Sunday, January 26, 2020
Nano-diamond Powder Layer Effect on Fast Neutrons Reflection A. Taghian, D. Rahi, H. Sadeghi Abstract: This paper has investigated the effect of nano-diamond powder on reflection of fast neutrons. It compares the effect of graphite and nano-dimond layers on reflection of fast neutrons. Nano-diamond as a new article that theres carbon in families of many of the behaviors and properties of carbon and other members of the family, the impact of the application of this article accepts it without knowing so, and understand it without understanding the carbon carbon and other members of the family is not possible. Nano-diamond in addition to diamonds, diamond properties such as hardness, resistance to different environments and The small size and a shell with active groups that it has different properties to conventional diamonds. On the one hand the diverse applications of properties and provide new and on the other hand, production and working with this article difficult. Of course, the proper use of diamond in different applications when possible, which is a non-diamond carbon and other impurities as possible are separated from it in addition any application requires special surface properties as well. The amount of impurities in synthetic diamond production depends on the extreme ways. We used 241Am-Be 100 Ã µCi, BF3 and LiI detector in the present study. Two materials have been coated. The experimental and simulated results have good agreement with consideration of errors. The results show that fast neutrons reflection could be carried out by nano-diamond powder better than graphite. Keyword: 1-Nano-diamond powder 2-Graphite 3-Neutron 4-Neutron reflection 5- BF3 detector 6-LiI detector 1-Introduction Neutrons shielding is based on the fast neutrons reflection as prompt and delay gamma are produced by neutron capture . The scattering cross section of hydrogen is high for neutrons. So, hydrogen containing material such as polyethylene and hydrocarbon are used for neutron shielding . Diamond has cubic lattice structure . In this structure, one carbon atom is surrounded by four atom of carbon with covalent bonds. Very strong covalent bond of a carbon adjacent atom is caused by increasing of elastic modulus and ultra-high temperature stability . Therefore, they make the strongest natural material. The structure of bulk material is 3D. But, the structure of nanomaterial is 2D (thin film), 1D (nanorod and nanotube) and zero dimensions (nanoparticle and nanocrystal). In addition to change properties of material, this technology increases the surface to volume ratio. Therefore, the ratio of surface reaction increases on the material. By development of nuclear technology over the past 40 years, rules and standards of the IAEA have become more difficult and smaller for absorbed dose of personalities and environments in different conditions. There have been many limitations for neutron shield construction such as mass and volume of the shield . 2-Investigatin of neutron reflector Reflectors are used in reactors to prevent neutrons escaping. The best reflector has small absorption cross section and large scattering cross section. Graphite and beryllium (according to solid phase) are usually used for reflection of neutrons. Actually, the size of structural units (a) must be comparable to the wavelength of neutrons (Ã »). Coherent and efficient scattering of neutrons is proportional to the ratio of Ã »/a. A neutron can be described by wavelength, Ã » and wave vector . The neutron energy is equal to , and are mass, energy and Plank constant respectively . The neutron beam intensity is decreased by transmission across material. The neutron beam intensity reduction is equal to , , and are thickness of material, number of atoms in unit volume and total cross section respectively [1,4]. 3-Experimental setup 3-1-BF3 detector BF3 detector is used for detection of thermal neutron. It works on proportional region. The isotope of 10B is used in the BF3 gas detector. The absorption cross section of 10B is large for absorbing of thermal neutrons. The BF3 counter detects the alpha and the lithium particles produced by the reaction [4,6,5]: The efficiency of BF3 detector is proportional to absorption cross section of 10B and it changes for neutrons with different energies. 3-2- LiI detector In addition of BF3 detector, LiI detector has been used for detection of neutron. 6LiI is an inorganic scintillator. Neutron detection by 6Li is based on the reaction The cross section for this reaction is of the l/v type up to 10 keV, with a value of 937 b at 0.025 eV [3, 6]. 3-3- The used material The neutron source was 241Am-Be 100 Ã µCi. The BF3 and LiI detectors were used with 2 cm diameter and 20 and 14 cm height respectively. The BF3 and LiI detectors were located on polyethylene base. 3-3-1- The origin and fabrication method of the nano-diamond powders Diamond powder production properties depend on the method. Desired characteristics are obtained by purification and properties are determined. A manufacturing process for milling the nano-diamond to the appropriate size is explosive method. Diamond powder production common methods are carried out in dry (environmental gas synthesis) and wet (water base) mediums. The Nano-diamond powder production was carried out by blasting method which could lead to the Carbon dioxide, carbon monoxide, nitrogen, nitrogen monoxide and etc. creation. The tiny particles of diamond are formed along with some solid impurities mixed with gases in the blast chamber. Table 1 shows the chemical analysis of ash samples. The results recorded in the table indicate the chemical analysis of ash residue from the combustion of the samples by wet chemical methods which are XRD, ICP. Table 1: The chemical analysis of ash samples are presented In the nano-diamond powder manufacturing process through blasting, diamond particles are formed at pressures higher than 200 kilo bars. At temperatures above 1000 Ã ° C, the low pressure converted particles into graphite. Methods of separation and purification of gas and liquid nano- diamonds are divided into two groups that raise the cost of investment. After all purification of the resulting material is carried out as the carbonic compound still has many types and amounts of impurities such as O, N, H, a small amount of metal and carbondioxide. Nano- diamond is then purified and turned ashen while the ash explosion leads to a large amount of black and dark -graphite production. Powder used in these experiments was purified by liquid method. In this method, different oxidizing agents such as acids, mixed acids, bases and salts are used. All these methods are only carried out in laboratory scale. Characteristics of nano-diamond powder used are shown in Table 2. Table 2: The properties of the used nano-diamond powder in experiments Figure 1 shows the measured spectrum of 100 Ã µCi 241Am-Be neutron source supplied by I.R. Iran Atomic Energy Agency and figure 2 show absorption cross section of 10B and 11B. Figure 1: Neutron spectrum of 241Am-Be Figure 2: Variation of neutron cross section of 10B and 11B isotopes 3-4-Geometry The experimental setups have been sketched in figure 3 and 4 for investigation of graphite and nano-diamond layers effect on reflection of fast neutrons. Figure 3: The experimental setup for investigation of graphite and nano-diamond layers effect on reflection of fast neutrons Figure 4: The experimental setup for investigation of graphite and nano-diamond layers effect on shielding of fast neutrons In the present study of neutron reflection, the height and radial of the cylinder are 35 cm and 11 cm respectively with one side open and the other closed. The neutron source is in center of the cylinder and the detector is placed in front of the open side. The cylinder is made of polyethylene with 2 mm thickness. Graphite and nano-diamond are coated with polyethylene in cylinder. The distance of the detector lateral surface and the open side of the cylinder was 20 cm. The thicknesses of coated graphite and nano-diamond were 1, 3, 5, 10, 15, 20, 25 and 30 mm. The background neutrons are originated from walls, floor and other instrument in the around environment. A polyethylene cube with 10 cm thickness and a lead block with 2 cm thickness are located between source and detector for absorption of emitted gamma rays and neutrons from source. This geometry detects gamma rays background and neutrons. This work repeats for each measurement with and without absorbers. The first and second counts are foreground and background respectively. If background subtracts from foreground count, the result will be net count of reflected neutrons from cylinder to detector. To investigate the neutron shielding properties, neutron source has been located in center of graphite cubic with 2 mm thickness. Also, the LiI detector has been set in front of one side of the graphite cubic. Graphite and nano-diamond are coated on the same side of graphite cubic. The distance between the detector lateral surface and the open side of the cubic was 15 cm. The thicknesses of coated graphite and nano-diamond were 1, 3, 5, 10, 15, 20, 25 and 30 mm. 4-Results of measurements As mentioned above, the thicknesses of graphite and nano-diamond were 1, 3, 5, 10, 15, 20, 25 and 30 mm respectively. In each measurement, the same thicknesses were compared at a margin oferrorequal to Ã ±23 percent. The errors come from neutron source and count measurement as the error of neutron source was Ã ±15 percent and the count measurement (N) one was N1/2.The neutron counts in different thicknesses of graphite and nano-diamond are shown in figure 5 and 6. Figure 5: Neutron count diagram for graphite and nano-diamond layers with different thicknesses (Reflection) Figure 6: Neutron count diagram for graphite and nano-diamond layers with different thickness (Shielding) 5-Simulated results by Monte-Carlo method All the system parts have been simulated by Monte-Carlo method. We have used MCNPX2.6 to calculate the absorbed dose. MCNPX2.6 is a general purpose of Monte Carlo radiation transport code designed to track many particle types over broad ranges of energies. Form of molecule, bond and density are changed in a nano chemical composition. Coulomb force determines the form of molecules. The total charge of the neutron is zero. Therefore, there is no effect on neutron cross section with matter of nano scale. Also, the neutron reaction is nuclear and it is independent of charge or electron cloud so that it can be simulated by MCNP code. Therefore, it is not important to consider the nano-scale of the nano-diamond. However, nano-scale affects density and it must be noted in Monte-Carlo input. The neutron flux has been calculated in the sensitive volume of BF3 and LiI detectors with different thicknesses of graphite and nano-diamond. The results are shown in figure 7 and 8. Figure 7: Calculated neutron flux in sensitive volume of BF3 detector in different thickness of graphite and nano-diamond layers (Reflection) Figure 8: Calculated neutron flux in sensitive volume of LiI detector in different thickness of graphite and nano-diamond layers (Shielding) Because of hydrogen presence in the nano-diamond composition, it can reflect neutrons better than graphite. The neutrons counting is increased by graphite and nano-diamond thickness enhancement. However, determining thenumberofneutrons is faster for nano-diamond layer. Fig. 4 and fig. 6 show that the reflected neutrons are increased by thickness enhancement. The differences arise from the measurement method as the measurements are done by BF3 detector which measures thermal neutrons. The simulated results are considered the all of neutrons. Also, Fig. 7 and 8 show that nano-diamond has a more shielding effect in comparison with graphite because the net count rate becomes smaller by using nano-diamond shielding. The differences are because of the measurements done by BF3 detector and the simulation results are considered as the spectrum of neutrons. 6-Conclusion Two main factors effecting on neutron reflection are cross section and density. Nano-diamond (C10H16) contains hydrogen and it has larger cross section interaction in comparison with graphite. In addition, the density of nano-diamond and graphite are 3.5 and 1.8 g/cm3 respectively. According to the results, true count of nano-diamond reflector is 2 times of graphite reflector. The simulated and experimental results have good agreement by consideration of errors. Also, the number of low energy neutrons in nano-diamond reflector is larger than in graphite one. Therefore, conventional material can be put aside and nano-diamond is used for neutron shielding. References Glenn F. Knoll, Ã¢â¬Å"Radiation Detection and MeasuremenÃ¢â¬ , Fourth Edition, 2010, , John Wiley Sons, Inc T. Taler, Characterization of Isolated Nnaodiamond Particle, Material Science and Engineering, North Carolina State University, 6-18 (2004). Nicholas Tsoulfanidis; Ã¢â¬ Measurement and Detection of RadiationÃ¢â¬ ; 2th edition, university of Missouri- Rollapress. 706 (1995). V. A. ArtemÃ¢â¬â¢ev, Ã¢â¬ Atomic EnergyÃ¢â¬ , Vol. 94, NO. 4, 282(2003). H.W. Schmitt, R.C. Block, R.L. Bailey, Total neutron cross section of 10B in the thermal neutron energy range, Volume17, JuneÃ¢â¬âJuly 1960, Pages 109Ã¢â¬â115. K. Kleinknecht, Dtectors for Particle Radiation, Cambridge University Press, London New York New Rochele, 120-125(1986).  Isfahan University, Faculty Of Advanced Science And Technologies, Department of Nuclear Engineering, Isfahan, Iran Ahmad Taghian; Email: [emailprotected]; Telephone: 00989128482357 Davood Rahi: Email: [emailprotected]  Malek Ashtar University Of Technology, Health Physics Department, Shahin shahr, Isfahan, Iran Hosein Sadeghi: Email: [emailprotected]
Friday, January 17, 2020
We spend a quiet, comfortable evening and I can't help watching Emily for most of it. It's obvious she hasn't seen television in a while because she's mesmerized. We are watching some Cajun cooking show on public access, but to see it through her eyes, it's like we are watching the most fascinating show known to man. Ã¢â¬Å"I put a little mo' wine in here, maybe a little mo' wine fo' me,Ã¢â¬ the host says in a Creole southern drawl. Ã¢â¬Å"Oh my gosh! Ethan, he is so funny! Ã¢â¬ËI gar-un-tee'!Ã¢â¬ she laughs as she mimics the chef, and I can't help the smile that cracks across my face. She could let the world swallow her whole with the weight of her situation, but she doesn't. Instead she carries on, seemingly carefree, laughing at the talkative old cook with the gift of gab. Ã¢â¬Å"Emily?Ã¢â¬ She glances over at me, still laughing at the TV. It's the moment I know I'm making the right decision. I take a deep breath, ready to lay things on the line. Ã¢â¬Å"Hang on! He's going to tell a story about squirrel hunting! This'll be good!Ã¢â¬ Emily says with enthusiasm. While I really need to get my thoughts out, I can't deny her this moment. It's so pure, so I decide to indulge her for the final five minutes of the show. As the Cookin' Cajun finishes, Emily focuses her attention on me. Ã¢â¬Å"You wanted to talk about something?Ã¢â¬ The light and sparkle in her eyes is amazing. She looks happy and carefree instead of nervous. She seems to assume the best of every situation. Given the circumstances, you'd think she would be nervous, but instead, she acts as though we're going to talk about whether she'll make oatmeal or chocolate chips cookies next. I suddenly feel something I haven't felt in a very long time: content. Ã¢â¬Å"Yeah,Ã¢â¬ I begin, though I'm not sure why I'm nervous, other than the fact she may say no. She may refuse my help. She may tell me to mind my own business, that she doesn't need anyone to look after her, but I have to try. Ã¢â¬Å"I want you to stay here.Ã¢â¬ Her mouth drops open, but no sound comes out. Ã¢â¬Å"With me,Ã¢â¬ I finish. I'm not sure whether her speechlessness is a result of shock or horror. I decide to play it safe with more justification. Ã¢â¬Å"You can't squat next door. It's not safe, it's illegal, and you don't need any hassles from the cops.Ã¢â¬ She sits for a moment with her eyes trained on her hands while her fingers twist with each other on her lap. Her hair is frizzy from the humidity, and despite having it pulled back, there are tiny tendrils sticking up forming an angelic halo around her face. After a few moments, she finally speaks. Ã¢â¬Å"So, what do you want in return?Ã¢â¬ What? I'm fully aware she has no money, so why would she think I would want her to pay- I'm not even finished with my own thought when I realize she's not talking about monetary payment. Nothing is ever free, and she thinks I want her in return for providing food and shelter. The thought strips me down to the core. Ã¢â¬Å"No!Ã¢â¬ I shout unnecessarily, but I can't help it. I do not want that! She's hiding her face, but I can see her scrunching her eyes closed. I take a breath to calm down and explain myself. Ã¢â¬Å"No,Ã¢â¬ I start again, much calmer than before. Ã¢â¬Å"I don't want anything from you, Emily. I want to help you. I know howÃ¢â¬ ¦Ã¢â¬ I stop and take a deep breath. I need her to understand where I'm coming from. Ã¢â¬Å"I know how hard this situation can be.Ã¢â¬ She flinches and snaps her head up to look me in the eye. Ã¢â¬Å"You don't wantÃ¢â¬ ¦you know, then?Ã¢â¬ She gestures between us to further her point. Lie. Ã¢â¬Å"No. The last thing I want is for you to be taken advantage of.Ã¢â¬ While the thought of being with her physically is an attractive offer, I would never want it under that set of circumstances. I know how easy it is to become a target when you're young and in need. Ã¢â¬Å"But, why? Everyone wants something, Ethan. There has to be something you want from me. I mean, it's okay if you wantÃ¢â¬ ¦ you knowÃ¢â¬ ¦Ã¢â¬ Her cheeks flame red as she says this. God, she's so naive she can't even say the word Ã¢â¬Å"sex.Ã¢â¬ It only solidifies my decision that I'm doing the right thing, but she's right. People always want something in return, so I will have to give her a reason why I don't want anything from her. I have to be honest with her and let her know that I'm all too familiar with her situation.
Thursday, January 9, 2020
If there are multiple questions in a comment, please allow the candidate to respond before asking the next question. (1) I know that a large lot size has been associated with increasing number of defective units. On page 1, you wrote: Ã¢â¬Å"production stages are characterizedÃ¢â¬ ¦.Ã¢â¬ . What is your evidence that fast production increases the generation of defective items (scrap)? (2) Your demand is deterministic and the bullwhip effect has no place in your thesis. The bullwhip effect has no effect on your model, why it was mentioned twice? What is its relevance in the thesis? (3) You assumed a single raw material to produce a single product. This makes Table 2.1 not representative of the literature review. For example, Jaber and Goyal (2009)Ã¢â¬ ¦show more contentÃ¢â¬ ¦What makes your model unique in that regard? (6) On page 43, you consider that p = d. This situation can never happen. So, why need to consider it? I also think that N0 can never reach infinity; there should be maximum and minimum values on M0 and N0. What are these values? The minimum value that either M0 or N0 can take is 1. Note that when h3 hÃ¢â¬â¢1, then neither M0 nor N0 is valid. In that case, they are forced to 1. Do you agree? (7) Transportation in Figure 3.4 and its fixed and variable costs are either factored into the total cost of the distribution centre or the finished product warehouse. That is, transportation is not a level in the supply chain. This makes the model three rather than four levels. If you disagree, then why transportation is important to consider in an MNC context? (8) Also, you wrongly phrased your model as a single item that is produced from different types of raw material; actually you assumed one type of raw material to produce a finished product. This is why it was possible for you to find an optimal solution. Furthermore, you neither considered the capacity of a transport vehicle nor the number of vehicles available. Why not? These points must be made clear in the thesis. (9) On page 31 you wrote: Ã¢â¬Å"Transferring raw materials from RMW to MUP in batches to the buffer area makes the raw material inventory dynamics different from the earlier worksÃ¢â¬ , what do you mean by this statement, and why it is important? Please
Wednesday, January 1, 2020
Sample details Pages: 3 Words: 927 Downloads: 6 Date added: 2017/06/26 Category Finance Essay Type Narrative essay Did you like this example? The price of any financial instrument is equal to the present value of the expected cash flows from the financial instrument (Fabozzi Mann, 2006, p. 121). In order to determine the price, it requires an estimate of the expected cash flows and required yield. DonÃ¢â¬â¢t waste time! Our writers will create an original "Price Of Any Financial Instrument Finance Essay" essay for you Create order Where the expected cash flows are refers to coupon payment and the required yield reflects the yield for financial instruments with comparable risk (Fabozzi, 2012, p. 16). The formula for pricing a bond: Where: P = bond price n = number of periods C = coupon payment r = periodic interest rate M = par value t = time period when the payment is to be received. The required yield is determined by investigating the yields offered on comparable bonds in the market (Fabozzi, 2012, p. 16). By comparable, it means option free bonds of the same credit quality and the same maturity. A fundamental of a bond is that the bond price changes in the opposite direction in the required yield (Mann Powers, 2002). It means that the required yield increases, the present value if the cash flow decrease and leads to price decrease. When coupon rate is equal to the required yield, the price of bond will be equal to par value. If the coupon rate is higher than required yield, the bond pr ice will be above par (sold at premium). However, if the required yield is greater than coupon rate, the bond price will be less than par value (sold at discount) (Mann Powers, 2002). As the bond move closer to maturity, most of the bonds will be priced equal to par value. Yield The yield on any investment, also known as internal rate of return is the interest rate that will make the present value of the cash flows from the investment equal to the cost of the investment (Fabozzi, 2012, p. 37). Mathematically, the yield (y) on any investment is the interest rate that satisfies the below equation. Where: CFt = cash flow in year t P = price of the investment N = number of years In order to solve the (y), it requires a trial and error method. The objective is to find the interest rate that will make the present value of the cash flows equal to the price (Fabozzi Mann, 2006, p. 121). It is the same formula to compute yield to maturity. There are several bond yield measures commonly quoted by dealers and used by portfolio managers. Current yield relates the annual coupon interest to the market price (Fabozzi Mann, 2006, p. 120). It takes into account only the coupon interest and no other source of return that will affect an investorÃ ¢ÃÆ'Ã ¢Ã ¢Ã¢â ¬Ã ¡ÃâÃ ¬ÃÆ'Ã ¢Ã ¢Ã¢â ¬Ã ¾ÃâÃ ¢s yield. Time value of money is ignored. Next, yield to call is assumes that issuer will call the bond at an assumed call data and the call price is the price that specified in the call schedule. The procedure for calculating the yield to any assumed call date is the same as any yield calculation: Where: M* = call price n* = number of periods until the assumed call date Yield to put is the interest rate that makes the present value of cash flows to be assumed put date plus the put price on the date as set forth in the put schedule equal to bond price (Fabozzi, 2012, p. 37). Lastly, yield to worst is the minimum of the yield to maturity, yield to call and yield to put. The procedure for calculating the yield to put is the same as any yield calculation: Where: M* = put price n* = number of periods until the assumed put date Arbitrage Opportunity in Bond Market Arbitrage refers to buying an instrument in one market and simultaneously selling it in another, gaining profit from the differences in buying and selling price (Fabozzi, 2012, p. 11). Arbitrage usually happens when the market is inefficient. The person who makes did this transaction by using the market inefficiency is called an arbitrager (Fabozzi, 2012, p. 11). In order to gain arbitrage in the bond market, once must buy a bond by borrowing from bank. During maturity, arbitrager will received the principal plus last coupon payment. Then use the amount received from the bond to repay back the bank. After repayment, the balance amount will be the arbitrage riskless profit (Choi, Getmansky Tookes, 2009). However, this rarely happens as demand of the bond increase will cause the bond price increases until the extent that there wonÃ ¢ÃÆ'Ã ¢Ã ¢Ã¢â ¬Ã ¡ÃâÃ ¬ÃÆ'Ã ¢Ã ¢Ã¢â ¬Ã ¾ÃâÃ ¢t be any arbitrage opportunity (Satya, n.d.). Choi, D., Getmansky, M., Tookes, H. ( 2009). Convertible bond arbitrage, liquidity externalities, and stock prices. Journal of Financial Economics, 91(2), 227-251. Fabozzi, F.J. (2012). Pricing of bonds. In bond markets, analysis and strategies 7th edition (p. 16). United States: Pearson Hall. Fabozzi, F.J. (2012). Pricing of bonds. In bond markets, analysis and strategies 7th edition (p. 37). United States: Pearson Hall. Fabozzi, F.J. (2012). Introduction. In bond markets, analysis and strategies 7th edition (p. 11). United States: Pearson Hall. Fabozzi, F.J., Mann, S.V. (2006). Bond pricing, yield measures, and total return. In the handbook of fixed income securities 7th edition (p. 107). United States: McGraw-Hill. Fabozzi, F.J., Mann, S.V. (2006). Bond pricing, yield measures, and total return. In the handbook of fixed income securities 7th edition (p. 120). United States: McGraw-Hill. Fabozzi, F.J., Mann, S.V. (2006). Bond pricing, yield measures, and total return. In the handbook of fixed inco me securities 7th edition (p. 121). United States: McGraw-Hill. Mann, S.V., Powers, E.A. (2002). Indexing a bondÃ ¢ÃÆ'Ã ¢Ã ¢Ã¢â ¬Ã ¡ÃâÃ ¬ÃÆ'Ã ¢Ã ¢Ã¢â ¬Ã ¾ÃâÃ ¢s call price: an analysis of make-whole call provision. Journal of Corporate Finance, 9(1), 535-554. Satya. (n.d.). Arbitrage opportunity in bond market. Retrieved March 10, 2013, from https://www.selfgrowth.com/articles/ArbitrageOpportunitiesInBondMarket.html