P. J. Nolan

210Pb dating by low background gamma counting

Lead-210 and radium-226 measurements by direct gamma assay can now provide a record of changing concentrations in lake sediments sufficiently reliable and precise to form a suitable basis for age/depth and dry-sedimentation-rate calculations. There are additional benefits in terms of non destructive sample preparation and simultaneous assay for other environmentally significant gamma-emitting radioisotopes (e.g. 137Cs and 241Am). Results from L. Fleet, S. W. Scotland illustrate the value of this approach especially in lakes with disturbed catchments where variable input of supported 210Pb has occurred.

Self-absorption corrections for well-type germanium detectors

Corrections for self-absorption are of vital importance to accurate determination by gamma spectroscopy of radionuclides such as 210Pb, 241Am and 234Th which emit low energy gamma radiation. A simple theoretical model for determining the necessary corrections for well-type germanium detectors is presented. In this model, self-absorption factors are expressed in terms of the mass attenuation coefficient of the sample and a parameter characterising the well geometry. Experimental measurements of self-absorption are used to evaluate the model and to determine a semi-empirical algorithm for improved estimates of the geometrical parameter.

The Clover: a new generation of composite Ge detectors

This paper presents the characteristics of a new generation of composite germanium detectors: the Clover detector. Its development was based on simulation calculations performed with the code GEANT3. An extensive study of its main characteristics involving the photopeak detection e

Confinement of antihydrogen for 1,000 seconds

ciency, the energy resolution and the timing performed with sources and in-beam experiments have been measured. A simple Doppler broadening correction procedure is proposed to improve the in-beam energy resolution of the Clover detector. An other important property, the sensitivity to the linear polarisation of c-rays has been measured. The performances obtained with the associated BGO suppression shield are also reported. All these results compare very well with the initial simulation calculations. ( 1999 Elsevier Science B.V. All rights reserved.

Measurements on prototype Ge and BGO detectors for the Eurogam array

Antihydrogen has been created, trapped and stored for 1,000 s. The improved holding time means that we now have access to the ground state of antimatter—long enough to test whether matter and antimatter obey the same physical laws.

The performance of a bismuth germanate escape suppressed spectrometer

Abstract This paper presents the results of tests, both with sources and in-beam experiments, on prototype Ge and BGO detectors of the Eurogam array. Timing and energy resolution data are reported along with results for various methods of ballistic deficit correction. The first measurements with the new “shared suppression” technique are presented.

Resonant quantum transitions in trapped antihydrogen atoms

Abstract An escape suppressed spectrometer has been built and its performance measured. The spectrometer consists of three elements. The first is a cylindrically symmetric suppression shield made from bismuth germanate and sodium iodide. The second is the germanium detector which is inserted into the shield along its axis. The germanium detector has the minimum of material behind it so that this space is filled by the third element, a bismuth germanate scintillator. The performance of the system has been measured with 241Am, 60Co and 137Cs sources.

210Pb dating of lake sediments and ombrotrophic peats by gamma essay

The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom’s stature lies in its simplicity and in the accuracy with which its spectrum can be measured and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and—by comparison with measurements on its antimatter counterpart, antihydrogen—the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves.

Construction and use of a three Ge(Li) Compton polarimeter

210Pb levels in lake sediments and ombrotrophic peats have been measured by gamma assay, using low background well-type and planar Germanium detectors. The associated 226Ra concentrations have been measured by gamma emissions from 214Pb at 352 keV. A comparison of 137Cs emissions at 32 keV and 662 keV, and 210Pb and 214Pb emissions for samples in radioactive equilibrium, indicates that self-absorption in lake sediment samples does appear to be significant at lower energy levels. Attenuation factors to correct for this have been determined. Results from a number of sites are presented. The analysis of peat samples has been facilitated by ashing material at 450°C prior to measurement.

Observation of the 1S–2S transition in trapped antihydrogen

Abstract A three Ge(Li) Compton polarimeter has been constructed, and its sensitivity to γ-ray linear polarisation determined in the energy range 0.4 to 4.4 MeV. An example is given describing its application to resolve a spin ambiguity for the 4868 keV level in 33 S populated by the reaction 30 Si(α,n) 33 S at an α-particle bombarding energy of 9.8 MeV.