Dale William Visser

Particle decay branching ratios for states of astrophysical importance in 19 Ne

O, which are of interestin understanding energy generation in x-ray bursts and in interpreting anticipated γ-ray observa-tions of novae. We detected decay protons and alpha particles using a silicon detector array incoincidence with tritons measured in the focal plane detector of our Enge split-pole spectrograph.The silicon array consists of five strip detectors of the type used in the Louvain-Edinburgh DetectorArray, subtending angles from 130

A Java-based data acquisition system for nuclear physics

Abstract Jam is a Java-based user-friendly data acquisition and analysis system developed for CAMAC-based nuclear physics experiments. The system is menu-driven and has been designed to minimize the expertise needed to perform the essential tasks necessary to collect and sort data. The front-end hardware is VME based and includes a MVME167 running VxWorks, which is networked to a Sun workstation. The sorting, display, and control routines are all written in Java, and the front-end code is written in C. With a Sparc 5 workstation, events with 10 parameters, 15 histograms, and 10 gate checks the system can collect and sort data up to event rates of 1 kHz . By only sorting a fraction of the events, but storing all events, it can be run at the front-end limit of 10 kHz . Javas promise of platform independence has been found to be realistic, and Jam has been used with no modifications to sort offline on multiple platforms. Jam has a modular design allowing it to be easily modified. For example, Jam has an interface to allow users to write their own fitting routines. This article discusses the systems design and performance, as well as some advantages and disadvantages of using Java.

The

The production of 26Al in novae is uncertain, in part, because of the uncertain rate of the 25Al(p,g)26Si reaction at novae temperatures. This reaction is thought to be dominated by a longsought 3+ level in 26Si, and the calculated reaction rate varies by orders of magnitude depending on the energy of this resonance. We present evidence concerning the spin of a level at 5.914 MeV in 26Si from the 28Si(p,t)26Si reaction studied at the Holifield Radioactive Beam Facility at ORNL. We find that the angular distribution for this level implies either a 2+ or 3+ assignment, with only a 3+ being consistent with the mirror nucleus, 26Mg. Additionally, we have used the updated 25Al(p,g)26Si reaction rate in a nova nucleosynthesis calculation and have addressed the effects of the remaining uncertainties in the rate on 26Al production.

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Two inconsistent sets of 24Al excitation-energy measurements have been used to determ ine esonance energies for the 23Mg(p,γ)24Al reaction. This discrepancy results in a factor of five vari ation in the calculated thermonuclear 23Mg(p,γ)24Al reaction rate at T = 0.25 GK, and presents a challenge to an imminent radioactive ion-beam measuremen t of this reaction that will rely on precisely known resonance energies. We have measured the 24Mg(3He,t)24Al reaction using a 30MeV 3He beam from the tandem Van de Graaff accelerator at Yale Univ ersity’s Wright Nuclear Structure Laboratory. The Yale Enge magnetic spectrograph was used to momentum-analyze reaction products; a position-sensitive ionization drift chamber backed by a scintillator at the focal plane was used to identify tritons and measure the exci tation energies of corresponding states in24Al. We find good general agreement with one of the two previous set of measurements and determine an energy of Ec.m. = 474(6) keV for what is thought to be the most important23Mg(p,γ)24Al resonance astrophysically [the previous measurements y ielded values of Ec.m. = 499(5) and 458(10) keV]. A more precise thermonuclear 23Mg(p,γ)24Al rate will help to constrain the determination of nuclear flow out of the NeNa cycle, and production of A ≥ 20 nuclides, in explosive hydrogen burning over a temperature range 0.2 < T < 1.0 GK.

Al

The nuclear structure of {sup 19}Ne near the proton threshold is of interest for understanding the rates of proton-induced reactions on {sup 18}F in novae. Analogues for several states in the mirror nucleus {sup 19}F have not yet been identified in {sup 19}Ne indicating the level structure of {sup 19}Ne in this region is incomplete. The {sup 18}F(d;n){sup 19}Ne and {sup 18}F(d,p){sup 19}F reactions have been measured simultaneously at E{sub c.m.} = 14.9 MeV. The experiments were performed at the Holifield Radioactive Ion Beam Facility (HRIBF) of Oak Ridge National Laboratory (ORNL) by bombarding a 720-mg/cm{sub 2} CD{sub 2} target with a radioactive {sup 18}F beam. The {sup 19}Ne states of interest near the proton threshold decay by breakup into a and {sup 15}O particles. These decay products were detected in coincidence with position-sensitive E-{Delta}E silicon telescopes. The {alpha} and {sup 15}N particles from the break up of the mirror nucleus {sup 19}F were also measured with these detectors. Particle identification, coincidence, and Q-value requirements enable us to distinguish the reaction of interest from other reactions. The reconstruction of relative energy of the detected particles reveals the excited states of {sup 19}Ne and {sup 19}F which are populated. The neutronmorexa0» (proton) angular distributions for states in {sup 19}Ne ({sup 19}F) were extracted using momentum conservation. The observed states in {sup 19}Ne and {sup 19}F will be presented.«xa0less

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In a recent investigation of the development of leakage currents in Silicon Strip Detectors used in experiments with high intensity stable beams, anomalous behavior was observed. Over a very short period of time the leakage current rose to levels that could be damaging to the detectors. A discussion of this evidence and how the problem was solved, with a viable model, will be given, leading to guidelines for use of such detectors in a stable beam environment.