A. I. Namenson

Hardness Assurance and Overtesting

A procedure is developed for estimating the advantage gained by testing electronic piece parts at levels of radiation higher than the specification level which they must survive. When the probability distribution of radiation stress to failure is approximately lognormal, and a test shows that with confidence, C, the survival probability is at least PT at the test level of stress RT, then with the same confidence the survival probability is at least PS at a lower specification level of stress RS where, Ps = F[ F¿(PT) + ln(RT/RS/¿ln(MAX)] The standard deviation, ¿ln(MAX), is the estimated maximum s.d. in the logarithms of stress to failure; the function, F(X), is the standard normal cumulative probability distribution function; and the function, F(P), is the antifunction of F(X) - that is, F(P) standard deviations above the mean of a normal distribution includes fraction P of the distribution. A discussion is given of how this formula also applies to those tests which are more properly acceptance/rejection tests rather than tests which establish a confidence that parts will survive a given radiation level with a given probability. The suggested overtesting technique is compared to other standard testing techniques.

Lot uniformity and small sample sizes in hardness assurance

Recent standard radiation test procedures allow wafer-level lot acceptance testing using as few as two or four parts with no failures. Such tests guarantee a high survivability of the accepted part only when the parts within a wafer exhibit a highly uniform response to radiation and when a large fraction of the wafers pass the test. The author points out the need for validating these tests, suggests techniques for doing so, and recommends modifications to current test procedures. >

Average Silicon Neutron Displacement Kerma Factor at 1 MeV

The average neutron displacement kerma factor in the vicinity of 1 MeV is difficult to derive for silicon because of sharp neutron cross section resonances in that region. To avoid these difficulties, the function AE(1-e-B/E) was fitted to tabulations of D(E) vs. E, where E is energy and D(E) is the neutron displacement kerma factor for silicon at 1 MeV. The values of A and B obtained from a least squares fit yielded an average value at 1 MeV of D¿(1 MeV)=95±4 MeV-mb.

Hardness Assurance Statistical Methodology for Semiconductor Devices

A statistical method is developed for determining electrical end-point limits for semiconductor devices subjected to radiation stress. The approach utilizes multiple lot radiation data and can be applied where lot-to-lot variations in radiation response are large compared to variations within a lot. Such limits may be used as design parameter limits or as failure limits for lot acceptance testing of future hardness-assured, semiconductor production lots. The method was applied for neutron and total gamma dose effects on low power bipolar transistors, digital TTL ICs, and a power transistor for which an adequate multiple-lot radiation database existed.

The nuclear structure of 193Os

Abstract The energy levels of 193 Os have been investigated using the 192 Os (n, γ) 193 Os reaction. Precise energy measurements of secondary γ-rays have been made with the high resolution curved crystal spectrometers and high flux of thermal neutrons available at the ILL. Primary γ-rays following average resonance capture with a mean neutron energy of 2 keV were studied at Brookhaven National Laboratory. The two sets of results have been combined with existing data to construct a level scheme up to 1300 keV incorporating a complete set of 1 2 − , 3 2 − states. Unique or limited spin assignments have been made for most of the levels. It has been shown that, as a result of the significant reduction in the fragmentation of single particle strength, the essential features of the states below 700 keV can be understood in terms of Coriolis coupled Nilsson model states.

POWER LAW WAVE NUMBER SPECTRA OF FRACTAL PARTICLE DISTRIBUTIONS ADVECTED BY FLOWING FLUIDS

Recently, it has been shown that an initial cloud of particles advected by a fluid may, under common circumstances (e.g., when the particles float on the fluid surface), eventually becomes distributed on a fractal set in space. This paper considers the characterization of such fractal spatial patterns by wave number spectra. If a scaling range exists in which the spectrum has an observable power law dependence, k−ρ, then the exponent ρ is given by ρ=D2+1−M, where D2 is the correlation dimension of the fractal attractor and M is the dimension of the relevant space. We find that observability of the power law may be obscured by fluctuations in the k‐spectrum, but that averaging can be employed to compensate for this. Theoretical results and supporting numerical computations utilizing a random map are presented. In the companion paper by Sommerer [Phys. Fluids 8, 2441 (1996)], an experimental example utilizing particles floating on the surface of a flowing fluid is given. (More generally we note that our res...

Resonance neutron capture by 170Yb and 172Yb

Abstract Primary γ-ray spectra following resonance neutron capture by 170 Yb and 172 Yb were observed using the NRL linac neutron time-of-flight facility. Spectra from the first four resonances in 170 Yb and the first three resonances in 172 Yb were studied with a 30 cm 3 Ge(Li) detector using natural and separated isotope targets. The intensity of γ-ray transitions to particular Nilsson bands in 171 Yb and 173 Yb was examined for non-statistical effects. Possible regularities similar to those observed in thermal capture are discussed.

Statistical Analysis of Step Stress Measurements in Hardness Assurance

The technique of maximum likelihood analysis can solve previously unresolved problems which arise in step stress measurements where the failure levels for each device can only be bounded between two often widely separated limits. The proposed analysis would be necessary in correctly computing means, standard deviations and safe survival limits.

Spins of low-energy neutron resonances in 175Lu, 189Os and 187Os

Abstract Resonances up to 300 eV in 175 Lu, 189 Os, and 187 Os are reported together with spin assignments and probabilities of correctness. Those spins reported with better than 90% confidence consist of 49, 17 and 10 resonances in 175 Lu, 189 Os, and 187 Os respectively. In 187 Os, 39 of the observed resonances have not been reported previously. Ratios of low-energy γ-ray intensities and γ-ray multiplicity were used for spin determinations. A method developed previously for analyzing these data has been extended to include analysis of uncertainties in relative populations, average reduced neutron widths, and strength functions of the two spin groups. The data in 189 Os is consistent with a 20 J +1 level-density dependence, but in the other two isotopes this rule is violated. We suggest spin cut-off factors of about 3 in this mass region. Small differences in gΓ n 0 > and in the strength functions for the two spin groups are not considered very significant.

Estimating Electronic Parameter End Points for Devices Which Suffer Abrupt Functional Failure during Radiation Testing

The abrupt failure of devices under test - especially during step-stress measurements presents special problems in determining parameter end points. This article shows how past procedures can be replaced by a method which can be applied with equal logical consistency to both the graceful degradation of parts as well as to the abrupt failure of parts. The article gives an example of how the method works and discusses its advantages and disadvantages