Y. Takami

Variation of luminescence decay in BaF2 crystal excited by electrons, alpha particles and fission fragments

Abstract The time dependence of the luminescence from BaF 2 crystal excited by electrons, alpha particles and fission fragments has been studied for wavelengths of 180–400 nm by a single-photon counting technique. A (220 ± 10) nm component with a lifetime of 0.88 ns is observed for electron and fission fragment excitation. No 220 nm component is observed for alpha particle excitation. The (300+50(−40)) nm component has lifetimes of 600 and 100 ns for electron excitation, 550 and 50 ns for alpha particle excitation, and 580 and 9 ns for fission fragment excitation. The variation in time dependence is attributed to the difference in track structure produced by ionizing charged particles for different LET.

The measurement and prediction of proton upset

The authors evaluate tolerance to proton upset for three kinds of memories and one microprocessor unit for space use by irradiating them with high-energy protons up to nearly 70 MeV. They predict the error rates of these memories using a modified semi-empirical equation of W.L. Bendel and E.L. Petersen (1983). A two-parameter method was used instead of Bendels one-parameter method. There is a large difference between these two methods with regard to the fitted parameters. The calculation of upset rates in orbits were carried out using these parameters and NASA AP8MAC, AP8MIC. For the 93419 RAM the result of this calculation was compared with the in-orbit data taken on the MOS-1 spacecraft. A good agreement was found between the two sets of upset-rate data. >

Degradation of Si/sub 1-x/Ge/sub x/ epitaxial heterojunction bipolar transistors by 1-MeV fast neutrons

Irradiation damage in n/sup +/-Si/p/sup +/-Si/sub 1-x/Ge/sub x//n-Si epitaxial heterojunction bipolar transistors (HBTs) by 1-MeV fast neutrons is studied as a function of fluence and germanium content for the first time. The degradation of the electrical performance of HBTs by irradiation increases with increasing fluence, while it decreases with increasing germanium content. The induced lattice defects in the base and the collector regions are studied by DLTS methods. In the base region, electron capture levels associated with interstitial boron are induced by irradiation, while two electron capture levels corresponding to the E centers and the divacancy are formed in the collector region. The degradation of device performance is then correlated with simulations of numbers of knock-on atoms. In order to examine the recovery behavior, isochronal thermal annealing is carried out for temperatures ranging from 75 to 300/spl deg/C. Based on the recovery of electrical performance, it is pointed out that the electron capture levels induced in the base and collector regions are mainly responsible for the increase of base current and the decrease of collector current.

Decay curves of NaI(Tl) scintillators with different Tl+ concentrations under excitation of electrons, alpha particles and fission fragments

Decay curves of NaI(Tl) crystals with Tl + concentrations of 0.01, 0.07, 0.1 and 0.22 mole% have been measured under excitation by photo-electrons from a 137 Cs source, alpha particles from an 241 Am source and fission fragments from a 252 Cf source. A striking difference between the decay curve for electron excitation and those for excitation by alpha particles and fission fragments is observed. A flat top of the decay curve which is observed under electron excitation is analyzed on the bases of energy transfer processes of electrons and V k centers to Tl + ions reported by Dietrich et al. [Phys. Rev. B 8 (1973) 589]. A flat top of the decay curve from NaI(Tl) with a Tl concentration of 0.01 mole% under alpha particle excitation is also observed. Faster decay components of 34±5 ns (in addition to the main scintillation component of 150±10 ns) and 15±5 ns (in addition to the main component of 100±10 ns) are observed under alpha particle excitation and fission fragment excitation, respectively. This findin...

Investigation of single event upset subject to protons of intermediate energy range (RAM)

Nuclear reaction models to reproduce p+Si nuclear reactions precisely in the incident proton energy region of below 50 MeV are investigated, and a computer code based on exciton models is developed. Si irradiation experiments in the intermediate energy region were performed to measure energy deposited by p+Si nuclear reactions with two totally depleted Si detectors in face-to-face arrangement. Coincident signals were analyzed by a two-dimensional pulse height analyzer. This method is shown to be effective in discriminating signals of contaminating particles. The experimental observations are in good agreement with the computed predictions. The single-event upset (SEU) cross section of the 93L422 (RAM) is also compared with the calculated values. >

Degradation and recovery of In/sub 0.53/Ga/sub 0.47/As photodiodes by 1-MeV fast neutrons

Irradiation damage in In/sub 0.53/Ga/sub 0.47/As p-i-n photodiodes by 1-MeV fast neutrons is studied as a function of fluence for the first time. The degradation of the electrical and optical performance of diodes increases with increasing fluence. The induced lattice defects in the In/sub 0.53/Ga/sub 0.47/As epitaxial layers and the InP substrate are studied by DLTS methods. In the In/sub 0.53/Ga/sub 0.47/As epitaxial layers, hole and electron capture levels are induced by irradiation. The influence of radiation source on device degradation is then discussed by comparison to 1-MeV electrons with respect to the numbers of knock-on atoms and the nonionizing energy loss (NIEL). In order to examine the recovery behavior, isochronal thermal annealing is carried out for temperatures ranging from 75 to 300/spl deg/C. After 300/spl deg/C thermal annealing, the light current only recovers to 20% of pre-irradiation for a fluence of 1/spl times/10/sup 13/ n/cm/sup 2/, while it recovers to 53% for a fluence of 1/spl times/10/sup 15/ e/cm/sup 2/. The different of recovery behavior is thought to be due a different type of radiation damage.

Degradation of Si1−xGex epitaxial devices by proton irradiation

Irradiation damage in n+‐Si/p+‐Si1−xGex/n‐Si epitaxial diodes and heterojunction bipolar transistors by protons is studied. The degradation of the performance increases with increasing proton fluence, whereas it decreases with increasing germanium content and proton energy. The damage coefficient for proton irradiation is nearly the same as for neutron irradiation and is about three orders of magnitude larger than that for electron irradiation. This difference is due to the different number of knock‐on atoms and the nonionizing energy loss, which is correlated to the difference of mass and the possibility of nuclear collisions.

Impact of neutron irradiation on optical performance of InGaAsP laser diodes

Abstract Results are presented of an extended study on the degradation and recovery behavior of optical and electrical performance and on induced lattice defects of 1.3 μm InGaAsP double channel planar buried heterostructure laser diodes with an In 0.76 Ga 0.24 As 0.55 P 0.45 multi-quantum well active region, subjected to a 1 MeV fast neutron and 1 MeV electron irradiation. The degradation of the device performance increases with increasing fluence. Two hole capture traps with near midgap energy level in the In 0.76 Ga 0.24 As 0.55 P 0.45 multi-quantum well active region are observed after a 1×10 16 n/cm 2 irradiation. These deep levels are thought to be associated with a Ga vacancy. The decrease of optical power is related to the induced lattice defects, leading to a reduction of the non-radiative recombination lifetime and of the carrier mobility due to scattering. The difference in radiation damage between 1 MeV fast neutrons and 1 MeV electrons is discussed taking into account the non-ionizing energy loss (NIEL). The radiation source dependence of performance degradation is attributed to the difference of mass and the probability of nuclear collision for the formation of lattice defects. The decreased optical power recovers by thermal annealing, and the recovery increases with increasing annealing temperature. The optical power recovers by 45% for 1 MeV neutron irradiation with a fluence of 1×10 15 n/cm 2 after a 300°C annealing.

Impact of 20-MeV /spl alpha/-ray irradiation on the V-band performance of AlGaAs pseudomorphic HEMTs

The irradiation damage in Si-planar-doped AlGaAs pseudomorphic HEMTs integrated in 50 GHz monolithic microwave integrated circuits (MMICs) and subjected to 20-MeV /spl alpha/ and /spl gamma/-ray irradiation is studied. Both the static and the high frequency device parameters have been analyzed. It is shown that the drain current and the effective mobility decrease after irradiation, while the threshold voltage shifts in a positive direction. The degradation of the device performance increases for higher fluence. The decrease of the mobility is thought to result from the scattering of channel electrons by the induced lattice defects and also from the decrease of the electron density in the two dimensional electron gas (2DEG) region. Moreover, the noise figure increases with increasing fluence, while the gain decreases. After 150/spl deg/C post-irradiation thermal annealing for 15 min, the noise figure and gain for 1/spl times/10/sup 12/ /spl alpha//cm/sup 2/ recovers by 67 and 19%, respectively.

A new type personnel neutron dosimeter with thin Si detectors

A recently developed Si detector system that is capable of distinguishing recoil protons from a hydrogen-rich radiator, depending on charged particles generated by /sup 6/Li(n, alpha)T nuclear reaction, is investigated, taking essential requirements for personnel dosimeters into account. This dosimeter is a REM counter based on a new principle. It possesses two different target materials and distinguishes low-energy neutrons from fast neutrons. Results of response measurements for both types of neutrons are presented, and the results are evaluated. It is concluded that this method can be used to make a compact personnel neutron dosimeter with sufficient detection efficiency. >