K. K. Gan

Particle‐ and photoinduced conductivity in type‐IIa diamonds

Electrical characteristics associated with radiation detection were measured on single‐crystal natural type‐IIa diamond using two techniques: charged particle‐induced conductivity and time‐resolved transient photoinduced conductivity. The two techniques complement each other: The charged particle‐induced conductivity technique measures the product of the carrier mobility μ and lifetime τ throughout the bulk of the material while the transient photoconductivity technique measures the carrier mobility and lifetime independently at the first few micrometers of the material surface. For each technique, the μτ product was determined by integration of the respective signals. The collection distance that a free carrier drifts in an electric field was extracted by each technique. As a result, a direct comparison of bulk and surface electrical properties was performed. The data from these two techniques are in agreement, indicating no difference in the electrical properties between the bulk and the surface of the ...

Rapidity Dependence of the Charged Particle Multiplicity Distributions in e+ e- Annihilation at 29-GeV

Abstract The charged particle multiplicity distribution for e+e− annihilations at s = 29 GeV has been measured using the High Resolution Spectrometer at PEP. The multiplicity distribution, expressed as a function of the mean, shows KNO scaling when compared to e+e− data at other energies. Multiplicity distributions for particles selected in different central rapidity spans are presented. All of these are well presented by the Negative binomial distribution. As the rapidity span is narrowed, the distributions become broader and approach a constant value of the parameter k.

THICKNESS DEPENDENCE OF THE ELECTRICAL CHARACTERISTICS OF CHEMICAL VAPOR DEPOSITED DIAMOND FILMS

The electrical characteristics of chemically vapor deposited (CVD) diamond films were measured as a function of film thickness. The samples studied were polycrystalline with the average grain size increasing from approximately 1 μm on the substrate side to approximately 30 μm on the growth surface for the thickest sample. Using time‐resolved transient photoconductivity and charged‐particle induced conductivity, the collection distance (d) that a free carrier drifts under the influence of an applied electric field was measured. Our data indicate that there is a gradient in the collection distance through the material. This gradient in electrical properties has implications for electronic uses of CVD diamond.

Development of diamond radiation detectors for SSC and LHC

Abstract Diamond is a nearly ideal material for use as a radiation detector in the high rate and high radiation environments of the SSC and LHC. The recent development of the chemical vapor deposition (CVD) method of diamond growth promises to make feasible the use of diamond in large quantities. We have carried out beam tests of various samples of CVD diamond supplied by several manufacturers and have measured signals from ionizing particles. Details of these measurements are presented.

First measurements with a diamond microstrip detector

Abstract We have constructed the first high resolution strip detector using chemical vapor deposited diamond as the detection medium. Devices produced with this material have the possibility of being extremely radiation hard with direct applications at high luminosity colliders. This paper details the detector material, the low noise readout electronics and the detector module. First results from a test with high momentum charged particles in a testbeam at CERN are described. We achieved a signal-to-noise of 6:1 and an efficiency of 85% for minimum ionizing particles in the testbeam. The detector has a strip pitch of 100 μm and a strip width of 50 μm. The measured position resolution we achieved was σ = 26 μm. Future development of diamond detectors with application in particle physics experiments and other fields is discussed.

Review of the development of diamond radiation sensors

Abstract Diamond radiation sensors produced by chemical vapour deposition are studied for the application as tracking detectors in high luminosity experiments. Sensors with a charge collection distance up to 250 μm have been manufactured. Their radiation hardness has been studied with pions, proton and neutrons up to fluences of 1.9×10 15 π cm −2 , 5×10 15 p cm −2 and 1.35×10 15 n cm −2 , respectively. Diamond micro-strip detectors with 50 μm pitch have been exposed in a high-energy test beam in order to investigate their charge collection properties. The measured spatial resolution using a centre-of-gravity position finding algorithm corresponds to the digital resolution for this strip pitch. First results from a strip tracker with a 2×4 cm 2 surface area are reported as well as the performance of a diamond tracker read out by radiation-hard electronics with 25 ns shaping time. Diamond pixel sensors have been prepared to match the geometries of the recently available read-out chip prototypes for ATLAS and CMS. Beam test results are shown from a diamond detector bump-bonded to an ATLAS prototype read-out. They demonstrate a 98% bump-bonding efficiency and a digital resolution in both dimensions.

Radiation hardness studies of CVD diamond detectors

Abstract The inherent properties of diamond make it an ideal material for tracking detectors especially in the high rate, high radiation environments of future colliders such as the LHC. In order to survive in this environment, detectors must be radiation hard. We have constructed charged particle detectors using high quality CVD diamond and performed radiation hardness tests on them. The signal response of diamond detectors to ionizing particles is measured before and after irradiation. Diamond detectors have been exposed to 60 Co photons at Argonne National Laboratory, 300 MeV/ c pions at PSI, 500 MeV protons at TRIUMF and 5 MeV alpha particles at Los Alamos National Laboratory. The results show that CVD diamond is an extremely radiation hard material well suited for particle detector production.

Recent results from the RD42 Diamond Detector Collaboration

Abstract Diamond, as the hardest material known, has an extremely high binding energy suggesting that it will be a radiation hard material. Given that it is also a semiconductor, one is led to believe that diamond might perform well as a high resolution semiconductor tracking detector in very hostile radiation environments in which more conventional detectors would fail. In this paper we, the RD42 Diamond Detector Collaboration, review the progress that we have made in the development of chemical vapor deposition (CVD) diamond as a detector material, its radiation hardness, and the performance we have achieved with diamond tracking detectors.

Comparison of charged particle multiplicities in quark and gluon jets produced in e+e- annihilation at 29 GeV

The charged particle multiplicities of the quark and gluon jets in the three-fold symmetric e+e− → qqg events at √s = 29 GeV have been studied using the high resolution spectrometer at PEP. A value of 〈n〉g = 6.7−2.1+1.1±1.0 for gluon jet s with an energy of 9.7−2.0+1.5 GeV is measured. The ratio, 〈n〉g/〈n〉q, is 1.29−0.41+0.21±0.20, which i s significantly lower than the value of 94 naively expected from the ration of the gluon-to-quark color charges.

Neutron irradiation of CVD diamond samples for tracking detectors

Abstract Diamond may make an excellent substrate for a tracking device in the near future, especially at colliders like LHC, where extreme running conditions are expected (high rates and high radiation levels). We report on neutron irradiation of several CVD-diamond samples at the ISIS facility (Rutherford Appleton Laboratory), which provides a fast neutron spectrum similar to that expected in a high luminosity collider experiment like CMS. We measured beam-induced currents and charge collection of diamonds exposed to fluences in excess of 10 15 n/cm 2 (peaking at 1 MeV), which should be the maximum value of the ten years total fluence at the design LHC luminosity. Physical hypotheses for the interactions of neutrons on CVD-diamond are proposed.