Single Escape Research Articles

Coercive Persuasion and the 'Culpable Mind'

1 September of 1965, a young marine driving a jeep was surrounded by Vietcong. Since he was due to leave Vietnam in two weeks, he had no rifle, only a pistol, but he killed two of the enemy before they took him prisoner and stripped him of his uniform. They marched him, virtually naked and without treatment for his wound, through jungle mountains for the next ten days. Local citizens abused and taunted him, poking his wound, his genitals, and his rectum with pointed bamboo. His single escape attempt ended with quick recapture and a severe beating. At the camp at the end of the march, the marine was placed in a six-by-six foot cage. His hands bound, he was unable to combat the ubiquitous leeches and mosquitoes. Twice a day he received a riceball covered with rancidfish sauce. Malnutrition, dysentery, malaria, and tropical parasites soon took their toll on the marine. There were no other Americans at this camp, and none of the South Vietnamese Army prisoners spoke more than a few words of English. Weeks later, the monotony was broken by the arrival of a man treated with deference by the Vietcong. He addressed the marine in impeccable English, identifying himself as Ho An Quong, a professor from Danang University whose mission was to re-educate the marine. Thereafter, they spent hours each day in conversation. When the marine pleaded for more food or for release from the cage, Mr. Ho explained that he was not a prisoner of war, but a war criminal. The marine had murdered two Vietnamese at the time of his capture. Before he could be let out of the cage, he must learn to acknowledge his past crimes, and earn the forgiveness of the Vietnamese people by signing a leaflet

Method for determination of silicon in plant materials by neutron activation analysis

Silicon has been found to be an essential element for the growth and development of many ecomomically important plants such as sugarcane, rice, oats, and wheat. A method is described for the quantitative determination of silicon in plant samples. Measurements were made with two Ge(Li) detectors matched with a multiplexing unit to provide a single amplified signal to a computerized analyzer system. For those materials containing greater than 0.5 weight percent silicon, the reaction29Si(n, p)29Al (1273 keV) provides a direct measurement of the quantity of silicon provided the irradiation is done in a special boron nitride capsule to reduce interferences from thermal neutron reactions and a correction is made for the single escape line from28Al (1268 keV). For lesser quantities of silicon, a technique which utilizes the fast neutron reaction28Si(n, p)28Al is preferred. Corrections for the interference produced by the presence of phosphorus31P(n, α)28Al are made by determining the phosphorus content following the instrumental analysis using a unique application of neutron activation analysis, i. e., measurement of tungsten in tungstomolybdophosphoric acid produced when molybdate and tungstate ions are added to dissolved samples of the plant material containing phosphorus. Aluminum, which may also produce an interference by thermal neutron reaction27Al(n, γ)28Al, is determined directly from the original activation data after subtracting out the effect of the phosphorus. Thus, three irradiations in the pneumatic sample irradiator are necessary; one short irradiation (1 min) without thermal neutron shielding, a longer irradiation (6 min) in the boron capsule, and a final irradiation of the tungstomolybdophosphoric acid provide all data required to accurately determine silicon in plant materials. A computer program has been developed that provides rapid reduction of the data in final report format. Elements such as sodium, chlorine, calcium, manganese, potassium, and magnesium extrinsic to the analysis for silicon are also determined by this method. The method has been tested on a large number of samples and reliable results are obtained with less than 0.2 g of sample.

Determination of detector efficiencies for gamma ray energies up to 12 MeV: I. Experimental methods

Several methods are outlined by which the detection efficiencies of gamma ray detectors may be determined experimentally with special regard to higher energies. They were applied to measure the detection efficiencies of a Ge(Li) semiconductor detector (appr. 26 cm 3) and NaI(Tl) scintillation counters (7.62 cm diam. × 7.62 cm height) in the energy range from 0.66 MeV to 12 MeV, partially to 17 MeV. Absolute efficiencies are given for the full energy peak, the single and double escape peaks due to pair production, the head of the energy loss distribution, and a modified total absorption.

In-beam neutron activation analysis of stainless steel and iron ore

Neutron capture gamma-ray activation analysis technique has been used for the non-destructive analysis of Fe, Cr, Ni, Mn and B in stainless steel and iron ore samples. It has been shown that the use of low energy capture gamma-rays, ranging from 0.2 to 1.4 MeV, helps considerably in reducing the time of analysis. The problem of congestion of peaks due to compton continuum and the double and single escape peaks in this region of the spectrum has been overcome by using a Ge(Li) detector in conjunction with a 15.25 cm thick bifurcated NaI(Tl) annulus in anticompton mode. The results obtained by this technique have been compared with those of the chemical analysis.

Efficiency determination for some standard type Ge(Li) detectors for gamma-rays in the energy range from 0.04 to 11 MeV

Absolute full energy and double escape peak efficiencies of 38 and 31 cm 3 true coaxial and of 5.8 cm 3 planar Ge(Li) detectors have been determined for γ-rays from 0.04 to 11 MeV in an arrangement typical for γγ-coincidence experiments with thermal neutron capture γ-rays from an external target. The results are compared with theoretical predictions. Experimental results for the ratios of double escape, single escape and full energy peak areas against the γ-ray energy are presented. The measurements have been performed with the γ-rays from the radioactive sources 153Gd, 169Yb and 154Eu and from the thermal neutron capture in 1H, 12C, 14N, 39K and 53Cr. To check the efficiency curves obtained in the present experiment, the relative intensities of some γ-ray transitions in the reactions 39K (n, γ) 40K and 45Sc(n, γ) 46Sc are compared with the results of other authors.

On the use of the single escape peak in Ge(Li) spectroscopy

The single escape (SE) peak in a Ge(Li) detector is shown to be wider than either a double escape or a full energy peak of the same pulse height. The extra width arises from Doppler broadening of the annihilation energy and is determined by the electron momentum distribution in germanium. In addition the centroid of an SE peak in a coaxial detector is Doppler shifted to higher energies because of the positron's mobility in the electric field in the detector. These effects necessitate caution in the use of SE peaks in energy measurements and system linearity tests, and in extraction of Fano factor or nuclear lifetime from linewidth measurements.

On the decay of cobalt 60

The gamma spectrum from Cobalt 60 decay has been investigated with a 40 cc Ge(Li) detector. A peak at 822 keV is shown to be not a gamma transition but a single escape peak and an upper limit of 10 is given to the branching ratio of the 2158 keV level.

The calibration of a Ge(Li) gamma-ray spectrometer for energy and relative intensity measurements

Two aspects of Ge(Li) gamma-ray spectrometry are discussed. The non-linearity of an amplifier-analyzer system was measured using a precision pulser and was checked with gamma-ray standards. The overall accuracy was 2 parts in 10 4. The relative detection efficiency of gamma-ray full-energy peaks was determined using sources with well measured relative gamma-ray emission rates. Two Ge(Li) detectors with active volumes of 3 cm 2×0.5 cm and 4 cm 2×0.5 cm were calibrated in the energy range 80—3200 keV. An overall accuracy of 5% in the energy region from 500–3200 keV and an accuracy of 10% over the entire range was obtained. The relative areas of the single escape peak and double escape peak to the full energy peak as a function of energy are included. The relative intensities of the 569.6, 1063.6 and 1771 keV gamma-rays following the decay of 207Bi were measured.

A Pair Spectrometer Using a Large Coaxial Lithium-Drifted Germanium Detector

A gamma-ray spectrometer, using a 30 cc coaxial Ge(Li) detector, which can be operated as a 3 crystal pair spectrometer at high energies and in the Compton suppression mode at low energies, provides an effective means for studying complex gamma spectra. Pair spectrometer operation enhances peak to background ratios by reducing background and eliminating single escape and full energy peaks. The peak to background ratio for the 2.614 MeV gamma of ThC is improved by about a factor of 70 with only a factor of 7 loss of efficiency. The energy resolution (fwhm) of the spectrometer is approximately 0.5% at 1 MeV and 0.1% at 7 MeV allowing capture gamma energies to be determined to an accuracy of about 1 keV. A comparison is given of the performance of the pair spectrometer using two smaller Ge(Li) detectors (3 cc and 5 cc) and the large 30 cc detector. Capture gamma spectra of Ti and Zr are given to illustrate the performance of the spectrometer.