Reverse Depletion Research Articles

Experimental results on radiation induced bulk damage effects in float-zone and epitaxial silicon detectors

A comparative study of the radiation hardness of silicon pad detectors, manufactured from float-zone and epitaxial n-type monocrystals and irradiated with protons and neutrons up to a fluence of 3.5 × 10 14 cm −2 is presented. The results are compared in terms of their reverse current, depletion voltage, and charge collection as a function of fluence during irradiation and as a function of time after irradiation.

Cytotoxicity and metabolism of [formula omitted] in HCT 116 colon cancer cells

We examined the cytotoxicity, biochemical effects and metabolism of 4-me methoxy-8-(β- d- ribofuranosylamino) pyrimido[5,4-d] pyrimidine (MRPP), a synthetic nucleoside inhibitor of phosphoribosylpyrophosphate synthetase, in HCT 116 human colorectal cancer cells. A 4-hr exposure to 1 and 10 μM MRPP inhibited cell growth over a 72-hr period by 76 and 89%, and inhibited clonogenic capacity by 36 and 65%, respectively. MRPP was avidly metabolized to the 5′-monophosphate derivative (MRPP-MP), and MRPP-MP formation increased with increasing MRPP exposure (μM·hr). MRPP-MP was stable, and the intracellular half-life was in excess of 48 hr. A 4-hr exposure to 10 μM MRPP resulted in significant decreases in ATP, UTP, GTP, CTP, dATP, dTTP, and PRPP pools. Near maximal ribonucleotide triphosphate depletion was achieved with ⩾24 μM·hr MRPP, and growth inhibition as a function of MRPP μM·hr closely reflected the biochemical effects. Ribonucleotide triphosphate pools remained depleted for up to 48 hr after drug removal, apparently as a consequence of the prolonged retention of MRPP-MP. MRPP (10 μM) inhibited the salvage of [ 3H]guanine, [ 3H]-adenine and [ 3H]guanosine, and concurrent exposure to MRPP and either 100 μM adenine, hypoxanthine, or guanine did not reverse ATP or GTP depletion. Concurrent exposure to 10 μM MRPP and either 10 μM adenosine, uridine or thymidine was accompanied by repletion of ATP, UTP, and dTTP pools, respectively, but depletion of other nucleotide pools was not corrected. In contrast, 10 μM guanosine did not correct GTP depletion in the presence of MRPP. The combination of 10 μM each of thymidine, uridine, adenosine and guanosine during and following a 24-hr exposure to MRPP provided partial protection against 0.1 or 1 μM MRPP, but did not affect the cytotoxicity associated with 10 μM MRPP. MRPP is a novel antimetabolite that inhibits both de novo and salvage pathways for purine synthesis and de novo pyrimidine synthesis.

Radiation hardness of silicon detectors for future colliders

The radiation hardness of silicon pad detectors, especially developed for the PLUG-calorimeter of the H1 experiment at HERA was investigated with respect to neutron and electron irradiation. Be(d,n)-neutrons with an average energy of 6.2 MeV up to a fluence of 10 15 n/cm 2 and 1.8 MeV electrons up to a dose of 1 MGy (10 16 e/cm 2) were used. Degradation effects of the diode properties regarding the reverse current, depletion voltage and charge collection efficiency are studied at room temperature and with no bias applied during irradiation. Special emphasis is put on the separation of the respective damage generation and its subsequent self annealing. The observed effects are discussed with respect to radiation levels to be envisioned for experiments with future colliding beam machines.

The Optimum Fuel and Power Distribution for a Pressurized Water Reactor Burnup Cycle

A method is developed to determine the optimum fuel and power distributions for a pressurized water reactor (PWR) burnup cycle. The backward diffusion calculation and the corewise Green's function method are used for the core model, which provides analytic derivatives for solving the nonlinear optimization problem using successive linear programming methods. The solution algorithm consists of a reverse depletion strategy that begins at the end of cycle and solves simultaneously for the optimal fuel and burnable absorber distributions while the core is depleted to the beginning of the cycle. The resulting optimal solutions minimize the required fissile fuel inventory and burnable absorber loading for a PWR.

Characteristics of diffused P-N junctions in epitaxial layers

A one-dimensional analysis has been made to determine properties of diffused p-n junctions in epitaxial layers with nonuniform impurity concentration. Impurity diffusion from the surface and from the substrate is assumed to have complementary error function distribution. The transcendental equations obtained by analytical integration of Poisson's equation were evaluated numerically with the IBM 7090/94. Junction depth, impurity gradient and impurity level at the junction are given for a variety of diffusion parameters and impurity concentrations. In addition, graphs are presented, showing the relationship between reverse voltage and depletion layer thickness, capacitance per unit area, and peak electric field for the case of silicon. A comparison between the actual impurity profile and the usual linear approximation using the impurity gradient at the junction gives the range of depletion layer thickness or reverse voltage in which such an approximation is justified. Further, examples are presented of the electric field distribution in the depletion layer for several impurity concentration profiles. Calculated and experimentally determined values of some readily accessible junction characteristics show reasonably good agreement.

Low Dose Gamma Irradiation of Semiconductor Diodes†

ABSTRACT Investigations have been carried out of the effects of small (10 kilorad) doses of 60Co gamma radiation on p—n junction germanium diodes, with particular reference to changes in reverse saturation current and junction depletion capacitance under reverse bias conditions. Significant post-irradiation changes were observed in both parameters and a mechanism is proposed to explain the major features of the observations.