Si Surface Barrier Detector Research Articles

Alpha decay properties of new protactinium isotopes

Evaporation residues produced in the reactions 40Ar + 181Ta and 40Ar + 184W were separated from the primary beam by the velocity filter SHIP and detected by a Δ E-E counter telescope. The technique of delayed coincidences was applied to individually identify the reaction products implanted into a Si surface barrier detector by their subsequent α-decays. The previously unknown nuclei 215Pa and 218Pa were identified by their known daughter decays. 215Pa was found to decay with E α = 8.085±0.015MeV and t 1/2 = 14± 2 3ms. For 218Pa two α-lines were found at 9.535±0.015MeV and 9.614±0.020MeV with a corresponding half-life of 120 +40 -20μs. The half-life of the 8.33 MeV α-decay of 217Pa. was determined to be 4.9 +0.6 -0.4 ms. Furthermore a new isomer was found in 217Pa which decays with E = 10.16±0.02MeV and t 1/2 = l.6 +1.0 -0.5ms. The decay of this isomer is tentatively interpreted as being hindered by an angular momentum of about 10ħ of the emitted α-particle. The ground state α-decay energies of these very proton-rich isotopes agree well with systematics but deviate considerably from theoretical mass predictions.

Serious Degradation Characters of CdTe Nuclear Detector by Electron or Gamma Irradiations

We present the degradation characteristics of M-S-M (metal-semiconductor-metal) type CdTe nuclear detectors fabricated from undoped p-type THM crystals under successive irradiations of 60Co gamma rays and 2 MeV electrons at room temperature. Radiation-induced degradations on detector performances are investigated by the evaluations both of the photopeak and Compton edge of 241Am and 137Cs gamma rays. The FWHM energy resolution and counting rate of the photopeak become worse with increasing gamma ana electron fluences. It is thus concluded that the ?? product in the electrons and holes are decreased in comparison with that before irradiation, probably due to the carrier trapping effect. Comparing with the radiation effects of a Si surface-barrier detector, we discuss the annealing behavior of the irradiated CdTe detector.

A new method for calibrating the pulse-height defect in solid state detectors

The pulse-height defect (PHD) of a Si surface barrier detector (1000 ωcm resistivity) has been measured with a cyclotron for elements from Kr to Au between energies of 15 to 160 MeV, and for elements from Ne to Fe between 5 and 50 MeV. A simple power-law formula for relating the PHD to the total energy is described. A procedure for calibrating a Si detector for the PhD from measurements for several elements has been developed and tested. This procedure reproduces the data to within the experimental error (±0.5% of the total energy). Application of the measured and calculated PHD values to another detector of similar resistivity seems to be accurate to better than 10% of the PHD. Our PHD data are also compared to an existing PHD formalism.

Measurements of pulse-height defect in AuSi detectors for H, He, C, N, O, Ne, Ar, Kr from ≈2 to ≈ 400 keV/nucleon

We report measurements of pulse-height defects in Si surface-barrier detectors for a variety of ions and energies. We find: (a) for ions up to Ne our measurements agree remarkably well with calculations based on energy loss and nuclear defect theory, (b) for heavier ions we find systematic deviations, (c) there is no evidence of a dead layer at the SiAu interface, and (d) our measurements are consistently reproducible for detectors fabricated in our laboratory.

Fusion products detection system in migmacell II

To observe the p+t branch of the D+d and d+d fusion reaction at E d = 0.55 MeV in Migmacell II, three 50 mm 2 Si surface barrier detectors were installed at 120°, −60° and −90° relative to the incoming D 2 + beam. Results of an experiment where the background D 2 gas pressure was controlled at around 1.2×10 −5 torr are presented. A computer simulation program has been developed to understand the shapes of the observed spectra. Proton counting rates obtained yield a migma number of 6×10 8 trapped ions in the cell.

Evaluating PtSi front contact to surface barrier detectors

The rectifying front contact of Si surface barrier detectors is usually an evaporated Au film. The properties of this contact may not be optimal in three respects: (a) stability against changing ambient conditions, (b) window thickness and (c) current injection properties. Results are presented of measurements made on PtSi front contacts, as an alternative. We find that while the leakage currents (including the temperature dependence) and ultimate resolution are comparable with typical AunSi results, the PtSiSi system is less sensitive to touching, and changing ambient conditions, and has possibilities for small window thickness. It is suggested that in some applications, the PtSi front contact can be a viable alternative to Au, for nuclear radiation detectors, as well as light detectors.

Search for long-lived superheavy elements in the reaction systemU238+ 9.6-MeV/nucleonCu63,65

A thick /sup 238/U target has been bombarded with /sup 63//sub,//sup 65/Cu ions at an incident beam energy of 9.6 MeV/nucleon. After radiochemical separations into CdS, HgS, and La-oxalate fractions, a search for evidence of the production of superheavy elements was undertaken using Si surface-barrier detectors and mica foils simultaneously for detection of spontaneous-fission events and high-energy ..cap alpha.. emission. No evidence for the presence of superheavy elements in the samples was found. Upper limits for production cross sections for superheavy elements in each of the three chemical samples, assuming an arbitrary half-life of 100 days and a target thickness equal to the entire reaction range of the incident ions from initial energy to the reaction barrier, are as follows: (a) CdS (Z = 108--115): 1 x 10/sup -34/ cm/sup 2/; (b) HgS (Z = 112): 6 x 10/sup -35/ cm/sup 2/; (c) La-oxalate (/sup 254/Cf): 8 x 10/sup -35/ cm/sup 2/. (AIP)

Observations on pulse-height defect for helium ions of energies

Observations on pulse-height defect for He ions of energies <30 keV in Si surface-barrier detectors are compared with existing calculations of stopping power in Au and of nuclear collision effects in Si.

Search for superheavy elements in the reaction238U+9.6 MeV/N63,65Cu

According to calculations of NIX and others, the formation of superheavy elements might occur in heavy-ion reaction systems such as the one under investigation in the present work i.e.,238U+63,65Cu at 9.6 MeV/nucleon. Since previous experiments have indicated that upper limits to the production cross-section for superheavy elements are extremely low, we have carried out two rather long irradiations of 27 hrs and 42 hrs, respectively, at the University of Manchester LINAC. The first run has already been reported on in the literature. In the case of the second run, after chemical separation into HgS, CdS, and La(OH)3 fractions, the samples were assayed simultaneously and continuously over a period of 6 months for alpha-and spontaneous-fission activity, using Si surface-barrier detector. Each sample was at the same time mounted on mice, for the purpose of scanning for fission tracks at a later date. No indications from the data have so far been found that superheavy elements were produced.

The Use of GaSe Semiconductor Detectors for Monitoring High Energy Muon Beams

GaSe semiconductor detectors have been successfully tested during one year for monitoring muon beams in the GeV range in the neutrino experiment at CERN. Their performances are comparable with those of commercial Si surface barrier detectors for this particular application. Crystal growth, detec tor fabrication and characterization are briefly described. Various advantages (cost, ruggedness, resistance to radiation damage, manufacturing simplicity, etc.) are discussed.

Multiple scattering of heavy ions through ΔE Si surface barrier detectors

The multiple scattering of 30–60 MeV 12C ions and 40–70 MeV 16O ions by ΔE Si surface barrier detectors of thicknesses 10.3 μm and 14 μm was measured with a position sensitive detector. The horizontal spatial distributions of the heavy ions were extracted from position measurements made both with and without the ΔE counter in place. Calculations based on the theories of Molière and Nigam, Sundaresan, and Wu (NSW) were made and compared to the data. The much simpler form of the NSW theory predicted fwhm which were much too large when compared to the experimental data while the Molière theory gave a reasonable description of the experimental distributions at the higher incident particle energies. However, the Molière calculations overestimated the fwhm by 28% in the case of 30 MeV 12C ions incident upon the 10.3 μm detector. Particle detection efficiencies for a typical time-of-flight system are presented.

An ultra thin ΔE E counter telescope with position sensitivity in two dimensions

A thin-window proportional counter ( ΔE)Si surface barrier detector ( E) telescope is described which has position sensitivity in two dimensions with a resolution of <0.40 mm fwhm ( σ rms<0.17 mm). The counter is well suited for particles with E M =0.2−5 MeV/amu and is very easy to construct and to use.

Nuclear Charge Distributions in the Isobars 92 to 100 Resulting from Thermal Neutron Fission of Uranium-235

The nuclear charge distribution of fission products from $^{235}\mathrm{U}({n}_{\mathrm{th}}, f)$ is determined for the isobaric chains 92 to 100. The results were obtained from the energy loss of monoisobaric and monoenergetic fission products in a $\ensuremath{\Delta}E$ Si surface-barrier detector. The odd-even effect is found also in the mass chains reported here for the first time, revealing an approximately sinusoidal variation of the charge distribution width with mass.

Direct determination of the nuclear charge distribution of mass separated fission products from [formula omitted

The nuclear charge distribution of mass separated monoenergetic fission products of the isobaric chains 90 and 91 were recorded with a ΔE Si-surface barrier detector. The achieved nuclear charge resolving power (fwhm) Z ΔZ was 43.

Measurement of theB11+Tb159complete-fusion cross section

The complete-fusion cross section for the $^{170}\mathrm{Yb}$ compound system, formed in the reaction of 115 MeV $^{11}\mathrm{B}$ with $^{159}\mathrm{Tb}$, has been measured using a counter telescope containing a thin gas proportional counter and a Si surface-barrier detector. The result is in excellent agreement with that obtained using mica track detectors.NUCLEAR REACTIONS Complete fusion $^{159}\mathrm{Tb}$($^{11}\mathrm{B}$, $^{170}\mathrm{Yb}$*), $E=115$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta})$ for evaporation residues.

The accurate fission cross-section of 239Pu from 0·005 eV to 0·1 eV and its reference value at 2200 m/s

A precise measurement of the fission cross-section of 239Pu was performed with a slow chopper at the Belgian BR2-reactor (energy range 0·000 to 0·1 eV). Simultaneous recordings of pulse-height and time-of-flight spectra of successively compared 239Pu layers and standard elemental boron layers were made. The detection of the 10B( n, α) 7Li and 239 Pu(n, ƒ) reaction fragments is made with excellent pulse-height resolution in low geometry with a AuSi surface barrier detector. The separation between the pile-up tail produced by the α-particles of 239Pu and the fission fragment energy-distribution was very good. The amount of 10B in the elemental boron layers was determined by weighing in vacuum combined with careful chemical and isotopic analysis of witness foils. The relative amounts of 10B were checked by neutron-counting in the geometry of the experiment. The amounts of 239Pu on the fission foils were determined from precise low-geometry α-counting and the knowledge of the isotopic composition and α-half-life values. The α-activity was controlled before and after the measurements. The fission cross-section was calculated in the energy-range from 0·005 to 0·1 eV and its absolute value deduced at 2200 m/s was 741·9 ± 3·4b. These cross-section values were used to calculate the Westcott g / tf -factor for a 20·44°C Maxwellian neutron distribution with as results g ƒ = 1·0553 ± 0·0013 .

Alpha particles from 197Au irradiated by 500 MeV bremsstrahlung

The energy and angular distributions of α-particles in the reaction 197Au(γ, α) have been measured at nine different angles for bremsstrahlung with peak energy 500 MeV. The measurements were made using a telescope consisting of three Si surface-barrier detectors. The experimental results are compared with cascade-evaporation calculations and the angular distribution indicates the presence of directly emitted α-particles in competition with evaporated ones.

A determination of the singlet neutron-neutron scattering length from the 2H(n, p)2n reaction

The proton energy differential cross section d 2σ dΩ d E p in the 2H(n, p)2n reaction at 14.1 MeV has been accurately measured at the mean proton angle \\ ̄ gq p = 4.0° ± 2.2° with a counter telescope consisting of two Si(Li) surface-barrier detectors and three gas proportional counters. Detailed descriptions on the experiment have been presented. In order to extract the 1S o n-n scattering length a nn , the measured break-up proton spectrum was compared in detail by the χ 2 minimization with the theoretical spectrum calculated in the framework of the Faddeev approach using the separable potentials. As the result, we obtained a nn = − 18.31 ± 0.22 fm with the effective range r nn = 2.84 fm which was fixed in this analysis. This value of a nn is comparable with the value predicted by Noyes and Lipinski who summarized recently the n-p and p-p scattering parameters. The assumption of charge independence of nuclear forces has been evidently violated. The a nn values deduced until now have been summarized, and it has been discussed that the a nn values extracted from the analysis based on the conventional approximations are unreliable at least at 14 MeV.

Structure, Directional-Correlation, and Doppler-Shift Lifetime Measurements inCu61viaNi58(He4,pγ)Reaction Spectrometry

The level structure and the decay properties of the levels in $^{61}\mathrm{Cu}$ up to 4082 keV of excitation have been carefully investigated via prompt $\ensuremath{\gamma}\ensuremath{\gamma}$ and $p\ensuremath{\gamma}$ coincidence experiments employing Ge(Li) $\ensuremath{\gamma}$-ray detectors and annular Si surface-barrier charged-particle detectors. From these experiments and from high-resolution singles energy and directional- correlation measurements an improved decay scheme has been obtained which includes 44 levels in $^{61}\mathrm{Cu}$ and incorporates 120 $\ensuremath{\gamma}$ rays. New levels at 2584.5, 3739.4, 3942.4, and 4081.8 keV were postulated, while the $\ensuremath{\gamma}$ decay of several previously reported levels between 3277-3802 keV was not observed. The singles directional correlations from many transitions were used to obtain (i) reliable branching ratios for the more intense $\ensuremath{\gamma}$ rays and (ii) multipole mixing ratios $\ensuremath{\delta}(\frac{E2}{M1})$ by employing both a ratio method and an independent analysis of the correlations via the compound statistical theory of nuclear reactions. Branching ratios for the weaker $\ensuremath{\gamma}$ rays were obtained from spectra taken at 55\ifmmode^\circ\else\textdegree\fi{} to the beam direction. The lifetimes of 31 levels in $^{61}\mathrm{Cu}$ were measured by the Doppler-shift attenuation method via the $^{58}\mathrm{Ni}(^{4}\mathrm{He},p\ensuremath{\gamma})$ reaction at bombardment energies between 9.7 and 12.2 MeV. Lifetimes were extracted from singles spectra obtained at 0, 15, 30, 45, 70, 90, and 110\ifmmode^\circ\else\textdegree\fi{} and from $p\ensuremath{\gamma}$ coincidence spectra obtained at 0\ifmmode^\circ\else\textdegree\fi{} to the beam direction, by employing both a centroid shift analysis for the data from all angles and a line-shape fitting analysis for the data from angles \ensuremath{\le}45\ifmmode^\circ\else\textdegree\fi{}. The stopping power of Ni previously calibrated for Cu ions, was used for the line-shape analysis and for obtaining reliable $F(\ensuremath{\tau})$ curves applicable to the present conditions of both the singles and the coincidence experiments. For a large number of transitions in $^{61}\mathrm{Cu}$ values for $B(E2)$ and $B(M1)$ were obtained. The $B(E2)$ and $B(M1)$ values together with the $\ensuremath{\delta}(\frac{E2}{M1})$ values and the branching ratios from the first 10 levels in $^{61}\mathrm{Cu}$ are compared with recent detailed calculations for $^{61}\mathrm{Cu}$ based on a unified model. Good general agreement is observed between experiment and theory for the $B(E2)$ values. Only moderate agreement between experiment and theory is observed for the $B(M1)$ and $\ensuremath{\delta}(\frac{E2}{M1})$ values.

Study ofHf173Levels Populated in the Decay ofTa173

The decay of $^{173}\mathrm{Ta}$ was studied using high resolution Ge(Li), Si(Li), and Si surface-barrier detectors in singles and coincidence modes. The $^{173}\mathrm{Ta}$ activity was produced via the reaction $^{165}\mathrm{Ho}(^{12}\mathrm{C}, 4n)^{173}\mathrm{Ta}$, at a carbon beam energy of 6.3-6.9 MeV per nucleon. All spectra were obtained from chemically separated Ta sources. Besides the previously known energy levels of $^{173}\mathrm{Hf}$, the following levels in keV were determined: 255.5, 451.9, 508.9, 635.8, 775.5, 785.3, 811.7, 927.5, 942.5, 1020.3, 1111.4, 1127.0, 1192.8, 1248.3, 1450.0, 1574.2, 1655.6, 1667.1, 1694.3, and 2263.3. Rotational bands based on the ${(\frac{1}{2})}^{\ensuremath{-}}[521]$ (g.s.), ${(\frac{5}{2})}^{\ensuremath{-}}[512]$ (107.2 keV), and ${(\frac{7}{2})}^{+}[633]$ (197.5 keV) Nilsson states were observed. The half-lives of the ${(\frac{5}{2})}^{\ensuremath{-}}[512]$ and the ${(\frac{1}{2})}^{+}[633]$ band heads were determined to be (182\ifmmode\pm\else\textpm\fi{}20) nsec and (160\ifmmode\pm\else\textpm\fi{}40) nsec, respectively. The probability of the radiative $E1$ transition between the [633] and [512] band heads was calculated within the framework of Nilsson model including the pairing and Coriolis interactions. From measurement of the ${\ensuremath{\beta}}^{+}$ end-point energy, the mass difference between $^{173}\mathrm{Ta}$ and $^{173}\mathrm{Hf}$ was determined to be 3670\ifmmode\pm\else\textpm\fi{}200 keV.