Search

10B+10B reactions are measured with 50 and 72 MeV beams. The large spin of both beam and target nuclei (Jπ=3+) is particularly suitable for the popul

The main source of F-19 in the universe has not yet been clearly identified and this issue represents one of the unanswered questions of stellar modeling. This lack of knowledge can be due to the F-19(alpha, p)Ne-22 reaction cross-section that has proven to be difficult at low energies: direct measurements stop only at about similar to 660 keV, leaving roughly half of the astrophysical relevant energy region (from 200 keV to 1.1 MeV) explored only by R-matrix calculations. In this work, we applied the Trojan Horse Method to the quasi-free three-body Li-6(F-19, p(22)Ne)d reaction performed at E-beam = 6 MeV in order to indirectly study the F-19(alpha, p)Ne-22 reaction in the sub-Coulomb energy region. In this way, we obtained the cross-section and the reaction rate in the temperature region of interest for astrophysics and free from electron screening effects. A brief analysis of the impact of the new measured reaction rate in AGB star nucleosynthesis is also presented.

Phototransfered thermoluminescence (PTTL) found its use in radiation dosimetry for dose reassessment primarily in photon radiation fields. After the dose has first been evaluated by a “normal” thermoluminescence (TL) measurement, the same detector is subjected to the PTTL dose reassessment procedure providing a new estimation by an independent measurement procedure. PTTL also gives a new possibility for a dose reassessment and for separate dose determination in the mixed fields. It was shown in our previous papers that it is possible to determine separately gamma and neutron dose components with a single detector due to different sensitivities of TL and subsequent PTTL to neutrons in comparison to gamma rays. The main disadvantage, the low sensitivity of both, TL and PTTL, to neutrons restricts the use only for the case of radiation accident. In this work we have investigated the possibilities of improvement the sensitivities of PTTL by heating the samples during UV irradiation and by using the sensitization technique involving a “pre-dose” followed by annealing. Two types of LiF:Mg,Ti detectors, TLD-100 and TLD-700, were examined by irradiation in 137 Cs gamma ray field and with neutrons of 14.5 MeV. After UV irradiation at different temperatures, PTTL increases reaching the values 2.1 and 2.5 times higher at 90 °C than that at 25 °C for TLD-100 and TLD-700 respectively. Increasing level is approximately the same for gamma rays and neutrons. After sensitization, TL signal is one half of that before sensitization. PTTL signal has increased 11 times for gamma rays and 5 times for neutrons at 25 °C with significant increase with increasing temperature during UV irradiation.

Radiophotoluminescent (RPL) glass dosimeter type SC-1 has been studied with respect to use it as a photon dosimeter in mixed neutron + gamma fields. SC-1 is composed of the flat glass element placed in a plastic capsule. Energy compensation tin filters to all directions shield the glass card in the capsule. This type of dosimeter was primarily designed for the measurements of photon dose and for use in environmental monitoring around nuclear plants and for accident dosimetry. For a gamma dosimeter to be useful in a mixed neutron + gamma field it is desirable that the neutron sensitivity is small and accurately known. The response has been characterized for 14.5 MeV neutrons, 238 Pu–Be spectra and thermal neutrons. The results show that the plastic holder has an influence to the response. The comparison with TLD-700 shows lower responses for neutrons for all spectra investigated. The relative low neutron sensitivity of RPL dosimeter type SC-1 enables its use for photon dosimetry in the mixed neutron + gamma fields.

19F experimental abundances is overestimated in respect to the theoretical one: it is therefore clear that further investigations are needed. We focused on the 19F(α, p) 22 Ne reaction, representing the main destruction channel in He-rich environments. The lowest energy at which this reaction has been studied with direct methods is E C.M. ≈ 0.91 MeV, while the Gamow region is between 0.39 ÷ 0.8 MeV, far below the Coulomb barrier (3.8 MeV). For this reason, an experiment at Rudjer Boskovic Institute (Zagreb) was performed, applying the Trojan Horse Method. Following this method we selected the quasi-free contribution coming from 6Li(19 F, p22 Ne)2 H at Ebeam=6 MeV at kinematically favourable angles, and the cross section at energies 0 < EC.M. < 1.4 MeV was extracted in arbitrary units, covering the astrophysical region of interest.

The Trojan Horse Method (THM) was applied to the p+d interaction in order to study the p+p scattering, the simplest case where the suppression of the Coulomb amplitude due to off-shell effects can be observed. The three-body p + d → p + p + n experiment was performed at 5 and 6 MeV and the shape of the quasi-free cross-section was investigated as a function of both the outgoing proton energy and the p-p relative energy. Preliminary results show a behaviour which turns out to be much similar to that of n+n, n+p and nuclear p+p cross-sections.

In radiation dosimetry, phototransfered thermoluminescence (PTTL) found its use for dose reassessment. After the dose has first been evaluated by a normal thermoluminescence (TL) measurement, the same dosimeter is subjected to the PTTL dose reassessment procedure with the intention of obtaining a new estimation by a completely independent measurement procedure. Recently, some experimental data indicated that PTTL could be used as a tool for dose discrimination in a mixed field using single TL detector. In this work, the short overview of the use of LiF-based TL detectors in mixed field dosimetry is presented. In the experimental part, TL (main dosimetry peak and high-temperature peak (HTP)) and PTTL characteristics for TLD-100 and TLD-700 detectors were investigated for 137Cs gamma rays and neutrons of 14.5 MeV. The results show that it is possible to determine separately gamma and neutron dose components with a single detector due to different sensitivities of TL and subsequent PTTL to neutrons in comparison to gamma rays.

The Li-6 + Li-6 -> 3 alpha reaction was measured in a kinematically complete experiment at 3.1 and 2.5 MeV to investigate the presence of quasifree processes at sub-Coulomb energies. Results from the present experiment show a very clear evidence of quasifree mechanisms with an alpha-particle spectator either in the target or in the projectile. To check the occurrence of quasifree processes, "energy sharing" and "angular correlation" analyses have been performed in the framework of the plane wave impulse approximation, both leading to consistent results. The huge peak in the angular correlation spectra, previously ascribed to the "anomalous quasifree" process, corresponds instead to the population of the 22.2-MeV (2(+), Gamma = 800 keV) state of Be-8.

The results of TLD-700 irradiations with 3 MeV protons using a Tandem Van de Graaff accelerator are shown. In order to estimate the contribution of X-rays, CaF 2 :Mn TL detectors were also irradiated under the same condition as TLD-700. Due to the presence of low-energy X-rays, the peak area method of high-temperature peak 7 of TLD-700 was found to be more suitable for proton dose determination. Thermoluminescent (TL) efficiency for protons using this peak relatively to 137 Cs gamma rays was calculated. The relative responses (peak 7) p /(peak 5) γ and (peak 7) p /(peak 7) γ of 0.16 and 9.6, respectively, were obtained. The relative efficiency for peak 7, η p,γ =8.0 was found taking into account the self-absorption of the TL photons in the dosimeter.

Measurements have been made of characteristic gamma rays spectra from A(n,n ′ γ)A reactions induced by 14.1 MeV neutrons on bulk samples of different substances: C, H 2 O, SiO 2 , C 3 H 6 N 6 and samples of soil. Background radiation was reduced by the associated alpha particle technique.

Selective determination of the fast neutron component in a mixed radiation field by the TL dosimetry was studied. TL responses due to the induced radioactivity in Al2O3:C dosimeters via the 27Al(n, gamma)24Na reaction were used to measure the neutron part in a mixed 14.5 MeV neutron and gamma irradiation field. The lowest detectable neutron dose was found to be in order of 10 mSv of personal dose equivalent for Al2O3:C.

We have studied decays of the 24Mg states at excitations 1-6 MeV above the 12C+12C decay threshold, using the 12C(16O, α)24Mg* reaction at E(16O) = 94 MeV. Some preliminary results are presented and further analysis is in progress.

The radiation chemical yield, G(HCl), was evaluated for chlorobenzene-based dosimetry systems irradiated by low-energy protons (3–5.5 MeV) and 60 Co gamma radiation under similar irradiation conditions. The irradiations were done with the Tandem Van de Graaff accelerator and the reference 60 Co gamma source. Two dosimetry systems were used in the measurements: the ECB solutions containing 10 vol.% chlorobenzene in aqueous 96 vol.% ethanol, and the CET dosimetry system containing 10 vol.% chlorobenzene, 10 vol.% ethanol and 80 vol.% trimethylpentane. The results show that the values of radiation chemical yield of hydrochloric acid, G(HCl), values for protons are lower than those for gammas. With the decrease of proton energy, the linear energy transfer (LET) increases and the reduction of G(HCl) becomes more pronounced: from lower by 5% (5.5 MeV) to lower by 14% (3.0 MeV) for the ECB system and from lower by 5% (5.0 MeV) to lower by 8% (3.0 MeV) for the CET system.

In a kinematically complete measurement of the $^{7}$Li($^{7}$Li,$\alpha$$^{6}$He)$^4$He reaction at $E_{i}$ = 8 MeV it was observed that the $^{10}$Be excited states at 9.6 and 10.2 MeV decay by $^{6}$He emission. The state at 10.2 MeV may be a member of a rotational band based on the 6.18 MeV 0$^+$ state.

The abundance of 19 F in the universe is strictly related to standard and extra-mixing processes taking place inside AGB-stars, that are considered to be the most important sites for its production. Nevertheless the way in which it is destroyed is far from being well understood. For this reason we studied the 19 F(α,p)22 Ne reaction, that is supposed to be the main destruction channel in the Helium-rich part of the star. In this experiment, the reaction has been studied in the energy range of relevance for astrophysics (0÷1 MeV) via the Trojan Horse Method (THM), using the three-body reaction 6 Li(19 F,p22 Ne)d.

We have studied the decays of the resonances of 24Mg at excitation energies 1–6 MeV above the 12C+12C decay threshold, using the 12C(16O,α)24Mg* reaction at E(16O) = 94 MeV. Some preliminary results are presented and further analysis is in progress.

Eksperimenti Ives-Stilwellovog tipa (IS) spadaju u klasu bazičnih eksperimenata za kinematičku provjeru Lorentzovih transformacija (LT), a usmjereni su na provjeru efekata dilatacije vremena. U skladu s pojmom prostorvremena Minkowskog fizikalne velicine su reprezentirane geometrijskim objektima 4D prostorvremena, a LT djeluje na kompletnu geometrijsku veličinu (u ovom slučaju valni četverovektor), a ne samo na njenu vremensku komponentu. Sva dosadašnja IS mjerenja relativističkog Dopplerovog efekta su vršena na nasuprotnim kutevima od 0 i 180 stupnjeva na kojima se relativistička aberacija ne pojavljuje. Takva mjerenja su nekompletna, jer se prostorne komponente valnog četverovektora zanemaruju. Zbog toga relativistički efekti nisu u eksperimentalnom smislu u cijelosti istraženi. Neka mjerenja na nasuprotnim kutevima različitim od 0 i 180 stupnjeva nisu pokazala relativističku asimetriju u Dopplerovom pomaku. Cilj ovog eksperimenta je razjasniti tu diskrepanciju mjerenjima na nasuprotnim kutevima različitim od 0 i 180 stupnjeva sa i bez korekcije za kut aberacije. Na korigiranim kutevima se očekuje opažanje relativističke asimetrije, čime bi se eksperimentalno potvrdilo da su relativistički Dopplerov efekt i aberacija manifestacije jedinstvenog fizikalnog procesa: Lorentzove transformacije potpune geometrijske veličine - valnog četverovektora iz jednog Lorentzovog sustava u drugi. U općem slučaju (npr. nestandardna sinhronizacija) te efekte nije moguće razdvojiti, odnosno nije ih moguće smatrati fizikalno dobro definiranima u 4D prostorvremenu. Kao gibajući izvor svjetlosti u našem eksperimentu služe pobuđeni neutralni vodikovi atomi dobiveni sudarima H2+ i H3+ iona ubrzanih u CW akceleratoru s molekularnim vodikom u niskotlačnoj, plinskoj vodikovoj meti, s dvostupanjskim sistemom za diferencijalno pumpanje. Emitirana svjetlost se analizira optičkim spektrometrom s dvije sonde, koje se pomoću goniometra postavljaju na nasuprotne kuteve korigirane za relativističku aberaciju. Iznos kuteva aberacije u intervalu energija od 150-275 keV je između 0.71 i 0.96 stupnjeva. Preliminarna spektroskopska mjerenja rađena su spektrometrom Avaspec-3648 Fiber Optics Spectrometer efektivnog spektralnog razlučivanja 0.6 nm. Mjereni su emisijski spektri pobuđenih vodikovih atoma transverzalno na smjer gibanja i pod kutem od 45 stupnjeva s obzirom na smjer gibanja vodikovih atoma. Ustanovljeno je da su dobro vidljive Balmerove H-alfa, H-beta, i H-gama emisione linije, kao i pomak spektralnih linija zbog Dopplerovog efekta.

A sinusoidal nanosecond chopping and bunching system, as well as a square wave microsecond and millisecond chopping system, were developed and applied on the post-acceleration beam of the existing 300 kV neutron generator. Bunching by a klystron buncher of the three gap type has been used. Using the sinusoidal system beam pulses with FWHM of approximately 3 ns have been obtained. The square wave system can produce pulses with adjustable width and frequency in the microsecond and millisecond region.

The {sup 2}H({ital t},{ital tp}){ital n} reaction was investigated in a kinematically complete experiment with a tritium beam at energies around 35 MeV. Evidence was found for the {sup 4}H ground state. Coincidence spectra were fitted by the contribution of quasifree processes, sequential decay through the {sup 4}He ground state, and the {ital n}-{ital p} final-state interaction. The best agreement with the data was obtained assuming the following {sup 4}H ground-state parameters: {ital E}{sub {ital r}}=3.1 MeV and {gamma}{sup 2}=2.3 MeV.

Isobaric analogues of three states in 10 Be forming a rotational band with high moment of inertia are expected in 10 B and 10 C . This article reports a measurement of excitation spectrum in 10 B obtained through 11 B (3 He ,α)10 B reaction. A T = 1 state is found on 11.3 MeV excitation energy. It is a possible candidate for the 4+ state of the analogue rotation band.

We address a successful indirect technique, the Trojan horse method, which allows one to measure the bare nucleus cross section for rearrangement reactions down to astrophysical energies. In particular, we consider here the application of the method to the p-p elastic scattering. This represents an important test of the main feature of the method, namely the suppression of Coulomb effects in the entrance channel due to off-energy-shell effects. In contrast to the on-energy-shell case, the extracted p-p cross section does not exhibit the Coulomb-nuclear interference minimum, as predicted by the half-off-energy shell calculations. This hypothesis is strengthened by the agreement between the Trojan horse p-p data and the calculated on-energy-shell n-n, n-p and nuclear p-p cross sections.

Inspection of a shipping container for the presence of the threat materials has been investigated in the laboratory by using a 14 MeV neutron beam, a BaF 2 gamma detector and the associated alpha particle technique. The associated alpha particle technique is proposed as a part of a two sensor system for contraband container inspections. This method is effective in the reduction of background radiation with the possibility of collimating electronically the neutron beam. The intrinsic time resolution has been experimentally estimated to be 1.3 ns (FWHM), which allows inspection of a minimum voxel having 7 cm depth along the neutron flight path. The neutron beam intensity plays a crucial role as a limiting factor for the acquisition time reduction. Single counting rates of the gamma and alpha detector were investigated as a function of the neutron intensity, distance between the gamma detector and the neutron source and the type of shielding. The time and the energy spectra for different neutron intensities were evaluated.

The detection of landmines by using available technologies is a time consuming, expensive and extremely dangerous job, so that there is a need for a technological breakthrough in this field. Atomic and nuclear physics based sensors might offer new possibilities in de-mining. Technology and methods derived from the studies applied to the detection of landmines can be successfully applied to the screening of cargo in customs inspections.

We have studied the ${}^{2}\mathrm{H}{(}^{6}\mathrm{Li},\ensuremath{\alpha}{)}^{4}\mathrm{He}$ two-body reaction by applying the ``Trojan horse'' method (THM) to the ${}^{6}\mathrm{Li}{(}^{6}\mathrm{Li},\ensuremath{\alpha}\ensuremath{\alpha}{)}^{4}\mathrm{He}$ three-body reaction. The astrophysical $S(E)$ factor has been extracted in the energy range between 10--800 keV for the two cases of target and projectile quasifree break-up. We found good agreement between the two data sets leading an improved determination of the $S(E)$ with $S(0)=16.9\ifmmode\pm\else\textpm\fi{}0.5 \mathrm{MeV}\mathrm{b}.$ Furthermore, the electron screening potential energy ${U}_{e}=320\ifmmode\pm\else\textpm\fi{}50$ eV has been extracted in a model-independent way by comparing direct and THM data. This value is significantly higher than the value predicted by current theoretical models.

The Li-6(Li-6,alpha alpha)He-4 three-body reaction has been studied in a kinematically complete experiment at E-6Li = 6 MeV, from which indirect information on the H-2(Li-6, alpha)He-4 two-body reaction at 13 less than or equal toE(c.m.) less than or equal to 750 keV has been extracted by applying the Trojan horse method. The method used a recent improved formulation. The derived astrophysical S(E) factor for the two-body process is compared with that obtained from direct experiments.

The 6Li(d,α)4He reaction, whose astrophysical importance is connected to the primordial nucleosynthesis in the framework of the Inhomogeneous Big Bang, has been studied by using the Trojan Horse Method (THM). We derive and discuss the cross section and the astrophysical S(E)-factor for Ecm=0.025−0.7 MeV. Results are compared with data from a direct measurement.

In today's society acts of terrorism must involve in some stages the illicit trafficking either of explosives, narcotics, chemical weapons, hazardous chemicals, radioactive materials and/or humans. Therefore the society must rely on the modern anti-trafficking infrastructure including adequate instrumental base. Old control measures slow down the traffic flow, they are time consuming and inefficient. Recently lots of efforts has be put into development of the concept of "the smart border", border management system that keeps pace with expanding trade while protecting from the threats of terrorist attack, illegal immigration, illegal drugs, and other contraband. Due to the size of container transport industry the shipping container control system must be an essential building block of the smart border concept. The world's total movement in containers is estimated to be 72m TEU ("20-foot equivalent units"). A single typical large container ship can carry up to 6, 000 TEU. Although the container has become indispensable to world commerce, it also turned out to be handy ways to smuggle drugs, contraband and illegal immigrants. Modern cargo inspection systems are non-invasive imaging techniques, the inspection systems using penetrating radiations (1.33 MeV gamma and 0.3 and 0.45 MeV x-rays) in the scanning geometry. Relative penetration of the commonly used radiation is 17.5, 10.0 and 4.43 cm-iron for 1.33, 0.45 and 0.3 MeV, respectively. The concept of the multisensor system is based on the integrated use of gamma or x-ray fast scanning of the interrogated object (i.e. the whole container) with subsequent detailed elemental analysis of suspicious volumes by using fast neutrons. The use of alpha particle tagged neutron beams is a unique feature of such device in that it can enhance by a large factor the signal/noise ratio of the system. In the work reported here the neutron beam was obtained by means of D+T reaction. The associated alpha particle detector was fixed in such a way that the associated neutron beam was in horizontal plane at 90º ; ; ; to the deutron beam. Slit in front of the scintlillator was used to define the geometrical dimensions of the beam on the interrogated object. The α -γ coincidence spectra were measured with the selection of α -γ coincidences performed by the 100 ns TAC range. The information on the position of the interrogated object was contained in the TAC spectrum, while object's composition gave rise to characteristic gamma ray spectrum. In addition, conceptual design of the system, and preliminary data, for the inspection of the shipping containers for radioactive materials in the small to medium size container ports are reported. The aim was to detect the presence of shielded or unshielded sources inside the shipping container. This could be accomplished during the movement of the container: (i) from the ship to the storage area by radiation detector mounted on the crane and (ii) from the storage area while leaving the container port by track or train by gate monitors or by using gamma inspection systems in the passive mode.

The quasifree scattering and reaction processes in the3H+2H→d→d+n interaction leaving a neutron as a spectator have been investigated at incident triton energies around 35 MeV. The results compare well with the predictions from Plane Wave Impulse Approximation, arbitrarily normalized to the data. The final energy prescription was used.

In response to a recent paper by Becchetti {ital et} {ital al}. it is shown that there are several experimental and theoretical evidences about the {sup 4}H clustering in lithium nuclei.

Special kinematical conditions for nuclear reactions with three and four particles in the final state in which a large part of the available phase space could be covered by a single measurement have been discussed. The 7L(d, αα)n reaction has been measured and used for illustration.

The sum of the /sup 9/Be(n,t/sub o/)/sup 7/Li and /sup 9/Be(n,t/sub 1/)/sup 7/Li reaction cross sections was measured at an incident neutron energy of 14.6 MeV using a counter telescope for triton detection. The angular distribution of these reactions was obtained for the center of mass angles up to 90 deg. It is nearly isotropic. Assuming a forward-backward symmetry of the angular distribution, the total cross section for the (n,t) reaction on /sup 9/Be is found to be 24 +-2 mb. This result compares favorably with the data from the tritium beta-counting experiments.

Learning how 19F is produced and destructed in AGB-stars is crucial. Fluorine abundance is in fact important, given that it is strongly tied to standard and extra-mixing processes taking place in AGB-stars. This kind of objects are considered to be the main sources of fluorine in galactic environment, in which experimental abundances are far overestimated. For this reason the reaction 19F(α, p)22Ne, that represents the main destruction channel in He-rich environment, was studied at energies corresponding to T∼2·108 K. Such reaction has been studied with direct method at Ebeam = 1100 keV for alpha particles impinging on a fluorine target, corresponding to EC.M. ∼ 900 keV, still far from the Gamow window, placed at 390÷800 keV, below the Coulomb barrier (3.81 MeV). An experiment was performed at Rujer Boskovic Institut (Zagreb), applying the Trojan Horse Method. With this experimental procedure we were able to select the quasi-free contribution coming from 6Li(19F,p 22Ne)2H at Ebeam = 6 MeV at kinematically...

7Li(p, α)4He quasi-free reaction contributions in the7Li (3He, αα)2H reaction are examined at low incident3He energies.