree with the reported data.

A Well-Type Ge(Li) Detector

The feasibility and usefulness of a coaxial Ge(Li) spectrometer as a well-type detector for sum spectra of coincident gamma rays is demonstrated. The value of the welltype geometry has previously been established in nuclear gamma spectroscopy with the use of (NaI(Tl) detectors. In this work a 16 cm3 hollow cylindrical germaniun detector has been made and mounted in such a way that access to the center of the detector is achieved from outside the cryostat. The detector is a fully depleted structure in which a hole of 1 cm diameter was ultrasonically cut, and a non-injecting contact applied to the inside surface. The measured resolution of the detector for a 1173 keV gamma ray sum peak from 144Pm was 2.6 keV f.w.h.m, which was mainly limited by statistics and preamplifier noise. The detection of sum lines arising from 2 or more coincident gamma rays is demonstrated by using the radioactive source of 144pm. With the source inside the well, for which the counting solid angle is nearly 4?, the sum peak of three lines at 1791 keV (696 + 618 + 477) was observed with an energy resolution of 3.5 keV f.w.h.m, and a peak to background ratio greater than 15:1. For the source outside the detector at a distance of 10 cm, this sum line was not observed above background for comparable counting statistics. Comparison is also made to results obtained from a 3 well-type NaI(Tl) crystal.

Decay ofIr196

Iridium-196 (120 min) has been produced by the ($d,\ensuremath{\alpha}$) reaction on ${\mathrm{Pt}}^{198}$. The iridium was chemically separated from the target material. Gamma-ray, beta-ray, gamma-gamma, beta-gamma, and gamma-ray sum coincidence spectra were measured. ${\mathrm{Ir}}^{196}$ decays by a single beta group with an end-point energy of 0.95 MeV. The beta decay is followed by a cascade of six gamma rays of 100, 355, 389, 442, 518, and 646 keV. This decay is compatible with the known level scheme of ${\mathrm{Pt}}^{196}$.

180° Compton Scattered-Annihilation Gamma-Ray Sum Peak Observed in Gamma-Ray Spectrometry.

Studies were made on the gamma spectra obtained when a source of Cu/sup 64/ is measured at high and low geometries, both unshielded and encapsulated. An enhanced summing effect at high geometry with a large amount of scattering material present was observed. When the source is encapsulated in wax, the result is annihilation and scattering close to the source of the positrons emitted in all directions. Thus, the conditions are maximized for the production of a sum peak. The distribution of Compton electrons from scattering results in a sharp maximum corresponding to 180 deg scattering. (P.C.H.)

Decay ofI134

The decay properties of 53 min I/sup 1//sup 3//sup 4/ were investigated with scintillation techniques. Energies (and intensities) of the rays determined from the single-cryatal and coincidence studies were 0.135 (3.2), 0.18, 0.23, 0.27, 0.32, ergies of 0.89 and 1.07 Mev. The single-crystal spectra were corrected experimentally for gamma-ray summing. Gamma coincidence spectra were measured by gating at energies of 0.135, 0.41, 0.61, 0.85, 0.89, 1.00, 1.07, 1.15, Beta-ray spectra were measured in coincidence with rays at 0.85, 1.00, 1.07, 1.15, 1.46, 1.62, and 1.79 Mev. These measurements and the single- crystal data disclosed beta rays with end-point energies of 2.41, 2.21, gamma- gamma experiment the 2.41-Mev beta-ray group was shown to populate a level in Xe/ sup 1//sup 3//sup 4/ at 1.74 Mev; therefore, the energy difference between the ground states of I/sup 1//sup 3//sup 4/ and Xe/sup 1//sup 3//sup 4/ was 4.15 plus or minus 0.06 Mev. A decay scheme was proposed with energy levels (and spins) in Xe/sup 1//sup 3//sup 4/ at 0.85 (2+), 3.30, and 3.41 Mev. A collective nature of the low-lying levels was suggested in that the 1.62 and 1.74 Mev states appeared to be members of a vibrational doublet at aboutmore » twice the energy of the first excited state. The half-life of I/sup 1//sup 3//sup 4/ was redetermined as 52.8 plus or minus 0.3 min (auth)« less