A folding model for crystal defects in the shape analysis of blocking lifetime measurements

A new method of analysis is presented for experiments that measure nuclear reaction times exploiting the blocking effect in single-crystals. It is based upon a direct comparison between measured and calculated blocking patterns, obtained by folding the angular distribution for perfect crystals with a function describing the influence of the defects. Such a function is found by comparing measured and calculated “prompt” patterns. The resulting equations are solved using Tikhonov's regularization procedure. The whole method is applied to a reanalysis of an earlier series of results on the ²⁷Al (p, α₀) resonance at E_p=632.2 keV. The resulting lifetime of the ²⁸Si 12.195 MeV level, τ = (85.3 ± 5.3) as, agrees with that deduced from resonance reaction yields, and is somewhat different from an earlier analysis based on the filling-in parameter R.     

Analysis of boron using the (p, α) reaction

The applicability of the strong and broad resonance of the reaction ${}^{11}\text{B(p}\text{, α)}{}^8\text{Be}$ at E_p = 675 keV to the elemental analysis of boron has been studied. To eliminate matrix effects and to optimize the measuring conditions a systematic study of the absolute thick-target yields of α-particles following proton bombardment has been carried out at E_p = 0.7 and 1.0 MeV for the elements Z = 3?9, 11?17s by. Summary spectra showing the α-peaks of light elements of interest in the elemental analysis of boron are given. An external beam measurement system has been developed to allow measurements to be carried out in He-gas at atmospheric pressure. Thus, problems arising in vacuo with insulating, medical and biological samples can be avoided. The detection limits of boron range from 0.1 ppm for biological samples containing nitrogen to below 0.01 ppm for samples with a low nitrogen concentration. An additional advantage of the method is that Li, F and N can be determined simultaneously with the boron analysis.     

Proton induced γ-ray emission yields for the analysis of light elements in aerosol samples in an external beam set-up

The PIXE technique is a reliable tool for the characterisation of thin aerosol samples, but it can underestimate the lightest measurable elements, like Na, Mg, Al, Si and P, owing to the absorption of their X-rays inside the sample. The PIGE technique is a valid help to determine corrections for such effect: in order to perform PIGE measurements relative to thin reference standards in an external beam set-up, we measured, at the external beam facility of the Tandetron accelerator of the LABEC laboratory in Florence, the γ-ray yields as a function of the proton beam energy for the reactions ¹⁹F(p,p′γ)¹⁹F (E_γ = 110 and 197 keV), ²³Na(p,p′γ)²³Na (E_γ = 440 keV) and ²⁷Al(p,p′γ)²⁷Al (E_γ = 843 and 1013 keV), in the proton energy range from 3 to 5 MeV. The measured yields are shown, and the determined most suitable energies for performing PIGE quantification of Na and Al are reported, together with the corresponding minimum detection limits (MDLs). The results of some test on PIGE accuracy and an evaluation of self-absorption effects in PIXE measurements on thin aerosol samples are also presented.     

Prompt gamma emission excitation functions for PIGE analysis

A proton energy scan from 2.2 to 3.8 MeV (Δ E = 20 keV) was performed to measure differential cross sections of prompt gamma reactions on Li, B, F, Mg, Al, Si and P at θ_lab = 90°. The purpose of the present work is to provide the basic data necessary to set up the PIGE (proton induced gamma ray emission) technique for the analysis of thin and intermediate samples.     

Profiling of titanium implanted into iron and nickel with the reaction 48Ti (p, γ)49V

A profiling technique for titanium is described which is based on an analog resonance in the cross section of the reaction ⁴⁸Ti(p, γ)⁴⁹V at E_P = 1.361 MeV. Primary γ radiation of the energy E_γ = 7.963 MeV is measured high detection efficiency is achieved. The properties of the technique are discussed and examples of its applications to Ti-implanted metals are given.     

Proton elastic scattering and proton induced γ-ray emission cross-sections on Na from 2 to 5 MeV

Differential cross-sections for proton elastic scattering on sodium and for γ-ray emission from the reactions ²³Na(p,p′γ)²³Na (E_γ = 440 keV and E_γ = 1636 keV) and ²³Na(p,α′γ)²⁰Ne (E_γ = 1634 keV) were measured for proton energies from 2.2 to 5.2 MeV using a 63 μg/cm² NaBr target evaporated on a self-supporting thin C film.The γ-rays were detected by a 38% relative efficiency Ge detector placed at an angle of 135° with respect to the beam direction, while the backscattered protons were collected by a Si surface barrier detector placed at a scattering angle of 150°. Absolute differential cross-sections were obtained with an overall uncertainty estimated to be better than ±6.0% for elastic scattering and ±12% for γ-ray emission, at all the beam energies.To provide a convincing test of the overall validity of the measured elastic scattering cross-section, thick target benchmark experiments at several proton energies are presented.     

Experimental study of the Ho(p,n) nuclear reaction for production of the therapeutic radioisotope Er

The 10.3 h half life radionuclide ¹⁶⁵Er, decaying by electron capture to stable ¹⁶⁵Ho, is an excellent candidate for Auger-electron therapy. In the frame of a systematic study of charged particle production routes of ¹⁶⁵Er, the excitation function of the ¹⁶⁵Ho(p,n)¹⁶⁵Er reaction was measured up to 35 MeV by using a stacked foil irradiation technique and X-ray spectroscopy. The measured excitation function shows a significant energy shift when compared to the only experimental dataset measured earlier and an acceptable agreement with the results of different nuclear reaction model codes. The thick target yields calculated from the excitation function at typical energies available at small cyclotrons (E_p = 11 MeV and E_p = 15 MeV) are 41 MBq/μAh = 11 GBq/C and 75 MBq/μAh = 21 GBq/C, respectively.     

Oxygen detection by non-Rutherford proton backscattering below 2.5 MeV

Oxygen detection by proton backscattering has been investigated. The oxygen detection sensitivity of 2.5 MeV proton backscattering is shown to exceed that of ⁴He backscattering by even a factor of about 15 depending on the matrix. The needed proton elastic scattering cross sections of oxygen for θ_lab = 170° have been measured in the energy range E_lab = 770–2480 keV relative to Ti and Sn elastic scattering cross sections using thin TiO₂ and SnO₂ samples. The angular dependence of the cross section was measured at energies E_lab = 1790, 1990, 2191, and 2382 keV for backscattering angles. The experimental cross sections were found to be 1.1–5.7 times the pure Coulomb cross section. Theoretical calculations for the scattering cross sections were performed and their inapplicability to experimental purposes is demonstrated. Fits to experimental data are given.     

Implanted boron profiles in silicon

¹⁰B and ¹¹B implants into amorphous Si, with energies ranging from 50 keV to 2 MeV and 10 keV to 1 MeV respectively, were profiled by the nuclear reactions ¹⁰B(n, α)⁷Li and ¹¹B(p, γ)¹²C. The projected range R_p and straggling ΔR_p agree within a few percent with recent calculations due to Ziegler, Biersack and Littmark (ZBL). These results show that the ZBL electronic stopping power is adequate to reproduce range parameters resulting from MeV implantations.     

Study of ion emission from a germanium crystal surface under impact of fast Pb ions in channeling conditions

A thin germanium crystal has been irradiated at GANIL by Pb beams of 29 MeV/A (charge state Q_in = 56 and 72) and of 5.6 MeV/A (Q_in = 28). The induced ion emission from the sample entrance surface was studied, impact per impact, as a function of Q_in, velocity v_in and energy loss ΔE in the crystal. The Pb ions transmitted through the crystal were analyzed in charge (Q_out) and energy using the SPEG spectrometer. The emitted ionized species were detected and analyzed in mass by a time-Of-flight multianode detector (LAG). Channeling was used to select peculiar ΔE values in Ge and hence peculiar Pb ion trajectories close to the emitting entrance surface. The experiment was performed in standard vacuum. No Ge emission was found. The dominating emitted species are H⁺ and hydrocarbon ions originating from the contamination layer on top of the crystal. The mean value 〈M〉 of the number of detected species per incoming Pb ion (multiplicity) varies as (Q_in/v_in)^p, with p values in agreement with previous results. We have clearly observed an influence of the energy deposition ΔE in Ge on the emission from the top contamination layer. When selecting increasing values of ΔE, we observed a rather slow increase of 〈M〉. On the contrary, the probabilities of high multiplicity values, which are essentially connected to fragmentation after emission, strongly increase with ΔE.     

Proton elastic scattering differential cross-section measurements of Sc

In the present study the differential cross sections of the ⁴⁵Sc(p,p)⁴⁵Sc reaction were measured. Two independent experiments were performed. At first a sandwiched thin ScBr₃ target was used for beam energies E_LAB = 2300-5500 keV (in steps of 25 and 50 keV) and for detector angles 140°, 160°, and 170°. Secondly a thick Sc₂O₃ sample was formed and irradiated for E_LAB = 3100-5500 keV with a detector placed at 140°, to validate the results of the first measurement.     

Determination of differential cross-sections for the natK(p, p0) and 39K(p, α0) reactions in the backscattering geometry

In the present work, new, differential cross-section values are presented for the ^natK(p, p₀) reaction in the energy range E_lab = 3000–5000 keV (with an energy step of 25 keV) and for detector angles between 140° and 170° (with an angular step of 10°). A qualitative discussion of the observed cross-section variations through the influence of strong, closely spaced resonances in the p + ³⁹K system is also presented. Information has also been extracted concerning the ³⁹K(p,α₀) reaction for E_lab = 4000–5000 keV in the same angular range. As a result, more than ～500 data points will soon be available to the scientific community through IBANDL (Ion Beam Analysis Nuclear Data Library – http://www-nds.iaea.org/ibandl/) and could thus be incorporated in widely used IBA algorithms (e.g. SIMNRA, WINDF, etc.) for potassium depth profiling at relatively high proton beam energies.     

Differential cross section measurements of the S(d,p)S reaction for nuclear reaction analysis purposes

Differential cross sections of the ³²S(d,p_{0,1,2,3,4-6,7}) reactions were determined for deuteron energies E_lab = 1975-2600 keV (in steps of 25 keV) and for detector angles between 140-170° in steps of 10°. A comparison of the experimental data with the existing ones and possible applications to nuclear reaction analysis (NRA) studies are discussed.     

Differential cross sections for the B(p,αo)Be and B(p,p0)B reactions, suitable for ion beam analysis

Boron depth profiling presents strong analytical challenges for all Ion Beam Analysis (IBA) techniques. In the past, both the ¹¹B(p,α_o)⁸Be (NRA) and the ¹¹B(p,p₀)¹¹B (EBS) reactions have been proposed and they seem to be quite suitable for analytical purposes. Nonetheless, both reactions have not been adequately studied in literature (as far as data suitable for material analysis in the backscattering geometry are concerned). Moreover, the existing datasets are relatively discrepant. In an attempt to clarify the situation, both reactions were studied in the present work between 135° and 160°, in steps of 5°, for the proton beam energy range between 2.2 and 4.2 MeV, in steps of 50 keV. An attempt to explain the occurring results in the framework of the resonance mechanism is also presented, along with a comparison with previously published data.     

The 10B(n, αγ)7Li cross-section between 0.1 and 2.2 MeV

The shape of the excitation function for the standard neutron reaction ¹⁰B(n, αγ)⁷Li in the energy range from 0.1 to 2.2 MeV has been determined relative to the angular distribution of the neutron source reaction T(p, n)³He at 1.6, 2.3, and 3.0 MeV proton energy. The 478 keV γ's produced in a 3-mm thick boron carbide sample were observed in a Ge(Li)-detector. The time-of-flight method was used to discriminate against events from neutrons of degraded energy.     

Energy calibration of the 500 kV heavy ion implanter ionas

Gamma ray yield functions of (p, αγ) and (p, γ) resonance reactions on semi-thick ¹⁹F, ²³Na, ^24,26Mg and ²⁷Al targets were measured and used to calibrate the accelerating voltage and energy resolution of the new 500 kV heavy ion implanter at Göttingen. The energy spread of the proton beam was found to vary linearly with the accelerating voltage from ΔE(200 keV) = 55 eV fwhm to ΔE(500 keV) = 105 eV; it is made up by a 0.012% high voltage ripple and the Doppler broadening of the resonances due to the thermal motion of the target nuclei. A long term stability of the proton energy of < 5 eV/h at 300 keV was achieved with new resistors in the voltage regulating system.Applications of the accelerator for the remeasurement of some resonance energies and widths and for depth profiling of light implanted ions in metals by the resonance broadening method will be briefly discussed.     

On the investigation of alpha-particle resonance elastic scattering from the 16O nucleus

Solid target measurements are conducted in order to investigate ¹⁶O(α, α₀)¹⁶O resonances in the energy region 2.0–3.6 MeV. Excitation functions are reported for scattering angles of 145° (θ_cm = 153°) and 165° (θ_cm = 168°), and resonances are observed at 2.522, 3.042, 3.082 and 3.372 MeV. The deduced widths of these resonances in the centre-of-mass frame are 19.00, 8.20, 3.36, and 15.10 keV respectively. It is reported that the widths of the first three resonances are in agreement with previous data, but the width of the 3.372 MeV resonance exceeds an early gas target result due to Cameron [5]. In addition, elastic scattering cross sections are compared with the gas target data and found to be consistent. It is concluded that the width of the 3^? resonance at 3.042 MeV is in agreement with the prediction due to multiparticle cluster calculations for ²⁰Ne.     

Depth profiling of carbon in silicon using the C(p, p′γ) reaction

An analytical method has been developed for the measurement of a carbon depth profile of the region a few tens of μm from the surface, using a ¹²C(p, p′γ) reaction. Measurements for a SiC sample coated with a silicon layer and a carbon-implanted silicon sample were performed using this method. Two charged particle detectors and two γ-ray detectors were utilized for the coincident detection of scattered protons and γ-rays from the first excited state (E_x = 4.4 MeV) of ¹²C. The measured depth profiles agree well with results obtained using a surface profiler and an Auger microprobe. These results demonstrate that this method is useful for the non-destructive analysis of carbon at depths of a few tens of μm from the surface.     

Measured activation cross sections below 10 MeV for the 51V(n,p)51Ti and 51V(n, α)48Sc reactions

The activation method is used to measure cross sections for the ⁵¹V(n, p)⁵¹Ti reaction from E_n = 2.856 to 9.267 MeV and for the ⁵¹V(n, α)⁴⁸Sc reaction from 5.515 to 9.567 MeV. Both measurements utilize ENDF/B-V evaluated neutron-induced fission cross sections of ²³⁸U as a standard. The experimental results from this work are compared with corresponding ENDF/B-V evaluated cross sections for V and substantial differences are evident. The most significant difference is a tendency for the measured values to exceed evaluated ones by as much as 50% in the vicinity of 8 MeV.     

Implantation profiles and sputtering studied by detecting the optical radiation from sputtered particles during ion bombardment

A method of sputter-etching and simultaneous registration of the emitted light is used to obtain depth profiles of implanted Li atoms. Measured mean penetration depths (R_p) and straggling values (ΔR_p) for implanted Li into Ag, V, Si and Al are reported. We find e.g. for 10 keV Li⁺ into $\text{V: R}{}_{\mathrm{n}}\text{= 400 ± 30}\text{A}\text{?}$ and $\text{ΔR}{}_{\mathrm{p}}\text{= 250 ± 30}\text{A}\text{?}$. Known implanted profiles are used as a scale of depth to determine sputtering yields of keV He⁺ ions. With this new method the sputtering yield of 40 keV He⁺ ions bombarding Ag was found to be 0.095 ± 0.020. Sputtering through a thin film is also used to determine sputtering yields. A remarkable increase in the light intensity from excited Ag I atoms is observed during sputtering through the interface between an Ag film and the underlying Al substrate. This is found to be due to a change in the excitation mechanism. Continuous features in the observed emission spectrum have in a few cases been identified as originating from deexcitation radiation of molecules formed in the sputtering process.