610 research outputs found
Neutron activation as an independent indicator of expected total yield in the production of 82Sr and 68Ge with 66 MeV protons
Introduction
A method based on neutron activation is being developed to assist in resolving discrepancies between the expected yield and actual yield of radionuclides produced with the vertical-beam target station (VBTS) at iThemba LABS.
The VBTS is routinely employed for multi-Ci batch productions of the radionuclide pairs 22Na/68Ga and 82Sr/68Ga using standardized natMg/natGa and natRb/natGa tandem targets, respectively [1]. The metal-clad target discs are bombarded with a primary beam of 66 MeV protons at an intensity of nominally 250 ”A. The encapsulation materials are either Nb (for Mg and Ga) or stainless steel (for Rb) which serve to contain the molten target materials during bombardment and act as a barrier to the high-velocity cooling water which surrounds the targets in a 4Ï geometry. The natRb/natGa targets are typically bombarded according to a two-week cycle while natMg/natGa targets are bombarded on an ad-hoc basis, depending on a somewhat unpredictable 22Na demand.
A too-large deviation between expected yield and actual yield has at times plagued this programme. These deviations can manifest both as an apparent loss or an apparent gain (relative to the expected yield) by up to about 15% in either direction. The resulting uncertainty of up to 30% (in the worst case) from one production batch to another can be costly and is unacceptable in a large-scale production regimen. This phenomenon is believed to be brought about by two types of problems:
(1) Production losses, e.g. during the radio-chemical separation process or incomplete recovery of activated target material during the decapsulation step.
(2) Incorrect values obtained for the accumulated proton charge.
A problem of type (1) will always result in a loss of yield. A problem of type (2) can manifest as an apparent loss or gain. In an effort to get a handle on this second type of problem, neutron activation of suitable material samples, embedded in a target holder, is being investigated as an independent indicator of the total yield. For this purpose, samples of Co, Mn, Ni and Zn were activated during production runs and Co was found to be the most appropriate. Preliminary results will be presented after first discussing why the determination of the accumulated pro-ton charge is a problem with the VBTS.
Materials and Methods
The VBTS consists of a central region in which a target holder is located during bombardment as well as two half-cylindrical radiation shields which completely surround the target. The shields can be moved away from the central region on dedicated rails, e.g. when repairs or maintenance is required. FIGURE 1 shows the VBTS with the shields moved to the âopenâ position. As some components of the station are located below the vault floor, with the target position near floor level, it proved difficult to electrically isolate the VBTS as was done for the two horizontal-beam target stations at iThemba LABS [1]. The VBTS does not act as a Faraday cup like the other target stations. Instead, the beam current and accumulated charge is measured by means of a calibrated capacitive probe [1,2].
There appears to be a variation in the response of the capacitive probe, sensitive to the beam microstructure, in particular a dependence on the beam packet length. This problem is not yet fully resolved.
FIGURE 2 (a) shows the beamstop of a VBTS target holder with several Co samples mounted on the outside as well as one each of Ni, Mn and Zn. The samples are small âtabletsâ with a 10 mm diameter and 1 mm thickness. The reactions of interest are 59Co(n,Îł)60Co, 59Co(n,3n)57Co, nat-Ni(n,X)60Co, natNi(n,X)57Co, natZn(n,X)65Zn and 55Mn(n,2n)54Mn. The relevant half-lives are 60Co(5.271 a), 57Co(271.8 d), 65Zn(244.3 d) and 54Mn(312.2 d). The half-life should be long compared to the two-week cycle in order to reduce the dependence on the exact beam history, which is very fragmented over any production period. In this respect, 60Co is considered to be particularly attractive as its long half-life of more than 5 years leads to a negligible effect by the beam history.
Note that the tandem targets, shown in FIGURE 2 (b), are mounted just upstream of the beamstop â in fact, the targets and beamstop form a single unit before being fitted into the target holder.
At the end of bombardment, all samples were assayed for their characteristic Îł-emissions using standard off-line Îł-ray spectrometry with an HPGe detector connected to a Genie 2000 MCA. Calculations of the neutron fluence density in the central sample volume on the beamstop were also performed using the Monte Carlo radiation transport code MCNPX. For these calculations, the entire VBTS, a Rb/Ga target and the vault walls were included in the model.
Results and Conclusion
All samples activated significantly â copious amounts of 60Co were detected in the Co discs after a two-week run.
The neutron fluence density for the case of a 250 ”A, 66 MeV proton beam on a natRb/natGa tandem target is shown in FIGURE 3. The dominance of low-energy neutrons is evident, which is in part due to the large amount of paraffin-wax shielding material in close proximity to the target. While reactions such as the (n,2n) and (n,3n) would be sensitive to the more energetic part of the neutron spectrum, the (n,γ) capture reaction benefits from the large low-energy component. This explains the copious amounts of 60Co formed. It was therefore decided to only retain the central Co sample for subsequent bombardments, as shown in FIGURE 4.
The first results are shown in TABLE 1. The accumulated charge as obtained from the capacitive probe (Q), the specific 60Co activity (A) at the end of bombardment (EOB), and their ratio (A/Q) are presented in the table, together with the deviation of individual ratios relative to their average for the case of the Mg/Ga tandem tar-gets only. Note that all samples were counted until the statistical uncertainties were negligible. Any systematic uncertainties are ignored at this stage as they are considered to remain the same from one batch production to another.
For the sake of argument, the average value of the ratio is taken as the expected value. A positive deviation of the A/Q value is then indicative of a too-small value of the accumulated charge obtained from the capacitive probe, leading to a corresponding overproduction. Likewise, a negative value is indicative of a too-large value of the accumulated charge, leading to a corresponding underproduction.
It is certainly true that the data in TABLE 1 are currently very limited. It is envisaged, however, that with time the growing database of values will assist in reducing the uncertainty in determining the accumulated charge and reduce the discrepancies between predicted and actual yields significantly. TABLE 1 illuminates the underlying problem satisfactorily. The four Mg/Ga tandem target bombardments, on identical targetry, were performed successively. The neutron activation correlates well the with actual yields, pointing directly to the current integration as the main source of error.
The method already proves to be useful. An indication of an over or underprediction can be obtained prior to the target processing by recovering and measuring the Co disc. This in-formation can be used to make a decision concerning the present batch production and/or the subsequent one. One can either add beam to the present production target and/or in-crease/reduce the total beam on the subsequent production target to compensate for an expected overproduction or shortfall.
In conclusion, we would like to stress that the capacitive probes show great promise and that better understanding and/or possibly some development of their signal processing algorithm may improve their ability to measure the accumulated charge to the desired accuracy. Segmented capacitive probes used at iThemba LABS and elsewhere for beam position measurement [1,3] are not affected by beam microstructure as only the ratios of the signal strengths on the different sectors are important. In this case, changes in response affect all sec-tors equally and the ratios are unaffected
The cyclotron production of selected radionuclides using medium energy protons
Thesis (PhD)--Stellenbosch University, 2008.ENGLISH ABSTRACT: Radiochemical research involving ion exchange chromatography is of paramount
importance to the future of radionuclide production at the Radionuclide Production
Group (RPG) of iThemba LABS. It is required for the production of high-activity
yields of radionuclides to effectively remove impurities and for the safety of the
operators performing such productions. The radiochemical separations of some new
products from their target material, as well as experiments to determine whether
production is viable, are described.
67Ga is currently being produced at the RPG and makes use of zinc targets. With the
production of ultra-pure 67Ga, it was necessary to remove any Fe(III) impurities from
the final product, such that it may be possible to label peptides with this product. The
use of Amberchrom CG161M for this purpose was found to be satisfactory.
Interest was shown in 88Y by an overseas company for the manufacture of sources.
While a method involving extraction of the radionuclide and the ion exchange thereof
using Chelex 100 chelating resin had been published, problems with the production
persisted. Three methods, using ion exchange chromatography, were devised to
produce the radionuclide, with two of them being adopted for production purposes.
Thick-target nuclear data have also recently been accumulated in collaboration with
colleagues from ATOMKI, Debrecen, Hungary.
There is a large demand for 82Sr for the manufacture of 82Sr/82Rb generators for
medical use. A method was developed to manufacture this radionuclide with thicker
(32 g) target material, bombarded in the Vertical Beam Target Station (VBTS), and to
separate 82Sr from its target material with the use of Purolite S950 chelating resin.
68Ge/68Ga generators are becoming increasingly important in the world of
radiopharmaceuticals. A project to develop a local generator was funded by the
Innovation Fund and research was performed to produce 68Ge, such that the generator
could be manufactured. This involved bombarding thicker Ga targets in the VBTS
and performing the chemical separation using AG MP-1 anion exchange resin. The final product was loaded onto generators, although tests performed on different
materials to the ones being marketed are also reported in this work.
A project was initiated to study the cluster radioactive decay of 223Ac via 14C and 15N
emission. To produce 223Ac for these observations, a Th target was bombarded. The
227Pa was separated from the target material using AG MP-1 macroporous anion
exchange resin and used as a source, which decayed to 223Ac. The chemical
separation and the drying of the final product onto a source plate were completed
within approximately 70 minutes from the end of bombardment. The work was
performed in collaboration with JINR, Russia, and University of Milan and INFN,
Italy.
133Ba has a half-life of over 10 years and is an expensive radionuclide to produce. It
has been used in medical and biological studies and there still appears to be a demand
for it. A method was devised, utilizing AG50W-X4 cation exchange resin, to separate
133Ba from its CsCl target material.
Agricultural specialists in the past have shown an interest in 28Mg, to determine the
uptake of the element in fruit. It has long been regarded by some of the local
researchers as an interesting project to investigate. It has been determined that the
product can be produced in reasonable quantities using LiCl target material, with ten
targets being bombarded in series using a 200 MeV proton beam delivered by the
Separated Sector Cyclotron. A method, involving the use of Purolite S950 chelating
resin, was devised to separate 28Mg from its target material.AFRIKAANSE OPSOMMING: Radiochemiese navorsing, wat ioonuitruiling chromatografie behels, is van uiterste
belang vir die toekoms van die produksie van radionukliede by die
Radionukliedproduksiegroep (RPG) van iThemba LABS. Dit is nodig vir die hoë
aktiwiteit opbrengs van radionuklied produkte om onsuiwerhede te verwyder en vir
die veiligheid van die operateurs wat die produksies moet uitvoer. Die skeiding van
nuwe produkte van hulle skyfmateriaal, sowel as eksperimente om vas te stel of ân
produksie uitvoerbaar is, word in die werk beskryf.
67Ga word tans by RPG vervaardig en maak gebruik van sink as skyfmateriaal. Vir
die produksie van âultra-suiwerâ 67Ga was dit belangrik om enige Fe(III)
onsuiwerhede uit die finale produk te verwyder om sodoende peptiede merking te kan
uitvoer. Die gebruik van Amberchrom CG161M hars was voldoende vir dié
eksperiment.
ân Oorsese maatskappy het belangstelling getoon in 88Y vir die vervaardiging van
bronne. Alhoewel ân metode wat die ekstraksie van die radionuklied en die ioonuitruiling
daarvan met die gebruik van Chelex 100 chelerende hars reeds gepubliseer
was, het probleme met die produksie voortgeduur. Drie metodes is opgestel om 88Y te
produseer, waarvan twee van die metodes tans gebruik word vir produksie doeleindes.
Dik-skyf kerndata is ook versamel in samewerking met kollegas van ATOMKI,
Debrecen, Hongarye.
Daar is ân groot aanvraag vir 82Sr vir die vervaardiging van 82Sr/82Rb generators vir
mediese doeleindes. ân Metode is ontwikkel om die radionuklied te vervaardig van
dikker skyfmateriaal (32 g), in die Vertikale Bundelstasie gebombardeer, en om 82Sr
van sy skyfmateriaal te skei met die gebruik van Purolite S950 chelerende hars.
68Ge/68Ga generators is besig om toenemend belangrik te word in die wĂȘreld van
radiofarmasie. iThemba LABS kry baie navrae om die produk te vervaardig. Die
projek was ook deel van die voorlegging aan die âInnovation Fundâ en ân manier is
ondersoek om 68Ge te vervaardig, wat benodig word om so ân generator te laai. Dik Ga skyfmateriaal word in die Vertikale Bundelstasie gebombardeer en ân chemiese
skeiding is uitgevoer deur gebruik te maak van AG MP-1 anioonuitruiling hars. Die
finale produk is op die generators gelaai vir toetsdoeleindes. Toetse is ook op ân ander
tipe generator uitgevoer en word in die werk beskryf.
ân Projek is begin om âclusterâ radioaktiewe verval van 223Ac, via 14C en 15N emissie,
te bestudeer. ân Th-skyf is met protone gebombardeer om die 223Ac te produseer vir
die eksperiment. 227Pa is vervaardig en geskei van die skyfmateriaal. Dit is gedoen
met die gebruik van AG MP-1 makroporeuse anioonuitruiling hars en drooggemaak
op ân bronplaat, waar dit verval het na 223Ac. Die chemiese skeiding en die
droogmaak van die finale produk op ân bronplaat is uitgevoer binne 70 minute na
Einde van Bombardering (EVB). Die werk is deel van ân samewerking met kollegas
van JINR, Rusland, en die Universiteit van Milaan, sowel as INFN, Italië.
133Ba het ân halveertyd van oor die tien jaar en is ân duur produk om te vervaardig.
Dit is al gebruik in mediese en biologiese studies en daar is deesdae ân redelike
aanvraag daarvoor. ân Metode is uitgewerk om 133Ba te skei van die CsCl
skyfmateriaal met die gebruik van AG50W-X4 katioonuitruiling hars.
Spesialiste in landboustudies het in die verlede belangstelling getoon in 28Mg. Dit
word gebruik om die absorpsie van dié element in vrugte te ondersoek. Die produk
kan vervaardig word met die gebruik van LiCl skyfmateriaal: tot soveel as tien skywe
(agter mekaar) word gebombardeer met ân 200 MeV protonbundel te iThemba LABS.
ân Metode, wat Purolite S950 behels, is daargestel om 28Mg van die skyfmateriaal te
skei
Publish and perish: a disturbing trend in the European Union's regulation of nutrition health claims made on foods
Identifying patients at risk of emergency admission for colorectal cancer.
BACKGROUND: Patients whose colorectal cancer is treated after an emergency admission tend to have late-stage cancer and a poor prognosis. We identified risk factors for an emergency admission by linking data from the National Bowel Cancer Audit (NBCA) and the English Hospital Episode Statistics (HES), an administrative database of all admissions to English National Health Service hospitals, which includes data on mode of admission. METHODS: We identified all adults included in the NBCA with a primary diagnosis of bowel cancer, excluding cancer of the appendix, between August 2007 and July 2011 whose record could be linked to HES. Multivariable logistic regression was used to estimate adjusted odds ratios (OR) for an emergency admission for colorectal cancer. All risk factors were adjusted for cancer site and calendar year. RESULTS: 97,909 adults were identified with a primary diagnosis of bowel cancer and 82,777 patients could be linked to HES. Patients who were older, female, of a non-white ethnic background, and more socioeconomically deprived, and those with dementia or cardiac, neurologic and liver disease had an increased risk of presenting as an emergency admission. The strongest risk factors were age (90 compared with 70 years: OR 2.99, 95% CI 2.84 to 3.15), dementia (OR 2.46, 2.18 to 2.79), and liver disease (OR 1.87, 1.69 to 2.08). CONCLUSIONS: Our study identifies risk factors that may impair health-seeking behaviour and access to healthcare. An earlier recognition of symptoms in patients with these risk factors may contribute to better outcomes
Organisation of Prostate Cancer Services in the English National Health Service.
AIMS: The National Prostate Cancer Audit (NPCA) started in April 2013 with the aim of assessing the process of care and its outcomes in men diagnosed with prostate cancer in England and Wales. One of the key aims of the audit was to assess the configuration and availability of specialist prostate cancer services in England. MATERIALS AND METHODS: In 2014, the NPCA undertook an organisational survey of all 143 acute National Health Service (NHS) Trusts and 48 specialist multidisciplinary team (MDT) hubs cross England. Questionnaires established the availability and location of core diagnostic, treatment and patient-centred support services for the management of non-metastatic prostate cancer in addition to specific diagnostic and treatment procedures that reflect the continuing evolution of prostate cancer management, such as high-intensity focused ultrasound (HIFU) and stereotactic body radiotherapy. RESULTS: The survey received a 100% response rate. The results showed considerable geographical variation with respect to the availability of core treatment modalities, the size of the target population and catchment areas served by specialist MDT hubs, as well as in the uptake of additional procedures and services. Specifically there are gaps in the availability of core radiotherapy procedures; high dose rate and low dose rate brachytherapy are available in 44% and 75% of specialist MDTs, respectively. By comparison, there seems to be a relative 'over-penetration' of surgical innovation, with 67% of specialist MDTs providing robotic-assisted laparoscopic prostatectomy and 21% HIFU. There is also evidence of increased centralisation of core surgical procedures and regional inequity in the availability of surgical innovation across England. CONCLUSIONS: The organisational survey of the NPCA has provided a comprehensive assessment of the structure and function of specialist MDTs in England and the availability of prostate cancer procedures and services. As part of the prospective audit, the NPCA will assess the effect of the availability of prostate cancer services on access regionally and subsequent outcomes of care according to evidence-based guidelines
Optimization of 68Ga production at an 18 MeV medical cyclotron with solid targets by means of cross-section measurement of  66Ga, 67Ga and 68Ga.
The future development of personalized nuclear medicine relies on the availability of novel medical radionuclides. In particular, radiometals are attracting considerable interest since they can be used to label both proteins and peptides. Among them, the ÎČ+-emitter 68Ga is widely used in nuclear medicine for positron emission tomography (PET). It is used in theranostics as the diagnostic partner of the therapeutic ÎČ--emitters 177Lu and 90Y for the treatment of a wide range of diseases, including prostate cancer. Currently, 68Ga is usually obtained via 68Ge/68Ga generators. However, their availability, high price and limited produced radioactivity per elution are a major barrier for a wider use of the 68Ga-based diagnostic radiotracers. A promising solution is the production of 68Ga by means of proton irradiation of enriched 68Zn liquid or solid targets. Along this line, a research program is ongoing at the Bern medical cyclotron, equipped with a solid target station. In this paper, we report on the measurements of 68Ga, 67Ga and 66Ga production cross-sections using natural Zn and enriched 68Zn material, which served as the basis to perform optimized 68Ga production tests with enriched 68Zn solid targets
Light emission and spin-polarised hole injection in InAs/GaAs quantum dot heterostructures with Schottky contact
EPL draftWe demonstrate the feasibility to obtain electroluminescence (EL), up to room temperature, from InGaAs self-assembled quantum dots (QDs) included in a forward-biased Schottky
diode. Moreover, using a ferromagnet (FM) as the contact layer, sizable circular polarization of
the EL emission in the presence of an external magnetic eld is obtained. A resonant behav-
ior of the degree of circular polarization (P) as a function of applied voltage (V ), for a given
value of magnetic eld, is observed. We explain our ndings using a model including tunneling
of (spin-polarised) holes through the metal-semiconductor interface, transport in the near surface
region of the heterostructure and out-of-equilibrium statistics of the injected carriers occupying
the available states in the QD heterostructure. In particular, the resonant P(V ) dependence is
related to the splitting of the qusi-Fermi level for two spin orientations in the FM.FCT, Portugal (project
POCI/FIS/58524/2004), the RFBR, Russia (grant 10-02-
00501), MEC (grants MAT2008-01555, QOIT-CSD2006-
00019) and CAM (S-2009/ESP-1503) (Spain)
Photodynamic therapy: A promising new modality for the treatment of cancer
The first reports on photodynamic therapy (PDT) date back to the 1970s. Since then, several thousands of patients, both with early stage and advanced stage solid tumours, have been treated with PDT and many claims have been made regarding its efficacy. Nevertheless, the therapy has not yet found general acceptance by oncologists. Therefore it seems legitimate to ask whether PDT can still be described as "a promising new therapy in the treatment of cancer". Clinically, PDT has been mainly used for bladder cancer, lung cancer and in malignant diseases of the skin and upper aerodigestive tract. The sensitizer used in the photodynamic treatment of most patients is Photofrin, (Photofrin, the commercial name of dihematoporphyrin ether/ester, containing > 80% of the active porphyrin dimers/oligomers (A.M.R. Fisher, A.L. Murphee and C.J. Gomer, Clinical and preclinical photodynamictherapy, Review Series Article, Lasers Surg. Med., 17 (1995) 2-31). It is a complex mixture of porphyrins derived from hematoporphyrin. Although this sensitizer is effective, it is not the most suitable photosensitizer for PDT. Prolonged skin photosensitivity and the relatively low absorbance at 630 nm, a wavelength where tissue penetration of light is not optimal, have been frequently cited as negative aspects hindering general acceptance. A multitude of new sensitizers is currently under evaluation. Most of these "second generation photosensitizers" are chemically pure, absorb light at around 650 nm or greater and induce no or less general skin photosensitivity. Another novel approach is the photosensitization of neoplasms by the induction of endogenous photosensitizers through the application of 5-aminolevulinic acid (ALA). This article addresses the use of PDT in the disciplines mentioned above and attempts to indicate developments of PDT which could be necessary for this therapy to gain a wider acceptance in the various field
Experimental Verification of the Chemical Sensitivity of Two-Site Double Core-Hole States Formed by an X-ray FEL
We have performed X-ray two-photon photoelectron spectroscopy (XTPPS) using
the Linac Coherent Light Source (LCLS) X-ray free-electron laser (FEL) in order
to study double core-hole (DCH) states of CO2, N2O and N2. The experiment
verifies the theory behind the chemical sensitivity of two-site (ts) DCH states
by comparing a set of small molecules with respect to the energy shift of the
tsDCH state and by extracting the relevant parameters from this shift.Comment: 11 pages, 2 figure
A Simple Operator Check of the Effective Fermion Mode Function during Inflation
We present a relatively simple operator formalism which reproduces the
leading infrared logarithm of the one loop quantum gravitational correction to
the fermion mode function on a locally de Sitter background. This rule may
serve as the basis for an eventual stochastic formulation of quantum gravity
during inflation. Such a formalism would not only effect a vast simplification
in obtaining the leading powers of at fixed loop orders, it would also
permit us to sum the series of leading logarithms. A potentially important
point is that our rule does not seem to be consistent with any simple infrared
truncation of the fields. Our analysis also highlights the importance of spin
as a gravitational interaction that persists even when kinetic energy has
redshifted to zero.Comment: 39 pages, no figuire.(1) New version has clarified the ultimate
motivation by adding sentences to the abstract and to the penultimate
paragraph of the introduction. (2) By combining a number of references and
equations we have managed to reduce the length by 2 page
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